Food Chemistry 145 (2014) 212–219
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Effects of a highly resistant rice starch and pre-incubation temperatures on the physicochemical properties of surimi gel from grass carp (Ctenopharyn Odon Idellus) Zhen Yang, Wei Wang, Haiyan Wang, Qingfu Ye ⇑ Institute of Nuclear Agricultural Sciences, Key Laboratory of Nuclear Agricultural Sciences of Ministry of Agriculture and Zhejiang Province, Zhejiang University, Hangzhou 310029, China
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Article history: Received 2 February 2013 Received in revised form 19 June 2013 Accepted 12 August 2013 Available online 21 August 2013 Keywords: Specific rice starch Grass carp surimi gel Pre-incubation
a b s t r a c t The effects of a specific rice starch (SRS), containing highly resistant starch (RSIII), on gel properties of grass carp (Ctenopharyngodon idella) and the influence of five levels of SRS (0%, 2%, 4%, 6%, and 8% w/ w) on gel physicochemical properties at three different pre-incubation temperatures (4 °C, 25 °C, and 40 °C) were investigated. Gels with increasing amounts of SRS addition showed lower expressible water contents and cooking loss values than did control gels. SDS gel electrophoresis revealed no changes in protein patterns, regardless of different SRS-added levels at the same pre-incubation temperature, but an evident decrease in the MHC when the pre-incubation temperature increased. The texture properties, colour attributes, SEM were optimal in the treatments containing 4% w/w SRS at the pre-incubation temperature 25 °C. Thus, the optimum SRS addition level and pre-incubation temperature are proposed to be 4% w/w and 25 °C, respectively. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Grass carp (Ctenopharyn Odon Idellus) is one of the most popular freshwater species in China, due to its rapid growth, low price, and nutritional benefits. Fish surimi products, which are made from fresh muscle material, have been widely accepted by the public, due to their pleasant taste and high quality. The increase in consumer demand for high-quality food products has promoted the development of new technologies and ingredients. Currently, several hydrocolloids are added during surimi gel production to improve the mechanical properties of surimi products; additives include modified starch, pectin, and konjac glucomannan (Barrera, Ramirez, Gonzalez-Cabriales, & Vazquez, 2002; Tuankriangkrai & Benjakul, 2010). However, improper utilisation of additives may have negative effects on human health (Ramírez, Uresti, Velazquez, & Vázquez, 2011). Thus, proper restructuring processes and additive materials, regarding fish muscle proteins, should be evaluated to ensure the high quality of products, as well as to improve human health. Starch is widely used as a food additive in surimi seafood products. Due to its high water-holding capacity and the ability to retain protein properties whilst maintaining gel properties (Campo-Deano & Tovar, 2011). Verrezbagnis, Bouchet, Gallant, Hermansson, and Kim (1993) divided starches into three groups ⇑ Corresponding author. Tel./fax: +86 571 86971423. E-mail address: [email protected] (Q. Ye). 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.08.040
according to their specific effects and functional properties when added to surimi: (1) waxy maize, normal maize, native potato, and modified potato starch help to improve gel strength and water retention ability in surimi gels; (2) rice and wheat starches added to starch-surimi gels, help to increase elongation values; (3) pea, amylomaize and Cremalys 516, an emulsified and complexed starch supplied by Roquette (Lestrem, France), shows reduced gel properties, increases expressible moisture and has higher gelatinisation temperatures when added to the surimi. Starches modified by crosslinking of hydroxypropylation provide the best freeze/ thaw stability (Park, 1995). Myosin, purified from myofibrillar protein, can change the heat-gelation profiles and generally increase gel rigidity at 80 °C; however, some other muscle-dependent myofibrillar proteins, such as actin and C-protein, indicate specific aggregation and gelation mechanisms for each myosin isoform (Boyer, Joandel, Roussilhes, Culioli, & Ouali, 1996). Additionally, starch and myofibrillar fish proteins can be gelled to achieve the proper texture; it takes at least 20 min for most starches and proteins to complete the gelation process when heated to 90 °C (Pillai, Sanghavi, Khire, Bombe, & Karir, 2000). Resistant starch is a component of dietary fibre and is defined as the fraction of dietary starch that escapes digestion in the small intestine (AACC International, 2010). Previous studies have reported that resistant starch can be subdivided into four fractions, RSI, RSII, RSIII, and RSIV (Englyst, Kingman, & Cummings, 1992): RSI corresponds to physically inaccessible starches, entrapped in a cellular matrix, as
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in cooked legume seeds; RSII is composed of starch granules from certain plants, containing uncooked starch, whose crystallinity makes it essentially non-susceptible to hydrolysis; RSIII consists mainly of retrograded starches, which may be formed from retrogradation of starch after cooking; RSIV, includes chemically modified starches, used by food manufacturers to alter the functional characteristics of the starch, such as ethers or esters. As a low-calorie and functional food ingredient, resistant starch has received significant attention for both its potential health benefits and its functional physical properties. In comparison to traditional fibres, it has high melting temperatures, reduced caloric content, low water-holding capacity, and shows minimal swelling, which may minimise the impacts of incorporating resistant starch (Aravind, Sissons, Fellows, Blazek, & Gilbert, 2013). Resistant starches also result in better appearance, texture, and chewiness compared with conventional fibres (Charalampopoulos, Wang, Pandiella, & Webb, 2002), which make them useful additives that improve the quality and texture of the final products (Baixauli, Salvador, MartinezCervera, & Fiszman, 2008). Thus, it is essential to take advantage of the functional properties of resistant starch to improve food quality and promote consumer health demands. Gelation can occur at low temperature (0 °C), medium temperature (25 °C) and relatively high temperature (40 °C) (Lanier & Lee, 1992). Different fish species have different gelation temperatures, and thus, different pre-incubation temperatures may significantly influence gel properties (Benjakul, Chantarasuwan, & Visessanguan, 2003; Benjakul, Visessanguan, & Chantarasuwan, 2004; Klesk, Yongsawatdigul, Park, Viratchakul, & Virulhakul, 2000). The effect of pre-incubation temperatures and time, combined with the specific rice starch (SRS), were studied at different gradients (4 °C for 24 h, 25 °C for 12 h, 40 °C for 2 h) to observe the surimi gel-forming ability and the optimised pre-incubation temperature of grass carp (Ctenopharyn Odon Idellus) by monitoring physicochemical properties of gel samples.
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content in the SRS sample was 10.6%, whilst this value was 0.93% in the control sample. Rheological, gelatinisation and retrogradation properties of SRS and control samples were also determined. 2.3. Rheological, gelatinisation and retrogradation properties of SRS and control SRS types made a clear difference and had a marked effect on rheological properties when compared with the control sample. The peak, hold and final viscosities (RVU) of the control were 223.02, 80.08 and 158.54; however, the values were 24.56, 21.53 and 33.06 in SRS samples. This indicated that SRS containing RSIII can significantly transform starch viscosity with nearly complete loss. The gelatinisation and retrogradation properties were measured using DSC. Results showed that SRS had special thermodynamic properties: the onset temperature (T0), peak maximum temperature (Tp), conclusion temperature (Tc), enthalpy of transition (DH) and gelatinisation range (R = 2 (Tp T0)) could not be detected. However, as for the control sample, the values were T0 = 74.2 °C, Tp = 79.0 °C, Tc = 83.6 °C, DH = 7.678 J/g, and R = 9.6 °C, respectively. 2.4. Expressible water content Expressible water content (EW), for each treatment, was measured using a method described by Uresti, López-Arias, GonzálezCabriales, Ramírez, and Vázquez (2003) with slight modifications. Samples of approximately 2 g (Wi) were placed between two layers of filter paper, loaded into 80 ml centrifuge tubes, and then centrifuged at 8228g for 15 min at 15 °C. After centrifugation, samples were carefully separated from the papers and then immediately reweighed (Wf). EW values were determined as follows:
EW% ¼ ½ðW i W f Þ=W i 100: 2. Materials and methods 2.1. Fish sample, surimi, and surimi gel preparation Fresh grass carp samples were purchased from a local seafood supermarket. In the laboratory, samples were gutted, washed with sterile-cold water, thoroughly drained, and then chopped into surimi using a mangler. The surimi paste samples were prepared by homogenising grass carp surimi for 2 min with 20 g of salt/kg (w/w) (Hernández-Briones, Velázquez, Vázquez, & Ramírez, 2009). Next, the paste was divided into five groups to mix with different levels of SRS, which was dissolved in ultrapure-cold (4 °C) water (200 ml/kg surimi) at 0 (control), 20, 40, 60, 80 g/kg (w/w). The samples were then immediately placed in polyvinylidine chloride dishes of 3.5 cm diameter and 1 cm thickness, respectively. After that, they were vacuum-packed in polythene bags and divided into three for pre-incubation: lot I was stored for 24 h at 4 °C, lot II was stored for 12 h at 25 °C, and lot III was heated for 2 h at 40 °C. Next, all samples were heated for 20 min at 90 °C in a water bath and then 30 min in a 4 °C water bath for cooling. All samples were stored overnight at 4 °C prior to analysis.
2.5. Cooking loss The liquid on the surface of each gel was wiped gently using a filter paper and then weighed before (G1) and after heating (90 °C, 20 min) (G2). Cooking loss (CL) was represented as the loss of liquid:
CL% ¼ ðG1 G2 Þ=G1 100: 2.6. Textural profile analysis (TPA) Texture analyses of grass carp surimi gel samples were performed using a Texture Analyser (TA-XT2i, Scientific Measuring Systems, Middlesex, UK). The Texture Expert Exceed version 1.22 computer programme by Stable Micro System was used for data collection and calculation. Each cylinder was compressed axially in two consecutive cycles of 5 mm compression, 5 s apart, with a flat plunger 5 mm in diameter (SMS-P/5). From the TPA curves, the following texture parameters were obtained from TPA curves: hardness, springiness, cohesiveness, chewiness, and resilience. Six cylindrical samples were prepared; before their analysis, they were equilibrated at ambient temperature for 1 h.
2.2. Specific rice starch 2.7. Freeze–thaw stability Specific rice starch (SRS), containing a high value of resistant starch type III (RSIII, YiTang RiceÒ), was supplied by the Institute of Nuclear Agricultural Sciences, Zhejiang University. Normal rice starch was used as a control and purchased from a local supermarket. Resistant starch (RS) detection showed that the RS
After samples for 24 h samples
pre-incubation at 25 °C and heated at 90 °C for 20 min, with different SRS levels were frozen in a 20 °C freezer and then thawed in a water bath at 30 °C for 1 h. Three were randomly selected for determination of expressible
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water content and textural profile analysis (methods described in Section 2.4. and Section 2.6.), whilst the remaining samples were placed back into the freezer for further freeze–thaw cycling for up to three cycles. 2.8. Colour evaluation Spectral reflectance of surimi gels was determined using a HunterLab (CM-400d, Konica Minolta, Tokyo, Japan). Measurement of L⁄ (lightness), a⁄ (redness/greenness), and b⁄ (yellowness/blueness) was conducted in six replications. Whiteness was calculated, based on the following equation:
h i1=2 2 2 Whiteness ¼ 100 ð100 L Þ þ a2 þ b :
2.9. Scanning electron microscopy (SEM) Scanning electron microscopy (SEM) images for each treatment were acquired using a method described by Oujifard, Benjakul, Ahmad, and Seyfabadi (2012) with slight modification. Microstructures of surimi gels were determined using SEM. Thickness values of 0.5–1 mm sliced samples were obtained from control and treated groups, respectively. Next, the slices were immersed in 3.5% glutaraldehyde for 24 h, and then transferred into 0.1 M phosphate buffer (pH 7.2) for 15 min; this process was repeated. Samples were soaked for 1 h in ultrapure water before dehydration in ethanol at serial concentrations of 50%, 70%, 80%, 90%, and 100%, then vacuum-freeze-dried. Dried samples were mounted on a bronze table and then gold-plated, using an ion coater (Eiko Engineering, Co., Ltd., Fukuoka, Japan). Specimens were observed using a scanning electron microscope (XL30-ESEM, FEI, Hillsboro, USA) at an acceleration voltage of 20 kV.
Fig. 1. Effect of different levels (0–8% w/w) of SRS at different pre-incubation temperatures (4 °C, 25 °C, 40 °C) on the cooking loss (CL) of grass carp surimi gels. A–C Different letters at the same SRS content differ significantly (p < 0.05). a–c Different letters at the same temperature treatment differ significantly (p < 0.05).
3. Results and discussion
6%, and 8% w/w) were observed following three different preincubation temperatures (4 °C for 24 h, 25 °C for 12 h, and 40 °C for 2 h). Fig. 1 shows significant difference (p < 0.05) in cooking loss between SRS-added groups and control samples (0% w/w SRS). Higher cooking loss was observed in control samples than in those with SRS added in each pre-incubation temperature group. Moreover, increases in CL varied significantly (p < 0.05) with different preincubation temperatures, particularly when no SRS was added. Increasing pre-incubation temperatures increased water loss after cooing, resulting in lower expressible water content when no SRS was added. CL content at 4 °C pre-incubation was only 2.42%, whilst this value was 3.43% at 25 °C and finally increased up to 7.77% at 40 °C. The results indicated that different gel-forming temperatures significantly influenced CL contents (p < 0.05). Additionally, this also showed that adding SRS can prevent water loss during cooking and that it has a good protective effect on the steaming stability compared with control samples. Fig. 2a–c shows a significant (p < 0.05) decrease in expressible water content between samples treated with SRS and control at the same pre-incubation temperature, whilst different pre-incubation temperatures did not significantly (p > 0.05) influence EW content at the same SRS level. EW values decreased as SRS content increased, suggesting that the water-holding capacity of the gel was increased with SRS addition. Jung, Kim, and Yoo (2007) reported that adding acetylated rice starch improved freeze–thaw stability and reduced expressible moisture contents of surimi gels. Additionally, the high water-absorbing ability or the hydrophilic group interacting with free-water may have altered it to bound-water, which was not easily extracted. Statistical analysis showed a highly positive non-linear relationship between SRS levels and EW values at pre-incubation temperatures of 4 °C and 25 °C (Y = 0.1400X2 3.3021X + 42.3765, R2 = 0.9864 2 2 (Fig. 2a); Y = 0.2386X 3.0762X + 38.7413, R = 0.9175 (Fig. 2b)), whilst a highly negative non-linear relationship was observed at 40 °C (Y = 0.1495X2 0.4740X + 37.5336, R2 = 0.9946, (Fig. 2c)).
3.1. Effect of SRS on cooking loss (CL) and expressible water content (EW)
3.2. Effect of SRS on TPA
Changes in cooking loss (CL, Fig. 1) and expressible water content (EW, Fig. 2a–c) of surimi gels with added SRS (0%, 2%, 4%,
The effects of SRS and pre-incubation temperature on the textural properties of surimi gels are shown in Table 1. Textural
2.10. SDS–polyacrylamide gel electrophoresis (SDS–PAGE) SDS–polyacrylamide gel electrophoresis was carried out according to the method described by Yongsawatdigul and Park (2002). Samples (3 g) were homogenised in 5% (w/v) SDS in a final volume of 30 ml. The homogenate was incubated at 85 °C for 1 h to dissolve total proteins and then centrifuged at 6171g for 10 min. Using a 4% stacking gel and a 10% separating gel; the supernatant was applied for SDS–PAGE analysis so that the protein amount was 20 lg. Electrophoresis was performed at a voltage of 80 V for 15 min and then at a constant voltage of 110 V. Proteins were stained in 0.125% Coomassie brilliant blue R-250 and destained in 25% ethanol and 10% acetic acid. After electrophoresis, photos were acquired using a fluorescent chemiluminescence imaging system (FluorChemE, Cell Biosciences, North San Jose, CA, USA). 2.11. Statistical analysis All experiment data were calculated as arithmetic means and standard deviations (mean ± SD) from repeated measurements. Significance between treatments was tested, based on one-way analysis of variance (ANOVA), using SPSS 16.0 software (IBM, Armonk, NY, USA).
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Fig. 2. Effect of different levels (0–8% w/w) of SRS at different pre-incubation temperatures on extractable water content (EW) of grass carp surimi gels: (a) 4 °C preincubation; (b) 25 °C pre-incubation; and (c) 40 °C pre-incubation. (d) Effect of different levels (0–8% w/w) of SRS at the pre-incubation temperature 25 °C on the freeze–thaw stability of grass carp surimi gels. A–BDifferent letters at the same SRS content differ significantly (p < 0.05). a–cDifferent letters at the same temperature treatment differ significantly (p < 0.05).
properties of grass carp surimi gels after cooking proved to be affected by SRS addition and pre-incubation temperatures. Hardness was not significantly (p > 0.05) influenced by SRS, except at 8% w/w SRS addition. Due to the crosslinking reaction between SRS–protein, SRS–SRS, and protein–protein, more force and energy were necessary to break down the gel system. Park, Cho, Kimura, and Seki (2005) reported a similar result that, as the level of the added potato starch increased, the breaking strength of the thermal gel of salted squid paste increased and starch-added gel became firm and less elastic. Additionally, Westphalen, Briggs, and Lonergan (2006) indicated that the hardness of heat-induced gels was correlated with water-holding capacity of myofibrillar protein gels and viscoelastic properties. Springiness, cohesiveness, chewiness, and resilience at 25 °C appear to result in better performance in nearly all groups with SRS-added or control samples compared to incubation at 4 °C and 40 °C. It was apparent that pre-incubation at 25 °C is more suitable for gel formation of grass carp surimi. Additionally, following 25 °C pre-incubation, springiness, cohesiveness, chewiness, and resilience were higher in all samples with SRS added compared with the control sample. The four TPA indices were highest at 4% w/w SRS addition, which decreased at higher percentages. The results suggested that SRS clearly affects the textural properties of surimi gels to improve both gel-forming ability and gel properties. Sensory evaluation showed that the pre-incubation temperature at 25 °C showed a higher score than did 4 °C and 40 °C when SRS 1%. However, we observed no significant (p > 0.05) decrease in whiteness until SRS addition reached 8% w/w at pre-incubation temperatures of 4 °C and 25 °C. This indicates that SRS protects against a reduction in whiteness when the gels were subjected to processing. Moreover, both pre-incubation temperature and SRS addition have a significant (p < 0.05) influence on a⁄ and b⁄ values compared with the control samples. Additionally, a temperature of 25 °C appears to be a ‘unique point’ that retains the maximum a⁄ values and minimum b⁄ values for each of the SRS-added groups and the control. Based on these results, L⁄ values declined as pre-incubation temperature increased. This may be because a higher temperature can promote the Maillard reaction between the generated free amino acid groups and the reducing sugar or oxidation products. As a consequence, more yellowish compounds are formed in the gel systems. Kim, Park, and Choi (2003) reported that sarcoplasmic proteins, such as haemoglobin and myoglobin, may enhance the Maillard browning reaction in acid- or alkali-treated gels. For L⁄, a⁄, and b⁄, fish gels prepared from grass carp mince pre-incubated at 25 °C with added SRS were superior to those pre-incubated at 4 °C or 40 °C, indicating suitable lightness, redness, and yellowness, respectively.
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Z. Yang et al. / Food Chemistry 145 (2014) 212–219 Table 2 Effect of different levels (0–8% w/w) of SRS at different pre-incubation temperatures on the colour attributes of grass carp surimi gels. Colour Whiteness 4 °C 25 °C 40 °C L⁄ 4 °C 25 °C 40 °C a⁄ 4 °C 25 °C 40 °C b⁄ 4 °C 25 °C 40 °C
0%
2%
4%
6%
8%
79.16 ± 0.44Aa 78.56 ± 0.60Aab 76.29 ± 1.13Ba
78.71 ± 0.84Aab 78.64 ± 0.53Aab 78.10 ± 0.42Abc
78.64 ± 0.56Aab 78.53 ± 0.54Aab 78.65 ± 0.44Ab
78.70 ± 0.48Aab 78.90 ± 0.69Aa 77.70 ± 0.57Bc
78.13 ± 0.47Ab 78.08 ± 0.44Ab 77.81 ± 0.24Ac
82.25 ± 0.45Aa 81.32 ± 0.66Aa 79.57 ± 1.10Ba
82.10 ± 0.79Aa 81.65 ± 0.52ABa 81.26 ± 0.41Bbc
81.54 ± 0.67Aab 81.22 ± 0.78Aa 81.91 ± 0.58Ab
81.88 ± 0.68Aab 81.63 ± 0.65ABa 80.92 ± 0.66Bc
81.26 ± 0.44Ab 80.86 ± 0.40Aa 80.98 ± 0.34Ac
1.407 ± 0.099Aa 1.393 ± 0.106Aa 1.040 ± 0.190Ba
1.298 ± 0.108Aab 0.970 ± 0.217Bb 1.143 ± 0.203ABa
1.310 ± 0.155Aab 0.508 ± 0.021Bc 0.953 ± 0.116Cab
11.45 ± 0.36Abd 10.88 ± 0.23Bbc 11.28 ± 0.19Cb
10.67 ± 0.10Ac 10.38 ± 0.34Ac 11.30 ± 0.29Bb
10.82 ± 0.22Aacd 10.42 ± 0.35Aac 11.98 ± 0.42Ba
1.255 ± 0.031Ab 0.620 ± 0.162Bc 0.755 ± 0.043Cb
1.215 ± 0.041Ab 0.547 ± 0.280Bc 0.798 ± 0.144Cb
11.12 ± 0.28ACd 10.35 ± 0.40Bc 11.52 ± 0.45Cb
11.20 ± 0.22ACd 10.67 ± 0.24Bc 11.39 ± 0.20Cb
A–C a–d
Different letters at the same SRS content differ significantly (p < 0.05). Different letters at the same temperature treatment differ significantly (p < 0.05).
3.5. Electrophoretic banding pattern of protein extracts Gelling is influenced by the collective effects of all proteins present in food systems (Barrera et al., 2002). Myosin, actin, and actomyosin are the most abundant proteins amongst myofibrillar proteins, whilst myosin is primarily responsible for the functional properties of meat products (Ramirez, Martin-Polo, & Bandman, 2000). Protein patterns of grass carp gels with different amounts of SRS added (0–8% w/w) are shown in Fig. 3. In our study, intensity of myosin heavy chain (MHC) decreased as pre-incubation temperature increased, whilst no changes were observed in protein patterns, regardless of amount of SRS added at the same preincubation temperature. These results indicate that SRS addition does not significantly influence protein patterns of grass carp gels, and that MHC may decrease when pre-incubated at a higher temperature. Previous studies have reported that the primary intense band in heat-induced gels was present, due to the absence of protein bands at a molecular weight of approximately 66 kDa (A band), whilst the B band (tropomyosin b) and C band (tropomyosin a) were relatively intense (33–37 kDa) (DeFreitas, Sebranek, Olson, & Carr, 1997). However, the A band (66 kDa) was also relatively
intense following pre-incubation and heating. This suggests that SRS has a protective effect and prevents lower protein profiles from being destroyed by the heating process. 3.6. Microstructure of surimi gel Pre-incubation at 25 °C was a suitable temperature for grass carp gel formation; micrographs of surimi gels from grass carp with 0–8% w/w of SRS added at 25 °C are shown in Fig. 4. A more compact and denser gel network with a thin band can be observed in the surimi gels with SRS added compared with the control sample (0% SRS). Additionally, at higher SRS content, interconnections between the three-dimensional protein network of grass carp gel increases. This is correlated with the highest hardness values, which reached a maximum at 8% (w/w of SRS addition). Moreover, the compact network may effectively hold water in the system, enabling surimi products to maintain a favourable textural profiles. Additionally, SRS added at 2% w/w showed dense holes, whilst 4% w/w SRS addition maintained the fine structure without generating a large hole. Thus, addition of 4% w/w SRS can be used to maintain surimi gel quality.
Fig. 3. Effect of different levels (0–8% w/w) of SRS at different pre-incubation temperatures (4 °C, 25 °C, 40 °C) on electrophoretic protein pattern of grass carp surimi gels.
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Fig. 4. Effect of different levels (0–8% w/w) of SRS at 25 °C pre-incubation on the microstructure of grass carp surimi gels.
4. Conclusion Analysis of grass carp surimi gels pre-incubated at different temperatures (4 °C, 25 °C, and 40 °C) showed that addition of SRS positively affects gel properties and physicochemical characteristics. As a food additive, SRS can be used to improve gel quality and significantly reduce the amount of traditional starch added to gels. Additionally, SRS showed a positive influence on the freeze–thaw stability of the surimi gels. Addition of 4% w/w SRS effectively decreased the expressible water content and cooking loss values. At a pre-incubation temperature of 25 °C and 4% w/w SRS, texture properties, colour attributes, and SEM were optimal. Additionally, SDS gel electrophoresis revealed no changes in proteins, regardless of the level of SRS added at the same preincubation temperature, but a decrease in the intensity of myosin heavy chain (MHC) was observed with increased pre-incubation
temperature. Therefore, SRS can be used as a gel-forming additive due to its ability to improve gel quality. Acknowledgements The study was supported by National High Technology Research and Development Projects 863 (2011AA100804), Ministry of Agriculture of China National Natural Science Foundation (201103007) and the project from the Science and Technology Department of Zhejiang Province (2010R50033). References AACC International. (2010). Approved methods of analysis (11th ed.) Methods 38– 12A, 44–15A, 54–21, 26–41. AACCI, St. Paul, MN. Aravind, N., Sissons, M., Fellows, C. M., Blazek, J., & Gilbert, E. P. (2013). Optimisation of resistant starch II and III levels in durum wheat pasta to reduce in vitro
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threadfin bream (Nemipterus bleekeri). LWT-Food Science and Technology, 47(2), 261–266. Park, J. W. (1995). Effects of salt, surimi, and/or starch content on fracture properties of gels at various test temperatures. Journal of Aquatic Food Product Technology, 4(2), 75–84. Park, S. H., Cho, S. Y., Kimura, M., & Seki, N. (2005). Effects of microbial transglutaminase and starch on the thermal gelation of salted squid muscle paste. Fishery Science, 71, 896–903. Pillai, A. G. S., Sanghavi, R. R., Khire, M., Bombe, P. D., & Karir, J. S. (2000). Process technology development for LOVA gun propellant. Indian Journal of Chemical Technology, 7(3), 100–104. Ramirez, J. A., Martin-Polo, M. O., & Bandman, E. (2000). Fish myosin aggregation as affected by freezing and initial physical state. Journal of Food Science, 65(4), 556–560. Ramírez, J. A., Uresti, R. M., Velazquez, G., & Vázquez, M. (2011). Food hydrocolloids as additives to improve the mechanical and functional properties of fish products: A review. Food Hydrocolloids, 25, 1842–1852. Simpson, R., Morrissey, M. T., Kolbe, E., Lanier, T. C., & MacDonald, G. A. (1994). Effects of varying sucrose concentrations in Pacific whiting (Merluccius productus) stabilized mince used for surimi production. Journal of Aquatic Food Product Technology, 3, 41–52. Tuankriangkrai, S., & Benjakul, S. (2010). Effect of modified tapioca starch on the stability of fish mince gels subjected to multiple freeze-thawing. Journal of Muscle Foods, 21(3), 399–416. Uresti, R. M., López-Arias, N., González-Cabriales, J. J., Ramírez, J. A., & Vázquez, M. (2003). Use of amidated low methoxyl pectin to produce fish restructured products. Food Hydrocolloids, 17, 171–176. Verrezbagnis, V., Bouchet, B., Gallant, D. J., Hermansson, A. M., & Kim, J. M. (1993). Relationship between the starch granule structure and the textural properties of heat-induced surimi gels. Food Structure, 12(3), 309–320. Wang, L., Xie, B. J., Xiong, G. Q., Wu, W. J., Wang, J., Qiao, Y., et al. (2013). The effect of freeze–thaw cycles on microstructure and physicochemical properties of four starch gels. Food Hydrocolloids, 31, 61–67. Westphalen, A. D., Briggs, J. L., & Lonergan, S. M. (2006). Influence of muscle type on rheological properties of porcine myofibrillar protein during heat-induced gelation. Meat Science, 72(4), 697–703. Xiong, G., Cheng, W., Ye, L., Du, X., Zhou, M., Lin, R., et al. (2009). Effects of konjac glucomannan on physicochemical properties of myofibrillar protein and surimi gels from grass carp (Ctenopharyngodon idella). Food Chemistry, 116(2), 413–418. Yongsawatdigul, J., & Park, J. W. (2002). Biochemical and conformational changes of actomyosin from threadfin bream stored in ice. Food Chemistry and Toxicology, 67(3), 985–990.
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Effects of a highly resistant rice starch and pre-incubation temperatures on the physicochemical properties of surimi gel from grass carp (Ctenopharyn Odon Idellus) Zhen Yang, Wei Wang, Haiyan Wang, Qingfu Ye ⇑ Institute of Nuclear Agricultural Sciences, Key Laboratory of Nuclear Agricultural Sciences of Ministry of Agriculture and Zhejiang Province, Zhejiang University, Hangzhou 310029, China
a r t i c l e
i n f o
Article history: Received 2 February 2013 Received in revised form 19 June 2013 Accepted 12 August 2013 Available online 21 August 2013 Keywords: Specific rice starch Grass carp surimi gel Pre-incubation
a b s t r a c t The effects of a specific rice starch (SRS), containing highly resistant starch (RSIII), on gel properties of grass carp (Ctenopharyngodon idella) and the influence of five levels of SRS (0%, 2%, 4%, 6%, and 8% w/ w) on gel physicochemical properties at three different pre-incubation temperatures (4 °C, 25 °C, and 40 °C) were investigated. Gels with increasing amounts of SRS addition showed lower expressible water contents and cooking loss values than did control gels. SDS gel electrophoresis revealed no changes in protein patterns, regardless of different SRS-added levels at the same pre-incubation temperature, but an evident decrease in the MHC when the pre-incubation temperature increased. The texture properties, colour attributes, SEM were optimal in the treatments containing 4% w/w SRS at the pre-incubation temperature 25 °C. Thus, the optimum SRS addition level and pre-incubation temperature are proposed to be 4% w/w and 25 °C, respectively. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Grass carp (Ctenopharyn Odon Idellus) is one of the most popular freshwater species in China, due to its rapid growth, low price, and nutritional benefits. Fish surimi products, which are made from fresh muscle material, have been widely accepted by the public, due to their pleasant taste and high quality. The increase in consumer demand for high-quality food products has promoted the development of new technologies and ingredients. Currently, several hydrocolloids are added during surimi gel production to improve the mechanical properties of surimi products; additives include modified starch, pectin, and konjac glucomannan (Barrera, Ramirez, Gonzalez-Cabriales, & Vazquez, 2002; Tuankriangkrai & Benjakul, 2010). However, improper utilisation of additives may have negative effects on human health (Ramírez, Uresti, Velazquez, & Vázquez, 2011). Thus, proper restructuring processes and additive materials, regarding fish muscle proteins, should be evaluated to ensure the high quality of products, as well as to improve human health. Starch is widely used as a food additive in surimi seafood products. Due to its high water-holding capacity and the ability to retain protein properties whilst maintaining gel properties (Campo-Deano & Tovar, 2011). Verrezbagnis, Bouchet, Gallant, Hermansson, and Kim (1993) divided starches into three groups ⇑ Corresponding author. Tel./fax: +86 571 86971423. E-mail address: [email protected] (Q. Ye). 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.08.040
according to their specific effects and functional properties when added to surimi: (1) waxy maize, normal maize, native potato, and modified potato starch help to improve gel strength and water retention ability in surimi gels; (2) rice and wheat starches added to starch-surimi gels, help to increase elongation values; (3) pea, amylomaize and Cremalys 516, an emulsified and complexed starch supplied by Roquette (Lestrem, France), shows reduced gel properties, increases expressible moisture and has higher gelatinisation temperatures when added to the surimi. Starches modified by crosslinking of hydroxypropylation provide the best freeze/ thaw stability (Park, 1995). Myosin, purified from myofibrillar protein, can change the heat-gelation profiles and generally increase gel rigidity at 80 °C; however, some other muscle-dependent myofibrillar proteins, such as actin and C-protein, indicate specific aggregation and gelation mechanisms for each myosin isoform (Boyer, Joandel, Roussilhes, Culioli, & Ouali, 1996). Additionally, starch and myofibrillar fish proteins can be gelled to achieve the proper texture; it takes at least 20 min for most starches and proteins to complete the gelation process when heated to 90 °C (Pillai, Sanghavi, Khire, Bombe, & Karir, 2000). Resistant starch is a component of dietary fibre and is defined as the fraction of dietary starch that escapes digestion in the small intestine (AACC International, 2010). Previous studies have reported that resistant starch can be subdivided into four fractions, RSI, RSII, RSIII, and RSIV (Englyst, Kingman, & Cummings, 1992): RSI corresponds to physically inaccessible starches, entrapped in a cellular matrix, as
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in cooked legume seeds; RSII is composed of starch granules from certain plants, containing uncooked starch, whose crystallinity makes it essentially non-susceptible to hydrolysis; RSIII consists mainly of retrograded starches, which may be formed from retrogradation of starch after cooking; RSIV, includes chemically modified starches, used by food manufacturers to alter the functional characteristics of the starch, such as ethers or esters. As a low-calorie and functional food ingredient, resistant starch has received significant attention for both its potential health benefits and its functional physical properties. In comparison to traditional fibres, it has high melting temperatures, reduced caloric content, low water-holding capacity, and shows minimal swelling, which may minimise the impacts of incorporating resistant starch (Aravind, Sissons, Fellows, Blazek, & Gilbert, 2013). Resistant starches also result in better appearance, texture, and chewiness compared with conventional fibres (Charalampopoulos, Wang, Pandiella, & Webb, 2002), which make them useful additives that improve the quality and texture of the final products (Baixauli, Salvador, MartinezCervera, & Fiszman, 2008). Thus, it is essential to take advantage of the functional properties of resistant starch to improve food quality and promote consumer health demands. Gelation can occur at low temperature (0 °C), medium temperature (25 °C) and relatively high temperature (40 °C) (Lanier & Lee, 1992). Different fish species have different gelation temperatures, and thus, different pre-incubation temperatures may significantly influence gel properties (Benjakul, Chantarasuwan, & Visessanguan, 2003; Benjakul, Visessanguan, & Chantarasuwan, 2004; Klesk, Yongsawatdigul, Park, Viratchakul, & Virulhakul, 2000). The effect of pre-incubation temperatures and time, combined with the specific rice starch (SRS), were studied at different gradients (4 °C for 24 h, 25 °C for 12 h, 40 °C for 2 h) to observe the surimi gel-forming ability and the optimised pre-incubation temperature of grass carp (Ctenopharyn Odon Idellus) by monitoring physicochemical properties of gel samples.
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content in the SRS sample was 10.6%, whilst this value was 0.93% in the control sample. Rheological, gelatinisation and retrogradation properties of SRS and control samples were also determined. 2.3. Rheological, gelatinisation and retrogradation properties of SRS and control SRS types made a clear difference and had a marked effect on rheological properties when compared with the control sample. The peak, hold and final viscosities (RVU) of the control were 223.02, 80.08 and 158.54; however, the values were 24.56, 21.53 and 33.06 in SRS samples. This indicated that SRS containing RSIII can significantly transform starch viscosity with nearly complete loss. The gelatinisation and retrogradation properties were measured using DSC. Results showed that SRS had special thermodynamic properties: the onset temperature (T0), peak maximum temperature (Tp), conclusion temperature (Tc), enthalpy of transition (DH) and gelatinisation range (R = 2 (Tp T0)) could not be detected. However, as for the control sample, the values were T0 = 74.2 °C, Tp = 79.0 °C, Tc = 83.6 °C, DH = 7.678 J/g, and R = 9.6 °C, respectively. 2.4. Expressible water content Expressible water content (EW), for each treatment, was measured using a method described by Uresti, López-Arias, GonzálezCabriales, Ramírez, and Vázquez (2003) with slight modifications. Samples of approximately 2 g (Wi) were placed between two layers of filter paper, loaded into 80 ml centrifuge tubes, and then centrifuged at 8228g for 15 min at 15 °C. After centrifugation, samples were carefully separated from the papers and then immediately reweighed (Wf). EW values were determined as follows:
EW% ¼ ½ðW i W f Þ=W i 100: 2. Materials and methods 2.1. Fish sample, surimi, and surimi gel preparation Fresh grass carp samples were purchased from a local seafood supermarket. In the laboratory, samples were gutted, washed with sterile-cold water, thoroughly drained, and then chopped into surimi using a mangler. The surimi paste samples were prepared by homogenising grass carp surimi for 2 min with 20 g of salt/kg (w/w) (Hernández-Briones, Velázquez, Vázquez, & Ramírez, 2009). Next, the paste was divided into five groups to mix with different levels of SRS, which was dissolved in ultrapure-cold (4 °C) water (200 ml/kg surimi) at 0 (control), 20, 40, 60, 80 g/kg (w/w). The samples were then immediately placed in polyvinylidine chloride dishes of 3.5 cm diameter and 1 cm thickness, respectively. After that, they were vacuum-packed in polythene bags and divided into three for pre-incubation: lot I was stored for 24 h at 4 °C, lot II was stored for 12 h at 25 °C, and lot III was heated for 2 h at 40 °C. Next, all samples were heated for 20 min at 90 °C in a water bath and then 30 min in a 4 °C water bath for cooling. All samples were stored overnight at 4 °C prior to analysis.
2.5. Cooking loss The liquid on the surface of each gel was wiped gently using a filter paper and then weighed before (G1) and after heating (90 °C, 20 min) (G2). Cooking loss (CL) was represented as the loss of liquid:
CL% ¼ ðG1 G2 Þ=G1 100: 2.6. Textural profile analysis (TPA) Texture analyses of grass carp surimi gel samples were performed using a Texture Analyser (TA-XT2i, Scientific Measuring Systems, Middlesex, UK). The Texture Expert Exceed version 1.22 computer programme by Stable Micro System was used for data collection and calculation. Each cylinder was compressed axially in two consecutive cycles of 5 mm compression, 5 s apart, with a flat plunger 5 mm in diameter (SMS-P/5). From the TPA curves, the following texture parameters were obtained from TPA curves: hardness, springiness, cohesiveness, chewiness, and resilience. Six cylindrical samples were prepared; before their analysis, they were equilibrated at ambient temperature for 1 h.
2.2. Specific rice starch 2.7. Freeze–thaw stability Specific rice starch (SRS), containing a high value of resistant starch type III (RSIII, YiTang RiceÒ), was supplied by the Institute of Nuclear Agricultural Sciences, Zhejiang University. Normal rice starch was used as a control and purchased from a local supermarket. Resistant starch (RS) detection showed that the RS
After samples for 24 h samples
pre-incubation at 25 °C and heated at 90 °C for 20 min, with different SRS levels were frozen in a 20 °C freezer and then thawed in a water bath at 30 °C for 1 h. Three were randomly selected for determination of expressible
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water content and textural profile analysis (methods described in Section 2.4. and Section 2.6.), whilst the remaining samples were placed back into the freezer for further freeze–thaw cycling for up to three cycles. 2.8. Colour evaluation Spectral reflectance of surimi gels was determined using a HunterLab (CM-400d, Konica Minolta, Tokyo, Japan). Measurement of L⁄ (lightness), a⁄ (redness/greenness), and b⁄ (yellowness/blueness) was conducted in six replications. Whiteness was calculated, based on the following equation:
h i1=2 2 2 Whiteness ¼ 100 ð100 L Þ þ a2 þ b :
2.9. Scanning electron microscopy (SEM) Scanning electron microscopy (SEM) images for each treatment were acquired using a method described by Oujifard, Benjakul, Ahmad, and Seyfabadi (2012) with slight modification. Microstructures of surimi gels were determined using SEM. Thickness values of 0.5–1 mm sliced samples were obtained from control and treated groups, respectively. Next, the slices were immersed in 3.5% glutaraldehyde for 24 h, and then transferred into 0.1 M phosphate buffer (pH 7.2) for 15 min; this process was repeated. Samples were soaked for 1 h in ultrapure water before dehydration in ethanol at serial concentrations of 50%, 70%, 80%, 90%, and 100%, then vacuum-freeze-dried. Dried samples were mounted on a bronze table and then gold-plated, using an ion coater (Eiko Engineering, Co., Ltd., Fukuoka, Japan). Specimens were observed using a scanning electron microscope (XL30-ESEM, FEI, Hillsboro, USA) at an acceleration voltage of 20 kV.
Fig. 1. Effect of different levels (0–8% w/w) of SRS at different pre-incubation temperatures (4 °C, 25 °C, 40 °C) on the cooking loss (CL) of grass carp surimi gels. A–C Different letters at the same SRS content differ significantly (p < 0.05). a–c Different letters at the same temperature treatment differ significantly (p < 0.05).
3. Results and discussion
6%, and 8% w/w) were observed following three different preincubation temperatures (4 °C for 24 h, 25 °C for 12 h, and 40 °C for 2 h). Fig. 1 shows significant difference (p < 0.05) in cooking loss between SRS-added groups and control samples (0% w/w SRS). Higher cooking loss was observed in control samples than in those with SRS added in each pre-incubation temperature group. Moreover, increases in CL varied significantly (p < 0.05) with different preincubation temperatures, particularly when no SRS was added. Increasing pre-incubation temperatures increased water loss after cooing, resulting in lower expressible water content when no SRS was added. CL content at 4 °C pre-incubation was only 2.42%, whilst this value was 3.43% at 25 °C and finally increased up to 7.77% at 40 °C. The results indicated that different gel-forming temperatures significantly influenced CL contents (p < 0.05). Additionally, this also showed that adding SRS can prevent water loss during cooking and that it has a good protective effect on the steaming stability compared with control samples. Fig. 2a–c shows a significant (p < 0.05) decrease in expressible water content between samples treated with SRS and control at the same pre-incubation temperature, whilst different pre-incubation temperatures did not significantly (p > 0.05) influence EW content at the same SRS level. EW values decreased as SRS content increased, suggesting that the water-holding capacity of the gel was increased with SRS addition. Jung, Kim, and Yoo (2007) reported that adding acetylated rice starch improved freeze–thaw stability and reduced expressible moisture contents of surimi gels. Additionally, the high water-absorbing ability or the hydrophilic group interacting with free-water may have altered it to bound-water, which was not easily extracted. Statistical analysis showed a highly positive non-linear relationship between SRS levels and EW values at pre-incubation temperatures of 4 °C and 25 °C (Y = 0.1400X2 3.3021X + 42.3765, R2 = 0.9864 2 2 (Fig. 2a); Y = 0.2386X 3.0762X + 38.7413, R = 0.9175 (Fig. 2b)), whilst a highly negative non-linear relationship was observed at 40 °C (Y = 0.1495X2 0.4740X + 37.5336, R2 = 0.9946, (Fig. 2c)).
3.1. Effect of SRS on cooking loss (CL) and expressible water content (EW)
3.2. Effect of SRS on TPA
Changes in cooking loss (CL, Fig. 1) and expressible water content (EW, Fig. 2a–c) of surimi gels with added SRS (0%, 2%, 4%,
The effects of SRS and pre-incubation temperature on the textural properties of surimi gels are shown in Table 1. Textural
2.10. SDS–polyacrylamide gel electrophoresis (SDS–PAGE) SDS–polyacrylamide gel electrophoresis was carried out according to the method described by Yongsawatdigul and Park (2002). Samples (3 g) were homogenised in 5% (w/v) SDS in a final volume of 30 ml. The homogenate was incubated at 85 °C for 1 h to dissolve total proteins and then centrifuged at 6171g for 10 min. Using a 4% stacking gel and a 10% separating gel; the supernatant was applied for SDS–PAGE analysis so that the protein amount was 20 lg. Electrophoresis was performed at a voltage of 80 V for 15 min and then at a constant voltage of 110 V. Proteins were stained in 0.125% Coomassie brilliant blue R-250 and destained in 25% ethanol and 10% acetic acid. After electrophoresis, photos were acquired using a fluorescent chemiluminescence imaging system (FluorChemE, Cell Biosciences, North San Jose, CA, USA). 2.11. Statistical analysis All experiment data were calculated as arithmetic means and standard deviations (mean ± SD) from repeated measurements. Significance between treatments was tested, based on one-way analysis of variance (ANOVA), using SPSS 16.0 software (IBM, Armonk, NY, USA).
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Fig. 2. Effect of different levels (0–8% w/w) of SRS at different pre-incubation temperatures on extractable water content (EW) of grass carp surimi gels: (a) 4 °C preincubation; (b) 25 °C pre-incubation; and (c) 40 °C pre-incubation. (d) Effect of different levels (0–8% w/w) of SRS at the pre-incubation temperature 25 °C on the freeze–thaw stability of grass carp surimi gels. A–BDifferent letters at the same SRS content differ significantly (p < 0.05). a–cDifferent letters at the same temperature treatment differ significantly (p < 0.05).
properties of grass carp surimi gels after cooking proved to be affected by SRS addition and pre-incubation temperatures. Hardness was not significantly (p > 0.05) influenced by SRS, except at 8% w/w SRS addition. Due to the crosslinking reaction between SRS–protein, SRS–SRS, and protein–protein, more force and energy were necessary to break down the gel system. Park, Cho, Kimura, and Seki (2005) reported a similar result that, as the level of the added potato starch increased, the breaking strength of the thermal gel of salted squid paste increased and starch-added gel became firm and less elastic. Additionally, Westphalen, Briggs, and Lonergan (2006) indicated that the hardness of heat-induced gels was correlated with water-holding capacity of myofibrillar protein gels and viscoelastic properties. Springiness, cohesiveness, chewiness, and resilience at 25 °C appear to result in better performance in nearly all groups with SRS-added or control samples compared to incubation at 4 °C and 40 °C. It was apparent that pre-incubation at 25 °C is more suitable for gel formation of grass carp surimi. Additionally, following 25 °C pre-incubation, springiness, cohesiveness, chewiness, and resilience were higher in all samples with SRS added compared with the control sample. The four TPA indices were highest at 4% w/w SRS addition, which decreased at higher percentages. The results suggested that SRS clearly affects the textural properties of surimi gels to improve both gel-forming ability and gel properties. Sensory evaluation showed that the pre-incubation temperature at 25 °C showed a higher score than did 4 °C and 40 °C when SRS 1%. However, we observed no significant (p > 0.05) decrease in whiteness until SRS addition reached 8% w/w at pre-incubation temperatures of 4 °C and 25 °C. This indicates that SRS protects against a reduction in whiteness when the gels were subjected to processing. Moreover, both pre-incubation temperature and SRS addition have a significant (p < 0.05) influence on a⁄ and b⁄ values compared with the control samples. Additionally, a temperature of 25 °C appears to be a ‘unique point’ that retains the maximum a⁄ values and minimum b⁄ values for each of the SRS-added groups and the control. Based on these results, L⁄ values declined as pre-incubation temperature increased. This may be because a higher temperature can promote the Maillard reaction between the generated free amino acid groups and the reducing sugar or oxidation products. As a consequence, more yellowish compounds are formed in the gel systems. Kim, Park, and Choi (2003) reported that sarcoplasmic proteins, such as haemoglobin and myoglobin, may enhance the Maillard browning reaction in acid- or alkali-treated gels. For L⁄, a⁄, and b⁄, fish gels prepared from grass carp mince pre-incubated at 25 °C with added SRS were superior to those pre-incubated at 4 °C or 40 °C, indicating suitable lightness, redness, and yellowness, respectively.
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Z. Yang et al. / Food Chemistry 145 (2014) 212–219 Table 2 Effect of different levels (0–8% w/w) of SRS at different pre-incubation temperatures on the colour attributes of grass carp surimi gels. Colour Whiteness 4 °C 25 °C 40 °C L⁄ 4 °C 25 °C 40 °C a⁄ 4 °C 25 °C 40 °C b⁄ 4 °C 25 °C 40 °C
0%
2%
4%
6%
8%
79.16 ± 0.44Aa 78.56 ± 0.60Aab 76.29 ± 1.13Ba
78.71 ± 0.84Aab 78.64 ± 0.53Aab 78.10 ± 0.42Abc
78.64 ± 0.56Aab 78.53 ± 0.54Aab 78.65 ± 0.44Ab
78.70 ± 0.48Aab 78.90 ± 0.69Aa 77.70 ± 0.57Bc
78.13 ± 0.47Ab 78.08 ± 0.44Ab 77.81 ± 0.24Ac
82.25 ± 0.45Aa 81.32 ± 0.66Aa 79.57 ± 1.10Ba
82.10 ± 0.79Aa 81.65 ± 0.52ABa 81.26 ± 0.41Bbc
81.54 ± 0.67Aab 81.22 ± 0.78Aa 81.91 ± 0.58Ab
81.88 ± 0.68Aab 81.63 ± 0.65ABa 80.92 ± 0.66Bc
81.26 ± 0.44Ab 80.86 ± 0.40Aa 80.98 ± 0.34Ac
1.407 ± 0.099Aa 1.393 ± 0.106Aa 1.040 ± 0.190Ba
1.298 ± 0.108Aab 0.970 ± 0.217Bb 1.143 ± 0.203ABa
1.310 ± 0.155Aab 0.508 ± 0.021Bc 0.953 ± 0.116Cab
11.45 ± 0.36Abd 10.88 ± 0.23Bbc 11.28 ± 0.19Cb
10.67 ± 0.10Ac 10.38 ± 0.34Ac 11.30 ± 0.29Bb
10.82 ± 0.22Aacd 10.42 ± 0.35Aac 11.98 ± 0.42Ba
1.255 ± 0.031Ab 0.620 ± 0.162Bc 0.755 ± 0.043Cb
1.215 ± 0.041Ab 0.547 ± 0.280Bc 0.798 ± 0.144Cb
11.12 ± 0.28ACd 10.35 ± 0.40Bc 11.52 ± 0.45Cb
11.20 ± 0.22ACd 10.67 ± 0.24Bc 11.39 ± 0.20Cb
A–C a–d
Different letters at the same SRS content differ significantly (p < 0.05). Different letters at the same temperature treatment differ significantly (p < 0.05).
3.5. Electrophoretic banding pattern of protein extracts Gelling is influenced by the collective effects of all proteins present in food systems (Barrera et al., 2002). Myosin, actin, and actomyosin are the most abundant proteins amongst myofibrillar proteins, whilst myosin is primarily responsible for the functional properties of meat products (Ramirez, Martin-Polo, & Bandman, 2000). Protein patterns of grass carp gels with different amounts of SRS added (0–8% w/w) are shown in Fig. 3. In our study, intensity of myosin heavy chain (MHC) decreased as pre-incubation temperature increased, whilst no changes were observed in protein patterns, regardless of amount of SRS added at the same preincubation temperature. These results indicate that SRS addition does not significantly influence protein patterns of grass carp gels, and that MHC may decrease when pre-incubated at a higher temperature. Previous studies have reported that the primary intense band in heat-induced gels was present, due to the absence of protein bands at a molecular weight of approximately 66 kDa (A band), whilst the B band (tropomyosin b) and C band (tropomyosin a) were relatively intense (33–37 kDa) (DeFreitas, Sebranek, Olson, & Carr, 1997). However, the A band (66 kDa) was also relatively
intense following pre-incubation and heating. This suggests that SRS has a protective effect and prevents lower protein profiles from being destroyed by the heating process. 3.6. Microstructure of surimi gel Pre-incubation at 25 °C was a suitable temperature for grass carp gel formation; micrographs of surimi gels from grass carp with 0–8% w/w of SRS added at 25 °C are shown in Fig. 4. A more compact and denser gel network with a thin band can be observed in the surimi gels with SRS added compared with the control sample (0% SRS). Additionally, at higher SRS content, interconnections between the three-dimensional protein network of grass carp gel increases. This is correlated with the highest hardness values, which reached a maximum at 8% (w/w of SRS addition). Moreover, the compact network may effectively hold water in the system, enabling surimi products to maintain a favourable textural profiles. Additionally, SRS added at 2% w/w showed dense holes, whilst 4% w/w SRS addition maintained the fine structure without generating a large hole. Thus, addition of 4% w/w SRS can be used to maintain surimi gel quality.
Fig. 3. Effect of different levels (0–8% w/w) of SRS at different pre-incubation temperatures (4 °C, 25 °C, 40 °C) on electrophoretic protein pattern of grass carp surimi gels.
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Fig. 4. Effect of different levels (0–8% w/w) of SRS at 25 °C pre-incubation on the microstructure of grass carp surimi gels.
4. Conclusion Analysis of grass carp surimi gels pre-incubated at different temperatures (4 °C, 25 °C, and 40 °C) showed that addition of SRS positively affects gel properties and physicochemical characteristics. As a food additive, SRS can be used to improve gel quality and significantly reduce the amount of traditional starch added to gels. Additionally, SRS showed a positive influence on the freeze–thaw stability of the surimi gels. Addition of 4% w/w SRS effectively decreased the expressible water content and cooking loss values. At a pre-incubation temperature of 25 °C and 4% w/w SRS, texture properties, colour attributes, and SEM were optimal. Additionally, SDS gel electrophoresis revealed no changes in proteins, regardless of the level of SRS added at the same preincubation temperature, but a decrease in the intensity of myosin heavy chain (MHC) was observed with increased pre-incubation
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