Antiretrogradation in Cooked Starch-Based Product Application of Tea Polyphenols Lijing Wu, Liming Che, and Xiao Dong Chen
Retrogradation in cooked starch-based products is a significant hindrance in extending the shelf life of these products as they become progressively hard to bite over short time periods (say 1 or 2 months). In this study, the effects of tea polyphenols (TPs) on cooked amylopectin-rich cassava starch have been investigated. Cassava starch was mixed with TPs and then gelatinized to form starch gels. The obtained gels were stored for up to 80 d and characterized by X-ray diffraction (XRD), hardness test, color analysis, and Fourier transform infrared spectroscopy (FT-IR). The results of XRD show that the formation of long-range ordered structure of amylopectin was retarded by the interaction of TPs with amylopectin via hydrogen bond. The results of hardness test show that the accelerating increase in the hardness of cassava starch gel was retarded by the addition of TPs. The increase in hardness versus time can be correlated well using a single-parameter exponential equation. The increase in hardness, variations in color, and FT-IR spectrum of the TPs treated samples during storage with TPs were relatively small, suggesting that the retrogradation of starch is inhibited by TPs. This work presents an opportunity of anti-retrogradation in the related products.
Keywords: amylopectin, cassava starch, retrogradation, tea polyphenols
Retrogradation of cooked-starch-based products is still one of the most frequently encountered problems in food industry, which causes many problems such as hardening and syneresis of the products. The potential application of tea polyphenols (TPs) as antiretrogradation additives is demonstrated in this work. Experimental results show that the addition of TPs retards the retrogradation of cassava starch during long-term storage remarkably.
Practical Application:
Introduction Cassava (Manihot esculenta Crantz), one of the 3 biggest tuber crops in the world, is widely cultivated in tropical and subtropical areas. It is adaptable to poor soils and has high return per unit of energy used in its cultivation. Cassava starch not only can be used as food but also has many industrial applications, such as fuel alcohol production and paper making (Tian and others 2008; Mej´ıa-Ag¨uero and others 2012). Cassava starch is rich in amylopectin and is praised for its clarity of gel, light color, and neutral flavor (Abraham 1993). It is widely used in food industry and can be made into jelly, snowy moon cakes, and so on. Usually, the soft and elastic texture of the products is favored by consumers. However, these products are of short shelf life as their rigidity increases markedly and the water retention capacity decreases sharply during storage, a direct consequence of starch retrogradation (Iturriaga and others 2010; Xu and others 2012). The retrogradation of starch refers to the recrystallization of amylase and amylopectin that occur in gelatinized starch during storage below gelatinization temperature (Hoover 1995). Amylose is responsible for the short-term retrogradation, while recrystallization of amylopectin is the main cause for the long-term retrogradation (Hoover 1995). Retrogradation of starch causes many MS 20140151 Submitted 1/28/2014, Accepted 7/20/2014. Authors Wu and Che are with Dept. of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen Univ., Xiamen 361005, P.R China. Author Chen is with Dept. of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen Univ., Xiamen 361005, P.R China. Authors Chen are with School of Chemical and Environmental Engineering, Soochow Univ., Soochow, 215123, P.R, China. Direct inquiries to author Che (E-mail: [email protected]).
R C 2014 Institute of Food Technologists
doi: 10.1111/1750-3841.12589 Further reproduction without permission is prohibited
problems, such as hardening and syneresis (Xu and others 2012). The loss of soft and elastic texture is the main reason of quality degradation of cooked starch-based products, such as rice and bread. Retrogradation of starch is directly related to the staling of bread. In the early 20th century, bakers had to carry out night work in order to avoid product loss through staling. Even nowadays, there continues to be product loss due to retrogradation, as it can lead to a dramatic increase in the hardness of baked goods, making them unattractive to consumers. For several baked products, such as baguettes, starch retrogradation is a greater problem for limiting the shelf life of the product than microbial stability (Ottenhof and Farhat 2004). In order to extend the shelf life of starch-based product, efforts from food industry were made to inhibit the retrogradation of starch, especially the recrystallization of amylopectin (Tian and others 2008). The most commonly used approaches to retard starch retrogradation are chemical and/or physical modifications (Singh and others 2007; Mutungi and others 2009; Han and others 2012). Han and others (2012) found that acetylation can retard the retrogradation of corn starch. Singh and others (2007) reported that hydroxypropylation and cross-linking (POCl3 and propyleneoxide) are also good alternatives. However, chemical modification of starch is not recommended as far as food safety is concerned. Physical modification of starch, such as heat-moisture treatment, is safer but usually less effective in retarding the retrogradation process of starch-based products (Xiao and others 2013). Adding antiretrogradation additives is another frequently used approach to retard the retrogradation of starch (Singh and others 2007; Tian and others 2008; Tian and others 2009; Xu and others 2012). α-Amylase, β-amylase, and β-cyclodextrin have
Vol. 00, Nr. 0, 2014 r Journal of Food Science E1
E: Food Engineering and Physical Properties
Abstract:
Antiretrogradation in cooked starch-based product . . .
o
16.9
A
5
10
15
20
Figure 1–X-ray diffraction patterns of cassava starch with (A) 0 wt.%, (B) 1 wt.%, (C) 2 wt.%, and (D) 3 wt.% TPs, respectively. The X-ray diffraction pattern from bottom to top represents 0-, 5-, 10-, 20-, 40-, and 60-d’s storage, respectively. The samples were stored at 6 °C.
B
25
30
35
5
40
10
15
20 25 2θ (degree)
30
35
40
10
15
20 25 2θ (degree)
30
35
40
2θ (degree)
E: Food Engineering and Physical Properties
C
5
D
10
15
20 25 2θ (degree)
30
35
40
5
been shown to be effective antiretrogradation additives (Tian and others 2008, 2009; Gomes-Ruffi and others 2012). Among them, β-cyclodextrin is the most favorable one, which not only retards the short-term but also the long-term retrogradation of rice starch by forming amylase-lipid–β-cyclodextrin complex (Tian and others 2008, 2009). Tea polyphenols (TPs), which contain a class of polyphenolic flavonoids known as catechin, have attracted more and more attention as effective antiretrogradation additives (Wu and others 2009; Xiao and others 2013). The major functional components
are (−)-epicatechin gallate (ECG), (−)-epicatechin (EC), (−)epigallocatechin (EGC), and (−)-epigallocatechin gallate (EGCG) (Ermakova and others 2005). In vitro and animal studies have provided strong evidences that TPs can provide health benefits such as antioxidative, antidiabetic, antimicrobial, anti-inflammatory, and anticarcinogenic properties (Ahmad and others 2000; Giovannini and Masella 2012). A number of works have been conducted to evaluate the effects of TPs on the physicochemical properties of starch. Beta and
5
80 0 wt. % TPs Normalized hardness
1 wt. % TPs
60
Hardness (mN)
4
2 wt. % TPs 3 wt. % TPs
40
20
0 wt. % TPs
1 wt. % TPs
2 wt. % TPs
3 wt. % TPs
Model prediction
3 2 1 0 0
0 0
20
40
60
80
t (d) Figure 2–Variation of hardness of cassava starch gels stored at 25 °C.
E2 Journal of Food Science r Vol. 00, Nr. 0, 2014
20
40 t (d)
60
80
Figure 3–Variation of normalized hardness of cassava starch gels stored at 25 °C. Experimental data are fitted by single-parameter exponential function.
Antiretrogradation in cooked starch-based product . . . Table 1– Fitting parameters for normalized hardness of cassava Reagent Co., Ltd (Shanghai, China) and are of analytical grade. starch gels using single-parameter exponential function. All the chemicals were used without further purification.
0 1 2 3
k 0.0176 0.0116 0.0072 0.0055
R2
Sample preparation
0.98 Cassava starch and TPs were mixed at a ratio of 30 : 0, 29.7 : 0.3, 0.94 0.92 29.4 : 0.6, or 29.1 : 0.9 (w : w). Fifteen-gram of the mixture was 0.94 added into 50 mL deionized water with 65 mg potassium sor-
Corke (2004) demonstrated that catechin can decrease the hot paste viscosity, final viscosity, and setback viscosity of sorghum and maize starch pastes. Xiao and others (2012) found the favorable antiretrogradation effect of green and black TPs on rice, maize, and potato starches. However, very few attentions have been paid to investigating the effect of TPs on the retrogradation of amylopectin-rich starch, such as cassava starch. Tian and others (2009) reported that β-cyclodextrin reduces the retrogradation of normal rice starch, but has no effect on the retrogradation of waxy rice starch that is enriched in amylopectin. Thus, the antiretrogradation effect of TPs should be validated against more starches, especially the amylopectin-rich starch. Literature review also shows that previous studies have been mainly focused on starch retrogradation during short-term storage, normally less than 30 d (Tian and others 2008, 2009; Wu and others 2009; Ji and others 2010; Xiao and others 2013). The phenomenon of starch retrogradation during longer term storage has not been studied systematically. The aim of this work is therefore to investigate the retrogradation of cassava starch with and without TPs during long-term storage. The retrogradation of the sample is characterized by Xray diffraction (XRD), hardness test, color analysis, and Fourier Transform infrared spectroscopy (FT-IR). The effects of TPs on the retrogradation of amylopectin-rich starch will also be discussed. It will provide people with information of amylopectin retrogradation during long-term storage as well as the anti-retrogradation effect of TPs. The information will find application in controlled retrogradation of cooked starch-based products.
Material and Methods Materials Powdered TPs were purchased from Anhui Redstar Pharmaceutical Co. Ltd (Anhui, China) containing 41.6% EGCG, 17.7% EGC, 9.2% ECG, and 6.0% EC. Cassava starch was purchased from local market (Fujian, China). Potassium sorbate, hydrochloric acid, and methyl silicone oil were obtained from Sinopharm Chemical
bate as antimicrobial additive. The pH value of the well-mixed suspension was adjusted to 4.5 using 1 mol/L hydrochloric acid (to inhibit the growth of bacteria using potassium sorbate). The suspension was then gelatinized in oil bath at 100 °C for 20 min under stirring. The obtained paste was transferred into cylindrical containers (2.5 cm in height and 4.0 cm in diameter) and cooled to room temperature to form cylindrical gels. The gel was covered with methyl silicone oil during storage to prevent water from evaporating. For hardness test, the procedure of sample preparation was similar to the one mentioned above. However, the starch suspension was cooked for 10 more minutes (30 min) to inhibit the growth of bacteria during storage.
XRD analysis of the retrogradation of cassava starch For XRD analysis, the gel was stored at 6 °C for 0, 5, 10, 20, 40, and 60 d, respectively. Prior to the test, the sample was freeze-dried and then pulverized to pass through a 60-mesh sieve. The analysis of the samples was carried out using an X-diffractometer (Ultima IV, Rigaku Corp., Tokyo, Japan). The scanning was performed at 20 kV and 35 mA. The scanning was applied at a diffraction angle (2θ ) from 4° to 40° at a rate of 4°/min. X’Pert High Score Plus, Jade version 6.5, and OriginPro version 7.5 were used to analyze the diffractograms. Hardness test of cassava starch gels The hardness test was performed at room temperature (about 25 °C). In order to reduce the negative effect of freeze-thaw cycles on the retrogradation of cassava starch, the gel was stored at 25 °C. The hardness of the gel was determined every 2 d for 80 d using a texture analyzer (TRAPEZIUM X EZ-S-1 N, Shimadzu Corp., Kyoto, Japan). The hardness of the sample with a thickness of approximately 1.5 cm and a diameter of 4.0 cm were determined using a cylindrical probe of 5 mm in diameter. The probing was applied on the sample disk surface. The sample was compressed at a loading speed of 2 mm/min until a maximum deformation of 20% was achieved. The deformation of 20% was set to avoid a complete destruction of gel structure. The maximum force detected during compression is the hardness of the sample. The compression was carried out at the center of the sample. Samples in triplicate were
Figure 4–Photos of cassava starch gels. The content of TPs is 0 wt.% (A), 1 wt.% (B), 2 wt.% (B), and 3 wt.% (D), respectivley. Vol. 00, Nr. 0, 2014 r Journal of Food Science E3
E: Food Engineering and Physical Properties
TPs concentration wt.%
Antiretrogradation in cooked starch-based product . . . Table 2– The color values of cassava starch gels.
TPs concentration wt.%
Color parameterf
t d 0
L∗
0
25.52 −0.81 −4.23 23.10 0.61 1.70 22.12 1.28 4.67 20.45 1.60 6.19
a∗
b∗ L∗ a∗
1
b∗
L∗ a∗ b∗ L∗ a∗ b∗
2
a
41.91 −1.14 −4.38 38.58 0.82 2.66 36.87 1.19 3.95 34.68 1.49 5.28
0.02c 0.15a 0.33a 0.04a 0.07a 0.90a 0.03a 0.30b 1.00a 0.07a 0.08b
± ± ± ± ± ± ± ± ± ± ± ±
20 1.02b 0.09a 0.18a 0.65b 0.06a 0.06b 0.30b 0.05a 0.26a 1.05b 0.15a 0.18a
53.05 −0.96 −3.38 46.69 1.16 3.18 40.82 1.76 5.52 37.41 1.99 6.3
± ± ± ± ± ± ± ± ± ± ± ±
40 0.71c 0.01b 0.30b 0.15c 0.12b 0.16c 0.67c 0.10b 0.03c 0.94c 0.27b 0.16b
57.98 −0.97 −2.61 51.71 1.74 4.36 47.02 2.43 6.78 40.52 1.97 6.75
± ± ± ± ± ± ± ± ± ± ± ±
60 0.60d 0.02b 0.31c 0.37d 0.09c 0.16d 0.38d 0.09c 0.06d 0.24d 0.06bc 0.11c
60.12 −0.96 −2.36 53.26 1.95 4.66 48.29 2.90 7.57 42.20 2.38 7.44
± ± ± ± ± ± ± ± ± ± ± ±
0.77e 0.04b 0.41c 0.40e 0.08c 0.26d 0.52d 0.10d 0.14e 0.10d 0.09c 0.18d
Values are mean ± standard deviation of 3 parallel samples. Means within a line followed by different letters are significantly different (P < 0.05).
tested to estimate the experimental error. The average values of Table 3– Fitting parameters for ࢞C of cassava starch gels using first-order exponential decay function. hardness were correlated using the following equation TPs concentration wt.%
Ht NHt = = exp(kt ) H0
(1) 0
where NHt is the normalized hardness of the sample at time t, Ht and H0 are the values of hardness determined at time t and 0, and k is the fitting parameter.
1 2 3
A
B
R2
35.24 30.68 26.42 20.92
14.63 13.95 13.95 9.867
0.9964 0.9998 0.9920 0.9887
Average value of 3 parallel samples was used to show the general trends. The color differences C were calculated as follows: Color analysis of cassava starch gels 2 2 2 The color of cassava starch gels was determined by a Spectrophoa t∗ − a 0∗ + b t∗ − b 0∗ + L ∗t − L ∗0 (2) Ct = tometer (CM-700d, Konica Minolta Inc., Tokyo, Japan) employwhere a∗ represents redness, b∗ represents yellowness, and L∗ ing the Hunter and CIE scale. For each sample, the determination was carried out in triplicate and the average value was recorded. represents lightness (Fam´a and others 2007). The subscript t indicates the values observed for each storage time (0, 10, 20, 40, and 60 d) and the subscript 0 indicates the values observed for each sample at zero storage time day. 40 Then C were fitted with first-order exponential decay equation t Ct = A 1 − exp − (3) 30 B where A and B are the fitting parameters. ∆C
E: Food Engineering and Physical Properties
3
± ± ± ± ± ± ± ± ± ± ± ±
10 0.10a
20 0 wt. % 1 wt. % 10
2 wt. % 3 wt. % Model prediction
0 0
15
30 t (d)
45
60
FT-IR analysis of the retrogradation of cassava starch Prior to FT-IR analysis, the gel was freeze-dried and then pulverized to pass through a 60-mesh sieve. The powder was then blended with dry potassium bromide powder. The blend was subsequently made into a pellet. The FT-IR spectrograms of cassava starch with 0, 1, 2, and 3 wt.% TPs (on dry bias) were acquired on a FT-IR spectrophotometer (Nicolet 6700, Thermo Fisher Scientific Inc., Waltham, MA, U.S.A.). Samples were scanned from 4000 to 400 cm−1 at a resolution of 2 cm−1 , with 32 coadded scans per sample. Statistical analysis
The experimental data were obtained in triplicates. Multiple Figure 5–Variation of ࢞C of cassava starch gels during long-term storage. Experimental data are fitted by first-order exponential decay function. The comparison test of Duncan at a probability level 0.05 was persamples were stored at 6 °C. formed, using Matlab version 7.11.0, to determine whether there E4 Journal of Food Science r Vol. 00, Nr. 0, 2014
is significant difference between the behaviors exhibited by the ordered semicrystalline structure imparts initial hardness to the starch gels. For the sample without TPs, a relatively sharp peak at starch gels tested. 16.9o (2θ ) appears after long-term storage (after about 20 d). The Results and Discussion peak is the result of long-range ordered structure formed mainly by amylopectin around the seed nuclei of short-range ordered XRD analysis of the retrogradation of cassava starch The antiretrogradation effect of TPs on cassava starch was first amylase (Tian and others 2008). Rodr´ıguez-Sandoval and others a “B”explored by XRD and the results are shown in Figure 1. Che and (2008) reported that the retrograded cassava starch shows o type crystalline structure characterized by a peak at 16.9 (2θ ). For others (2008) reported that native cassava starch is semicrystalline o with relatively sharp peaks at 15.0°, 17.0°, 17.9°, and 22.9° (2θ ) the samples with TPs, the peak at 16.9 (2θ ) is not found on their on XRD pattern. These peaks are not found in Figure 1, which XRD patterns, which implies that retrogradation of amylopectin means that the crystalline structure of cassava starch was destroyed is retarded. Richardson and others (2004) reported that emulsifier decreases during gelatinization. the amount of free starch, altering the retrogradation characterRetrogradation of starch involves reassociation of amylose and istics of starch. Wu and others (2012) further proved that TPs amylopectin chains through hydrogen bond during storage. The and rice starch interact with each other via hydrogen bond durreassociation of amylose is responsible for short-term retrogradaing gelatinization. TPs contain abundant highly reactive hydroxyl tion of starch, which occurs immediately after cooling the sample groups (-OH). The -OH of TPs may interact with the -OH of to room temperature and can be completed within few hours. cassava starch to form hydrogen bonds. The interaction decreases The reassociation of amylopectin, on the other hand, is responsithe amount of free starch and restraint the reassociation of starch ble for long-term retrogradation of starch, which takes relatively polymers (Beta and Corke 2004; Xiao and others 2013). long time up to a few months (Tian and others 2008). The sharp peaks on XRD pattern arise from long-range ordered structure of the material on the level of atoms, which is conventionally referred as crystalline structure. While the broad diffuse maxima is attributed to short-range ordered structure of the material, which is usually referred as semicrystalline structure. The cassava starch gels with and without TPs all show a broad maximum on XRD patterns, which is the result of short-range ordered structrue formed mainly by amylose. The short-range
Hardness test of cassava starch gels The mechanical properties, such as hardness, cohesiveness, and springiness of starch gel, are quite sensitive to the retrogradation of starch and thus can be used as the indexes of starch retrogradation. The most adverse effect of starch retrogradation is the increase in hardness of the starch-based products. The variation of hardness of cassava starch gels is presented in Figure 2.
Figure 6–FT-IR spectra of cassava starch with (A) 0 wt.%, (B) 1 wt.%, (C) 2 wt.%, and (D) 3 wt.% TPs, respectively. The FT-IR spectrum from bottom to top represents 0-, 5-, 10-, 20-, 40-, and 60-d’s storage, respectively. The samples were stored at 6 °C. Vol. 00, Nr. 0, 2014 r Journal of Food Science E5
E: Food Engineering and Physical Properties
Antiretrogradation in cooked starch-based product . . .
Antiretrogradation in cooked starch-based product . . .
E: Food Engineering and Physical Properties
The cassava starch gel obtained was soft with relative low value of hardness when compared with other starches, such as sweet potato starch (data are not reported here). Yu and others (2009) reported that the hardness of rice starch decreases with increasing amylopectin content. The hardness of the sample decreases with the increase of TPs’ content and increases during long-term storage as a result of starch retrogradation. In order to evaluate the variation of hardness, the hardness of the sample was normalized by its initial value and the results are shown in Figure 3. The normalized hardness of the sample increases exponentially during long-term storage, that is, increases by an accelerating rate. It is contrary to the report by Tian and others (2008) that the hardness of rice starch gel tended to be stable after 1-week storage. Liu and others (2012) also demonstrated that the hardness of waxy starch gel increased by a decreasing rate. As a matter of fact, the accelerating increase in hardness of starch gel during storage has never been reported. One of the reasons is that the storage time was not long enough in these works. The accelerating increase in hardness suggests that the hardness of starch gel is more sensitive to the formation of long-range ordered structure by amylopectin. The increase in normalized hardness of the sample decreases with the increase of TPs’ content, for example, the normalized hardness of the sample without TPs is about 400%, while it is only about 160% for the sample with 3 wt.% of TPs. As shown in Figure 3, the increase in normalized hardness of the samples can be fitted well by single-parameter exponential function. The fitting parameters are shown in Table 1. The accelerating increase in hardness of the sample is indicated by a rate constant k greater than 0. The rate constant k decreases from 0.0176 to 0.0055 when the content of TPs is increased from 0 wt.% to 3 wt.%, suggesting that the addition of TPs plays a crucial role in retarding the hardening of starch gel caused by retrogradation. Miles and others (1985) and Ring and others (1987) attributed the initial firmness of the starch gel to the formation of an amylose matrix and the subsequent increase in firmness to reversible crystallization of amylopectin. Cassava starch has relatively low content of amylose and thus forms a soft and elastic gel (Abraham 1993). The interaction of TPs with amylose via hydrogen bond retards the formation of amylose matrix, and thus results in a softer starch gel. That is the reason why the hardness of starch gel decreases with increasing TPs content. On the other hand, the interaction of TPs with amylopectin via hydrogen bond retards the formation of long-range ordered structure further, which limits the increase in hardness of cassava starch gel. The formation of crystalline structure was reported to be the main reason of increase in hardness of starch-based products. The addition of TPs restricts the formation of crystalline structure and thus limits the increase in hardness of cassava starch gels.
tion, in turn. The evolution of color difference ࢞C of the gel during storage is shown in Figure 5. It is interesting to note that ࢞C keeps on increasing at a decreasing rate, which is contrary to the evolution of gel hardness. The evolution of ࢞C can be fitted very well by first-order exponential decay function and the fitting parameters are shown in Table 3. As shown in Figure 5, cassava starch gel without TPs has the highest ࢞C values among the samples throughout the entire period of storage. The color difference ࢞C decreases with the increase of TPs’ concentration. This is further validated by the fitting parameters in Table 3, that is, A and C decrease with the increase of TPs’ concentration. It means that the appearance of cassava starch gel with TPs is more stable. The evolution of ࢞C further proves that the addition of TPs inhibits the retrogradation of cassava starch.
FT-IR analysis of the retrogradation of cassava starch The FT-IR spectra of the samples were displayed in Figure 6. Spectrum change can be divided into band narrowing caused by ordering of the polymers and change of band intensity caused by alteration in specific conformations of starch such as crystallinity (Fan and others 2012). The spectra of the samples show peaks at around 3400 cm−1 that might be assigned to inter- and intramolecular hydrogen-bonded hydroxyl groups and at 2800 cm−1 that might be attributed to CH2 − stretching. COO- stretching vibration is indicated by peaks at around 1400 and 1640 cm−1 (Han and others 2012). Meanwhile, bands at wavelengths of 1300 to 900 cm−1 have been reported to be sensitive to the gelation of starch and mainly result from C-O and C-C vibrational modes (Fan and others 2012; Lian and others 2013). Figure 6(A) and (B) show that the intensitiy of spectra increases with the increase of storage time. It demonstrates that starches without TPs and with only 1 wt.% TPs show obivious retrogadation trend. However, when the content of TPs is increased to 2 and 3 wt.%, the retrogadation of starch was retarded as the band intensity keeps almost constant during storage (Figure 6C and D). This is consistent with the findings of XRD and hardness test that TPs can inhibit the retrogradation of cassava starch.
Conclusion The effects of TPs on the retrogradation of cassava starch (that is, anti-retrogradation) during long-term storage were evaluated by XRD, hardness test, color analysis, and FT-IR. Cassava starch retrogrades during storage below gelatinizaiton temperature due maily to the recrystallization of amyplopectin. The retrogradation results in an accelerating increase in hardness of cassava starch gel. TPs interact with amylopectin via hydrogen bond, which retards the formation of long-range ordered structure of amylopectin during storage. The addition of TPs in cassava starch gel thus inhibits the retrogradation of starch significantly. The texture and color of cassava starch gel with TPs do not change much during long-term storage, thus a long shelf life in these 2 aspects is expected. The health benefits of TPs also make TPs-containing starch-based food high value-added product. One of the research aspects that should be concerned in the future is the effect of TPs on the growth of bacteria in this kind of starch-based produts.
Color analysis of cassava starch gels The photos of cassava starch gels are shown in Figure 4. The sample without TPs is white and transparent to opaque gel. The obtained TPs are yellow to brown powder. The addition of TPs gives the gel a dark brown color, the more TPs, the thicker of the color. This is also indicated by the color value of the sample, that is, the value of L∗ decreases with the increase in TPs’ concentration (Table 2). The value of L∗ of the sample increases during long-term storage, suggesting that the sample gets more and more opaque due Acknowledgments to starch retrogradation. The work was supported by the grants from Natl. High The evolution of color is the result of starch retrogradation, Technology Research and Development Program of China (No. and thus can be used as one of the indexes of starch retrograda- 2011AA100802-3). E6 Journal of Food Science r Vol. 00, Nr. 0, 2014
Author Contributions Lijing Wu collected test data, interpreted the results, and drafted the manuscript. Liming Che designed the study. Xiao Dong Chen modified the manuscript.
References Abraham TE. 1993. Stabilization of paste viscosity of cassava starch by heat moisture treatment. Starch – St¨arke 45(4):131–5. Ahmad N, Gupta S, Mukhtar H. 2000. Green tea polyphenol epigallocatechin-3-gallate differentially modulates nuclear factor kappa B in cancer cells versus normal cells. Arch Biochem Biophys 376(2):338–46. Beta T, Corke H. 2004. Effect of ferulic acid and catechin on sorghum and maize starch pasting properties. Cereal Chem J 81(3):418–22. Che L-M, Wang B, Li D, Wang L-J, Chiu YL, Chen XD, Mao Z-H. 2008. Effect of highpressure homogenization on the structure and thermal properties of maize starch. J Food Eng 87(3):436–44. Ermakova S, Choi BY, Choi HS, Kang BS, Bode AM, Dong Z. 2005. The intermediate filament protein vimentin is a new target for epigallocatechin gallate. J Biol Chem 280(17):16882–90. Fam´a L, Goyanes S, Gerschenson L. 2007. Influence of storage time at room temperature on the physicochemical properties of cassava starch films. Carbohydr Polym 70(3):265–73. Fan DM, Ma WR, Wang LY, Huang JL, Zhao JX, Zhang H, Chen W. 2012. Determination of structural changes in microwaved rice starch using Fourier transform infrared and Raman spectroscopy. Starch – St¨arke 64(8):598–606. Giovannini C, Masella R. 2012. Role of polyphenols in cell death control. Nutr Neurosci 15(3):134–49. Gomes-Ruffi CR, Cunha RHd, Almeida EL, Chang YK, Steel CJ. 2012. Effect of the emulsifier sodium stearoyl lactylate and of the enzyme maltogenic amylase on the quality of pan bread during storage. LWT – Food Sci Technol 49(1):96–101. Han F, Liu M, Gong H, L¨u S, Ni B, Zhang B. 2012. Synthesis, characterization and functional properties of low substituted acetylated corn starch. Intl J Biol Macromol 50(4):1026–34. Hoover R. 1995. Starch retrogradation. Food Rev Intl 11(2):331–46. Iturriaga LB, Lopez de Mishima B, A˜non MC. 2010. A study of the retrogradation process in five argentine rice starches. LWT – Food Sci Technol 43(4):670–4. Ji Y, Zhu K, Chen Z-C, Zhou H, Ma J, Qian H. 2010. Effects of different additives on rice cake texture and cake staling. J Texture Stud 41(5):703–13. Lian X, Zhu W, Wen Y, Li L, Zhao X. 2013. Effects of soy protein hydrolysates on maize starch retrogradation studied by IR spectra and ESI-MS analysis. Intl J Biol Macromol 59:143–50.
Liu ZD, Gong BQ, Zhang L, An HJ, Liu BX. 2012. The influence of emulsifiers on retrogradation properties of waxy starch. Adv Comput Environ Sci 142:351–8. Mej´ıa-Ag¨uero LE, Galeno F, Hern´andez-Hern´andez O, Matehus J, Tovar J. 2012. Starch determination, amylose content and susceptibility to in vitro amylolysis in flours from the roots of 25 cassava varieties. J Sci Food Agric 92(3):673–8. Miles MJ, Morris VJ, Orford PD, Ring SG. 1985. The roles of amylose and amylopectin in the gelation and retrogradation of starch. Carbohydr Res 135(2):271–81. Mutungi C, Rost F, Onyango C, Jaros D, Rohm H. 2009. Crystallinity, thermal and morphological characteristics of resistant starch type III produced by hydrothermal treatment of debranched cassava starch. Starch – St¨arke 61(11):634–45. Ottenhof MA, Farhat IA. 2004. Starch retrogradation. Biotechnol Genet Eng Rev 21:215–28. Richardson G, Kidman S, Langton M, Hermansson A-M. 2004. Differences in amylose aggregation and starch gel formation with emulsifiers. Carbohydr Polym 58(1):7–13. Ring SG, Colonna P, I’Anson KJ, Kalichevsky MT, Miles MJ, Morris VJ, Orford PD. 1987. The gelation and crystallisation of amylopectin. Carbohydr Res 162(2):277–93. Rodr´ıguez-Sandoval E, Fern´andez-Quintero A, Cuvelier G, Relkin P, Bello-P´erez LA. 2008. Starch retrogradation in cassava flour from cooked parenchyma. Starch – St¨arke 60(3–4):174– 80. Singh J, Kaur L, McCarthy OJ. 2007. Factors influencing the physico-chemical, morphological, thermal and rheological properties of some chemically modified starches for food applications—a review. Food Hydrocolloids 21(1):1–22. Tian Y, Li Y, Manthey FA, Xu X, Jin Z, Deng L. 2009. Influence of β-cyclodextrin on the short-term retrogradation of rice starch. Food Chem 116(1):54–8. Tian Y, Xu X, Li Y, Jin Z, Chen H, Wang H. 2008. Effect of β-cyclodextrin on the long-term retrogradation of rice starch. Eur Food Res Technol 228(5):743–8. Wu Y, Chen Z, Li X, Li M. 2009. Effect of tea polyphenols on the retrogradation of rice starch. Food Res Intl 42(2):221–5. Wu C, Liu R, Huang W, Rayas-Duarte P, Wang F, Yao Y. 2012. Effect of sourdough fermentation on the quality of Chinese Northern-style steamed breads. J Cereal Sci 56(2):127–33. Xiao H, Lin Q, Liu G-Q, Wu Y, Wu W, Fu X. 2013. Inhibitory effects of green tea polyphenols on the retrogradation of starches from different botanical sources. Food Bioprocess Technol 6(8):2177–81. Xiao H, Lin Q, Liu G-Q, Yu F. 2012. Evaluation of black tea polyphenol extract against the retrogradation of starches from various plant sources. Molecules 17(12):8147–58. Xu Z, Zhong F, Li Y, Shoemaker CF, Yokoyama WH, Xia W. 2012. Effect of polysaccharides on the gelatinization properties of cornstarch dispersions. J Agric Food Chem 60(2):658–64. Yu S, Ma Y, Sun D-W. 2009. Impact of amylose content on starch retrogradation and texture of cooked milled rice during storage. J Cereal Sci 50(2):139–44.
Vol. 00, Nr. 0, 2014 r Journal of Food Science E7
E: Food Engineering and Physical Properties
Antiretrogradation in cooked starch-based product . . .
Retrogradation in cooked starch-based products is a significant hindrance in extending the shelf life of these products as they become progressively hard to bite over short time periods (say 1 or 2 months). In this study, the effects of tea polyphenols (TPs) on cooked amylopectin-rich cassava starch have been investigated. Cassava starch was mixed with TPs and then gelatinized to form starch gels. The obtained gels were stored for up to 80 d and characterized by X-ray diffraction (XRD), hardness test, color analysis, and Fourier transform infrared spectroscopy (FT-IR). The results of XRD show that the formation of long-range ordered structure of amylopectin was retarded by the interaction of TPs with amylopectin via hydrogen bond. The results of hardness test show that the accelerating increase in the hardness of cassava starch gel was retarded by the addition of TPs. The increase in hardness versus time can be correlated well using a single-parameter exponential equation. The increase in hardness, variations in color, and FT-IR spectrum of the TPs treated samples during storage with TPs were relatively small, suggesting that the retrogradation of starch is inhibited by TPs. This work presents an opportunity of anti-retrogradation in the related products.
Keywords: amylopectin, cassava starch, retrogradation, tea polyphenols
Retrogradation of cooked-starch-based products is still one of the most frequently encountered problems in food industry, which causes many problems such as hardening and syneresis of the products. The potential application of tea polyphenols (TPs) as antiretrogradation additives is demonstrated in this work. Experimental results show that the addition of TPs retards the retrogradation of cassava starch during long-term storage remarkably.
Practical Application:
Introduction Cassava (Manihot esculenta Crantz), one of the 3 biggest tuber crops in the world, is widely cultivated in tropical and subtropical areas. It is adaptable to poor soils and has high return per unit of energy used in its cultivation. Cassava starch not only can be used as food but also has many industrial applications, such as fuel alcohol production and paper making (Tian and others 2008; Mej´ıa-Ag¨uero and others 2012). Cassava starch is rich in amylopectin and is praised for its clarity of gel, light color, and neutral flavor (Abraham 1993). It is widely used in food industry and can be made into jelly, snowy moon cakes, and so on. Usually, the soft and elastic texture of the products is favored by consumers. However, these products are of short shelf life as their rigidity increases markedly and the water retention capacity decreases sharply during storage, a direct consequence of starch retrogradation (Iturriaga and others 2010; Xu and others 2012). The retrogradation of starch refers to the recrystallization of amylase and amylopectin that occur in gelatinized starch during storage below gelatinization temperature (Hoover 1995). Amylose is responsible for the short-term retrogradation, while recrystallization of amylopectin is the main cause for the long-term retrogradation (Hoover 1995). Retrogradation of starch causes many MS 20140151 Submitted 1/28/2014, Accepted 7/20/2014. Authors Wu and Che are with Dept. of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen Univ., Xiamen 361005, P.R China. Author Chen is with Dept. of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen Univ., Xiamen 361005, P.R China. Authors Chen are with School of Chemical and Environmental Engineering, Soochow Univ., Soochow, 215123, P.R, China. Direct inquiries to author Che (E-mail: [email protected]).
R C 2014 Institute of Food Technologists
doi: 10.1111/1750-3841.12589 Further reproduction without permission is prohibited
problems, such as hardening and syneresis (Xu and others 2012). The loss of soft and elastic texture is the main reason of quality degradation of cooked starch-based products, such as rice and bread. Retrogradation of starch is directly related to the staling of bread. In the early 20th century, bakers had to carry out night work in order to avoid product loss through staling. Even nowadays, there continues to be product loss due to retrogradation, as it can lead to a dramatic increase in the hardness of baked goods, making them unattractive to consumers. For several baked products, such as baguettes, starch retrogradation is a greater problem for limiting the shelf life of the product than microbial stability (Ottenhof and Farhat 2004). In order to extend the shelf life of starch-based product, efforts from food industry were made to inhibit the retrogradation of starch, especially the recrystallization of amylopectin (Tian and others 2008). The most commonly used approaches to retard starch retrogradation are chemical and/or physical modifications (Singh and others 2007; Mutungi and others 2009; Han and others 2012). Han and others (2012) found that acetylation can retard the retrogradation of corn starch. Singh and others (2007) reported that hydroxypropylation and cross-linking (POCl3 and propyleneoxide) are also good alternatives. However, chemical modification of starch is not recommended as far as food safety is concerned. Physical modification of starch, such as heat-moisture treatment, is safer but usually less effective in retarding the retrogradation process of starch-based products (Xiao and others 2013). Adding antiretrogradation additives is another frequently used approach to retard the retrogradation of starch (Singh and others 2007; Tian and others 2008; Tian and others 2009; Xu and others 2012). α-Amylase, β-amylase, and β-cyclodextrin have
Vol. 00, Nr. 0, 2014 r Journal of Food Science E1
E: Food Engineering and Physical Properties
Abstract:
Antiretrogradation in cooked starch-based product . . .
o
16.9
A
5
10
15
20
Figure 1–X-ray diffraction patterns of cassava starch with (A) 0 wt.%, (B) 1 wt.%, (C) 2 wt.%, and (D) 3 wt.% TPs, respectively. The X-ray diffraction pattern from bottom to top represents 0-, 5-, 10-, 20-, 40-, and 60-d’s storage, respectively. The samples were stored at 6 °C.
B
25
30
35
5
40
10
15
20 25 2θ (degree)
30
35
40
10
15
20 25 2θ (degree)
30
35
40
2θ (degree)
E: Food Engineering and Physical Properties
C
5
D
10
15
20 25 2θ (degree)
30
35
40
5
been shown to be effective antiretrogradation additives (Tian and others 2008, 2009; Gomes-Ruffi and others 2012). Among them, β-cyclodextrin is the most favorable one, which not only retards the short-term but also the long-term retrogradation of rice starch by forming amylase-lipid–β-cyclodextrin complex (Tian and others 2008, 2009). Tea polyphenols (TPs), which contain a class of polyphenolic flavonoids known as catechin, have attracted more and more attention as effective antiretrogradation additives (Wu and others 2009; Xiao and others 2013). The major functional components
are (−)-epicatechin gallate (ECG), (−)-epicatechin (EC), (−)epigallocatechin (EGC), and (−)-epigallocatechin gallate (EGCG) (Ermakova and others 2005). In vitro and animal studies have provided strong evidences that TPs can provide health benefits such as antioxidative, antidiabetic, antimicrobial, anti-inflammatory, and anticarcinogenic properties (Ahmad and others 2000; Giovannini and Masella 2012). A number of works have been conducted to evaluate the effects of TPs on the physicochemical properties of starch. Beta and
5
80 0 wt. % TPs Normalized hardness
1 wt. % TPs
60
Hardness (mN)
4
2 wt. % TPs 3 wt. % TPs
40
20
0 wt. % TPs
1 wt. % TPs
2 wt. % TPs
3 wt. % TPs
Model prediction
3 2 1 0 0
0 0
20
40
60
80
t (d) Figure 2–Variation of hardness of cassava starch gels stored at 25 °C.
E2 Journal of Food Science r Vol. 00, Nr. 0, 2014
20
40 t (d)
60
80
Figure 3–Variation of normalized hardness of cassava starch gels stored at 25 °C. Experimental data are fitted by single-parameter exponential function.
Antiretrogradation in cooked starch-based product . . . Table 1– Fitting parameters for normalized hardness of cassava Reagent Co., Ltd (Shanghai, China) and are of analytical grade. starch gels using single-parameter exponential function. All the chemicals were used without further purification.
0 1 2 3
k 0.0176 0.0116 0.0072 0.0055
R2
Sample preparation
0.98 Cassava starch and TPs were mixed at a ratio of 30 : 0, 29.7 : 0.3, 0.94 0.92 29.4 : 0.6, or 29.1 : 0.9 (w : w). Fifteen-gram of the mixture was 0.94 added into 50 mL deionized water with 65 mg potassium sor-
Corke (2004) demonstrated that catechin can decrease the hot paste viscosity, final viscosity, and setback viscosity of sorghum and maize starch pastes. Xiao and others (2012) found the favorable antiretrogradation effect of green and black TPs on rice, maize, and potato starches. However, very few attentions have been paid to investigating the effect of TPs on the retrogradation of amylopectin-rich starch, such as cassava starch. Tian and others (2009) reported that β-cyclodextrin reduces the retrogradation of normal rice starch, but has no effect on the retrogradation of waxy rice starch that is enriched in amylopectin. Thus, the antiretrogradation effect of TPs should be validated against more starches, especially the amylopectin-rich starch. Literature review also shows that previous studies have been mainly focused on starch retrogradation during short-term storage, normally less than 30 d (Tian and others 2008, 2009; Wu and others 2009; Ji and others 2010; Xiao and others 2013). The phenomenon of starch retrogradation during longer term storage has not been studied systematically. The aim of this work is therefore to investigate the retrogradation of cassava starch with and without TPs during long-term storage. The retrogradation of the sample is characterized by Xray diffraction (XRD), hardness test, color analysis, and Fourier Transform infrared spectroscopy (FT-IR). The effects of TPs on the retrogradation of amylopectin-rich starch will also be discussed. It will provide people with information of amylopectin retrogradation during long-term storage as well as the anti-retrogradation effect of TPs. The information will find application in controlled retrogradation of cooked starch-based products.
Material and Methods Materials Powdered TPs were purchased from Anhui Redstar Pharmaceutical Co. Ltd (Anhui, China) containing 41.6% EGCG, 17.7% EGC, 9.2% ECG, and 6.0% EC. Cassava starch was purchased from local market (Fujian, China). Potassium sorbate, hydrochloric acid, and methyl silicone oil were obtained from Sinopharm Chemical
bate as antimicrobial additive. The pH value of the well-mixed suspension was adjusted to 4.5 using 1 mol/L hydrochloric acid (to inhibit the growth of bacteria using potassium sorbate). The suspension was then gelatinized in oil bath at 100 °C for 20 min under stirring. The obtained paste was transferred into cylindrical containers (2.5 cm in height and 4.0 cm in diameter) and cooled to room temperature to form cylindrical gels. The gel was covered with methyl silicone oil during storage to prevent water from evaporating. For hardness test, the procedure of sample preparation was similar to the one mentioned above. However, the starch suspension was cooked for 10 more minutes (30 min) to inhibit the growth of bacteria during storage.
XRD analysis of the retrogradation of cassava starch For XRD analysis, the gel was stored at 6 °C for 0, 5, 10, 20, 40, and 60 d, respectively. Prior to the test, the sample was freeze-dried and then pulverized to pass through a 60-mesh sieve. The analysis of the samples was carried out using an X-diffractometer (Ultima IV, Rigaku Corp., Tokyo, Japan). The scanning was performed at 20 kV and 35 mA. The scanning was applied at a diffraction angle (2θ ) from 4° to 40° at a rate of 4°/min. X’Pert High Score Plus, Jade version 6.5, and OriginPro version 7.5 were used to analyze the diffractograms. Hardness test of cassava starch gels The hardness test was performed at room temperature (about 25 °C). In order to reduce the negative effect of freeze-thaw cycles on the retrogradation of cassava starch, the gel was stored at 25 °C. The hardness of the gel was determined every 2 d for 80 d using a texture analyzer (TRAPEZIUM X EZ-S-1 N, Shimadzu Corp., Kyoto, Japan). The hardness of the sample with a thickness of approximately 1.5 cm and a diameter of 4.0 cm were determined using a cylindrical probe of 5 mm in diameter. The probing was applied on the sample disk surface. The sample was compressed at a loading speed of 2 mm/min until a maximum deformation of 20% was achieved. The deformation of 20% was set to avoid a complete destruction of gel structure. The maximum force detected during compression is the hardness of the sample. The compression was carried out at the center of the sample. Samples in triplicate were
Figure 4–Photos of cassava starch gels. The content of TPs is 0 wt.% (A), 1 wt.% (B), 2 wt.% (B), and 3 wt.% (D), respectivley. Vol. 00, Nr. 0, 2014 r Journal of Food Science E3
E: Food Engineering and Physical Properties
TPs concentration wt.%
Antiretrogradation in cooked starch-based product . . . Table 2– The color values of cassava starch gels.
TPs concentration wt.%
Color parameterf
t d 0
L∗
0
25.52 −0.81 −4.23 23.10 0.61 1.70 22.12 1.28 4.67 20.45 1.60 6.19
a∗
b∗ L∗ a∗
1
b∗
L∗ a∗ b∗ L∗ a∗ b∗
2
a
41.91 −1.14 −4.38 38.58 0.82 2.66 36.87 1.19 3.95 34.68 1.49 5.28
0.02c 0.15a 0.33a 0.04a 0.07a 0.90a 0.03a 0.30b 1.00a 0.07a 0.08b
± ± ± ± ± ± ± ± ± ± ± ±
20 1.02b 0.09a 0.18a 0.65b 0.06a 0.06b 0.30b 0.05a 0.26a 1.05b 0.15a 0.18a
53.05 −0.96 −3.38 46.69 1.16 3.18 40.82 1.76 5.52 37.41 1.99 6.3
± ± ± ± ± ± ± ± ± ± ± ±
40 0.71c 0.01b 0.30b 0.15c 0.12b 0.16c 0.67c 0.10b 0.03c 0.94c 0.27b 0.16b
57.98 −0.97 −2.61 51.71 1.74 4.36 47.02 2.43 6.78 40.52 1.97 6.75
± ± ± ± ± ± ± ± ± ± ± ±
60 0.60d 0.02b 0.31c 0.37d 0.09c 0.16d 0.38d 0.09c 0.06d 0.24d 0.06bc 0.11c
60.12 −0.96 −2.36 53.26 1.95 4.66 48.29 2.90 7.57 42.20 2.38 7.44
± ± ± ± ± ± ± ± ± ± ± ±
0.77e 0.04b 0.41c 0.40e 0.08c 0.26d 0.52d 0.10d 0.14e 0.10d 0.09c 0.18d
Values are mean ± standard deviation of 3 parallel samples. Means within a line followed by different letters are significantly different (P < 0.05).
tested to estimate the experimental error. The average values of Table 3– Fitting parameters for ࢞C of cassava starch gels using first-order exponential decay function. hardness were correlated using the following equation TPs concentration wt.%
Ht NHt = = exp(kt ) H0
(1) 0
where NHt is the normalized hardness of the sample at time t, Ht and H0 are the values of hardness determined at time t and 0, and k is the fitting parameter.
1 2 3
A
B
R2
35.24 30.68 26.42 20.92
14.63 13.95 13.95 9.867
0.9964 0.9998 0.9920 0.9887
Average value of 3 parallel samples was used to show the general trends. The color differences C were calculated as follows: Color analysis of cassava starch gels 2 2 2 The color of cassava starch gels was determined by a Spectrophoa t∗ − a 0∗ + b t∗ − b 0∗ + L ∗t − L ∗0 (2) Ct = tometer (CM-700d, Konica Minolta Inc., Tokyo, Japan) employwhere a∗ represents redness, b∗ represents yellowness, and L∗ ing the Hunter and CIE scale. For each sample, the determination was carried out in triplicate and the average value was recorded. represents lightness (Fam´a and others 2007). The subscript t indicates the values observed for each storage time (0, 10, 20, 40, and 60 d) and the subscript 0 indicates the values observed for each sample at zero storage time day. 40 Then C were fitted with first-order exponential decay equation t Ct = A 1 − exp − (3) 30 B where A and B are the fitting parameters. ∆C
E: Food Engineering and Physical Properties
3
± ± ± ± ± ± ± ± ± ± ± ±
10 0.10a
20 0 wt. % 1 wt. % 10
2 wt. % 3 wt. % Model prediction
0 0
15
30 t (d)
45
60
FT-IR analysis of the retrogradation of cassava starch Prior to FT-IR analysis, the gel was freeze-dried and then pulverized to pass through a 60-mesh sieve. The powder was then blended with dry potassium bromide powder. The blend was subsequently made into a pellet. The FT-IR spectrograms of cassava starch with 0, 1, 2, and 3 wt.% TPs (on dry bias) were acquired on a FT-IR spectrophotometer (Nicolet 6700, Thermo Fisher Scientific Inc., Waltham, MA, U.S.A.). Samples were scanned from 4000 to 400 cm−1 at a resolution of 2 cm−1 , with 32 coadded scans per sample. Statistical analysis
The experimental data were obtained in triplicates. Multiple Figure 5–Variation of ࢞C of cassava starch gels during long-term storage. Experimental data are fitted by first-order exponential decay function. The comparison test of Duncan at a probability level 0.05 was persamples were stored at 6 °C. formed, using Matlab version 7.11.0, to determine whether there E4 Journal of Food Science r Vol. 00, Nr. 0, 2014
is significant difference between the behaviors exhibited by the ordered semicrystalline structure imparts initial hardness to the starch gels. For the sample without TPs, a relatively sharp peak at starch gels tested. 16.9o (2θ ) appears after long-term storage (after about 20 d). The Results and Discussion peak is the result of long-range ordered structure formed mainly by amylopectin around the seed nuclei of short-range ordered XRD analysis of the retrogradation of cassava starch The antiretrogradation effect of TPs on cassava starch was first amylase (Tian and others 2008). Rodr´ıguez-Sandoval and others a “B”explored by XRD and the results are shown in Figure 1. Che and (2008) reported that the retrograded cassava starch shows o type crystalline structure characterized by a peak at 16.9 (2θ ). For others (2008) reported that native cassava starch is semicrystalline o with relatively sharp peaks at 15.0°, 17.0°, 17.9°, and 22.9° (2θ ) the samples with TPs, the peak at 16.9 (2θ ) is not found on their on XRD pattern. These peaks are not found in Figure 1, which XRD patterns, which implies that retrogradation of amylopectin means that the crystalline structure of cassava starch was destroyed is retarded. Richardson and others (2004) reported that emulsifier decreases during gelatinization. the amount of free starch, altering the retrogradation characterRetrogradation of starch involves reassociation of amylose and istics of starch. Wu and others (2012) further proved that TPs amylopectin chains through hydrogen bond during storage. The and rice starch interact with each other via hydrogen bond durreassociation of amylose is responsible for short-term retrogradaing gelatinization. TPs contain abundant highly reactive hydroxyl tion of starch, which occurs immediately after cooling the sample groups (-OH). The -OH of TPs may interact with the -OH of to room temperature and can be completed within few hours. cassava starch to form hydrogen bonds. The interaction decreases The reassociation of amylopectin, on the other hand, is responsithe amount of free starch and restraint the reassociation of starch ble for long-term retrogradation of starch, which takes relatively polymers (Beta and Corke 2004; Xiao and others 2013). long time up to a few months (Tian and others 2008). The sharp peaks on XRD pattern arise from long-range ordered structure of the material on the level of atoms, which is conventionally referred as crystalline structure. While the broad diffuse maxima is attributed to short-range ordered structure of the material, which is usually referred as semicrystalline structure. The cassava starch gels with and without TPs all show a broad maximum on XRD patterns, which is the result of short-range ordered structrue formed mainly by amylose. The short-range
Hardness test of cassava starch gels The mechanical properties, such as hardness, cohesiveness, and springiness of starch gel, are quite sensitive to the retrogradation of starch and thus can be used as the indexes of starch retrogradation. The most adverse effect of starch retrogradation is the increase in hardness of the starch-based products. The variation of hardness of cassava starch gels is presented in Figure 2.
Figure 6–FT-IR spectra of cassava starch with (A) 0 wt.%, (B) 1 wt.%, (C) 2 wt.%, and (D) 3 wt.% TPs, respectively. The FT-IR spectrum from bottom to top represents 0-, 5-, 10-, 20-, 40-, and 60-d’s storage, respectively. The samples were stored at 6 °C. Vol. 00, Nr. 0, 2014 r Journal of Food Science E5
E: Food Engineering and Physical Properties
Antiretrogradation in cooked starch-based product . . .
Antiretrogradation in cooked starch-based product . . .
E: Food Engineering and Physical Properties
The cassava starch gel obtained was soft with relative low value of hardness when compared with other starches, such as sweet potato starch (data are not reported here). Yu and others (2009) reported that the hardness of rice starch decreases with increasing amylopectin content. The hardness of the sample decreases with the increase of TPs’ content and increases during long-term storage as a result of starch retrogradation. In order to evaluate the variation of hardness, the hardness of the sample was normalized by its initial value and the results are shown in Figure 3. The normalized hardness of the sample increases exponentially during long-term storage, that is, increases by an accelerating rate. It is contrary to the report by Tian and others (2008) that the hardness of rice starch gel tended to be stable after 1-week storage. Liu and others (2012) also demonstrated that the hardness of waxy starch gel increased by a decreasing rate. As a matter of fact, the accelerating increase in hardness of starch gel during storage has never been reported. One of the reasons is that the storage time was not long enough in these works. The accelerating increase in hardness suggests that the hardness of starch gel is more sensitive to the formation of long-range ordered structure by amylopectin. The increase in normalized hardness of the sample decreases with the increase of TPs’ content, for example, the normalized hardness of the sample without TPs is about 400%, while it is only about 160% for the sample with 3 wt.% of TPs. As shown in Figure 3, the increase in normalized hardness of the samples can be fitted well by single-parameter exponential function. The fitting parameters are shown in Table 1. The accelerating increase in hardness of the sample is indicated by a rate constant k greater than 0. The rate constant k decreases from 0.0176 to 0.0055 when the content of TPs is increased from 0 wt.% to 3 wt.%, suggesting that the addition of TPs plays a crucial role in retarding the hardening of starch gel caused by retrogradation. Miles and others (1985) and Ring and others (1987) attributed the initial firmness of the starch gel to the formation of an amylose matrix and the subsequent increase in firmness to reversible crystallization of amylopectin. Cassava starch has relatively low content of amylose and thus forms a soft and elastic gel (Abraham 1993). The interaction of TPs with amylose via hydrogen bond retards the formation of amylose matrix, and thus results in a softer starch gel. That is the reason why the hardness of starch gel decreases with increasing TPs content. On the other hand, the interaction of TPs with amylopectin via hydrogen bond retards the formation of long-range ordered structure further, which limits the increase in hardness of cassava starch gel. The formation of crystalline structure was reported to be the main reason of increase in hardness of starch-based products. The addition of TPs restricts the formation of crystalline structure and thus limits the increase in hardness of cassava starch gels.
tion, in turn. The evolution of color difference ࢞C of the gel during storage is shown in Figure 5. It is interesting to note that ࢞C keeps on increasing at a decreasing rate, which is contrary to the evolution of gel hardness. The evolution of ࢞C can be fitted very well by first-order exponential decay function and the fitting parameters are shown in Table 3. As shown in Figure 5, cassava starch gel without TPs has the highest ࢞C values among the samples throughout the entire period of storage. The color difference ࢞C decreases with the increase of TPs’ concentration. This is further validated by the fitting parameters in Table 3, that is, A and C decrease with the increase of TPs’ concentration. It means that the appearance of cassava starch gel with TPs is more stable. The evolution of ࢞C further proves that the addition of TPs inhibits the retrogradation of cassava starch.
FT-IR analysis of the retrogradation of cassava starch The FT-IR spectra of the samples were displayed in Figure 6. Spectrum change can be divided into band narrowing caused by ordering of the polymers and change of band intensity caused by alteration in specific conformations of starch such as crystallinity (Fan and others 2012). The spectra of the samples show peaks at around 3400 cm−1 that might be assigned to inter- and intramolecular hydrogen-bonded hydroxyl groups and at 2800 cm−1 that might be attributed to CH2 − stretching. COO- stretching vibration is indicated by peaks at around 1400 and 1640 cm−1 (Han and others 2012). Meanwhile, bands at wavelengths of 1300 to 900 cm−1 have been reported to be sensitive to the gelation of starch and mainly result from C-O and C-C vibrational modes (Fan and others 2012; Lian and others 2013). Figure 6(A) and (B) show that the intensitiy of spectra increases with the increase of storage time. It demonstrates that starches without TPs and with only 1 wt.% TPs show obivious retrogadation trend. However, when the content of TPs is increased to 2 and 3 wt.%, the retrogadation of starch was retarded as the band intensity keeps almost constant during storage (Figure 6C and D). This is consistent with the findings of XRD and hardness test that TPs can inhibit the retrogradation of cassava starch.
Conclusion The effects of TPs on the retrogradation of cassava starch (that is, anti-retrogradation) during long-term storage were evaluated by XRD, hardness test, color analysis, and FT-IR. Cassava starch retrogrades during storage below gelatinizaiton temperature due maily to the recrystallization of amyplopectin. The retrogradation results in an accelerating increase in hardness of cassava starch gel. TPs interact with amylopectin via hydrogen bond, which retards the formation of long-range ordered structure of amylopectin during storage. The addition of TPs in cassava starch gel thus inhibits the retrogradation of starch significantly. The texture and color of cassava starch gel with TPs do not change much during long-term storage, thus a long shelf life in these 2 aspects is expected. The health benefits of TPs also make TPs-containing starch-based food high value-added product. One of the research aspects that should be concerned in the future is the effect of TPs on the growth of bacteria in this kind of starch-based produts.
Color analysis of cassava starch gels The photos of cassava starch gels are shown in Figure 4. The sample without TPs is white and transparent to opaque gel. The obtained TPs are yellow to brown powder. The addition of TPs gives the gel a dark brown color, the more TPs, the thicker of the color. This is also indicated by the color value of the sample, that is, the value of L∗ decreases with the increase in TPs’ concentration (Table 2). The value of L∗ of the sample increases during long-term storage, suggesting that the sample gets more and more opaque due Acknowledgments to starch retrogradation. The work was supported by the grants from Natl. High The evolution of color is the result of starch retrogradation, Technology Research and Development Program of China (No. and thus can be used as one of the indexes of starch retrograda- 2011AA100802-3). E6 Journal of Food Science r Vol. 00, Nr. 0, 2014
Author Contributions Lijing Wu collected test data, interpreted the results, and drafted the manuscript. Liming Che designed the study. Xiao Dong Chen modified the manuscript.
References Abraham TE. 1993. Stabilization of paste viscosity of cassava starch by heat moisture treatment. Starch – St¨arke 45(4):131–5. Ahmad N, Gupta S, Mukhtar H. 2000. Green tea polyphenol epigallocatechin-3-gallate differentially modulates nuclear factor kappa B in cancer cells versus normal cells. Arch Biochem Biophys 376(2):338–46. Beta T, Corke H. 2004. Effect of ferulic acid and catechin on sorghum and maize starch pasting properties. Cereal Chem J 81(3):418–22. Che L-M, Wang B, Li D, Wang L-J, Chiu YL, Chen XD, Mao Z-H. 2008. Effect of highpressure homogenization on the structure and thermal properties of maize starch. J Food Eng 87(3):436–44. Ermakova S, Choi BY, Choi HS, Kang BS, Bode AM, Dong Z. 2005. The intermediate filament protein vimentin is a new target for epigallocatechin gallate. J Biol Chem 280(17):16882–90. Fam´a L, Goyanes S, Gerschenson L. 2007. Influence of storage time at room temperature on the physicochemical properties of cassava starch films. Carbohydr Polym 70(3):265–73. Fan DM, Ma WR, Wang LY, Huang JL, Zhao JX, Zhang H, Chen W. 2012. Determination of structural changes in microwaved rice starch using Fourier transform infrared and Raman spectroscopy. Starch – St¨arke 64(8):598–606. Giovannini C, Masella R. 2012. Role of polyphenols in cell death control. Nutr Neurosci 15(3):134–49. Gomes-Ruffi CR, Cunha RHd, Almeida EL, Chang YK, Steel CJ. 2012. Effect of the emulsifier sodium stearoyl lactylate and of the enzyme maltogenic amylase on the quality of pan bread during storage. LWT – Food Sci Technol 49(1):96–101. Han F, Liu M, Gong H, L¨u S, Ni B, Zhang B. 2012. Synthesis, characterization and functional properties of low substituted acetylated corn starch. Intl J Biol Macromol 50(4):1026–34. Hoover R. 1995. Starch retrogradation. Food Rev Intl 11(2):331–46. Iturriaga LB, Lopez de Mishima B, A˜non MC. 2010. A study of the retrogradation process in five argentine rice starches. LWT – Food Sci Technol 43(4):670–4. Ji Y, Zhu K, Chen Z-C, Zhou H, Ma J, Qian H. 2010. Effects of different additives on rice cake texture and cake staling. J Texture Stud 41(5):703–13. Lian X, Zhu W, Wen Y, Li L, Zhao X. 2013. Effects of soy protein hydrolysates on maize starch retrogradation studied by IR spectra and ESI-MS analysis. Intl J Biol Macromol 59:143–50.
Liu ZD, Gong BQ, Zhang L, An HJ, Liu BX. 2012. The influence of emulsifiers on retrogradation properties of waxy starch. Adv Comput Environ Sci 142:351–8. Mej´ıa-Ag¨uero LE, Galeno F, Hern´andez-Hern´andez O, Matehus J, Tovar J. 2012. Starch determination, amylose content and susceptibility to in vitro amylolysis in flours from the roots of 25 cassava varieties. J Sci Food Agric 92(3):673–8. Miles MJ, Morris VJ, Orford PD, Ring SG. 1985. The roles of amylose and amylopectin in the gelation and retrogradation of starch. Carbohydr Res 135(2):271–81. Mutungi C, Rost F, Onyango C, Jaros D, Rohm H. 2009. Crystallinity, thermal and morphological characteristics of resistant starch type III produced by hydrothermal treatment of debranched cassava starch. Starch – St¨arke 61(11):634–45. Ottenhof MA, Farhat IA. 2004. Starch retrogradation. Biotechnol Genet Eng Rev 21:215–28. Richardson G, Kidman S, Langton M, Hermansson A-M. 2004. Differences in amylose aggregation and starch gel formation with emulsifiers. Carbohydr Polym 58(1):7–13. Ring SG, Colonna P, I’Anson KJ, Kalichevsky MT, Miles MJ, Morris VJ, Orford PD. 1987. The gelation and crystallisation of amylopectin. Carbohydr Res 162(2):277–93. Rodr´ıguez-Sandoval E, Fern´andez-Quintero A, Cuvelier G, Relkin P, Bello-P´erez LA. 2008. Starch retrogradation in cassava flour from cooked parenchyma. Starch – St¨arke 60(3–4):174– 80. Singh J, Kaur L, McCarthy OJ. 2007. Factors influencing the physico-chemical, morphological, thermal and rheological properties of some chemically modified starches for food applications—a review. Food Hydrocolloids 21(1):1–22. Tian Y, Li Y, Manthey FA, Xu X, Jin Z, Deng L. 2009. Influence of β-cyclodextrin on the short-term retrogradation of rice starch. Food Chem 116(1):54–8. Tian Y, Xu X, Li Y, Jin Z, Chen H, Wang H. 2008. Effect of β-cyclodextrin on the long-term retrogradation of rice starch. Eur Food Res Technol 228(5):743–8. Wu Y, Chen Z, Li X, Li M. 2009. Effect of tea polyphenols on the retrogradation of rice starch. Food Res Intl 42(2):221–5. Wu C, Liu R, Huang W, Rayas-Duarte P, Wang F, Yao Y. 2012. Effect of sourdough fermentation on the quality of Chinese Northern-style steamed breads. J Cereal Sci 56(2):127–33. Xiao H, Lin Q, Liu G-Q, Wu Y, Wu W, Fu X. 2013. Inhibitory effects of green tea polyphenols on the retrogradation of starches from different botanical sources. Food Bioprocess Technol 6(8):2177–81. Xiao H, Lin Q, Liu G-Q, Yu F. 2012. Evaluation of black tea polyphenol extract against the retrogradation of starches from various plant sources. Molecules 17(12):8147–58. Xu Z, Zhong F, Li Y, Shoemaker CF, Yokoyama WH, Xia W. 2012. Effect of polysaccharides on the gelatinization properties of cornstarch dispersions. J Agric Food Chem 60(2):658–64. Yu S, Ma Y, Sun D-W. 2009. Impact of amylose content on starch retrogradation and texture of cooked milled rice during storage. J Cereal Sci 50(2):139–44.
Vol. 00, Nr. 0, 2014 r Journal of Food Science E7
E: Food Engineering and Physical Properties
Antiretrogradation in cooked starch-based product . . .
