Whey protein effects on properties and structure of hairtail surimi gel

Abstract

Whey protein was added to hairtail surimi gel (HSG), the properties and structural changes were determined, and whey protein effects on them were investigated after incorporating 0.00% to 10.00% whey protein. Optimal results at 6.00% addition of whey protein were observed in texture, color, and water-holding capacity (WHC). Texture analysis exhibited a reduction in cohesiveness, resilience, and chewiness of HSG, while simultaneously increasing its firmness and springiness. Furthermore, the whiteness of HSG decreased by 5.00% and optimal WHC was observed at its maximum value. The electron microscopy images showed that HSG had a compact and smooth structure with a smaller pore size after whey protein was added. Nuclear magnetic resonance analysis demonstrated the gradual transformation of free water into immobile water in gel matrix, reaching up to 93.21%. Additionally, the formation of ionic bonds increased significantly to 2.954 mg/mL. Differential scanning calorimetry showed that the denaturation temperature of myosin was increased, however, that of actin was reduced. These insights contribute to surimi production optimization which can significantly enhance the functional characteristics of HSG, providing a basis for improved surimi-based products.

Keywords

Hairtail surimi gel whey protein water holding capacity gel characteristics

INTRODUCTION

Hairtail is one of the most popular commercial marine fishes in coastal regions (Liao et al., 2023). It is rich in nutrients, such as proteins, unsaturated fatty acids, and trace elements (Inga et al., 2009). However, the major challenge remains the poor gelling capacity of hairtail surimi; thus, most of the research has focused on modifying HSG to enhance surimi quality (Hasanpour et al., 2012). Many food additives have already been used in surimi gel modification. Some water-soluble hydrocolloid gums such as curdlan and κ-carrageenan helps to enhance the quality of silver carp surimi gel (Chen et al., 2020). Furthermore, polysaccharides such as modified hydroxypropylated cassava starch have also been proven to improve the WHC and gel strength of silver carp surimi (Mi et al., 2019). Research conducted by Pan et al. (2017) indicates that adding appropriate concentration of CaCl₂ can improve the textural characteristics of low-fat meat products. However, the effectiveness of these modification methods is often suboptimal, leading to poor product quality and low consumer acceptance (Walayat et al., 2022). Enzymes such as lipase have been reported to improve the gelling quality of fish surimi effectively enhancing the gel quality of catfish surimi and reducing its lipid content compared to the washing process (Jiao et al., 2021). However, they are expensive, easily inactivated, and unstable (Narwal et al., 2016). Therefore, investigating adequate modifiers and methods to improve its gelling capacity is both important and valuable.

Whey protein not only has high nutritional value, but also has good processing characteristics, especially for its gelation characteristics. It can impart unique structure and texture to food. However, the research on the effect of whey protein on gelling properties of surimi is limited. It has been reported that whey protein can be used as a protease inhibitor in a variety of marine fish surimi to inhibit the autolysis of protein effectively. Yongsawatdigul and Piyadhammaviboon (2004) reported that egg albumen and whey protein had a good inhibitory effect on the autolysis of lizardfish surimi. Therefore, it is evident that whey protein improved the ability of gel formation. Benjakul et al. (2010) showed that the use of whey protein in a combination with calcium ions could effectively improve the gelling properties of goatfish surimi. Studies have demonstrated that whey protein increased the gelling strength and water retention at the concentration of 6.00% to 10.00% (Shi et al., 2014).

It is necessary and significant to investigate the effects of whey protein on the HSG since the surimi from different varieties of fish contain various kinds and contents of proteins, leading to different gelling properties. Meanwhile, HSG exhibits poor properties, and until now, no studies on the effects of whey protein on HSG have been reported. Hence, the objective for this work was to explore its effects on the structures and properties of the surimi gel, aiming to provide a theoretical basis and technology to enhance the quality of hairtail surimi and the application of whey protein.

MATERIALS AND METHODS

Materials

Frozen hairtail surimi was purchased from Luxiong Ltd (Fuzhou, Fujian, China). Whey protein was obtained from Siyuan Biotechnology Ltd (Luohe, Henan, China). The chemicals of analytical grade were used and purchased from Fengchuan Chemical Reagent Co., Ltd (Tianjin, China).

Sample preparation

Frozen hairtail surimi was first thawed for an hour at 20 °C. Then cut into small cubes and chopped for 3 min at a low speed. After that, the salt (2.00% w/w) was added in the surimi and chopped again at the speed of 1000 r/min for 3 min. Whey protein was added in separate batches at concentrations of 0.00%, 2.00%, 4.00%, 6.00%, 8.00%, and 10.00% w/w and that mixture was then chopped for 3 min with the temperature maintained at 4 °C. Then the mixture was transferred into a plastic bag with a 20 mm diameter and subjected to a two-step heat treatment: initially at 40 °C for 30 min, followed by 90 °C for 20 min (Chaijan et al., 2010). After the heating, the gel sample were immediately cooled in cold water for 60 min and then stored at 4 °C temperature for further analyses.

Determination of texture

The prepared HSG was cut into cylindrical shape with a height and the diameter of 25 mm and 20 mm, respectively. Texture Analyzer TA-XT2i (Stable Micro Systems, Surrey, UK) was used for texture profile analysis. The sample was compressed twice using a p/36 probe (diameter: 36 mm) to measure its firmness, springiness, cohesiveness, resilience and chewiness. The pretest speed, test speed, and posttest speed were 1 mm/s, 2 mm/s, and 1 mm/s, respectively. The percentage of deformation was set to 40.00% with the double compression interval of 5 s and trigger force of 5 g. Each set of samples was subjected to three parallel tests (Yang et al., 2022).

Determination of whiteness

The whiteness measurement was conducted by following the method described by Shen (2001), the surimi gel was sliced into sections of 3 mm thickness and flattened uniformly. The colorimetric parameters L*, a*, and b* were evaluated by using a WSB-VI colorimeter (Daji Photoelectric Instrument Co., Ltd, Hangzhou, China) at room temperature. The values of whiteness were calculated by the following equation:

W = 100 - [{(100 - L *)}^{2} + a^{* 2} + b^{* 2}]^{0.5}

(1)

where L^*= lightness; a^*= redness; b^*= yellowness.

Determination of water-holding capacity

The surimi gel was sliced into 5 mm thick pieces and initially weighed (recorded as m₀ (g)). Each slice was then placed between three layers of filter paper and pressed with a 5 kg weight resulting in the squeezing of water. Afterward, the gel was weighed again, and the value was recorded as m₁ (g). This procedure demonstrated that greater water loss corresponds to a lower WHC. The WHC was expressed as the percentage of initial sample weight. The results were calculated by using the following equation, as described by Yongsawatdigul and Piyadhammaviboon (2004):

WHC (%) = \frac{m_{0} - m_{1}}{m_{0}} \times 100

(2)

Scanning electron microscopy analysis

The microstructure of the gel samples were analyzed using an SU-1510 scanning electron microscope (Hitachi, Ltd, Tokyo, Japan). The surimi gel samples were initially prepared by cutting them into little cubes with 2 × 3 mm and 2 × 1 mm measurement, fixed with glutaraldehyde (2.50%), and then cooled at 4 °C overnight. The fixed samples were washed three times, each for 15 min, with the phosphate buffer (0.1 mol/L, pH 7.3) and then dehydrated using different concentrations of ethanol (30.00%, 50.00%, 70.00%, 80.00%, 90.00%, and 100.00%). Finally, the treated samples were freeze-dried by using a BILON-3000FD freeze-dryer (Thermo Fisher Scientific Inc., MA, USA), and after being coated with gold–palladium, samples were examined at an accelerating voltage of 20 kV (Dong et al., 2023).

Nuclear magnetic resonance and magnetic resonance imaging analysis

The relaxation time and pseudocolor image of water proton density measurements were performed on MicroMR-25 nuclear magnetic resonance (NMR) analyzer (New Mai Electronic Technology Co., Ltd, Shanghai, China). Two grams of surimi gel were wrapped in preservative film, put into a glass tube, and then placed into the NMR probe (the temperature was maintained at the level of 32 °C). The main parameters included pulses, time echo (TE), time waiting (TW), and number of scans (NS). Pulses = 90°, 180° pulses of 4 μs and 12 μs respectively, TE = 0.5 ms, TW = 1600 ms, NS = 8. The relaxation time (T₂) of the HSG was replicated three times using NMR inversion software. A T₂ inversion map was designed, and the signal intensity was normalized.

By means of the magnetic resonance imaging measurements, the pseudocolor images of proton density were obtained. Three images were taken for each sample and the primary parameters included: slice gap = 2 mm, slice width = 3 mm, time repetition (TR) = 1600, TE = 10 ms, and average = 15 (Xu et al., 2017).

Determination of chemical interactions

The following four solutions were prepared: 1.5 M urea (SC) + 0.05 M NaCl (SA), 0.6 M NaCl (SB), 0.6 M NaCl, and 8 M urea (SD) + 0.6 M NaCl. Two grams of minced gel samples were homogenized with 10 mL of each solution by using a homogenizer for 30 min and then allowed to stand still for 1 h, subsequently, the samples were then centrifuged at the speed of 10,000 r/min, 4 °C for 20 min using a WAS-3TW centrifuge (Thermo Fisher Scientific Inc., MA, USA). The content of protein in the supernatant was measured using the biuret method, with bovine serum albumin as the standard. The contribution of hydrogen bonds, ionic bonds, and hydrophobic interactions were calculated as follows: ionic bonds (the difference between protein being solubilized in SB and protein being solubilized in SA), hydrogen bonds (the difference between protein being solubilized in SC and protein being solubilized in SB), and hydrophobic interactions (the difference between protein being solubilized in SD and protein being solubilized in SC). The results represent the average value of these three measurements expressed as mg of soluble protein/mL of homogenate (Cao et al., 2022).

Determination of thermal denaturation temperature of surimi protein

The thermal characteristics of protein in hairtail surimi were investigated using a 7000 series differential scanning calorimetry (DSC) analyzer (Hitachi, Ltd, Tokyo, Japan) equipped with an air cooling compressor and a liquid nitrogen cooling system. Sample weights were accurately measured at 2 mg sample was taken and placed in hermetically sealed aluminum pans. A hermetically sealed empty pan was used a reference and placed on the sample stage of the equipment. A heating rate of 5 °C/min was applied over the temperature range of 30–130 °C. Finally, the DSC spectra were obtained.

Statistical analysis

Statistical analysis was conducted by using a completely randomized factorial design. All the experiments were carried out independently, and for each treatment, three sample replications were conducted. The data used were the average calculated from the results of three replicates. These analyses were performed with the EXCEL (Microsoft^®, USA), ORIJIN, and SPSS statistical analysis systems. The results were expressed as the mean ± standard deviation with confidence intervals of 95.00% (p < .05).

RESULTS AND DISCUSSION

Whey protein effect on the texture of HSG

Table 1 depicts the effect of whey protein on the texture properties of high-strength surimi gel. Increasing whey protein content leads to significant decrease (p < .05) in cohesiveness, chewiness, and resilience. Compared to the control group, the cohesiveness and resilience decreased by 21.63% and 32.97%, respectively. No significant changes (p > .05) were recorded with whey protein addition above 8.00%. The lowest chewiness value of 3.201 N was observed at 10.00% whey protein, marking a substantial 22.12% reduction. Moreover, the firmness and springiness in HSG reaching maximum values of 14.983 N and 0.850, respectively, were observed at 6.00% whey protein concentration. These values exhibited increases of 29.68% and 7.87%, respectively, as compared to the control group. The results demonstrated the concentration of exogenous protein suitable to improve the gel strength of surimi. Surimi with high gel strength can resist external forces effectively and it is less susceptible to damage from external forces. It is consistent with the study from Rawdkuen and Benjakul (2008) that the whey protein concentrate was effective in increasing gel strength of tropical fish surimi.

Table 1.

Effect of different whey protein dosage on texture of HSG.

Whey protein dosage (%)	Firmness (N)	Springiness	Cohesiveness	Resilience	Chewiness (N)
0	11.554 ± 0.238^e	0.788 ± 0.007^d	0.416 ± 0.010^a	0.182 ± 0.007^a	4.110 ± 0.098^a
2	12.880 ± 0.870^c	0.794 ± 0.005^cd	0.391 ± 0.008^b	0.162 ± 0.008^b	4.097 ± 0.159^a
4	13.692 ± 0.177^b	0.809 ± 0.009^bc	0.375 ± 0.006^c	0.152 ± 0.005^b	4.082 ± 0.007^a
6	14.983 ± 0.226^a	0.850 ± 0.012^a	0.336 ± 0.007^d	0.130 ± 0.005^c	4.072 ± 0.073^a
8	14.795 ± 0.034^a	0.803 ± 0.011^cd	0.317 ± 0.009^e	0.117 ± 0.005^d	3.678 ± 0.108^b
10	12.367 ± 0.185^d	0.823 ± 0.008^b	0.326 ± 0.005^de	0.122 ± 0.005^cd	3.201 ± 0.072^c

Notes: HSG: hairtail surimi gel.

The table shows mean values ± standard deviation, different letters in the same column indicate that there is a significant difference.

Whey protein effect on the whiteness of HSG

Figure 1(a) illustrates a significant decline in the whiteness of HSG as the whey protein content increases. The color attributes of HSG exhibit significant dependency on both the type and quantity of additives (Rawdkuen et al., 2007). When whey protein was added at 10.00%, the whiteness of surimi gel was 54.40. It was reduced by 5.00%, compared to that of surimi gel without whey protein. This is probably because whey protein has a certain milky yellow color, which affects the color of surimi gel, resulting in a yellowish color and a reduction of the whiteness. The higher dosage of whey protein reduced the whiteness more significantly.

Figure 1.

(a) Effect of whey protein on the whiteness of HSG (b) effect of whey protein on water-holding capacity of HSG.

Whey protein effect on the WHC of HSG

The WHC of HSG with whey protein at different concentrations is given in Figure 1(b). With the increase of whey protein dosage from 0.00% to 6.00%, the WHC was remarkably increased from 76.98% to 94.56%, and it reached the maximum value when whey protein was added at 6.00%. The WHC decreased when whey protein dosage was increased from 6.00% to 10.00%, this is due to increase in whey protein concentration, which results in the decrease of protein content in the HSG, causing the WHC to decrease and forming the inferior and loose gel network.

The WHC increased remarkably with 6.00% whey protein dosage. The WHC decreased when the whey protein dosage exceeded 6.00%. However, it was still greater than the control group, which indicated that WHC of surimi gel can be improved by whey protein. The possible explanation is that whey protein has a certain degree of water absorption, in addition, it interacts with surimi protein to form a more compact network structure, thus water is locked. The increased WHC of HSG indicated that more water was bond or retained in the gel network (Chanarat and Benjakul, 2013). These findings are consistent with the results of Hu et al. (2015). The proper dosage of whey protein can enhance the gel network and improve the WHC (Hu et al., 2015).

Whey protein effect on the microstructure of HSG

The impact of whey protein on the microstructure of HSG is depicted in Figure 2. Control group exhibited a rough, more discontinuous, and disorganized appearance. After the addition of whey protein, the three-dimensional structure of each surimi gel group was denser, and its shape looked like an ellipse. Compared to the 2.00% and 4.00% sample groups, the structures of the 6.00%, 8.00% and 10.00% sample groups exhibited increased density and smaller pore size. Specifically, the 6.00% sample group demonstrated enhanced homogeneity, compactness, and stability relative to other groups, presenting smaller clusters of aggregated protein and forming a smoother surface. These observations suggested that whey protein likely distributed uniformly as a filler within the gel network.

Figure 2.

Effect of whey protein on the microstructure of HSG (a) HSG without whey protein (b) HSG added with 2% whey protein (c) HSG added with 4% whey protein (d) HSG added with 6% whey protein (e) HSG added with 8% whey protein (f) HSG added with 10% whey protein.

Cathepsin is the main endogenous protease that causes gel deterioration of surimi products (Liu et al., 2008). Piyachomkwan and Penner (1994) reported that whey protein is an inhibitor of cathepsin, or as an additive, can effectively reduce the activity of cathepsin of myosin, thus it can slow down the dissolution of myofibrillar protein in surimi. The addition of 6.00% whey protein forms a denser and uniform three-dimensional network structure, mainly due to the filling effect, gelation and cathepsin inhibition of whey protein. The addition of whey protein made HSG exhibit good gel properties and WHC, and to a certain extent, it could inhibit the deterioration of HSG.

Whey protein effect on the water status of HSG

The data obtained from the NMR spectrum (Figure 3) indicate that, in comparison to the control group, the relaxation time T₂ of the surimi gel initially shifted leftward with increasing whey protein content. Specifically, the relaxation time of the control group, measured at 248.65 ms, decreased to 172.45 ms with the addition of 6.00% whey protein. However, when the whey protein content exceeded 6.00%, the relaxation time shifted rightward, indicating an initial increase followed by a subsequent decrease in water-binding force, indicating the reduction in the degree of freedom initially, followed by its subsequent increase. Furthermore, the binding water capacity of 8.00% sample group was similar to that of 10.00% sample group, possibly attributed to the strength and network structure of HSG. Han et al. (2014) observed that a dense gel network structure facilitates increased moisture retention. Meanwhile, the formation of a regular ordered microporous structure can reduce the fluidity of the gel and consequently reduce transverse relaxation time. These results are consistent with the conclusion of this study highlighting the optimal WHC and compact microstructure of HSG when the whey protein dosage is at 6.00%.

Figure 3.

Inversion diagram of transversal relaxation time T₂ of HSG with different whey protein additions.

Whey protein effect on the water distribution of HSG

It can be observed from Figure 4(a) that the distribution of three states of water in the HSG of each group changed after adding whey protein. The difference in changes in the bound water ratio of each group in the HSG was not significant (p > .05) as compared to the control group. Immobilized water ratio was recorded as 6.00% > 4.00% > 8.00% > 0.00% > 10.00% > 2.00%, whereas the free water ratio was revealed as 2.00% > 10.00% > 0.00% > 8.00% > 4.00% > 6.00% with a significant difference (p < .05). In the sample group of 6.00% sample group, free water ratio was lower than that of the other groups, while the relative ratio of immobilized water was the highest in value, reaching up to 93.21%.

Figure 4.

(a) Relative proportion of three states of water (b) pseudocolor image of water proton density of the HSG.

Regarding the microstructure (Figure 2), it is evident that the pore size of the surimi gel network in the control group was larger, facilitating the conversion of water into free water and subsequent lost. However, the three-dimensional mesh structure of the 6.00% sample group appeared regular, homogeneous, and stereoscopic, with a smooth surface and robust gelation capacity, resulting in a higher ratio of immobilized water and consequently, higher WHC. Probably it is because of a small amount of whey protein has a good filling effect due to its gelation capacity. However, as the content of whey protein increased, it diluted the myofibrillar protein in surimi and prevented the cross-linking between surimi proteins. To a certain extent, it influenced the gel network formation and even reduced the water-binding capacity.

Whey protein effect on the water proton density of HSG

Figure 4(b) presents pseudo color image illustrating the water proton density of the HSG. The gray scale ranges from 0 to 250, while the color gradient represents different gray scale values directly proportional to the water proton density (Ye et al., 2022). By interpreting the pseudo color of the gel, we can easily compare the water quantity in HSG having different concentration of whey protein. Compared to the control group, the gray value initially increased and then decreased with the addition of whey protein. In other words, the water content in surimi gel exhibited an initial increase followed by a decrease with the increasing whey protein content, reaching its peak value at 6.00%. This is consistent with the results of WHC of HSG.

Whey protein effect on the chemical interactions of HSG

The results presented in Table 2 highlight the significant effect of whey protein on ionic bond, hydrogen bond, and hydrophobic interactions in HSG. With the increasing content of whey protein, the contribution of an ionic bond, hydrogen bond and hydrophobic interactions increased significantly (p < .05) with its maximum value at 6.00% concentration of whey protein and decline afterward. When whey protein is added excessively, it integrates with the protein in the surimi, enveloping protein groups, and occupying the protein gel network structure, thereby leading to a reduction in chemical forces.

Table 2.

Effect of different whey protein concentrations on chemical interactions in HSG.

The amount of whey protein (%)	Ionic bonds (mg/mL）	Hydrogen bonds (mg/mL）	Hydrophobic interactions (mg/mL）
0	1.059 ± 0.068^d	0.436 ± 0.043^d	0.585 ± 0.061^d
2	1.888 ± 0.067^c	0.572 ± 0.030^c	0.818 ± 0.145^c
4	2.689 ± 0.104^b	0.637 ± 0.031^b	1.006 ± 0.029^b
6	2.954 ± 0.053^a	0.787 ± 0.012^a	1.587 ± 0.034^a
8	2.898 ± 0.002^a	0.762 ± 0.014^a	1.436 ± 0.125^a
10	2.871 ± 0.031^a	0.753 ± 0.012^a	1.157 ± 0.065^b

Notes: HSG: hairtail surimi gel.

The table shows mean values ± standard deviation, different letters in the same column indicate that there is a significant difference.

The data presented in Table 2 demonstrate a significant increase in the ionic bond within the surimi gel system corresponding to the increased whey protein concentration. Its value increased from 1.059 mg/mL in the absence of whey protein to 2.954 mg/mL with the addition of 6.00% whey protein. As the whey protein content continued to increase, a significant quantity of whey protein permeated the protein network structure, leading to a reduction in protein content. This hindered the interaction between proteins, subsequently decreasing the ionic bond. These results are in line with the findings obtained for firmness and springiness in HSG.

The presence of hydrogen bonds in the HSG plays a significant role in the stability of system and enhances the gel strength during the cooling process of the surimi gel. In the blended whey protein-surimi gel, when the amount of whey protein was at its low level, the hydrogen bond increased significantly (p < .05) reaching up to its maximum value of 0.787 mg/mL at 6.00% addition. The increase in hydrogen bond may be attributed with the addition of whey protein, which enhances interaction between whey protein and surimi protein, thereby promoting hydrogen bond formation between proteins. Alternatively, it may be the result of change in the protein secondary structure, such as α-helix structure.

In the absence of whey protein, the hydrophobic interaction was measured at 0.585 mg/mL, increasing to 1.587 mg/mL at 6.00% addition. This escalation can be attributed to whey protein altering molecular structure and microenvironment of protein. Surimi protein is heated and exposed to water in order to provide external conditions and to form hydrophobic interactions for surimi protein and whey protein. To maintain the stability of thermodynamic system, the hydrophobic interaction between two adjacent proteins is enhanced, resulting in the aggregation of proteins and thus forming a more stable complex gel system of whey protein–surimi protein. The enhancement of hydrophobic interactions during heating is the primary factor improving the gel strength of surimi gel, act as a chemical force to maintain the stable conformation of surimi gel (Chen et al., 2021).

Whey protein effect on the denaturation temperature of hairtail surimi protein

According to Figure 5, two distinct absorption peaks are observed in the DSC spectra during the process of temperature rising, corresponding to the endothermic peaks of myosin and actin in hairtail surimi. The results given in Table 3 demonstrate that myofibrillar protein of hairtail surimi has two denaturation temperatures, in the absence of whey protein, the temperatures were recorded at 33.26 °C (first peak) and 99.18 °C (second peak) with enthalpy values of 50.61 J/g and 46.96 J/g, respectively. After adding 6.00% whey protein, the denaturation temperature of myosin increased by 8.99% and reached up to 36.25 °C, that of actin was 76.63 °C, reduced by 22.74%. This indicated that whey protein is responsible to increase the denaturation temperature of myosin during gelation process while decreasing the thermostability of actin. Furthermore, compared to the control group, actin transitions shifted to lower temperature with the addition of whey protein. The high migration magnitude of the myosin indicated that it has more sensitivity toward the addition of whey protein. This suggests that whey protein may impact the structure of myosin, by filling in the protein matrix, thereby enhancing surimi stability resulting in a higher thermal denaturation temperature.

Figure 5.

DSC spectra of hairtail surimi during the process of temperature rising (a) HSG added with 0% whey protein (b) HSG added with 6% whey protein.

Table 3.

Parameters of the thermal characteristics of HSG with whey protein during the process of temperature rising.

Sample	The first peak temperature (°C）	Enthalpy （J/g）	The second peak temperature (°C）	Enthalpy （J/g）
Surimi	33.26 ± 0.78	50.61 ± 0.58	99.18 ± 0.61	46.96 ± 0.44
Surimi with 6% whey protein	36.25 ± 0.63	45.01 ± 0.43	76.63 ± 0.84	56.82 ± 0.35

HSG: hairtail surimi gel.

CONCLUSIONS

Our study demonstrates that adding whey protein to HSG improves its textural properties and structural integrity, particularly at a concentration of 6.00%. Whey protein reduced the cohesiveness, resilience and chewiness of HSG, while increasing the hardness and springiness. The whiteness of HSG was reduced by 5.00%. When 6.00% of whey protein was added, the value of WHC was the highest and increased from 76.98% to 94.56%. The electron microscopy images showed that the microstructure was well-structured, compact, and smooth. Free water in the gel was gradually transformed into immobilized water after adding whey protein. Its content reached the highest level of 93.21% when the amount of whey protein was at 6.00%. During the formation of the whey protein-surimi gel, more ionic bonds were generated to maintain the newly formed protein gel structure. Whey protein at the dosage of 6.00% increased the denaturation temperature of myosin from 33.26 °C to 36.25 °C. However, that of actin was reduced from 99.18 °C to 76.63 °C, in other words, whey protein can increase the denaturation temperature of myosin in the process of surimi gelation and also decrease the thermostability of actin. These findings are crucial for developing higher-quality surimi-based products, with whey protein serving as a potent additive.

Footnotes

DECLARATION OF CONFLICTING INTERESTS

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

FUNDING

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Aijun Hu

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