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Textural, rheological and chemical properties of surimi nutritionally-enhanced with lecithin
LWT - Food Science and Technology 122 (2020) 108984
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Textural, rheological and chemical properties of surimi nutritionallyenhanced with lecithin
T
Xuxia Zhoua,b,c, Honghan Lina,b, Shichen Zhua,b,c, Xia Xua,b, Fei Lyua,b, Yuting Dinga,b,c,∗ a
Department of Food Science and Technology, Zhejiang University of Technology, Hangzhou 310014, China National R&D Branch Center for Pelagic Aquatic Products Processing (Hangzhou), Hangzhou 310014, China c Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, 116034, China b
ARTICLE INFO
ABSTRACT
Keywords: Lecithin Surimi products Myofibrillar protein Dynamic rheological properties Interfacial shear rheology
Surimi-based products enhanced with lipid nutrients have been getting more and more attention. To develop a lecithin-rich surimi product, the effects of lecithin addition at different levels (0–2.0 g/100 g) on chemical, rheological and quality properties of surimi were investigated. Although addition of lecithin decreased the breaking force and deformation of surimi, no significant effects were found for 0.4 g/100 g and 0.8 g/100 g groups (P > 0.05), and also, the water holding capacity (WHC) of surimi was the highest when 0.4 g/100 g lecithin was added. The addition of lecithin reduced heat-induced protein gelation to a certain degree as demonstrated by decreased storage modulus (G′) and loss modulus (G″) by dynamic rheology analysis. Lecithin resulted in increase of the surface hydrophobicity (S0) and decrease of hydrophobic interactions and disulfide bonds of the protein, while showed no significant effect on total sulfhydryl groups (P > 0.05). And no significant influence on the gel network structure of surimi was found when 0.4–1.2 g/100 g lecithin was incorporated. It can be demonstrated that a lecithin concentration of 0.4–0.8 g/100 g is recommended for lecithinrich surimi product production.
1. Introduction Surimi products, ready-to-eat seafood products with high protein and low fat, are increasingly popular among consumers and have broad market. They are made by surimi with secondary processing to form a flexible gel system and shaped into various forms to attract customers. For example, fish balls, fish sausages and fish tofu have become daily food in China. Nowadays, there have been many studies in improving the gel strength, water-holding capacity and sensory characteristics of surimi gel, mainly through addition of exogenous additives such as TGase (Li, Xiong, Yin, Hu, & You, 2019), starch (Zhang et al., 2013), egg white (Zhou, Chen, et al., 2019a), dietary fiber (Yin, Yao, et al., 2019b), colloid (Hernández-Briones, Velázquez, Vázquez, & Ramírez, 2009; Petcharat & Benjakul, 2018), non-fish protein (Lin, Zhang, et al., 2019b), phenolic compounds (Balange & Benjakul, 2009) and polysaccharides (Zhang, Xiong, et al. 2019). Novel processing methods including microwave heating (Fu et al., 2012; Jiao et al., 2019), ultrahigh pressure (Wang, Li, Zheng, Zhang, & Guo, 2019) and pH shift method (Zhou & Yang, 2019), were also used to improve gel properties. Apart from improvement of structural characteristics, nutritional quality is another important field of surimi research, and functional
∗
exogenous additive supplement has been getting more and more attention. Zhang, Xiong, et al. (2019) added a functional polysaccharide (yeast β-glucan), which not only has biological functions such as antitumor and anti-virus but also acts as a fat replacer, to surimi. At present, a variety of oils have been added to surimi for the production of oilfortified surimi products (Debusca, Tahergorabi, Beamer, Partington, & Jaczynski, 2013; Hsu & Chiang, 2002; Jiao et al., 2019; Shi et al., 2014). Pietrowski, Tahergorabi, Matak, Tou, and Jaczynski (2011) added oils rich in ω-3 PUFA to surimi as a nutritional supplement because of their biochemical effects (Pietrowski et al., 2011). Virgin coconut oil, which is usually incorporated into medicines and baby foods, was also added to surimi for its abundant medium-chain fatty acids short-chain fatty acids (Gani, Benjakul, & Nuthong, 2018). However, partial population should not take too much fat, such as diabetic patients (Wong, 2016). Compared with other lipids, lecithin is a lipid that is essential in the cells of the body with many benefits (Ramadan, 2008). As a physiological precursor of acetylcholine (ACh), choline cannot be synthesized by the brain directly, therefore, part of the choline used in the brain is obtained through diet, mainly through the intake of lecithin which can enhance serum free choline levels effectively and increase the phosphatidylcholine output in bile (LeBlanc
Corresponding author. Department of Food Science and Technology, Zhejiang University of Technology, Hangzhou, 310014, China. E-mail address: [email protected] (Y. Ding).
https://doi.org/10.1016/j.lwt.2019.108984 Received 22 September 2019; Received in revised form 20 December 2019; Accepted 20 December 2019 Available online 23 December 2019 0023-6438/ © 2020 Elsevier Ltd. All rights reserved.
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et al., 1998). So, choline is commonly added to infant formula for the healthy growth of the baby (Zhang, Yin, et al. 2019). Lecithin is also equipped with antioxidant activity, memory improvement, immunological function and regulation of both lipid metabolism and cardiovascular risks (Sun, Chen, Wang, & Lin, 2018). Soy lecithin was reported to be able to reduce cholesterol levels significantly and improve blood lipid profile (Ristić Medić et al., 2003). And it has been reported by previous studies that phospholipids are essential for the survival of some crustaceans and have a positive effect on the ovarian development of crustaceans (Zhou, Shi, et al., 2019b). Meanwhile, lecithin consists of phospholipids including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI) (Aguilar-Zarate, Macias-Rodriguez, Toro-Vazquez, & Marangoni, 2019; Mantovani, Fattori, Michelon, & Cunha, 2016; Sun, Chen, et al., 2018; Sun, Wang, & Guo, 2018; Xia, Ma, Chen, Li, & Zhang, 2018). Phospholipid derivatives are amphiphilic because they contain a positively charged choline and a negative phosphate group. They can change the surface activity of proteins, such as flexibility and hydrophobicity, and can also be added as a functional ingredient to foods (Sun, Wang, et al., 2018). Nowadays, lecithin is mainly used as an emulsifier in food processing for the preparation of emulsions (Oke, Jacob, & Paliyath, 2010), and there are several studies on the special effects of lecithin on meat products. Xia et al. (2018) reported that lecithin could improve the gel properties by making the gel network denser and more homogenous. However, there's still no report about the effects of lecithin on surimi gels. Therefore, in the present study, different concentrations of lecithin were added to surimi products, not only as a nutritional supplement, but also provide a reference on the effects of lecithin on surimi products characteristics, with focus on textural, rheological and chemical properties of surimi gels.
2.3. Gel strength analysis The prepared surimi gel was cut into a cylinder of ϕ 22 mm × 25 mm and equilibrated at room temperature for 30 min. The values of the breaking force (force/g) and deformation (breaking distance) of the surimi gel were determined by a TA.XT Plus (London, England) equipped with a P/5s spherical plunger. The test conditions were as follows, pre-test speed: 2.00 mm/s; test speed: 1.00 mm/s; speed after test: 2.00 mm/s; trigger force 10.0 g; displacement: 15 mm (Yin, Yao, et al., 2019b; Zhou & Yang, 2019). 2.4. Textural profile analysis (TPA) The textural properties of the surimi product were performed using a texture analyzer (TA.XT Plus; London, England). By simulating human oral mastication, samples were compressed twice with P/36R cylindrical probe to obtain a result similar to sensory evaluation, and could effectively reflect the texture characteristics of surimi gel, such as hardness, springiness, cohesiveness, gumminess and chewiness (Buamard & Benjakul, 2019). The surimi gel was equilibrated at room temperature for 30 min prior to measurement. The conditions for TPA test were as follows: pre-test speed 2.00 mm/s; test speed 1.00 mm/s; post-test speed 2.00 mm/s; trigger force 10.0 g; deformation 40%. 2.5. Water-holding capacity analysis Water-holding capacity (WHC) of the surimi product was determined according to the method of Cao et al. (2018) and Zhou, Chen, et al. (2019a) with slight modification. Briefly, slices approximately 5 g of the surimi product were wrapped in double-layer filter paper in a 50 mL centrifuge tube, and centrifuged at 10397×g for 15 min at 4 °C. After centrifugation, the surimi gels were weighed again. WHC was calculated by Equation: WHC (%) = W2/W1 × 100%, where W1 is the initial weight of gels, g; W2 is the final weight of gels, g.
2. Materials and methods 2.1. Materials Frozen surimi (Grade AA) from gurnard (Lepidotrigla microptera) provided by Zhejiang Industrial Group Co., Ltd. (Zhoushan, Zhejiang, China) was cut into small blocks (500 g) and stored in a refrigerator (−20 °C) before used. Food grade soy lecithin was bought from Zhongbaotang Technology Co., Ltd. All other chemicals used were of analytical grade and were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).
2.6. Dynamic rheological properties analysis Dynamic rheological test was carried out with a rheometer (MCR302, Shanghai, China) according to the method of Petcharat and Benjakul (2018) with slight modification. A little surimi sol was placed in the center of the platform and silicon oil was used to prevent water. The gap of parallel steel plate was adjusted to be 1 mm. Deformation of 1% and frequency of 0.1 Hz were used for temperature sweep test, in which the sample was gradually heated from 20 °C to 90 °C at a heating rate of 2 °C/min. Storage modulus G′ and loss modulus G″ were recorded during the heating process.
2.2. Preparation of surimi gel A certain amount of frozen surimi was thawed at 4 °C for 12 h. Salt was added to reach a concentration of 2.5 g/100 g and the mixture was chopped for 2 min with a chopping machine (YC-5, Shanghai, China), and then 0.2 g/100 g sodium hexametaphosphate and 0.1 g/100 g sodium pyrophosphate were added and the mixture were chopped for another 2.5 min. The temperature was controlled below 10 °C during the whole process. The mixed samples were divided into six groups and different levels of lecithin dissolved in water (0 g/100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi) were added, respectively. Water was added when necessary to keep the total amount of water and lecithin accounts for 10 g/100 g of the surimi. To prepare surimi products, surimi with different levels of lecithin were well-mixed and placed in a mortar and manually crushed evenly into a collagen casing with a diameter of 22 mm. The bubbles in the casing were removed and the two sections of the casing were tightened and then the products were subjected to two-step heating process, namely firstly heated at 40 °C for 30 min and then heated at 90 °C for 20 min. Immediately after heating, the surimi gels were chilled in ice water and refrigerated at 4 °C overnight for properties analysis.
2.7. Determination of chemical properties Myofibrillar protein of surimi was prepared according to the method of Gao, Huang, Zeng, & Brennan (2019) with minor modification. Two grams of surimi was homogenized in 20 mL of 20 mmol/L Tris-HCl buffer (50 mmol/L KCI, pH 7) and centrifuged at 6654×g for 10 min at 4 °C (CR21GⅡ, Hitachi Limited, Japan). The pellet was diluted with quintuple volume of 20 mmol/L Tris-HCl buffer (0.6 mol/L KCI, pH 7) and homogenized. The homogenate was kept at 4 °C for 1 h and then centrifuged (10397 ⅹ g, 4 °C, 10 min) to obtain myofibrillar protein solution. Sulfhydryl group and surface hydrophobicity of the myofibrillar protein were measured immediately. Sulfhydryl groups of the myofibrillar protein from surimi gel were determined according to the method of Lin, Hong, et al. (2019a) with minor modification. Myofibrillar protein solution (0.5 mL) was mixed with 4.5 mL 0.2 mol/L HCl-Tris buffer (8 mol/L urea, 2% SDS and 10 mmol/L EDTA, pH 6.8) for the determination.
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Surface hydrophobicity of the myofibrillar protein sample from surimi was determined using ANS probe according to the method of Yin, He, et al. (2019). Fluorescence intensities were subsequently measured using a spectrofluorometer (F-280, Tianjin, China) with emission wavelength at 470 nm and excitation 390 nm, respectively. Chemical interactions of the myofibrillar protein were determined according to the method of Cao et al. (2018). Two grams of surimi was mixed with 10 mL of 0.05 mol/L NaCl (SA), 0.6 mol/L NaCl (SB), 0.6 mol/L NaCl + 1.5 mol/L urea (SC), 0.6 mol/L NaCl + 8 mol/L urea (SD) and 0.6 mol/L NaCl + 8 mol/L urea +0.05 mol/L β-mercaptoethanol (SE) homogenized for 1 min. The homogeneous solution was stirred for 1 h at 4 °C and centrifuged at 6654×g for 15 min, then the protein concentration in the supernatant was determined by Coomassie brilliant blue method to determine the existence of ionic bonds (the difference between SB and SA), the hydrogen bonds (the difference between SC and SB), hydrophobic interactions (differences between SD and SC) and disulfide bonds (differences between SE and SD).
resistance, and deformation is positively correlated with elasticity. The lower breaking force indicated that the addition of lecithin reduced the gel strength and fracture resistance of the surimi product. This may be due to the hydrophilicity of lecithin which make it combine with water to hinder the cross-linking of proteins in the surimi, weaken or destroy the gel structure, and cause the breaking force and deformation of the surimi product to decrease. These results were in accordance with that of Marin, Aleman, Sanchez-Faure, Montero, and Gomez-Guillen (2018). Although the encapsulated extracts were different, the breaking force and deformation were all decreased to some extent when the surimi gels were incorporated with phosphatidylcholine (Marin et al., 2018). However, low concentration of lecithin (0.4–0.8 g/100 g) didn't cause significant decrease compared with the control without lecithin (P < 0.05). 3.1.2. Textural profiles TPA is an empirical method widely used to evaluate various food textures to provide information on the mechanical properties of foods. Table 1 summarizes the textural characteristic indices, including hardness, adhesiveness, springiness, cohesiveness, and resilience of surimi gel. It can find that lecithin had a significant effect on hardness, springiness, cohesiveness, and resilience (P < 0.05), which was basically a downward trend, but has little effect on adhesiveness. It was consistent with previous reports that the hardness of surimi gel decreased with the addition of lecithin (Xia et al., 2018). But gel hardness increased when the amount of lecithin added was increased from 1.2 g/ 100 g to 2 g/100 g, which may be attributed to the lecithin combined with lesser number of water molecules because of the decrease in the moisture content of the surimi gel. What's more, the increased solid content of the surimi gel with the increase of the lecithin concentration might also contribute to the increase of the hardness to some extent (Oke et al., 2010). And it was speculated that the addition of lecithin made the gel network more disordered than the control and decreased the elasticity of the surimi gel.
2.8. Microstructure analysis Microstructure of surimi products was determined according to the method of Zhou, Chen, et al. (2019) with a scanning electron microscope (SU8010, Hitachi Limited, Japan). 2.9. Statistical analysis The experimental data were processed using SPSS software (SPSS Inc., Chicago, Ill., USA) for analysis of variance and significant difference was defined at p < 0.05. The data were plotted using Origin 8.6 (OriginLab Co., USA). 3. Results and discussion 3.1. Effect of lecithin on the textural properties of surimi gels 3.1.1. Gel strength Breaking force was one of the essential indices for estimating the quality of surimi gel, reflecting the textural property of surimi gel and playing a decisive role in demonstrating the quality of surimi gel products. It can be seen from Fig. 1 that the breaking force and distance to rupture values of surimi gels decreased with the addition of lecithin. Generally, the breaking force represents gel strength and gel destructive
3.1.3. Water-holding capacity WHC indicates the ability of gel to combine with water and it is usually based on protein-water interactions, gel structure and water distribution (Marin et al., 2018). As shown in Fig. 2, the WHC of surimi gels continued to decrease with the increase of lecithin concentration (P < 0.05). During the heat-induced gelation process, the protein formed a gel network structure while binding with water molecule and trapping other components (Guo et al., 2019). The decrease in WHC was probably due to the loss of water caused by the destruction of the gel network and the weakened protein-water interaction. In previous reports, lecithin could prevent the formation of disulfide bonds and weaken the cross-linking of proteins (Xia et al., 2018). However, when the amount of lecithin was 0.4 g/100 g, the WHC of the surimi gel increased slightly (P > 0.05). It was speculated because of the hydrophilicity of lecithin that more water molecules were trapped, which did not significantly affect the gel strength. 3.2. Effect of lecithin on the rheological properties of surimi gels The change in storage modulus and loss modulus of surimi paste added with lecithin is shown in Fig. 3. The storage modulus reflects the heating process. It could be seen from Fig. 3 that G″ was much smaller than G′, indicating that the elastic component of the surimi gel system was higher. Generally, the G′ is a measure of deformation energy stored in the sample during the shearing process, representing the elastic behavior of a sample, and G″ representing the viscous properties of a sample. The changes in G′ during the heating process were as shown in Fig. 3A. As the temperature rose, the G′ of the surimi gel decreased slightly first, and then rose sharply at approximately 48 °C. The
Fig. 1. Breaking force and deformation of surimi gels without and with different concentrations of lecithin. The concentrations of lecithin were 0 g/100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
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Table 1 Effects of lecithin on TPA properties of surimi gel. Lecithin Content (g/100 g) 0 0.4 0.8 1.2 1.6 2.0
Hardness (g) 3355.1 3345.8 3250.5 2978.6 3027.6 3226.1
± ± ± ± ± ±
Adhesiveness b
46.5 126.9b 44.7b 121.6a 54.6a 68.9b
−134.5 −135.0 −132.6 −135.8 −141.6 −137.8
± ± ± ± ± ±
Springiness a
2.5 7.8a 4.3a 0.3a 2.0a 7.0a
0.861 0.860 0.859 0.839 0.845 0.871
± ± ± ± ± ±
Cohesiveness bc
0.008 0.012bc 0.009bc 0.008a 0.007ab 0.015c
0.691 0.687 0.685 0.666 0.665 0.673
± ± ± ± ± ±
Resilience (N) b
0.003 0.002b 0.002b 0.015a 0.002a 0.008a
0.336 0.329 0.324 0.311 0.311 0.317
± ± ± ± ± ±
0.005c 0.001c 0.001bc 0.009a 0.002a 0.005ab
Mean ± SD (standard deviation) four replications. Different letters within the same column indicate a significant difference (p < 0.05).
Fig. 2. WHC of surimi gels without and with different concentrations of lecithin. The concentrations of lecithin were 0 g/100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g % of the surimi, respectively.
decrease in G′ was attributed to gel degradation of the surimi gel. Subsequently increase of G′ was mainly attributed to the denaturation of myosin heavy chain and the denaturation of actomyosin to form a dense and irreversible gel network. The larger the G′, the better the gel elasticity of the surimi, and this was consistent with the TPA result. The gel elasticity trend was consistent. G″ showed a large drop at low temperature, then decreased sharply at about 50 °C to the minimum value and increased after 50 °C. The overall trend of the G′ of gel samples with lecithin decreased compared with the control without lecithin. It was possible that lecithin was not conducive to the formation of gel network under high temperature, but promoted protein aggregation to form a relatively more disordered gel network, resulting in a decrease in the elasticity and storage modulus of the surimi product.
Fig. 3. G′ of surimi gels without and with lecithin at different contents (A), G″ of surimi gels without and with lecithin at different contents (B). The concentrations of lecithin were 0 g/100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
3.3. Effect of lecithin on the chemical properties of surimi protein 3.3.1. Sulfhydryl groups As the main component of myofibrillar proteins, myosin and actin contain 42 and 12 sulfhydryl groups respectively (Lin, Hong, et al., 2019a). Total sulfhydryl groups, which were considered as the most reactive functional group in proteins (Kobayashi, Mayer, & Park, 2017), include both surface active sulfhydryl groups and the buried sulfhydryl groups in the protein interior. As shown in Fig. 4, the effect of lecithin on total sulfhydryl content was slight (P > 0.05). As the concentration of lecithin increased, the content of total sulfhydryl groups increased slightly, but not significantly (P > 0.05). Previous studies indicated that during the preparation of surimi gel, lecithin can enhance the degree of protein unfolding (van Nieuwenhuyzen & Szuhaj, 1998) and expose the
buried sulfhydryl groups to the surface of the protein at setting process, both resulting in an increase in sulfhydryl content. Sulfhydryl groups could be oxidized to form disulfide bonds and is an important indicator of protein oxidation (Lin, Hong, et al., 2019a). It could be seen from Table 2 that the disulfide bond content was significantly decreased. Disulfide bonds were important for the formation of gel network, however, breakdown of it occurred during heating (Zhang, Li, Shi, Zhu, & Luo, 2018). It could be seen that although lecithin increased the exposure of sulfhydryl groups, it was not conducive to the formation of disulfide bonds, which might because that the aggregation of lecithin and protein covered part of sulfhydryl groups.
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Fig. 5. Surface hydrophobicity of surimi gels without and with different concentrations of lecithin. The concentrations of lecithin were 0 g/100 g, 0.4 g/ 100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
Fig. 4. Surface reactive sulfhydryl content of surimi gels without and with different concentrations of lecithin. The concentrations of lecithin were 0 g/ 100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
speculated that lecithin destroyed and promoted the breakdown of disulfide bonds while the aggregation of lecithin and protein covered part of sulfhydryl groups.
3.3.2. Surface hydrophobicity (S0) Fig. 5 showed that the S0 of surimi protein increased significantly with the increase of the lecithin concentration (P < 0.05). An increase in S0 usually indicates protein denaturation and this result indicated lecithin promoted the unfolding of myofibrillar proteins and the exposure of internal hydrophobic groups (Yin, He, et al., 2019a). However, the hydrophobic interaction of surimi protein declined with the addition of lecithin as shown in Table 2. This might be owing to the steric hindrance caused by hydrophobic interaction between lecithin and protein, which hindered the hydrophobic interaction between proteins and further affected the gel strength of surimi products.
3.4. Effect of lecithin on the microstructure of surimi gel It can be observed from Fig. 6 that when the amount of lecithin ranged from 0 g/100 g to 1.2 g/100 g, the microstructure of the surimi gel was basically smooth and no significant difference was found (P > 0.05). The control surimi gel showed many smaller gaps might because of the higher moisture content. However, when the amount of lecithin was increased to 1.6 g/100 g and 2.0 g/100 g, large gaps were found in the surimi gel although it seemed to be more compact.
3.3.3. Chemical interactions Table 2 showed that when the amount of lecithin added was less than 1.2 g/100 g, the main interactions between proteins were hydrophobic interaction and disulfide bonds, and hydrophobic interaction became domination with the increase of lecithin concentration, suggesting lecithin play an important role in surimi gel network. van Nieuwenhuyzen and Szuhaj (1998) reported the hydrophobic interaction played an important role between protein and phospholipid. Lecithin had a significant effect on ionic and hydrogen bonds (P < 0.05), which were important for stabilizing protein conformation (Liu, Zhao, Xie, & Xiong, 2011), however, neither of them were the main force. Both the hydrophobic interaction and the disulfide bonds decreased as the concentration of lecithin increased. It was postulated that the hydrophobic interaction between lecithin and protein affected the crosslinking between proteins. And the decline in disulfide bonds might be
4. Conclusions The present study provides a way of developing a novel nutritionally enhanced surimi-based seafood products rich in lecithin. Although high level of lecithin addition decreased the breaking force, deformation and heat-induced protein gelation of surimi to a certain degree, 0.8% concentration or less of lecithin didn't change the texture properties of surimi products significantly, while nitrifying surimi products with health-beneficial nutrient and even improving the WHC of surimi when 0.4% lecithin was added. Further studies aiming to further improve the gel properties with higher concentration of lecithin are recommended.
Table 2 Effects of lecithin on chemical interactions of myofibrillar protein. Lecithin Content (g/100 g) 0 0.4 0.8 1.2 1.6 2.0
Ionic bonds (mg/mL) 0.047 0.089 0.071 0.109 0.022 0.101
± ± ± ± ± ±
b
0.004 0.007d 0.005c 0.006e 0.001a 0.009e
Hydrogen bonds (mg/mL) 0.820 0.341 0.252 0.201 0.375 0.350
± ± ± ± ± ±
e
0.014 0.020c 0.018b 0.010a 0.008d 0.007c
Hydrophobic interaction (mg/mL) 4.039 3.152 2.613 2.492 2.411 2.342
± ± ± ± ± ±
c
0.297 0.117b 0.050a 0.134a 0.137a 0.159a
Disulfide bond (mg/mL) 4.716 2.641 1.646 1.085 0.598 0.270
± ± ± ± ± ±
Mean ± SD (standard deviation) from three replications. Different letters within the same column indicate a significant difference (p < 0.05).
5
0.169f 0.133e 0.240d 0.037c 0.062b 0.022a
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Fig. 6. Microstructure ( × 2000) of surimi gels added with lecithin of different concentration (0–2.0 g/100 g). The concentrations of lecithin were 0 g/100 g, 0.4 g/ 100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
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Textural, rheological and chemical properties of surimi nutritionallyenhanced with lecithin
T
Xuxia Zhoua,b,c, Honghan Lina,b, Shichen Zhua,b,c, Xia Xua,b, Fei Lyua,b, Yuting Dinga,b,c,∗ a
Department of Food Science and Technology, Zhejiang University of Technology, Hangzhou 310014, China National R&D Branch Center for Pelagic Aquatic Products Processing (Hangzhou), Hangzhou 310014, China c Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, 116034, China b
ARTICLE INFO
ABSTRACT
Keywords: Lecithin Surimi products Myofibrillar protein Dynamic rheological properties Interfacial shear rheology
Surimi-based products enhanced with lipid nutrients have been getting more and more attention. To develop a lecithin-rich surimi product, the effects of lecithin addition at different levels (0–2.0 g/100 g) on chemical, rheological and quality properties of surimi were investigated. Although addition of lecithin decreased the breaking force and deformation of surimi, no significant effects were found for 0.4 g/100 g and 0.8 g/100 g groups (P > 0.05), and also, the water holding capacity (WHC) of surimi was the highest when 0.4 g/100 g lecithin was added. The addition of lecithin reduced heat-induced protein gelation to a certain degree as demonstrated by decreased storage modulus (G′) and loss modulus (G″) by dynamic rheology analysis. Lecithin resulted in increase of the surface hydrophobicity (S0) and decrease of hydrophobic interactions and disulfide bonds of the protein, while showed no significant effect on total sulfhydryl groups (P > 0.05). And no significant influence on the gel network structure of surimi was found when 0.4–1.2 g/100 g lecithin was incorporated. It can be demonstrated that a lecithin concentration of 0.4–0.8 g/100 g is recommended for lecithinrich surimi product production.
1. Introduction Surimi products, ready-to-eat seafood products with high protein and low fat, are increasingly popular among consumers and have broad market. They are made by surimi with secondary processing to form a flexible gel system and shaped into various forms to attract customers. For example, fish balls, fish sausages and fish tofu have become daily food in China. Nowadays, there have been many studies in improving the gel strength, water-holding capacity and sensory characteristics of surimi gel, mainly through addition of exogenous additives such as TGase (Li, Xiong, Yin, Hu, & You, 2019), starch (Zhang et al., 2013), egg white (Zhou, Chen, et al., 2019a), dietary fiber (Yin, Yao, et al., 2019b), colloid (Hernández-Briones, Velázquez, Vázquez, & Ramírez, 2009; Petcharat & Benjakul, 2018), non-fish protein (Lin, Zhang, et al., 2019b), phenolic compounds (Balange & Benjakul, 2009) and polysaccharides (Zhang, Xiong, et al. 2019). Novel processing methods including microwave heating (Fu et al., 2012; Jiao et al., 2019), ultrahigh pressure (Wang, Li, Zheng, Zhang, & Guo, 2019) and pH shift method (Zhou & Yang, 2019), were also used to improve gel properties. Apart from improvement of structural characteristics, nutritional quality is another important field of surimi research, and functional
∗
exogenous additive supplement has been getting more and more attention. Zhang, Xiong, et al. (2019) added a functional polysaccharide (yeast β-glucan), which not only has biological functions such as antitumor and anti-virus but also acts as a fat replacer, to surimi. At present, a variety of oils have been added to surimi for the production of oilfortified surimi products (Debusca, Tahergorabi, Beamer, Partington, & Jaczynski, 2013; Hsu & Chiang, 2002; Jiao et al., 2019; Shi et al., 2014). Pietrowski, Tahergorabi, Matak, Tou, and Jaczynski (2011) added oils rich in ω-3 PUFA to surimi as a nutritional supplement because of their biochemical effects (Pietrowski et al., 2011). Virgin coconut oil, which is usually incorporated into medicines and baby foods, was also added to surimi for its abundant medium-chain fatty acids short-chain fatty acids (Gani, Benjakul, & Nuthong, 2018). However, partial population should not take too much fat, such as diabetic patients (Wong, 2016). Compared with other lipids, lecithin is a lipid that is essential in the cells of the body with many benefits (Ramadan, 2008). As a physiological precursor of acetylcholine (ACh), choline cannot be synthesized by the brain directly, therefore, part of the choline used in the brain is obtained through diet, mainly through the intake of lecithin which can enhance serum free choline levels effectively and increase the phosphatidylcholine output in bile (LeBlanc
Corresponding author. Department of Food Science and Technology, Zhejiang University of Technology, Hangzhou, 310014, China. E-mail address: [email protected] (Y. Ding).
https://doi.org/10.1016/j.lwt.2019.108984 Received 22 September 2019; Received in revised form 20 December 2019; Accepted 20 December 2019 Available online 23 December 2019 0023-6438/ © 2020 Elsevier Ltd. All rights reserved.
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et al., 1998). So, choline is commonly added to infant formula for the healthy growth of the baby (Zhang, Yin, et al. 2019). Lecithin is also equipped with antioxidant activity, memory improvement, immunological function and regulation of both lipid metabolism and cardiovascular risks (Sun, Chen, Wang, & Lin, 2018). Soy lecithin was reported to be able to reduce cholesterol levels significantly and improve blood lipid profile (Ristić Medić et al., 2003). And it has been reported by previous studies that phospholipids are essential for the survival of some crustaceans and have a positive effect on the ovarian development of crustaceans (Zhou, Shi, et al., 2019b). Meanwhile, lecithin consists of phospholipids including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI) (Aguilar-Zarate, Macias-Rodriguez, Toro-Vazquez, & Marangoni, 2019; Mantovani, Fattori, Michelon, & Cunha, 2016; Sun, Chen, et al., 2018; Sun, Wang, & Guo, 2018; Xia, Ma, Chen, Li, & Zhang, 2018). Phospholipid derivatives are amphiphilic because they contain a positively charged choline and a negative phosphate group. They can change the surface activity of proteins, such as flexibility and hydrophobicity, and can also be added as a functional ingredient to foods (Sun, Wang, et al., 2018). Nowadays, lecithin is mainly used as an emulsifier in food processing for the preparation of emulsions (Oke, Jacob, & Paliyath, 2010), and there are several studies on the special effects of lecithin on meat products. Xia et al. (2018) reported that lecithin could improve the gel properties by making the gel network denser and more homogenous. However, there's still no report about the effects of lecithin on surimi gels. Therefore, in the present study, different concentrations of lecithin were added to surimi products, not only as a nutritional supplement, but also provide a reference on the effects of lecithin on surimi products characteristics, with focus on textural, rheological and chemical properties of surimi gels.
2.3. Gel strength analysis The prepared surimi gel was cut into a cylinder of ϕ 22 mm × 25 mm and equilibrated at room temperature for 30 min. The values of the breaking force (force/g) and deformation (breaking distance) of the surimi gel were determined by a TA.XT Plus (London, England) equipped with a P/5s spherical plunger. The test conditions were as follows, pre-test speed: 2.00 mm/s; test speed: 1.00 mm/s; speed after test: 2.00 mm/s; trigger force 10.0 g; displacement: 15 mm (Yin, Yao, et al., 2019b; Zhou & Yang, 2019). 2.4. Textural profile analysis (TPA) The textural properties of the surimi product were performed using a texture analyzer (TA.XT Plus; London, England). By simulating human oral mastication, samples were compressed twice with P/36R cylindrical probe to obtain a result similar to sensory evaluation, and could effectively reflect the texture characteristics of surimi gel, such as hardness, springiness, cohesiveness, gumminess and chewiness (Buamard & Benjakul, 2019). The surimi gel was equilibrated at room temperature for 30 min prior to measurement. The conditions for TPA test were as follows: pre-test speed 2.00 mm/s; test speed 1.00 mm/s; post-test speed 2.00 mm/s; trigger force 10.0 g; deformation 40%. 2.5. Water-holding capacity analysis Water-holding capacity (WHC) of the surimi product was determined according to the method of Cao et al. (2018) and Zhou, Chen, et al. (2019a) with slight modification. Briefly, slices approximately 5 g of the surimi product were wrapped in double-layer filter paper in a 50 mL centrifuge tube, and centrifuged at 10397×g for 15 min at 4 °C. After centrifugation, the surimi gels were weighed again. WHC was calculated by Equation: WHC (%) = W2/W1 × 100%, where W1 is the initial weight of gels, g; W2 is the final weight of gels, g.
2. Materials and methods 2.1. Materials Frozen surimi (Grade AA) from gurnard (Lepidotrigla microptera) provided by Zhejiang Industrial Group Co., Ltd. (Zhoushan, Zhejiang, China) was cut into small blocks (500 g) and stored in a refrigerator (−20 °C) before used. Food grade soy lecithin was bought from Zhongbaotang Technology Co., Ltd. All other chemicals used were of analytical grade and were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).
2.6. Dynamic rheological properties analysis Dynamic rheological test was carried out with a rheometer (MCR302, Shanghai, China) according to the method of Petcharat and Benjakul (2018) with slight modification. A little surimi sol was placed in the center of the platform and silicon oil was used to prevent water. The gap of parallel steel plate was adjusted to be 1 mm. Deformation of 1% and frequency of 0.1 Hz were used for temperature sweep test, in which the sample was gradually heated from 20 °C to 90 °C at a heating rate of 2 °C/min. Storage modulus G′ and loss modulus G″ were recorded during the heating process.
2.2. Preparation of surimi gel A certain amount of frozen surimi was thawed at 4 °C for 12 h. Salt was added to reach a concentration of 2.5 g/100 g and the mixture was chopped for 2 min with a chopping machine (YC-5, Shanghai, China), and then 0.2 g/100 g sodium hexametaphosphate and 0.1 g/100 g sodium pyrophosphate were added and the mixture were chopped for another 2.5 min. The temperature was controlled below 10 °C during the whole process. The mixed samples were divided into six groups and different levels of lecithin dissolved in water (0 g/100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi) were added, respectively. Water was added when necessary to keep the total amount of water and lecithin accounts for 10 g/100 g of the surimi. To prepare surimi products, surimi with different levels of lecithin were well-mixed and placed in a mortar and manually crushed evenly into a collagen casing with a diameter of 22 mm. The bubbles in the casing were removed and the two sections of the casing were tightened and then the products were subjected to two-step heating process, namely firstly heated at 40 °C for 30 min and then heated at 90 °C for 20 min. Immediately after heating, the surimi gels were chilled in ice water and refrigerated at 4 °C overnight for properties analysis.
2.7. Determination of chemical properties Myofibrillar protein of surimi was prepared according to the method of Gao, Huang, Zeng, & Brennan (2019) with minor modification. Two grams of surimi was homogenized in 20 mL of 20 mmol/L Tris-HCl buffer (50 mmol/L KCI, pH 7) and centrifuged at 6654×g for 10 min at 4 °C (CR21GⅡ, Hitachi Limited, Japan). The pellet was diluted with quintuple volume of 20 mmol/L Tris-HCl buffer (0.6 mol/L KCI, pH 7) and homogenized. The homogenate was kept at 4 °C for 1 h and then centrifuged (10397 ⅹ g, 4 °C, 10 min) to obtain myofibrillar protein solution. Sulfhydryl group and surface hydrophobicity of the myofibrillar protein were measured immediately. Sulfhydryl groups of the myofibrillar protein from surimi gel were determined according to the method of Lin, Hong, et al. (2019a) with minor modification. Myofibrillar protein solution (0.5 mL) was mixed with 4.5 mL 0.2 mol/L HCl-Tris buffer (8 mol/L urea, 2% SDS and 10 mmol/L EDTA, pH 6.8) for the determination.
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Surface hydrophobicity of the myofibrillar protein sample from surimi was determined using ANS probe according to the method of Yin, He, et al. (2019). Fluorescence intensities were subsequently measured using a spectrofluorometer (F-280, Tianjin, China) with emission wavelength at 470 nm and excitation 390 nm, respectively. Chemical interactions of the myofibrillar protein were determined according to the method of Cao et al. (2018). Two grams of surimi was mixed with 10 mL of 0.05 mol/L NaCl (SA), 0.6 mol/L NaCl (SB), 0.6 mol/L NaCl + 1.5 mol/L urea (SC), 0.6 mol/L NaCl + 8 mol/L urea (SD) and 0.6 mol/L NaCl + 8 mol/L urea +0.05 mol/L β-mercaptoethanol (SE) homogenized for 1 min. The homogeneous solution was stirred for 1 h at 4 °C and centrifuged at 6654×g for 15 min, then the protein concentration in the supernatant was determined by Coomassie brilliant blue method to determine the existence of ionic bonds (the difference between SB and SA), the hydrogen bonds (the difference between SC and SB), hydrophobic interactions (differences between SD and SC) and disulfide bonds (differences between SE and SD).
resistance, and deformation is positively correlated with elasticity. The lower breaking force indicated that the addition of lecithin reduced the gel strength and fracture resistance of the surimi product. This may be due to the hydrophilicity of lecithin which make it combine with water to hinder the cross-linking of proteins in the surimi, weaken or destroy the gel structure, and cause the breaking force and deformation of the surimi product to decrease. These results were in accordance with that of Marin, Aleman, Sanchez-Faure, Montero, and Gomez-Guillen (2018). Although the encapsulated extracts were different, the breaking force and deformation were all decreased to some extent when the surimi gels were incorporated with phosphatidylcholine (Marin et al., 2018). However, low concentration of lecithin (0.4–0.8 g/100 g) didn't cause significant decrease compared with the control without lecithin (P < 0.05). 3.1.2. Textural profiles TPA is an empirical method widely used to evaluate various food textures to provide information on the mechanical properties of foods. Table 1 summarizes the textural characteristic indices, including hardness, adhesiveness, springiness, cohesiveness, and resilience of surimi gel. It can find that lecithin had a significant effect on hardness, springiness, cohesiveness, and resilience (P < 0.05), which was basically a downward trend, but has little effect on adhesiveness. It was consistent with previous reports that the hardness of surimi gel decreased with the addition of lecithin (Xia et al., 2018). But gel hardness increased when the amount of lecithin added was increased from 1.2 g/ 100 g to 2 g/100 g, which may be attributed to the lecithin combined with lesser number of water molecules because of the decrease in the moisture content of the surimi gel. What's more, the increased solid content of the surimi gel with the increase of the lecithin concentration might also contribute to the increase of the hardness to some extent (Oke et al., 2010). And it was speculated that the addition of lecithin made the gel network more disordered than the control and decreased the elasticity of the surimi gel.
2.8. Microstructure analysis Microstructure of surimi products was determined according to the method of Zhou, Chen, et al. (2019) with a scanning electron microscope (SU8010, Hitachi Limited, Japan). 2.9. Statistical analysis The experimental data were processed using SPSS software (SPSS Inc., Chicago, Ill., USA) for analysis of variance and significant difference was defined at p < 0.05. The data were plotted using Origin 8.6 (OriginLab Co., USA). 3. Results and discussion 3.1. Effect of lecithin on the textural properties of surimi gels 3.1.1. Gel strength Breaking force was one of the essential indices for estimating the quality of surimi gel, reflecting the textural property of surimi gel and playing a decisive role in demonstrating the quality of surimi gel products. It can be seen from Fig. 1 that the breaking force and distance to rupture values of surimi gels decreased with the addition of lecithin. Generally, the breaking force represents gel strength and gel destructive
3.1.3. Water-holding capacity WHC indicates the ability of gel to combine with water and it is usually based on protein-water interactions, gel structure and water distribution (Marin et al., 2018). As shown in Fig. 2, the WHC of surimi gels continued to decrease with the increase of lecithin concentration (P < 0.05). During the heat-induced gelation process, the protein formed a gel network structure while binding with water molecule and trapping other components (Guo et al., 2019). The decrease in WHC was probably due to the loss of water caused by the destruction of the gel network and the weakened protein-water interaction. In previous reports, lecithin could prevent the formation of disulfide bonds and weaken the cross-linking of proteins (Xia et al., 2018). However, when the amount of lecithin was 0.4 g/100 g, the WHC of the surimi gel increased slightly (P > 0.05). It was speculated because of the hydrophilicity of lecithin that more water molecules were trapped, which did not significantly affect the gel strength. 3.2. Effect of lecithin on the rheological properties of surimi gels The change in storage modulus and loss modulus of surimi paste added with lecithin is shown in Fig. 3. The storage modulus reflects the heating process. It could be seen from Fig. 3 that G″ was much smaller than G′, indicating that the elastic component of the surimi gel system was higher. Generally, the G′ is a measure of deformation energy stored in the sample during the shearing process, representing the elastic behavior of a sample, and G″ representing the viscous properties of a sample. The changes in G′ during the heating process were as shown in Fig. 3A. As the temperature rose, the G′ of the surimi gel decreased slightly first, and then rose sharply at approximately 48 °C. The
Fig. 1. Breaking force and deformation of surimi gels without and with different concentrations of lecithin. The concentrations of lecithin were 0 g/100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
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Table 1 Effects of lecithin on TPA properties of surimi gel. Lecithin Content (g/100 g) 0 0.4 0.8 1.2 1.6 2.0
Hardness (g) 3355.1 3345.8 3250.5 2978.6 3027.6 3226.1
± ± ± ± ± ±
Adhesiveness b
46.5 126.9b 44.7b 121.6a 54.6a 68.9b
−134.5 −135.0 −132.6 −135.8 −141.6 −137.8
± ± ± ± ± ±
Springiness a
2.5 7.8a 4.3a 0.3a 2.0a 7.0a
0.861 0.860 0.859 0.839 0.845 0.871
± ± ± ± ± ±
Cohesiveness bc
0.008 0.012bc 0.009bc 0.008a 0.007ab 0.015c
0.691 0.687 0.685 0.666 0.665 0.673
± ± ± ± ± ±
Resilience (N) b
0.003 0.002b 0.002b 0.015a 0.002a 0.008a
0.336 0.329 0.324 0.311 0.311 0.317
± ± ± ± ± ±
0.005c 0.001c 0.001bc 0.009a 0.002a 0.005ab
Mean ± SD (standard deviation) four replications. Different letters within the same column indicate a significant difference (p < 0.05).
Fig. 2. WHC of surimi gels without and with different concentrations of lecithin. The concentrations of lecithin were 0 g/100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g % of the surimi, respectively.
decrease in G′ was attributed to gel degradation of the surimi gel. Subsequently increase of G′ was mainly attributed to the denaturation of myosin heavy chain and the denaturation of actomyosin to form a dense and irreversible gel network. The larger the G′, the better the gel elasticity of the surimi, and this was consistent with the TPA result. The gel elasticity trend was consistent. G″ showed a large drop at low temperature, then decreased sharply at about 50 °C to the minimum value and increased after 50 °C. The overall trend of the G′ of gel samples with lecithin decreased compared with the control without lecithin. It was possible that lecithin was not conducive to the formation of gel network under high temperature, but promoted protein aggregation to form a relatively more disordered gel network, resulting in a decrease in the elasticity and storage modulus of the surimi product.
Fig. 3. G′ of surimi gels without and with lecithin at different contents (A), G″ of surimi gels without and with lecithin at different contents (B). The concentrations of lecithin were 0 g/100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
3.3. Effect of lecithin on the chemical properties of surimi protein 3.3.1. Sulfhydryl groups As the main component of myofibrillar proteins, myosin and actin contain 42 and 12 sulfhydryl groups respectively (Lin, Hong, et al., 2019a). Total sulfhydryl groups, which were considered as the most reactive functional group in proteins (Kobayashi, Mayer, & Park, 2017), include both surface active sulfhydryl groups and the buried sulfhydryl groups in the protein interior. As shown in Fig. 4, the effect of lecithin on total sulfhydryl content was slight (P > 0.05). As the concentration of lecithin increased, the content of total sulfhydryl groups increased slightly, but not significantly (P > 0.05). Previous studies indicated that during the preparation of surimi gel, lecithin can enhance the degree of protein unfolding (van Nieuwenhuyzen & Szuhaj, 1998) and expose the
buried sulfhydryl groups to the surface of the protein at setting process, both resulting in an increase in sulfhydryl content. Sulfhydryl groups could be oxidized to form disulfide bonds and is an important indicator of protein oxidation (Lin, Hong, et al., 2019a). It could be seen from Table 2 that the disulfide bond content was significantly decreased. Disulfide bonds were important for the formation of gel network, however, breakdown of it occurred during heating (Zhang, Li, Shi, Zhu, & Luo, 2018). It could be seen that although lecithin increased the exposure of sulfhydryl groups, it was not conducive to the formation of disulfide bonds, which might because that the aggregation of lecithin and protein covered part of sulfhydryl groups.
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Fig. 5. Surface hydrophobicity of surimi gels without and with different concentrations of lecithin. The concentrations of lecithin were 0 g/100 g, 0.4 g/ 100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
Fig. 4. Surface reactive sulfhydryl content of surimi gels without and with different concentrations of lecithin. The concentrations of lecithin were 0 g/ 100 g, 0.4 g/100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
speculated that lecithin destroyed and promoted the breakdown of disulfide bonds while the aggregation of lecithin and protein covered part of sulfhydryl groups.
3.3.2. Surface hydrophobicity (S0) Fig. 5 showed that the S0 of surimi protein increased significantly with the increase of the lecithin concentration (P < 0.05). An increase in S0 usually indicates protein denaturation and this result indicated lecithin promoted the unfolding of myofibrillar proteins and the exposure of internal hydrophobic groups (Yin, He, et al., 2019a). However, the hydrophobic interaction of surimi protein declined with the addition of lecithin as shown in Table 2. This might be owing to the steric hindrance caused by hydrophobic interaction between lecithin and protein, which hindered the hydrophobic interaction between proteins and further affected the gel strength of surimi products.
3.4. Effect of lecithin on the microstructure of surimi gel It can be observed from Fig. 6 that when the amount of lecithin ranged from 0 g/100 g to 1.2 g/100 g, the microstructure of the surimi gel was basically smooth and no significant difference was found (P > 0.05). The control surimi gel showed many smaller gaps might because of the higher moisture content. However, when the amount of lecithin was increased to 1.6 g/100 g and 2.0 g/100 g, large gaps were found in the surimi gel although it seemed to be more compact.
3.3.3. Chemical interactions Table 2 showed that when the amount of lecithin added was less than 1.2 g/100 g, the main interactions between proteins were hydrophobic interaction and disulfide bonds, and hydrophobic interaction became domination with the increase of lecithin concentration, suggesting lecithin play an important role in surimi gel network. van Nieuwenhuyzen and Szuhaj (1998) reported the hydrophobic interaction played an important role between protein and phospholipid. Lecithin had a significant effect on ionic and hydrogen bonds (P < 0.05), which were important for stabilizing protein conformation (Liu, Zhao, Xie, & Xiong, 2011), however, neither of them were the main force. Both the hydrophobic interaction and the disulfide bonds decreased as the concentration of lecithin increased. It was postulated that the hydrophobic interaction between lecithin and protein affected the crosslinking between proteins. And the decline in disulfide bonds might be
4. Conclusions The present study provides a way of developing a novel nutritionally enhanced surimi-based seafood products rich in lecithin. Although high level of lecithin addition decreased the breaking force, deformation and heat-induced protein gelation of surimi to a certain degree, 0.8% concentration or less of lecithin didn't change the texture properties of surimi products significantly, while nitrifying surimi products with health-beneficial nutrient and even improving the WHC of surimi when 0.4% lecithin was added. Further studies aiming to further improve the gel properties with higher concentration of lecithin are recommended.
Table 2 Effects of lecithin on chemical interactions of myofibrillar protein. Lecithin Content (g/100 g) 0 0.4 0.8 1.2 1.6 2.0
Ionic bonds (mg/mL) 0.047 0.089 0.071 0.109 0.022 0.101
± ± ± ± ± ±
b
0.004 0.007d 0.005c 0.006e 0.001a 0.009e
Hydrogen bonds (mg/mL) 0.820 0.341 0.252 0.201 0.375 0.350
± ± ± ± ± ±
e
0.014 0.020c 0.018b 0.010a 0.008d 0.007c
Hydrophobic interaction (mg/mL) 4.039 3.152 2.613 2.492 2.411 2.342
± ± ± ± ± ±
c
0.297 0.117b 0.050a 0.134a 0.137a 0.159a
Disulfide bond (mg/mL) 4.716 2.641 1.646 1.085 0.598 0.270
± ± ± ± ± ±
Mean ± SD (standard deviation) from three replications. Different letters within the same column indicate a significant difference (p < 0.05).
5
0.169f 0.133e 0.240d 0.037c 0.062b 0.022a
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Fig. 6. Microstructure ( × 2000) of surimi gels added with lecithin of different concentration (0–2.0 g/100 g). The concentrations of lecithin were 0 g/100 g, 0.4 g/ 100 g, 0.8 g/100 g, 1.2 g/100 g, 1.6 g/100 g, 2.0 g/100 g of the surimi, respectively.
CRediT authorship contribution statement
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