Accepted Manuscript Title: Assessment of the physical, mechanical, and moisture-retention properties of pullulan-based ternary co-blended films Author: Hongyang Pan Bo Jiang Jie Chen Zhengyu Jin PII: DOI: Reference:
S0144-8617(14)00514-1 http://dx.doi.org/doi:10.1016/j.carbpol.2014.05.044 CARP 8911
To appear in: Received date: Revised date: Accepted date:
9-2-2014 12-5-2014 13-5-2014
Please cite this article as: Pan, H., Jiang, B., Chen, J., & Jin, Z.,Assessment of the physical, mechanical, and moisture-retention properties of pullulan-based ternary co-blended films, Carbohydrate Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.05.044 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Assessment of the physical, mechanical, and moisture-retention properties of
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pullulan-based ternary co-blended films
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Hongyang Pana, *, Bo Jianga, Jie Chena, Zhengyu Jina, b
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a
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214122, P. R. China
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b
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China
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State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi
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School of Food Science and Technology, Jiangnan University, Wuxi 214122, P. R.
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Corresponding author. Telephone number:+86-510-85919656. Fax number:
+86-510-85919656. E-mail address: [email protected] (H. Pan). 1
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Research Highlights
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In this manuscript:
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1) A co-drying method to modify the properties of co-blended polysaccharides was
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reported.
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2) A method to evaluate moisture retention properties of films in IMF was reported.
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3) Ternary co-dried blended films with PGA showed better water retention ability.
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4) A model between film characteristics and moisture-retention values was
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established.
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5) The model could be used to evaluate water retention, anti-moisture absorption.
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Abstract: Multi-component substances made through direct blending or blending
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with co-drying can form films on the surfaces of intermediate moisture foods (IMFs), which help retain moisture and protect food texture and flavor. An IMF film system based on pullulan, with glycerol serving as the plasticizer, was studied using alginate and four different types of polysaccharides (propyleneglycol alginate, pectin,
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carrageenan, and aloe polysaccharide) as the blend-modified substances. The physical,
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mechanical, color, transparency, and moisture-retention properties of the co-blended
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films with the polysaccharides were assessed. A new formula was established for the
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average moisture retention property, water barrier, tensile strength, elongation at break, 2
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and oxygen barrier property of the ternary co-blended films using the Design Expert
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software. The new model established for moisture content measurement used an
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indirect method of film formation on food surfaces by humectants, which should
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expedite model validation and allow a better comprehension of moisture transfer
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through edible films.
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Keywords: intermediate moisture food; ternary co-blended film; water vapor
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permeability; pullulan; moisture retention
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1. Introduction
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As an intermediate moisture food (IMF), the moisture of vacuum-freeze-dried
fiddleheads is between 10% and 15%, and the water activity is between 0.5 and 0.6. Moreover, vacuum freeze-drying is one of the oldest methods of preserving fiddleheads (Karel & Heidelbaugh, 1973; Miranda, Berna, Bon, & Mulet, 2011;
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Pavey & Schack, 1969). The main components of vacuum-freeze-dried fiddleheads
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include protein, carbohydrates, lipids, and other humectants (DeLong, Hodges, Prange,
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Forney, Fan, Bishop, et al., 2013). Compared with traditional dried or high-moisture
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fiddleheads, intermediate moisture vacuum-freeze-dried fiddleheads have many 3
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advantages. The first benefit is a lower energy consumption during processing and
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transportation compared with dried, refrigerated, frozen, and canned foods. Vacuum
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freeze-drying also lessens the destruction of the fiddleheads during processing
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compared with comparable stronger methods, such as dehydration and heat treatment.
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The low water activity (0.5-0.6) of vacuum-freeze-dried fiddleheads will control
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microorganisms and better maintain their preservation at room temperature (shelf life:
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1/2 year to 1 year); Finally, fiddleheads prepared in this manner are mild taste and
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easy to eat because they are directly edible without heating or rehydrating (Brimelow,
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1985). However, vacuum-freeze-dried fiddleheads still present several problems, such
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as being affected by dry or wet conditions, structural destruction, and loss of flavor,
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all of which significantly influence the nutritional value and the consumer acceptance
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(Hierro, de la Hoz, & Ordonez, 2004; Rao, Rocca-Smith, & Labuza, 2012).
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The public perception of the potential toxicological properties of food additives
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has also limited the widespread development of vacuum-freeze-dried fiddleheads for
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human consumption. Recent applications have focused on developing vacuum-freeze-dried fiddleheads for use in space programs and the military. The addition of humectants to fresh vegetables or fruits can reduce the water activity into ranges that allow their storage without refrigeration (Carrasco & Cisneros-Zevallos,
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2002; Gliemmo, Campos, & Gerschenson, 2004; Rojas & Gerschenson, 2001).The
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addition of humectants and plasticizers is the basic method for controlling the
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moisture and structure of vacuum-freeze-dried fiddleheads. The common humectants
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used are sugars (such as glucose, fructose, fructose syrup, glucose syrup, and 4
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polysaccharides), polyhydroxy compounds (such as sorbitol and glycerol), and salts
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(Gliemmo, Campos, & Gerschenson, 2004; Rojas & Gerschenson, 2001; Sritongtae,
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Mahawanich, & Duangmal, 2011). The study of polysaccharides as humectants started years ago. Ternary blends of
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polysaccharide solutions prepared through the co-drying method can have synergistic
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effects, that endow the composite with superior functional features, including
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increasing the viscosity of a single polysaccharide solution, improving the gelation
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function, and increasing the barrier and mechanical performance of the film formed
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(Ohashi, Ura, Takeuchi, et al., 1991; Salvador, Sanz, & Fiszman, 2001). Over the
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years, the study of blending polysaccharides has mainly focused on the simple
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physical mixing and synergy of two polysaccharides. In addition, few studies have
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focused on the characteristics of polysaccharide solutions formed by a ternary system
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(Damasio, Fiszman, Costell, & Dura´n, 1990; Salvador, Sanz, & Fiszman, 2001).
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Generally speaking, the electrostatic interactions between the different large
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molecules in polysaccharides are the reason for which blended systems perform better. Ternary polysaccharides produced through the co-drying method can be used as food humectants in IMF, as they improve the preservation and manufacturing properties, by increasing the water barrier, mechanical strength, and appearance acceptance. The
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traditional testing of the characteristics of humectants mainly focused on the moisture
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variation under specific conditions, thus establishing the relationships between the
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humectant effectiveness and time (Hou, Li, Zhang, Xue, Yu, Wang, et al., 2012; Yang,
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Guo, Zhou, Zhou, Xue, Miao, et al., 2010). 5
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This article assesses the humectant effectiveness of the ternary blending of
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polysaccharides by co-drying on vacuum freeze-dried fiddleheads. Furthermore, this
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article studies the film characteristics of polysaccharides on the surface of the
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fiddleheads. These results were used to establish a correlation model between the film
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characteristics of water barrier, oxygen barrier, mechanical strength and moisture
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effectiveness. This measurement will be used to fully evaluate the humectant
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characteristics of ternary blended polysaccharides, including their water retention,
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anti-moisture absorption, mechanical property, and improvements in their appearance
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acceptance.
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2. Materials and Methods
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2.1. Materials
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Following emergence and before 10 cm of growth, the fiddleheads of Matteuccia
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struthiopteris were harvested from Changbai Mountain in northeast China during
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2012. The crosiers were either refrigerated or maintained on ice until they were
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cleaned and then stored at 4 °C. All of the tissue samples were freeze-dried and stored at 4 °C until further analysis.
The pullulan (PUL) and aloe polysaccharide (ALO) were obtained from Jiangnan
University (Wuxi, China). The reagents used for film preparation and testing (glycerol,
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alginate (ALG), propyleneglycol alginate (PGA), pectin (PEC), carrageenan (CAR),
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magnesium nitrate, sodium hydroxide, and anhydrous calcium chloride) were
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purchased from Fisher Sci. Ltd. (Shanghai, China).
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2.2. Co-dried PUL/ALG and PUL/ALG/polysaccharides blended preparation 6
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Solutions of 50.00 g/L PUL and 50.00 g/L ALG were prepared in distilled water at 60 °C, and 0.05 (g/g PUL) polysaccharides (PGA, PEC, CAR, and ALO) were then
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added to the solutions. The concentration of the solution was adjusted to achieve a
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viscosity of less than 500 cps, and the pH was adjusted to 7.0 using 2 M NaOH. The
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spray drying was performed using a BUCHI B-290 Mini Spray Dryer with an
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atomizer speed of 15,000 rpm, an inlet temperature of 200 °C, and an outlet
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temperature of 95 °C. The resultant dried powder (PUL/ALG/PGA-CO,
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PUL/ALG/PEC-CO, PUL/ALG/CAR-CO, and PUL/ALG/ALO-CO) was the neutral
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ternary polysaccharide co-dried powder.
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The pH was adjusted to 7.0 with a 50.00 g/L PUL solution and a 50.00 g/L ALG
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solution, and the blend-modified powder was adjusted to obtain a binary neutral
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co-dried powder (PUL/ALG-CO).
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2.3. PUL/ALG film and PUL/ALG/polysaccharides film preparation
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PUL/ALG/polysaccharides, PUL/ALG/polysaccharides-CO) were slowly added into stirring deionized water. The stirring was maintained for 2 h to uniformly disperse the powders into the aqueous solution to obtain a stable solution of 50.00 g/L. The solution, the pH of which was adjusted to 7.0 with 2 M NaOH, was prepared and
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heated in a 250-mL Erlenmeyer flask for 30 min in a water bath at 80 °C. The
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emulsions were then cooled in an ice bath. Glycerol (0.30 g/g PUL) was added in the
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amount required to achieve the desired final film composition, and the film-forming
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solutions were de-gassed under vacuum of 0.09 MPa for 10 min using a vacuum 7
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pump (SHZ-D(III), Yuhua Instruments Co. Ltd., Gongyi, China). The films were prepared by placing the specific amount of the degassed film-forming solution or emulsion that would provide 3.00 g of total solids on a
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smooth high-density polyethylene (HDPE) casting plate resting on a leveled granite
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surface, because it is not hygroscopic and has good resistance in WVP. Additionally,
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HDPE has good chemical stability, which means that it is insoluble in any organic
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solvent, and has good resistance to corrosion by acids, bases, and all types of salts
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(Araujo, Mano, Teixeira, Spinace, & De Paoli, 2010).The films were dried for
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approximately 20 h in the oven at 53% relative humidity (RH) and 25 °C. All of the
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dried films could be peeled intact from the casting surface. The films used for water
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barrier property assessment and mechanical testing were conditioned at 53 ± 1% RH
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and 25 ± 1 °C by placing them in a desiccator containing a saturated solution of
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Mg(NO3)2·6(H2O) for at least 72 h. The compositions of the different polysaccharide
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films, including the PUL/ALG, PUL/ALG/PGA, PUL/ALG/PEC, PUL/ALG/CAR,
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and PUL/ALG/ALO films prepared from direct blended polysaccharide powder and the PUL/ALG-CO, PUL/ALG/PGA-CO, PUL/ALG/PEC-CO, PUL/ALG/CAR-CO, and PUL/ALG/ALO-CO films prepared from the neutral co-dried polysaccharide powders, are shown in Table 1. 2.4. Film thickness measurement The film thickness was determined using a digital micrometer (High-Accuracy
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Digimatic Digital Micrometer, USA). The film strips were placed between the jaws of
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the micrometer, and the gap was reduced until the friction was minimal. The mean 8
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thickness (m) of the films was measured from the average of numerical values at 10
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locations.
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2.5. Water vapor permeability (WVP) measurement The water vapor transmission rate (WVTR) of the film specimens were
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measured according to a modified ASTM E96 method (ASTM, 2002; Gennadios,
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McHugh, & Weller, 1994; Ou, Wang, Tang, Huang, & Jackson, 2005). Glass cups
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with a diameter of 3.00 cm and depth of 4.00 cm were used for this measurement. To
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maintain 0% RH in the cup headspace, 3.00 g of dried CaCl2 was added to the cup,
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and the film was then sealed over the rim of the cup by applying molten paraffin. The
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cups were placed in hermetically sealed jars maintained at 20 °C and 100% RH. The
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RH was maintained by placing 1,000 mL of water in the bottom of the jar. The cups
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were weighed every 12 h for a period of one week. The amount of water that
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permeated the films was determined from the weight gain of the cups. The WVTR
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and WVP were calculated using the following equations:
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WVTR=Δw/Δt×A, WVP= WVTR×L/Δp where WVTR is expressed in g/h·m2, Δw/Δt is the rate of water gain in g/h, A is the exposed area of the film in m2, L is the mean thickness of the film specimens in m, and Δp is the difference between the partial water vapor pressure on the two sides of
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the film specimens in Pa. The water vapor pressure on the high-stream side of the film
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was 2.34 kPa (i.e., saturated water vapor pressure at 20 °C), whereas that of the
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low-stream side was assumed to be zero.
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2.6. Measurement of mechanical properties 9
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Before testing their mechanical properties, the film samples were equilibrated for
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one week at 25 °C and 53% RH. Two mechanical parameters of the films, namely the
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tensile strength (TS) and the elongation at break (E%), were determined using a
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texture analyzer (TA-XT2i, Stable Micro Systems, Surrey, UK). The film samples
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were cut into 10-mm-wide and 800-mm-long strips using a sharp razor blade. Ten
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samples of each film type were tested. The tensile properties of the films were
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measured according to the ASTM standard method D882-02 (de Carvalho & Grosso,
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2004). The TS was calculated based on the original cross-sectional area of the test
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specimen using the equation TS = F/A, where TS is the tensile strength (MPa), F is
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the force (N) at maximum load, and A is the initial cross-sectional area (m2) of the
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film specimen. The E% value was calculated by dividing the extension-at-break of the
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specimen by the initial gauge length and multiplying by 100.
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2.7. Oxygen barrier property (OP) measurement
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A 60-mL jar was filled with 30.0 mL of fresh soybean oil, covered with different
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films, sealed using a bungee cord, and stored at a controlled temperature (60 °C) for 10 days. The peroxide value of the soybean oil samples was determined through sodium thiosulfate titration (Tang, Jiang, Wen, & Yang, 2005). All of the tests were conducted in triplicate.
2.8. Measurement of moisture retention ability The moisture retention properties were measured in this study using multiple
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variable differentials. First, 100.00 g of uniformly mixed vacuum-freeze-dried
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fiddleheads were weighed and equilibrated for 48 h at 22 ± 1 °C and (60 ± 2)% RH. 10
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This sample was then separated into two groups (50.00 g in each group). One group
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was prepared through a uniform spraying of blend-modified polysaccharide and
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glycerin at the proportion of 5.00 g/100 g of vacuum-freeze-dried fiddleheads. The
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other group was prepared by spraying the equivalent amount of distilled water as the
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reference. The two groups were equilibrated for 48 h at 22 ± 1 °C and (60 ± 2)% RH
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(Sun, Du, Yang, Shi, Li, Wang, et al., 2006; Yang, et al., 2010). For the measurement
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of the changes in the aqueous ratio of the vacuum freeze-dried fiddleheads during the
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moisture removal and absorption processes, the two groups were equilibrated in a
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chamber with a constant temperature (22 ± 1 °C) and humidity (RH of (A ± 2)%) for
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48 h. Four groups of samples were prepared in 70-mm weighing bottles with
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approximately 6.00 g in each group. The aqueous ratios of the samples from two
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groups were tested using the oven method (deviation ≤ 0.1%), and the average of the
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tested values was defined as the original aqueous ratio of the sample. The other two
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groups were maintained in a sulfuric acid desiccator with a relative humidity of 30 ±
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2% to observe the moisture removal process and (80 ± 2)% RH to observe the moisture absorption process. The sulfuric acid desiccators were maintained in a chamber with constant temperature (22 ± 1 °C) and humidity to study the changes in the aqueous ratios during moisture removal and the absorption process of
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vacuum-freeze-dried fiddleheads. Equilibration of the vacuum-freeze-dried
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fiddleheads was generally achieved after 48 h in the different environments with
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different relative humidities. Therefore, the observations associated with the aqueous
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ratio changes during moisture removal and the absorption process were performed 11
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over a period of 5 days. The samples were weighed and the time was recorded every 4
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h during the first three days (no less than three times per day). During the last two
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days, the samples were weighed once per day. At each time point, the aqueous ratio
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difference (compared with the original aqueous ratio) and the weight difference were
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recorded.
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was plotted. Utilizing the slope of the water content curve at the early stage and its
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comparison to the equilibrium aqueous ratio at the later stage, the moisture retention
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property of vacuum-freeze-dried fiddleheads with the addition of humectants (and the
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appropriate reference) was compared and evaluated (Sun, et al., 2006).
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2.9. Color and film transparency measurement
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USA) and expressed as L*, a*, and b*. The film transparency was determined
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according to the method developed by Ubonrat Siripatrawan using a UV
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spectrophotometer (UV-2802H, Unico, Shanghai) and calculated according to the following equation (Siripatrawan & Harte, 2010): T=log T600/thickness,
where T600 is the fractional transmittance at 600 nm and thickness is the film thickness
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(mm). According to this equation, high values of T indicate low transparency and a
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higher degree of opacity. All of the tests were conducted in triplicate.
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2.10. Experimental design and statistical analysis
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Three independent property measurements were conducted at different times to 12
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obtain three experimental replications (n = 3) for all PUL-based films. The data were
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analyzed using SPSS 17.0 for Windows (SPSS Inc., Chicago, IL, USA). The
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comparisons between the PUL-based films were made through an analysis of variance
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(ANOVA) with post-hoc comparisons of the mean values using Duncan’s
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multiple-range test. The differences between the mean values were considered
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significant at p < 0.05. The effects of the four independent variables, specifically the
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WVP, TS, E%, and OP measurements, on the moisture retention ability of the
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blend-modified polysaccharide edible films were studied using a four-factor CCD
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(Central Composite Design).
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The 10 blend-modified polysaccharide samples were established based on the
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CCD with four independent variables. Multiple regression analysis was applied to
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predict the linear, quadratic, and interaction terms of the independent variables in the
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RSM (Response Surface Method). A regression analysis was performed to estimate
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the response function as a polynomial model: Y = b0 + ∑biXi, where Y is the response
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calculated by the model, b0 is a constant, and bi is the linear coefficient. The data were modeled through multiple regression analysis based on a stepwise analysis. Only those variables that were found to be significant at the p < 0.05 level were selected for the model construction. The significant terms in the model for each response were
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found through an analysis of variance (ANOVA). The acceptability of the model was
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analyzed, accounting for the lack of fit, adequate precision, and pure error. The
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experimental data were compared with the fitted values predicted by the models to
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verify the suitability of the regression models. Each experiment was repeated in 13
Page 13 of 32
triplicate, and the mean values, including the pooled standard error of the mean
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(SEM), were then determined.
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3. Results and discussion
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3.1. Properties of co-blended polysaccharide films
Due to the beneficial compatibility with the polysaccharide added, a good mixed
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gel system was formed, and polysaccharide films with satisfactory smoothness and
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transparency were obtained. The quantity of dry matter in the film liquid per unit of
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flat area was maintained constant throughout the experiment to keep the film
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thickness constant (0.10 ± 0.01 mm), which ensured minimal influence of the film
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thickness when measuring the film properties (Gennadios, McHugh, & Weller, 1994).
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The co-blended polysaccharide solution determines the co-blended film
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properties to some extent. The measurement results for the properties of the binary
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and ternary co-blended systems, including WVP, TS, E%, and OP, after the addition
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of the polysaccharides are shown in Table 1. From these results, a better performance,
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based on improved water barrier properties, mechanical properties, and OP, was found with the PUL/ALG-CO binary co-blended film after blend-modification compared with the PUL/ALG film obtained through direct addition. The WVP of the ternary co-blended film formed by the direct addition of PEC,
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CAR, and ALO was higher than that of the PUL/ALG film, whereas the direct
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addition of PGA increased the water barrier property. The TS and E% of the ternary
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co-blended film with the direct addition of ALO were lower than those of the
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PUL/ALG film, whereas the TS and E% of the ternary co-blended film with the 14
Page 14 of 32
addition of PGA, PEC, and CAR were higher than those of the binary films. Contrary
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to the negative influence of CAR and ALO on the OP, the OP of a ternary co-blended
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film with the direct addition of PGA and PEC would be better than that of a binary
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co-blended film. As shown in Table 1, the additions of PGA, PEC, and CAR by
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co-drying significantly improved the water barrier property, which is the same effect
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as those of the TS, E%, and OP of the ternary co-blended film with the addition of
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ALO. Among all of the samples, the WVP of the ternary co-blended
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PUL/ALG/PGA-CO film obtained with the co-drying modification was decreased by
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69.8% compared with that of the PUL/ALG film. Generally speaking, the compounds
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formed by different polysaccharides exhibited stronger functional properties, such as
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the gel property and the aggregative property. Three independent gel systems were
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formed because the interactions of the different components of different complex
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types of polysaccharides were reduced due to the electronic incompatibility of
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polysaccharides (Zaleska, Ring, & Tomasik, 2000). However, the electronic
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compatibility of the polysaccharides and their interactions increased after modification through co-drying, but the detailed mechanisms underlying the formation of these co-dried films are not completely understood (Hosseini, Rezaei, Zandi, & Ghavi, 2013). Moreover, the surface activity, functional property, and water
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barrier property of the co-dried powder were significantly improved by this method.
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Different polysaccharides in ternary co-blended films have different effects on the
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water barrier properties of the films produced by the direct blending and co-drying
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modifications due to the different interactions between different polysaccharides. The 15
Page 15 of 32
PGA and PUL/ALG films formed a stronger gel network structure due to their
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hydrogen bonding and electrostatic interactions, which also resulted in the best water
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barrier property. In contrast, PEC and PUL/ALG formed a weaker hydrogen bonding
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network, which resulted in a comparatively poorer water barrier property. CAR has
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different gel forming stages than the other polysaccharides, resulting in poor
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compatibility and a comparatively higher WVP. ALO only formed weak, non-covalent
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bonds with PUL/ALG, resulting in the highest WVP and the worst water barrier
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property (Villagomez-Zavala, Gomez-Corona, Martinez, Perez-Orozco, Vernon-Carter,
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& Pedroza-Islas, 2008).
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The addition of PGA, PEC, and CAR significantly improved the film plasticity
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and mechanical property. The TS of the ternary films obtained through the addition of
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polysaccharides by co-drying increased 13.3%, 34.4%, 38.6%, and 13.46%,
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respectively, compared with those of the films obtained by direct addition.
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Alternatively, the E% of these ternary films with the addition of polysaccharides by
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co-drying increased 487.5%, 78.6%, 99.8%, and 97.2%, respectively, compared with those of the films obtained through direct addition. As shown in Table 1, with the exception of ALO, the co-blending modification of
PGA, PEC, and CAR significantly improved the OP of the ternary films formed. The
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oxygen permeability ratio of the ternary co-blended films decreased 39.5%, 33.7%,
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and 26.6%, respectively, compared with that of the PUL/ALG film. The oxygen
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permeability of the ternary blend-modified PUL/ALG/PGA-CO, PUL/ALG/PEC-CO,
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PUL/ALG/CAR-CO, and PUL/ALG/ALO-CO films decreased 36.5%, 33.4%, 33.0%, 16
Page 16 of 32
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and 19.5%, respectively, compared with these films made through direct blending.
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It can be concluded that the ternary co-drying of the modified polysaccharide films, especially the function of drying-modified PGA on the co-blending property of
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polysaccharides, can increase the application value of co-blended films to some
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extent.
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3.2. Dehydration and hygroscopicity
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352
Methods with several differentials were utilized to study the moisture removal
357
process of 12 groups of vacuum-freeze-dried fiddlehead samples that were sprayed
358
with 10 different types of blend-modified polysaccharides, glycerin, and a reference
359
compound in a (22 ± 1) °C environment with a RH of (30 ± 2)% and then subjected to
360
a moisture absorption process at (22 ± 1) °C with a RH of (80 ± 2)%. The aqueous
361
ratios were also measured simultaneously. Curves of the aqueous ratio of the
362
vacuum-freeze-dried fiddleheads as a function of the measuring time were then
363
prepared and are shown in Fig. 1a and Fig. 1b.
365 366 367
M
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364
an
356
At 30% RH, the water content (%) of all vacuum-freeze-dried fiddlehead
samples coated with the blend-modified polysaccharides decreased gradually over a period of 120 h, which is quite similar to the behavior obtained with glycerol and the reference. The sequence of the aqueous ratios of the vacuum-freeze-dried fiddleheads
368
(within 120 h) was as follows: PUL/ALG/PGA-CO > PUL/ALG/PEC-CO >
369
PUL/ALG/CAR-CO > PUL/ALG-CO > PUL/ALG/PGA > PUL/ALG >
370
PUL/ALG/PEC > PUL/ALG/CAR > glycerin > PUL/ALG/ALO-CO >
371
PUL/ALG/ALO > reference. The analysis of variance was performed to determine the 17
Page 17 of 32
factors that influence the aqueous ratio of vacuum-freeze-dried fiddleheads, and the
373
results are shown in Table 1. This analysis indicated that the addition time, the type of
374
co-blended polysaccharide added, and its interactions had a significantly different
375
influence on the aqueous rate of the vacuum-freeze-dried fiddleheads. Multiple
376
comparisons regarding the influence of different humectants were performed, and
377
results are shown in Fig. 1a and Fig. 1b . This figure indicates that the aqueous ratios
378
of the vacuum-freeze-dried fiddleheads after the humectant treatment, including
379
PUL/ALG/PGA-CO, PUL/ALG/PEC-CO, and PUL/ALG/CAR-CO, were
380
significantly higher than those of the vacuum-freeze-dried fiddleheads in the other
381
nine treatment groups (Fig. 1a). The co-dried blended ternary polysaccharides are
382
expected to have proportionally more polar residues, which imparts the ability to form
383
hydrogen bonds with water and increase the moisture absorption and retention
384
properties (Gbogouri, Linder, Fanni, & Parmentier, 2004). Therefore, the ternary
385
co-blended polysaccharides, particularly PUL/ALG/PGA-CO, showed good moisture
387 388 389
cr
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an
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d
te
Ac ce p
386
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372
absorption and retention properties. Furthermore, in 30% RH, the best humectant moisturizing property was found with 0.5% PUL/ALG/PGA-CO, followed by 0.5% PUL/ALG/PEC-CO and 0.5% PUL/ALG/CAR-CO. Generally speaking, the three humectants mentioned are suitable for the application of this technique in an
390
environment with lower humidity. A later study will focus on the correlation of the
391
comprehensive performance and moisture retention properties of the films to
392
investigate the feasibility of a new method for moisture retention assessment.
393
For the typical behavior of water vapor-sensitive hydrophilic polysaccharides, 18
Page 18 of 32
the selection of humectants in an environment with high humidity was stricter,there,
395
the focus should be placed on the products’ moisture-resistant properties (Ryu, Kim,
396
Park, Lee, & Lee, 2007; Silhacek & Murphy, 2008). At 80% RH, the weight of the
397
residual moisture in the vacuum-freeze-dried fiddleheads increased during the 120 h
398
of the study. The sequence of moisture-retention ability was as follows:
399
PUL/ALG/ALO > glycerin > PUL/ALG/ALO-CO > reference > PUL/ALG/CAR >
400
PUL/ALG/PEC > PUL/ALG > PUL/ALG/PGA > PUL/ALG-CO >
401
PUL/ALG/CAR-CO > PUL/ALG/PEC-CO > PUL/ALG/PGA-CO. The aqueous
402
ratios of vacuum-freeze-dried fiddleheads treated with PUL/ALG/ALO, glycerin, and
403
PUL/ALG/ALO-CO were higher than that of the control sample treated with distilled
404
water, indicating that these three humectants exhibit poor moisture barrier properties.
405
The water-resistance properties of the vacuum-freeze-dried fiddleheads following the
406
addition of PUL/ALG/PGA-CO and PUL/ALG/PEC-CO were significantly higher
407
than those of the other samples in the high-humidity environment (Fig. 1b), which
409 410 411 412 413
cr
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an
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d
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Ac ce p
408
ip t
394
coincides with their amphiphilic structure (Pennick, Chavan, Summers, & Rawlings, 2012). Therefore, under high-humidity conditions, , PUL/ALG/PGA-CO and PUL/ALG/PEC-CO are the preferred humectants due to their moisture barrier properties.
3.3. Correlation between WVP, TS, E% and OP, and moisture retention ability The traditional method for measuring the moisture retention property is too
414
complicated and does not provide exhaustive and accurate results. Therefore, this
415
study was designed to assess the moisture-retention property based on the film 19
Page 19 of 32
properties (water barrier, moisture barrier, and mechanical properties with particular
417
focus on the penetration of aromatic components). Thus, this assessment was more
418
comprehensive. To study the accuracy of this assessment method, a correlative
419
analysis was performed on the properties of ternary co-blended films and their
420
moisture-retention properties as measured by a differential method (Hou, et al., 2012;
421
Sun, et al., 2006).
cr us
422
ip t
416
The values of water content for each of the blend-modified polysaccharide edible films are shown in Fig. 1a and Fig. 1b. The linear coefficient of WVP (X1), TS (X2),
424
E% (X3), and OP (X4) for each of the response variables is given in Table 2. The R2
425
and adjusted R2 values for the significant (p < 0.05) response surface models varied
426
from 0.9108 to 0.9530 and from 0.8395 to 0.9154, respectively. These values were
427
obtained for the moisture-retention ability at a storage temperature of 22 °C with a
428
RH of 30% or 80% for 120 h. The selected variables yielded the highest values of R2
429
and adjusted R2 for each response variable studied. All of the models were significant
431 432 433
M
d
te
Ac ce p
430
an
423
for all of the variables (RH = 30% (p = 0.0016) and RH = 80% (p = 0.0078); (Table 2)). Therefore, the RSM was able to predict most of the variations in the moisture retentions properties as a function of the blend-modified polysaccharide edible film variables. The effect of the WVP was highly significant (p < 0.05) for the
434
moisture-retention ability (Table 2), and it was considered the highest coefficient of
435
the main linear effects. Similar results have also been reported by other researchers
436
(Bosquez-Molina, Guerrero-Legarreta, & Vernon-Carter, 2003; Lin, Du, Liang, Wang,
437
Wang, & Yang, 2011). These results can be explained by the fact that the water 20
Page 20 of 32
barrier property of the co-blended film most related to film moisture is the retention
439
property (Bosquez-Molina, Guerrero-Legarreta, & Vernon-Carter, 2003; Lin, Du,
440
Liang, Wang, Wang, & Yang, 2011). The fitted models were suitable, showing
441
significant regression, no lack of fit, and satisfactory coefficients (Table 2).
The predicted values were obtained through a model-fitting technique using the
cr
442
ip t
438
Design Expert software. Fitting the data to a linear model and the subsequent
444
ANOVA showed that the linear model was suitable. There was a suitable relationship
445
between the predicted values and the experimental values (Fig. 2). The model was
446
used to find an optimal region for the response variable studied and to define the
447
relationship between the three independent variables and the response variables. The
448
optimum blending was found to be PUL/ALG/PGA-CO, which gave the best
449
moisture-retention ability.
452 453 454 455
an
M
d
te
451
For validation of the model, the acceptability of the response surface equations was checked through a comparison of the experimental and fitted values predicted by
Ac ce p
450
us
443
the response regression models. No significant difference (p > 0.05) was found between the experimental and predicted values. 3.4. Changes in color and film transparency Film color is an important index in terms of general appearance and consumer
456
acceptance. The L*, a*, and b* values of the blended films are shown in Table 3.
457
There were no significant differences (p > 0.05) in the L* value between all of the
458
films. In general, the ALG film exhibited a slight yellow appearance that darkened as
459
the thickness increased. The blended films presented increases in a* and b* with the 21
Page 21 of 32
direct and co-dried addition of PGA, PEC, CAR, or ALO, indicating that the film
461
became more yellowish after the incorporation of PGA, PEC, CAR, or ALO. The
462
differences observed in the films’ color could be ascribed to different interactions that
463
may have occurred during the blending process and the storage of PUL/ALG and the
464
different polysaccharides (Prodpran, Benjakul, & Artharn, 2007).
cr
The transparency of the PUL/ALG film was low (indicated by the high value of
us
465
ip t
460
T), which could be linked to the drying process. During drying, the PUL/ALG
467
film-forming solution was easily influenced by the wind in the oven, as indicated by
468
visible ripples on the surface of the PUL/ALG film, which undoubtedly increased the
469
final T value (Wu, Zhong, Li, Shoemaker, & Xia, 2013). There were significant
470
differences in the T values (p ≤ 0.05) between the blended films, which indicates that
471
the incorporation of PGA, PEC, CAR, or ALO did affect the transparency of the
472
films.
473
4. Conclusions
475 476 477
M
d
te
Ac ce p
474
an
466
In comparison to the common humectants used, ternary co-blended
polysaccharide films prepared using the co-drying method can significantly improve the film properties and moisture retention. Three types of directly mixed biopolymers are often not stable. However, the preparation of a co-dried mixture noticeably
478
decreased the incompatibility of both the particle sizes and the chemical properties of
479
the polysaccharides and increased the thermodynamic compatibility (Ohashi, et al.,
480
1991; Salvador, Sanz, & Fiszman, 2001); therefore, the compatibility of the three
481
phases was greatly improved. This research indicates that ternary co-blended 22
Page 22 of 32
polysaccharide films prepared through the co-drying method can be used as an
483
alternative to traditional humectants and applied for the preservation of IMFs. With
484
the exception of the traditional measuring methods, the assessment of the moisture
485
retention properties of humectants can be performed based on the film formed on the
486
food surface, and this measurement can be used for the total assessment of four film
487
parameters, namely WVP, TS, E%, and OP.
488
Acknowledgments
us
cr
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482
This study was financially supported by the Natural Science Foundation of China
490
(No. 31230057) and the National Key Technology R&D Program for the 12th
491
Five-Year Plan (Nos. 2012BAD37B01 and 2012BAD37B02).
492
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Hosseini, S. F., Rezaei, M., Zandi, M., & Ghavi, F. F. (2013). Preparation and functional properties of fish gelatin-chitosan blend edible films. Food Chem, 136, 1490-1495.
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Tang, C. H., Jiang, Y., Wen, Q. B., & Yang, X. Q. (2005). Effect of transglutaminase treatment on the properties of cast films of soy protein isolates. J Biotechnol, 120, 296-307. Villagomez-Zavala, D. L., Gomez-Corona, C., Martinez, E. S., Perez-Orozco, J. P., Vernon-Carter, E. J., & Pedroza-Islas, R. (2008). Comparative Study of the Mechanical Properties of Edible Films IngenieriaQuimica, 7, 263-273.
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Yang, S. L., Guo, Z. Y., Zhou, Y. L., Zhou, L. L., Xue, Q. Z., Miao, F. P., & Qin, S. (2010). Synthesis and moisture absorption and retention activities of a carboxymethyl and a quaternary ammonium derivative of alpha,alpha-trehalose. Carbohydr Res, 345, 120-123. Zaleska, H., Ring, S. G., & Tomasik, P. (2000). Apple pectin complexes with whey protein isolate.
Ac ce p
559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587
Food Hydrocolloids, 14, 377-382.
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Page 25 of 32
ip t cr
Table 1 The WVP, TS, E%, OP, and moisture retention ability of the blend-modified polysaccharide edible films.a
us
588 589
Average moisture retention value (RH=80%) (Y2) 16.39 ± 1.40 C 16.33 ± 1.36 C 16.46 ± 1.41 D 16.51 ± 1.43 D 17.82 ± 2.10 E 16.18 ± 1.28 B 15.29 ± 0.63 A 15.42 ± 0.69 A 16.12 ± 1.23 B 17.75 ± 2.22 E
Ac
591 592 593 594 595 596
ce pt
ed
M an
Average moisture WVP OP Blending Blend-modified polysaccharide 3 2 (g·mm/m²·h·kP TS (MPa) (X2) E% (X3) (cm ·mm/m ·day· retention value method edible films (RH=30%) a) (X1) kPa) (X4) (Y1) PUL/ALG (50.00 g/L) 1.69 ± 0.08 AB 69.34 ± 4.45 C 5.71 ± 0.16 FG 326.58 ± 12.07 D 10.84 ± 2.09 E PUL/ALG/PGA (50.00 g/L) 1.61 ± 0.03 A 91.47 ± 8.12 A 7.89 ± 0.33 D 311.38 ± 8.82 D 10.93 ± 2.04 D Direct PUL/ALG/PEC (50.00 g/L) 1.80 ± 0.03 B 71.32 ± 7.22 C 7.66 ± 0.29 D 324.72 ± 6.16 D 10.77 ± 2.11 F addition PUL/ALG/CAR (50.00 g/L) 1.93 ± 0.07 C 70.11 ± 6.01 C 6.19 ± 0.18 E 357.65 ± 12.96 C 10.63 ± 2.13 G PUL/ALG/ALO (50.00 g/L) 2.78 ± 0.09 D 60.04 ± 8.74 C 2.11 ± 0.12 I 498.07 ± 9.50 A 9.33 ± 2.45 H PUL/ALG-CO (50.00 g/L) 1.04 ± 0.03 E 91.20 ± 6.24 B 5.96 ± 0.21 EF 289.64 ± 7.76 E 11.05 ± 1.97 C PUL/ALG/PGA-CO (50.00 g/L) 0.51 ± 0.05 G 103.68 ± 3.63 A 46.35 ± 1.12 A 197.65 ± 11.82 G 12.18 ± 1.39 A Co-dried PUL/ALG/PEC-CO (50.00 g/L) 1.11 ± 0.04 EF 95.86 ± 5.55 A 13.68 ± 0.23 B 216.40 ± 5.58 G 11.62 ± 1.63 B addition PUL/ALG/CAR-CO (50.00 g/L) 1.20 ± 0.08 F 97.17 ± 6.08 A 12.37 ± 0.12 C 239.76 ± 7.35 F 11.56 ± 1.69 B PUL/ALG/ALO-CO (50.00 g/L) 1.92 ± 0.03 C 68.12 ± 4.63 C 4.16 ± 0.06 H 401.13 ± 29.24 B 9.50 ± 2.28 H a 590 The values are the means ± the standard deviation. Different letters in the same column indicate significant differences (p ≤ 0.05).
26
Page 26 of 32
Table 2 The regression coefficients, R2, adjusted R2, and lack of fit for the final reduced models. Average moisture Average moisture retention values Regression coefficient retention values (RH=80%) (Y2) (RH=30%) (Y1) b0 13.236 13.361 b1 0.466 -0.449 b2 0.003 0.003 b3 0.012 -0.009 b4 -0.011 0.011 R Square 0.9530 0.9108 Adjusted R Square 0.9154 0.8395 Lack of fit (F-value) 25.3486 12.7691 Lack of fit (p-value) 0.0016 0.0078 bi (i = 1, 2, 3, or 4), the estimated regression coefficient for the main linear effects. 1, WVP (g·mm/m²·h·kPa); 2, TS (MPa); 3, E%; 4, OP (cm3·mm/m2·day·kPa).
an
M d te Ac ce p
600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628
us
cr
ip t
597 598 599
27
Page 27 of 32
ip t cr
us
Table 3 Thickness, color, and transparency of the blend-modified polysaccharide edible films.a Blend-modified Film thickness Blending L* a* b* T polysaccharide edible (mm) method films PUL/ALG 45.17 ± 0.47 EF 86.06 ± 0.19 A 0.42 ± 0.04 F 0.77 ± 0.04 F 1.62 ± 0.04 A PUL/ALG/PGA 48.30 ± 1.01 D 86.00 ± 0.20 A 0.54 ± 0.04 E 1.03 ± 0.07 E 0.67 ± 0.05 EF Direct PUL/ALG/PEC 49.03 ± 0.66 D 85.96 ± 0.12 A 0.63 ± 0.03 DE 1.06 ± 0.06 E 0.78 ± 0.04 CD addition PUL/ALG/CAR 51.43 ± 0.84 B 85.92 ± 0.10 A 0.71 ± 0.03 C 1.09 ± 0.05 E 0.83 ± 0.02 C PUL/ALG/ALO 52.60 ± 1.17 AB 85.76 ± 0.03 A 0.87 ± 0.05 A 1.17 ± 0.06 DE 1.02 ± 0.04 B PUL/ALG-CO 44.15 ± 1.00 FG 86.02 ± 0.11 A 0.47 ± 0.04 EF 0.80 ± 0.04 F 1.57 ± 0.09 A PUL/ALG/PGA-CO 43.26 ± 0.97 G 85.85 ± 0.08 A 0.54 ± 0.03 E 1.37 ± 0.09 C 0.64 ± 0.02 F Co-dried PUL/ALG/PEC-CO 49.55 ± 0.30 CD 85.99 ± 0.11 A 0.67 ± 0.07 CD 1.43 ± 0.05 AB 0.72 ± 0.05 DE addition PUL/ALG/CAR-CO 51.42 ± 1.22 BC 86.04 ± 0.17 A 0.73 ± 0.03 BC 1.54 ± 0.06 A 0.75 ± 0.04 D PUL/ALG/ALO-CO 54.44 ± 0.89 A 85.74 ± 0.08 A 0.78 ± 0.03 AB 1.21 ± 0.02 D 0.94 ± 0.07B a The values are the means ± the standard deviation. Different letters in the same column indicate significant differences (p ≤ 0.05).
Ac
631 632 633 634 635 636 637 638 639 640 641
ce pt
ed
M an
629 630
28
Page 28 of 32
te
d
M
an
us
cr
ip t
Fig. 1a. Dehydration of the blend-modified polysaccharides, glycerin, and the reference Fig. 1b. Hygroscopicity of the blend-modified polysaccharides, glycerin, and the reference. Fig. 2. Predicted and experimental values of (a) the average moisture retention values at RH = 30% and (b) the average moisture retention values at RH = 80% for the blend-modified polysaccharide edible films.
Ac ce p
642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685
29
Page 29 of 32
ip t cr us an M d te Ac ce p
686 687 688 689 690 691 692 693 694
Fig. 1a. Dehydration of the blend-modified polysaccharides, glycerin, and the reference.
30
Page 30 of 32
ip t cr us an M d te 696 697 698 699 700 701 702 703 704 705 706
Ac ce p
695
Fig. 1b. Hygroscopicity of the blend-modified polysaccharides, glycerin, and the reference.
31
Page 31 of 32
ip t us
cr 708 709 710 711
Ac ce p
te
d
M
an
707
Fig. 2. Predicted and experimental values of (a) the average moisture retention values at RH = 30% and (b) the average moisture retention values at RH = 80% for the blend-modified polysaccharide edible films.
32
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S0144-8617(14)00514-1 http://dx.doi.org/doi:10.1016/j.carbpol.2014.05.044 CARP 8911
To appear in: Received date: Revised date: Accepted date:
9-2-2014 12-5-2014 13-5-2014
Please cite this article as: Pan, H., Jiang, B., Chen, J., & Jin, Z.,Assessment of the physical, mechanical, and moisture-retention properties of pullulan-based ternary co-blended films, Carbohydrate Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.05.044 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Assessment of the physical, mechanical, and moisture-retention properties of
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pullulan-based ternary co-blended films
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Hongyang Pana, *, Bo Jianga, Jie Chena, Zhengyu Jina, b
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a
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214122, P. R. China
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b
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China
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State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi
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School of Food Science and Technology, Jiangnan University, Wuxi 214122, P. R.
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*
Corresponding author. Telephone number:+86-510-85919656. Fax number:
+86-510-85919656. E-mail address: [email protected] (H. Pan). 1
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Research Highlights
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In this manuscript:
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1) A co-drying method to modify the properties of co-blended polysaccharides was
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reported.
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2) A method to evaluate moisture retention properties of films in IMF was reported.
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3) Ternary co-dried blended films with PGA showed better water retention ability.
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4) A model between film characteristics and moisture-retention values was
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established.
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5) The model could be used to evaluate water retention, anti-moisture absorption.
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Abstract: Multi-component substances made through direct blending or blending
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with co-drying can form films on the surfaces of intermediate moisture foods (IMFs), which help retain moisture and protect food texture and flavor. An IMF film system based on pullulan, with glycerol serving as the plasticizer, was studied using alginate and four different types of polysaccharides (propyleneglycol alginate, pectin,
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carrageenan, and aloe polysaccharide) as the blend-modified substances. The physical,
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mechanical, color, transparency, and moisture-retention properties of the co-blended
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films with the polysaccharides were assessed. A new formula was established for the
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average moisture retention property, water barrier, tensile strength, elongation at break, 2
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and oxygen barrier property of the ternary co-blended films using the Design Expert
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software. The new model established for moisture content measurement used an
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indirect method of film formation on food surfaces by humectants, which should
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expedite model validation and allow a better comprehension of moisture transfer
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through edible films.
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Keywords: intermediate moisture food; ternary co-blended film; water vapor
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permeability; pullulan; moisture retention
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1. Introduction
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As an intermediate moisture food (IMF), the moisture of vacuum-freeze-dried
fiddleheads is between 10% and 15%, and the water activity is between 0.5 and 0.6. Moreover, vacuum freeze-drying is one of the oldest methods of preserving fiddleheads (Karel & Heidelbaugh, 1973; Miranda, Berna, Bon, & Mulet, 2011;
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Pavey & Schack, 1969). The main components of vacuum-freeze-dried fiddleheads
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include protein, carbohydrates, lipids, and other humectants (DeLong, Hodges, Prange,
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Forney, Fan, Bishop, et al., 2013). Compared with traditional dried or high-moisture
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fiddleheads, intermediate moisture vacuum-freeze-dried fiddleheads have many 3
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advantages. The first benefit is a lower energy consumption during processing and
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transportation compared with dried, refrigerated, frozen, and canned foods. Vacuum
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freeze-drying also lessens the destruction of the fiddleheads during processing
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compared with comparable stronger methods, such as dehydration and heat treatment.
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The low water activity (0.5-0.6) of vacuum-freeze-dried fiddleheads will control
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microorganisms and better maintain their preservation at room temperature (shelf life:
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1/2 year to 1 year); Finally, fiddleheads prepared in this manner are mild taste and
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easy to eat because they are directly edible without heating or rehydrating (Brimelow,
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1985). However, vacuum-freeze-dried fiddleheads still present several problems, such
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as being affected by dry or wet conditions, structural destruction, and loss of flavor,
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all of which significantly influence the nutritional value and the consumer acceptance
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(Hierro, de la Hoz, & Ordonez, 2004; Rao, Rocca-Smith, & Labuza, 2012).
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The public perception of the potential toxicological properties of food additives
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has also limited the widespread development of vacuum-freeze-dried fiddleheads for
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human consumption. Recent applications have focused on developing vacuum-freeze-dried fiddleheads for use in space programs and the military. The addition of humectants to fresh vegetables or fruits can reduce the water activity into ranges that allow their storage without refrigeration (Carrasco & Cisneros-Zevallos,
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2002; Gliemmo, Campos, & Gerschenson, 2004; Rojas & Gerschenson, 2001).The
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addition of humectants and plasticizers is the basic method for controlling the
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moisture and structure of vacuum-freeze-dried fiddleheads. The common humectants
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used are sugars (such as glucose, fructose, fructose syrup, glucose syrup, and 4
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polysaccharides), polyhydroxy compounds (such as sorbitol and glycerol), and salts
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(Gliemmo, Campos, & Gerschenson, 2004; Rojas & Gerschenson, 2001; Sritongtae,
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Mahawanich, & Duangmal, 2011). The study of polysaccharides as humectants started years ago. Ternary blends of
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polysaccharide solutions prepared through the co-drying method can have synergistic
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effects, that endow the composite with superior functional features, including
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increasing the viscosity of a single polysaccharide solution, improving the gelation
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function, and increasing the barrier and mechanical performance of the film formed
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(Ohashi, Ura, Takeuchi, et al., 1991; Salvador, Sanz, & Fiszman, 2001). Over the
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years, the study of blending polysaccharides has mainly focused on the simple
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physical mixing and synergy of two polysaccharides. In addition, few studies have
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focused on the characteristics of polysaccharide solutions formed by a ternary system
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(Damasio, Fiszman, Costell, & Dura´n, 1990; Salvador, Sanz, & Fiszman, 2001).
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Generally speaking, the electrostatic interactions between the different large
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molecules in polysaccharides are the reason for which blended systems perform better. Ternary polysaccharides produced through the co-drying method can be used as food humectants in IMF, as they improve the preservation and manufacturing properties, by increasing the water barrier, mechanical strength, and appearance acceptance. The
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traditional testing of the characteristics of humectants mainly focused on the moisture
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variation under specific conditions, thus establishing the relationships between the
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humectant effectiveness and time (Hou, Li, Zhang, Xue, Yu, Wang, et al., 2012; Yang,
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Guo, Zhou, Zhou, Xue, Miao, et al., 2010). 5
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This article assesses the humectant effectiveness of the ternary blending of
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polysaccharides by co-drying on vacuum freeze-dried fiddleheads. Furthermore, this
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article studies the film characteristics of polysaccharides on the surface of the
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fiddleheads. These results were used to establish a correlation model between the film
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characteristics of water barrier, oxygen barrier, mechanical strength and moisture
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effectiveness. This measurement will be used to fully evaluate the humectant
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characteristics of ternary blended polysaccharides, including their water retention,
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anti-moisture absorption, mechanical property, and improvements in their appearance
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acceptance.
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2. Materials and Methods
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2.1. Materials
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Following emergence and before 10 cm of growth, the fiddleheads of Matteuccia
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struthiopteris were harvested from Changbai Mountain in northeast China during
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2012. The crosiers were either refrigerated or maintained on ice until they were
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cleaned and then stored at 4 °C. All of the tissue samples were freeze-dried and stored at 4 °C until further analysis.
The pullulan (PUL) and aloe polysaccharide (ALO) were obtained from Jiangnan
University (Wuxi, China). The reagents used for film preparation and testing (glycerol,
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alginate (ALG), propyleneglycol alginate (PGA), pectin (PEC), carrageenan (CAR),
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magnesium nitrate, sodium hydroxide, and anhydrous calcium chloride) were
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purchased from Fisher Sci. Ltd. (Shanghai, China).
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2.2. Co-dried PUL/ALG and PUL/ALG/polysaccharides blended preparation 6
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Solutions of 50.00 g/L PUL and 50.00 g/L ALG were prepared in distilled water at 60 °C, and 0.05 (g/g PUL) polysaccharides (PGA, PEC, CAR, and ALO) were then
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added to the solutions. The concentration of the solution was adjusted to achieve a
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viscosity of less than 500 cps, and the pH was adjusted to 7.0 using 2 M NaOH. The
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spray drying was performed using a BUCHI B-290 Mini Spray Dryer with an
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atomizer speed of 15,000 rpm, an inlet temperature of 200 °C, and an outlet
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temperature of 95 °C. The resultant dried powder (PUL/ALG/PGA-CO,
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PUL/ALG/PEC-CO, PUL/ALG/CAR-CO, and PUL/ALG/ALO-CO) was the neutral
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ternary polysaccharide co-dried powder.
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The pH was adjusted to 7.0 with a 50.00 g/L PUL solution and a 50.00 g/L ALG
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solution, and the blend-modified powder was adjusted to obtain a binary neutral
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co-dried powder (PUL/ALG-CO).
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2.3. PUL/ALG film and PUL/ALG/polysaccharides film preparation
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The different powders obtained (PUL/ALG, PUL/ALG-CO, and
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PUL/ALG/polysaccharides, PUL/ALG/polysaccharides-CO) were slowly added into stirring deionized water. The stirring was maintained for 2 h to uniformly disperse the powders into the aqueous solution to obtain a stable solution of 50.00 g/L. The solution, the pH of which was adjusted to 7.0 with 2 M NaOH, was prepared and
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heated in a 250-mL Erlenmeyer flask for 30 min in a water bath at 80 °C. The
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emulsions were then cooled in an ice bath. Glycerol (0.30 g/g PUL) was added in the
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amount required to achieve the desired final film composition, and the film-forming
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solutions were de-gassed under vacuum of 0.09 MPa for 10 min using a vacuum 7
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pump (SHZ-D(III), Yuhua Instruments Co. Ltd., Gongyi, China). The films were prepared by placing the specific amount of the degassed film-forming solution or emulsion that would provide 3.00 g of total solids on a
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smooth high-density polyethylene (HDPE) casting plate resting on a leveled granite
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surface, because it is not hygroscopic and has good resistance in WVP. Additionally,
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HDPE has good chemical stability, which means that it is insoluble in any organic
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solvent, and has good resistance to corrosion by acids, bases, and all types of salts
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(Araujo, Mano, Teixeira, Spinace, & De Paoli, 2010).The films were dried for
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approximately 20 h in the oven at 53% relative humidity (RH) and 25 °C. All of the
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dried films could be peeled intact from the casting surface. The films used for water
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barrier property assessment and mechanical testing were conditioned at 53 ± 1% RH
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and 25 ± 1 °C by placing them in a desiccator containing a saturated solution of
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Mg(NO3)2·6(H2O) for at least 72 h. The compositions of the different polysaccharide
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films, including the PUL/ALG, PUL/ALG/PGA, PUL/ALG/PEC, PUL/ALG/CAR,
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and PUL/ALG/ALO films prepared from direct blended polysaccharide powder and the PUL/ALG-CO, PUL/ALG/PGA-CO, PUL/ALG/PEC-CO, PUL/ALG/CAR-CO, and PUL/ALG/ALO-CO films prepared from the neutral co-dried polysaccharide powders, are shown in Table 1. 2.4. Film thickness measurement The film thickness was determined using a digital micrometer (High-Accuracy
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Digimatic Digital Micrometer, USA). The film strips were placed between the jaws of
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the micrometer, and the gap was reduced until the friction was minimal. The mean 8
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thickness (m) of the films was measured from the average of numerical values at 10
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locations.
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2.5. Water vapor permeability (WVP) measurement The water vapor transmission rate (WVTR) of the film specimens were
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measured according to a modified ASTM E96 method (ASTM, 2002; Gennadios,
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McHugh, & Weller, 1994; Ou, Wang, Tang, Huang, & Jackson, 2005). Glass cups
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with a diameter of 3.00 cm and depth of 4.00 cm were used for this measurement. To
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maintain 0% RH in the cup headspace, 3.00 g of dried CaCl2 was added to the cup,
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and the film was then sealed over the rim of the cup by applying molten paraffin. The
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cups were placed in hermetically sealed jars maintained at 20 °C and 100% RH. The
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RH was maintained by placing 1,000 mL of water in the bottom of the jar. The cups
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were weighed every 12 h for a period of one week. The amount of water that
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permeated the films was determined from the weight gain of the cups. The WVTR
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and WVP were calculated using the following equations:
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WVTR=Δw/Δt×A, WVP= WVTR×L/Δp where WVTR is expressed in g/h·m2, Δw/Δt is the rate of water gain in g/h, A is the exposed area of the film in m2, L is the mean thickness of the film specimens in m, and Δp is the difference between the partial water vapor pressure on the two sides of
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the film specimens in Pa. The water vapor pressure on the high-stream side of the film
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was 2.34 kPa (i.e., saturated water vapor pressure at 20 °C), whereas that of the
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low-stream side was assumed to be zero.
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2.6. Measurement of mechanical properties 9
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Before testing their mechanical properties, the film samples were equilibrated for
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one week at 25 °C and 53% RH. Two mechanical parameters of the films, namely the
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tensile strength (TS) and the elongation at break (E%), were determined using a
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texture analyzer (TA-XT2i, Stable Micro Systems, Surrey, UK). The film samples
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were cut into 10-mm-wide and 800-mm-long strips using a sharp razor blade. Ten
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samples of each film type were tested. The tensile properties of the films were
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measured according to the ASTM standard method D882-02 (de Carvalho & Grosso,
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2004). The TS was calculated based on the original cross-sectional area of the test
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specimen using the equation TS = F/A, where TS is the tensile strength (MPa), F is
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the force (N) at maximum load, and A is the initial cross-sectional area (m2) of the
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film specimen. The E% value was calculated by dividing the extension-at-break of the
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specimen by the initial gauge length and multiplying by 100.
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2.7. Oxygen barrier property (OP) measurement
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A 60-mL jar was filled with 30.0 mL of fresh soybean oil, covered with different
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films, sealed using a bungee cord, and stored at a controlled temperature (60 °C) for 10 days. The peroxide value of the soybean oil samples was determined through sodium thiosulfate titration (Tang, Jiang, Wen, & Yang, 2005). All of the tests were conducted in triplicate.
2.8. Measurement of moisture retention ability The moisture retention properties were measured in this study using multiple
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variable differentials. First, 100.00 g of uniformly mixed vacuum-freeze-dried
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fiddleheads were weighed and equilibrated for 48 h at 22 ± 1 °C and (60 ± 2)% RH. 10
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This sample was then separated into two groups (50.00 g in each group). One group
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was prepared through a uniform spraying of blend-modified polysaccharide and
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glycerin at the proportion of 5.00 g/100 g of vacuum-freeze-dried fiddleheads. The
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other group was prepared by spraying the equivalent amount of distilled water as the
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reference. The two groups were equilibrated for 48 h at 22 ± 1 °C and (60 ± 2)% RH
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(Sun, Du, Yang, Shi, Li, Wang, et al., 2006; Yang, et al., 2010). For the measurement
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of the changes in the aqueous ratio of the vacuum freeze-dried fiddleheads during the
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moisture removal and absorption processes, the two groups were equilibrated in a
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chamber with a constant temperature (22 ± 1 °C) and humidity (RH of (A ± 2)%) for
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48 h. Four groups of samples were prepared in 70-mm weighing bottles with
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approximately 6.00 g in each group. The aqueous ratios of the samples from two
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groups were tested using the oven method (deviation ≤ 0.1%), and the average of the
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tested values was defined as the original aqueous ratio of the sample. The other two
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groups were maintained in a sulfuric acid desiccator with a relative humidity of 30 ±
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2% to observe the moisture removal process and (80 ± 2)% RH to observe the moisture absorption process. The sulfuric acid desiccators were maintained in a chamber with constant temperature (22 ± 1 °C) and humidity to study the changes in the aqueous ratios during moisture removal and the absorption process of
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vacuum-freeze-dried fiddleheads. Equilibration of the vacuum-freeze-dried
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fiddleheads was generally achieved after 48 h in the different environments with
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different relative humidities. Therefore, the observations associated with the aqueous
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ratio changes during moisture removal and the absorption process were performed 11
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over a period of 5 days. The samples were weighed and the time was recorded every 4
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h during the first three days (no less than three times per day). During the last two
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days, the samples were weighed once per day. At each time point, the aqueous ratio
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difference (compared with the original aqueous ratio) and the weight difference were
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recorded.
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was plotted. Utilizing the slope of the water content curve at the early stage and its
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comparison to the equilibrium aqueous ratio at the later stage, the moisture retention
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property of vacuum-freeze-dried fiddleheads with the addition of humectants (and the
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appropriate reference) was compared and evaluated (Sun, et al., 2006).
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2.9. Color and film transparency measurement
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USA) and expressed as L*, a*, and b*. The film transparency was determined
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according to the method developed by Ubonrat Siripatrawan using a UV
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spectrophotometer (UV-2802H, Unico, Shanghai) and calculated according to the following equation (Siripatrawan & Harte, 2010): T=log T600/thickness,
where T600 is the fractional transmittance at 600 nm and thickness is the film thickness
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(mm). According to this equation, high values of T indicate low transparency and a
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higher degree of opacity. All of the tests were conducted in triplicate.
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2.10. Experimental design and statistical analysis
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Three independent property measurements were conducted at different times to 12
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obtain three experimental replications (n = 3) for all PUL-based films. The data were
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analyzed using SPSS 17.0 for Windows (SPSS Inc., Chicago, IL, USA). The
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comparisons between the PUL-based films were made through an analysis of variance
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(ANOVA) with post-hoc comparisons of the mean values using Duncan’s
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multiple-range test. The differences between the mean values were considered
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significant at p < 0.05. The effects of the four independent variables, specifically the
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WVP, TS, E%, and OP measurements, on the moisture retention ability of the
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blend-modified polysaccharide edible films were studied using a four-factor CCD
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(Central Composite Design).
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The 10 blend-modified polysaccharide samples were established based on the
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CCD with four independent variables. Multiple regression analysis was applied to
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predict the linear, quadratic, and interaction terms of the independent variables in the
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RSM (Response Surface Method). A regression analysis was performed to estimate
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the response function as a polynomial model: Y = b0 + ∑biXi, where Y is the response
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calculated by the model, b0 is a constant, and bi is the linear coefficient. The data were modeled through multiple regression analysis based on a stepwise analysis. Only those variables that were found to be significant at the p < 0.05 level were selected for the model construction. The significant terms in the model for each response were
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found through an analysis of variance (ANOVA). The acceptability of the model was
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analyzed, accounting for the lack of fit, adequate precision, and pure error. The
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experimental data were compared with the fitted values predicted by the models to
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verify the suitability of the regression models. Each experiment was repeated in 13
Page 13 of 32
triplicate, and the mean values, including the pooled standard error of the mean
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(SEM), were then determined.
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3. Results and discussion
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3.1. Properties of co-blended polysaccharide films
Due to the beneficial compatibility with the polysaccharide added, a good mixed
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gel system was formed, and polysaccharide films with satisfactory smoothness and
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transparency were obtained. The quantity of dry matter in the film liquid per unit of
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flat area was maintained constant throughout the experiment to keep the film
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thickness constant (0.10 ± 0.01 mm), which ensured minimal influence of the film
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thickness when measuring the film properties (Gennadios, McHugh, & Weller, 1994).
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The co-blended polysaccharide solution determines the co-blended film
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properties to some extent. The measurement results for the properties of the binary
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and ternary co-blended systems, including WVP, TS, E%, and OP, after the addition
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of the polysaccharides are shown in Table 1. From these results, a better performance,
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based on improved water barrier properties, mechanical properties, and OP, was found with the PUL/ALG-CO binary co-blended film after blend-modification compared with the PUL/ALG film obtained through direct addition. The WVP of the ternary co-blended film formed by the direct addition of PEC,
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CAR, and ALO was higher than that of the PUL/ALG film, whereas the direct
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addition of PGA increased the water barrier property. The TS and E% of the ternary
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co-blended film with the direct addition of ALO were lower than those of the
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PUL/ALG film, whereas the TS and E% of the ternary co-blended film with the 14
Page 14 of 32
addition of PGA, PEC, and CAR were higher than those of the binary films. Contrary
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to the negative influence of CAR and ALO on the OP, the OP of a ternary co-blended
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film with the direct addition of PGA and PEC would be better than that of a binary
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co-blended film. As shown in Table 1, the additions of PGA, PEC, and CAR by
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co-drying significantly improved the water barrier property, which is the same effect
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as those of the TS, E%, and OP of the ternary co-blended film with the addition of
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ALO. Among all of the samples, the WVP of the ternary co-blended
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PUL/ALG/PGA-CO film obtained with the co-drying modification was decreased by
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69.8% compared with that of the PUL/ALG film. Generally speaking, the compounds
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formed by different polysaccharides exhibited stronger functional properties, such as
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the gel property and the aggregative property. Three independent gel systems were
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formed because the interactions of the different components of different complex
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types of polysaccharides were reduced due to the electronic incompatibility of
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polysaccharides (Zaleska, Ring, & Tomasik, 2000). However, the electronic
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compatibility of the polysaccharides and their interactions increased after modification through co-drying, but the detailed mechanisms underlying the formation of these co-dried films are not completely understood (Hosseini, Rezaei, Zandi, & Ghavi, 2013). Moreover, the surface activity, functional property, and water
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barrier property of the co-dried powder were significantly improved by this method.
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Different polysaccharides in ternary co-blended films have different effects on the
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water barrier properties of the films produced by the direct blending and co-drying
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modifications due to the different interactions between different polysaccharides. The 15
Page 15 of 32
PGA and PUL/ALG films formed a stronger gel network structure due to their
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hydrogen bonding and electrostatic interactions, which also resulted in the best water
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barrier property. In contrast, PEC and PUL/ALG formed a weaker hydrogen bonding
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network, which resulted in a comparatively poorer water barrier property. CAR has
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different gel forming stages than the other polysaccharides, resulting in poor
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compatibility and a comparatively higher WVP. ALO only formed weak, non-covalent
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bonds with PUL/ALG, resulting in the highest WVP and the worst water barrier
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property (Villagomez-Zavala, Gomez-Corona, Martinez, Perez-Orozco, Vernon-Carter,
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& Pedroza-Islas, 2008).
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The addition of PGA, PEC, and CAR significantly improved the film plasticity
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and mechanical property. The TS of the ternary films obtained through the addition of
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polysaccharides by co-drying increased 13.3%, 34.4%, 38.6%, and 13.46%,
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respectively, compared with those of the films obtained by direct addition.
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Alternatively, the E% of these ternary films with the addition of polysaccharides by
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co-drying increased 487.5%, 78.6%, 99.8%, and 97.2%, respectively, compared with those of the films obtained through direct addition. As shown in Table 1, with the exception of ALO, the co-blending modification of
PGA, PEC, and CAR significantly improved the OP of the ternary films formed. The
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oxygen permeability ratio of the ternary co-blended films decreased 39.5%, 33.7%,
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and 26.6%, respectively, compared with that of the PUL/ALG film. The oxygen
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permeability of the ternary blend-modified PUL/ALG/PGA-CO, PUL/ALG/PEC-CO,
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PUL/ALG/CAR-CO, and PUL/ALG/ALO-CO films decreased 36.5%, 33.4%, 33.0%, 16
Page 16 of 32
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and 19.5%, respectively, compared with these films made through direct blending.
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It can be concluded that the ternary co-drying of the modified polysaccharide films, especially the function of drying-modified PGA on the co-blending property of
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polysaccharides, can increase the application value of co-blended films to some
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extent.
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3.2. Dehydration and hygroscopicity
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Methods with several differentials were utilized to study the moisture removal
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process of 12 groups of vacuum-freeze-dried fiddlehead samples that were sprayed
358
with 10 different types of blend-modified polysaccharides, glycerin, and a reference
359
compound in a (22 ± 1) °C environment with a RH of (30 ± 2)% and then subjected to
360
a moisture absorption process at (22 ± 1) °C with a RH of (80 ± 2)%. The aqueous
361
ratios were also measured simultaneously. Curves of the aqueous ratio of the
362
vacuum-freeze-dried fiddleheads as a function of the measuring time were then
363
prepared and are shown in Fig. 1a and Fig. 1b.
365 366 367
M
d
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364
an
356
At 30% RH, the water content (%) of all vacuum-freeze-dried fiddlehead
samples coated with the blend-modified polysaccharides decreased gradually over a period of 120 h, which is quite similar to the behavior obtained with glycerol and the reference. The sequence of the aqueous ratios of the vacuum-freeze-dried fiddleheads
368
(within 120 h) was as follows: PUL/ALG/PGA-CO > PUL/ALG/PEC-CO >
369
PUL/ALG/CAR-CO > PUL/ALG-CO > PUL/ALG/PGA > PUL/ALG >
370
PUL/ALG/PEC > PUL/ALG/CAR > glycerin > PUL/ALG/ALO-CO >
371
PUL/ALG/ALO > reference. The analysis of variance was performed to determine the 17
Page 17 of 32
factors that influence the aqueous ratio of vacuum-freeze-dried fiddleheads, and the
373
results are shown in Table 1. This analysis indicated that the addition time, the type of
374
co-blended polysaccharide added, and its interactions had a significantly different
375
influence on the aqueous rate of the vacuum-freeze-dried fiddleheads. Multiple
376
comparisons regarding the influence of different humectants were performed, and
377
results are shown in Fig. 1a and Fig. 1b . This figure indicates that the aqueous ratios
378
of the vacuum-freeze-dried fiddleheads after the humectant treatment, including
379
PUL/ALG/PGA-CO, PUL/ALG/PEC-CO, and PUL/ALG/CAR-CO, were
380
significantly higher than those of the vacuum-freeze-dried fiddleheads in the other
381
nine treatment groups (Fig. 1a). The co-dried blended ternary polysaccharides are
382
expected to have proportionally more polar residues, which imparts the ability to form
383
hydrogen bonds with water and increase the moisture absorption and retention
384
properties (Gbogouri, Linder, Fanni, & Parmentier, 2004). Therefore, the ternary
385
co-blended polysaccharides, particularly PUL/ALG/PGA-CO, showed good moisture
387 388 389
cr
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an
M
d
te
Ac ce p
386
ip t
372
absorption and retention properties. Furthermore, in 30% RH, the best humectant moisturizing property was found with 0.5% PUL/ALG/PGA-CO, followed by 0.5% PUL/ALG/PEC-CO and 0.5% PUL/ALG/CAR-CO. Generally speaking, the three humectants mentioned are suitable for the application of this technique in an
390
environment with lower humidity. A later study will focus on the correlation of the
391
comprehensive performance and moisture retention properties of the films to
392
investigate the feasibility of a new method for moisture retention assessment.
393
For the typical behavior of water vapor-sensitive hydrophilic polysaccharides, 18
Page 18 of 32
the selection of humectants in an environment with high humidity was stricter,there,
395
the focus should be placed on the products’ moisture-resistant properties (Ryu, Kim,
396
Park, Lee, & Lee, 2007; Silhacek & Murphy, 2008). At 80% RH, the weight of the
397
residual moisture in the vacuum-freeze-dried fiddleheads increased during the 120 h
398
of the study. The sequence of moisture-retention ability was as follows:
399
PUL/ALG/ALO > glycerin > PUL/ALG/ALO-CO > reference > PUL/ALG/CAR >
400
PUL/ALG/PEC > PUL/ALG > PUL/ALG/PGA > PUL/ALG-CO >
401
PUL/ALG/CAR-CO > PUL/ALG/PEC-CO > PUL/ALG/PGA-CO. The aqueous
402
ratios of vacuum-freeze-dried fiddleheads treated with PUL/ALG/ALO, glycerin, and
403
PUL/ALG/ALO-CO were higher than that of the control sample treated with distilled
404
water, indicating that these three humectants exhibit poor moisture barrier properties.
405
The water-resistance properties of the vacuum-freeze-dried fiddleheads following the
406
addition of PUL/ALG/PGA-CO and PUL/ALG/PEC-CO were significantly higher
407
than those of the other samples in the high-humidity environment (Fig. 1b), which
409 410 411 412 413
cr
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an
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d
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Ac ce p
408
ip t
394
coincides with their amphiphilic structure (Pennick, Chavan, Summers, & Rawlings, 2012). Therefore, under high-humidity conditions, , PUL/ALG/PGA-CO and PUL/ALG/PEC-CO are the preferred humectants due to their moisture barrier properties.
3.3. Correlation between WVP, TS, E% and OP, and moisture retention ability The traditional method for measuring the moisture retention property is too
414
complicated and does not provide exhaustive and accurate results. Therefore, this
415
study was designed to assess the moisture-retention property based on the film 19
Page 19 of 32
properties (water barrier, moisture barrier, and mechanical properties with particular
417
focus on the penetration of aromatic components). Thus, this assessment was more
418
comprehensive. To study the accuracy of this assessment method, a correlative
419
analysis was performed on the properties of ternary co-blended films and their
420
moisture-retention properties as measured by a differential method (Hou, et al., 2012;
421
Sun, et al., 2006).
cr us
422
ip t
416
The values of water content for each of the blend-modified polysaccharide edible films are shown in Fig. 1a and Fig. 1b. The linear coefficient of WVP (X1), TS (X2),
424
E% (X3), and OP (X4) for each of the response variables is given in Table 2. The R2
425
and adjusted R2 values for the significant (p < 0.05) response surface models varied
426
from 0.9108 to 0.9530 and from 0.8395 to 0.9154, respectively. These values were
427
obtained for the moisture-retention ability at a storage temperature of 22 °C with a
428
RH of 30% or 80% for 120 h. The selected variables yielded the highest values of R2
429
and adjusted R2 for each response variable studied. All of the models were significant
431 432 433
M
d
te
Ac ce p
430
an
423
for all of the variables (RH = 30% (p = 0.0016) and RH = 80% (p = 0.0078); (Table 2)). Therefore, the RSM was able to predict most of the variations in the moisture retentions properties as a function of the blend-modified polysaccharide edible film variables. The effect of the WVP was highly significant (p < 0.05) for the
434
moisture-retention ability (Table 2), and it was considered the highest coefficient of
435
the main linear effects. Similar results have also been reported by other researchers
436
(Bosquez-Molina, Guerrero-Legarreta, & Vernon-Carter, 2003; Lin, Du, Liang, Wang,
437
Wang, & Yang, 2011). These results can be explained by the fact that the water 20
Page 20 of 32
barrier property of the co-blended film most related to film moisture is the retention
439
property (Bosquez-Molina, Guerrero-Legarreta, & Vernon-Carter, 2003; Lin, Du,
440
Liang, Wang, Wang, & Yang, 2011). The fitted models were suitable, showing
441
significant regression, no lack of fit, and satisfactory coefficients (Table 2).
The predicted values were obtained through a model-fitting technique using the
cr
442
ip t
438
Design Expert software. Fitting the data to a linear model and the subsequent
444
ANOVA showed that the linear model was suitable. There was a suitable relationship
445
between the predicted values and the experimental values (Fig. 2). The model was
446
used to find an optimal region for the response variable studied and to define the
447
relationship between the three independent variables and the response variables. The
448
optimum blending was found to be PUL/ALG/PGA-CO, which gave the best
449
moisture-retention ability.
452 453 454 455
an
M
d
te
451
For validation of the model, the acceptability of the response surface equations was checked through a comparison of the experimental and fitted values predicted by
Ac ce p
450
us
443
the response regression models. No significant difference (p > 0.05) was found between the experimental and predicted values. 3.4. Changes in color and film transparency Film color is an important index in terms of general appearance and consumer
456
acceptance. The L*, a*, and b* values of the blended films are shown in Table 3.
457
There were no significant differences (p > 0.05) in the L* value between all of the
458
films. In general, the ALG film exhibited a slight yellow appearance that darkened as
459
the thickness increased. The blended films presented increases in a* and b* with the 21
Page 21 of 32
direct and co-dried addition of PGA, PEC, CAR, or ALO, indicating that the film
461
became more yellowish after the incorporation of PGA, PEC, CAR, or ALO. The
462
differences observed in the films’ color could be ascribed to different interactions that
463
may have occurred during the blending process and the storage of PUL/ALG and the
464
different polysaccharides (Prodpran, Benjakul, & Artharn, 2007).
cr
The transparency of the PUL/ALG film was low (indicated by the high value of
us
465
ip t
460
T), which could be linked to the drying process. During drying, the PUL/ALG
467
film-forming solution was easily influenced by the wind in the oven, as indicated by
468
visible ripples on the surface of the PUL/ALG film, which undoubtedly increased the
469
final T value (Wu, Zhong, Li, Shoemaker, & Xia, 2013). There were significant
470
differences in the T values (p ≤ 0.05) between the blended films, which indicates that
471
the incorporation of PGA, PEC, CAR, or ALO did affect the transparency of the
472
films.
473
4. Conclusions
475 476 477
M
d
te
Ac ce p
474
an
466
In comparison to the common humectants used, ternary co-blended
polysaccharide films prepared using the co-drying method can significantly improve the film properties and moisture retention. Three types of directly mixed biopolymers are often not stable. However, the preparation of a co-dried mixture noticeably
478
decreased the incompatibility of both the particle sizes and the chemical properties of
479
the polysaccharides and increased the thermodynamic compatibility (Ohashi, et al.,
480
1991; Salvador, Sanz, & Fiszman, 2001); therefore, the compatibility of the three
481
phases was greatly improved. This research indicates that ternary co-blended 22
Page 22 of 32
polysaccharide films prepared through the co-drying method can be used as an
483
alternative to traditional humectants and applied for the preservation of IMFs. With
484
the exception of the traditional measuring methods, the assessment of the moisture
485
retention properties of humectants can be performed based on the film formed on the
486
food surface, and this measurement can be used for the total assessment of four film
487
parameters, namely WVP, TS, E%, and OP.
488
Acknowledgments
us
cr
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482
This study was financially supported by the Natural Science Foundation of China
490
(No. 31230057) and the National Key Technology R&D Program for the 12th
491
Five-Year Plan (Nos. 2012BAD37B01 and 2012BAD37B02).
492
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Hosseini, S. F., Rezaei, M., Zandi, M., & Ghavi, F. F. (2013). Preparation and functional properties of fish gelatin-chitosan blend edible films. Food Chem, 136, 1490-1495.
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Karel, M., & Heidelbaugh, N. D. (1973). Recent research and development in the field of low-moisture
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Tang, C. H., Jiang, Y., Wen, Q. B., & Yang, X. Q. (2005). Effect of transglutaminase treatment on the properties of cast films of soy protein isolates. J Biotechnol, 120, 296-307. Villagomez-Zavala, D. L., Gomez-Corona, C., Martinez, E. S., Perez-Orozco, J. P., Vernon-Carter, E. J., & Pedroza-Islas, R. (2008). Comparative Study of the Mechanical Properties of Edible Films IngenieriaQuimica, 7, 263-273.
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Yang, S. L., Guo, Z. Y., Zhou, Y. L., Zhou, L. L., Xue, Q. Z., Miao, F. P., & Qin, S. (2010). Synthesis and moisture absorption and retention activities of a carboxymethyl and a quaternary ammonium derivative of alpha,alpha-trehalose. Carbohydr Res, 345, 120-123. Zaleska, H., Ring, S. G., & Tomasik, P. (2000). Apple pectin complexes with whey protein isolate.
Ac ce p
559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587
Food Hydrocolloids, 14, 377-382.
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Page 25 of 32
ip t cr
Table 1 The WVP, TS, E%, OP, and moisture retention ability of the blend-modified polysaccharide edible films.a
us
588 589
Average moisture retention value (RH=80%) (Y2) 16.39 ± 1.40 C 16.33 ± 1.36 C 16.46 ± 1.41 D 16.51 ± 1.43 D 17.82 ± 2.10 E 16.18 ± 1.28 B 15.29 ± 0.63 A 15.42 ± 0.69 A 16.12 ± 1.23 B 17.75 ± 2.22 E
Ac
591 592 593 594 595 596
ce pt
ed
M an
Average moisture WVP OP Blending Blend-modified polysaccharide 3 2 (g·mm/m²·h·kP TS (MPa) (X2) E% (X3) (cm ·mm/m ·day· retention value method edible films (RH=30%) a) (X1) kPa) (X4) (Y1) PUL/ALG (50.00 g/L) 1.69 ± 0.08 AB 69.34 ± 4.45 C 5.71 ± 0.16 FG 326.58 ± 12.07 D 10.84 ± 2.09 E PUL/ALG/PGA (50.00 g/L) 1.61 ± 0.03 A 91.47 ± 8.12 A 7.89 ± 0.33 D 311.38 ± 8.82 D 10.93 ± 2.04 D Direct PUL/ALG/PEC (50.00 g/L) 1.80 ± 0.03 B 71.32 ± 7.22 C 7.66 ± 0.29 D 324.72 ± 6.16 D 10.77 ± 2.11 F addition PUL/ALG/CAR (50.00 g/L) 1.93 ± 0.07 C 70.11 ± 6.01 C 6.19 ± 0.18 E 357.65 ± 12.96 C 10.63 ± 2.13 G PUL/ALG/ALO (50.00 g/L) 2.78 ± 0.09 D 60.04 ± 8.74 C 2.11 ± 0.12 I 498.07 ± 9.50 A 9.33 ± 2.45 H PUL/ALG-CO (50.00 g/L) 1.04 ± 0.03 E 91.20 ± 6.24 B 5.96 ± 0.21 EF 289.64 ± 7.76 E 11.05 ± 1.97 C PUL/ALG/PGA-CO (50.00 g/L) 0.51 ± 0.05 G 103.68 ± 3.63 A 46.35 ± 1.12 A 197.65 ± 11.82 G 12.18 ± 1.39 A Co-dried PUL/ALG/PEC-CO (50.00 g/L) 1.11 ± 0.04 EF 95.86 ± 5.55 A 13.68 ± 0.23 B 216.40 ± 5.58 G 11.62 ± 1.63 B addition PUL/ALG/CAR-CO (50.00 g/L) 1.20 ± 0.08 F 97.17 ± 6.08 A 12.37 ± 0.12 C 239.76 ± 7.35 F 11.56 ± 1.69 B PUL/ALG/ALO-CO (50.00 g/L) 1.92 ± 0.03 C 68.12 ± 4.63 C 4.16 ± 0.06 H 401.13 ± 29.24 B 9.50 ± 2.28 H a 590 The values are the means ± the standard deviation. Different letters in the same column indicate significant differences (p ≤ 0.05).
26
Page 26 of 32
Table 2 The regression coefficients, R2, adjusted R2, and lack of fit for the final reduced models. Average moisture Average moisture retention values Regression coefficient retention values (RH=80%) (Y2) (RH=30%) (Y1) b0 13.236 13.361 b1 0.466 -0.449 b2 0.003 0.003 b3 0.012 -0.009 b4 -0.011 0.011 R Square 0.9530 0.9108 Adjusted R Square 0.9154 0.8395 Lack of fit (F-value) 25.3486 12.7691 Lack of fit (p-value) 0.0016 0.0078 bi (i = 1, 2, 3, or 4), the estimated regression coefficient for the main linear effects. 1, WVP (g·mm/m²·h·kPa); 2, TS (MPa); 3, E%; 4, OP (cm3·mm/m2·day·kPa).
an
M d te Ac ce p
600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628
us
cr
ip t
597 598 599
27
Page 27 of 32
ip t cr
us
Table 3 Thickness, color, and transparency of the blend-modified polysaccharide edible films.a Blend-modified Film thickness Blending L* a* b* T polysaccharide edible (mm) method films PUL/ALG 45.17 ± 0.47 EF 86.06 ± 0.19 A 0.42 ± 0.04 F 0.77 ± 0.04 F 1.62 ± 0.04 A PUL/ALG/PGA 48.30 ± 1.01 D 86.00 ± 0.20 A 0.54 ± 0.04 E 1.03 ± 0.07 E 0.67 ± 0.05 EF Direct PUL/ALG/PEC 49.03 ± 0.66 D 85.96 ± 0.12 A 0.63 ± 0.03 DE 1.06 ± 0.06 E 0.78 ± 0.04 CD addition PUL/ALG/CAR 51.43 ± 0.84 B 85.92 ± 0.10 A 0.71 ± 0.03 C 1.09 ± 0.05 E 0.83 ± 0.02 C PUL/ALG/ALO 52.60 ± 1.17 AB 85.76 ± 0.03 A 0.87 ± 0.05 A 1.17 ± 0.06 DE 1.02 ± 0.04 B PUL/ALG-CO 44.15 ± 1.00 FG 86.02 ± 0.11 A 0.47 ± 0.04 EF 0.80 ± 0.04 F 1.57 ± 0.09 A PUL/ALG/PGA-CO 43.26 ± 0.97 G 85.85 ± 0.08 A 0.54 ± 0.03 E 1.37 ± 0.09 C 0.64 ± 0.02 F Co-dried PUL/ALG/PEC-CO 49.55 ± 0.30 CD 85.99 ± 0.11 A 0.67 ± 0.07 CD 1.43 ± 0.05 AB 0.72 ± 0.05 DE addition PUL/ALG/CAR-CO 51.42 ± 1.22 BC 86.04 ± 0.17 A 0.73 ± 0.03 BC 1.54 ± 0.06 A 0.75 ± 0.04 D PUL/ALG/ALO-CO 54.44 ± 0.89 A 85.74 ± 0.08 A 0.78 ± 0.03 AB 1.21 ± 0.02 D 0.94 ± 0.07B a The values are the means ± the standard deviation. Different letters in the same column indicate significant differences (p ≤ 0.05).
Ac
631 632 633 634 635 636 637 638 639 640 641
ce pt
ed
M an
629 630
28
Page 28 of 32
te
d
M
an
us
cr
ip t
Fig. 1a. Dehydration of the blend-modified polysaccharides, glycerin, and the reference Fig. 1b. Hygroscopicity of the blend-modified polysaccharides, glycerin, and the reference. Fig. 2. Predicted and experimental values of (a) the average moisture retention values at RH = 30% and (b) the average moisture retention values at RH = 80% for the blend-modified polysaccharide edible films.
Ac ce p
642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685
29
Page 29 of 32
ip t cr us an M d te Ac ce p
686 687 688 689 690 691 692 693 694
Fig. 1a. Dehydration of the blend-modified polysaccharides, glycerin, and the reference.
30
Page 30 of 32
ip t cr us an M d te 696 697 698 699 700 701 702 703 704 705 706
Ac ce p
695
Fig. 1b. Hygroscopicity of the blend-modified polysaccharides, glycerin, and the reference.
31
Page 31 of 32
ip t us
cr 708 709 710 711
Ac ce p
te
d
M
an
707
Fig. 2. Predicted and experimental values of (a) the average moisture retention values at RH = 30% and (b) the average moisture retention values at RH = 80% for the blend-modified polysaccharide edible films.
32
Page 32 of 32
