## 3 Results and Discussion
### Textural Properties of Heat-Set Unfrozen and Freeze-Thawed Surimi Gels  
In the present study, textural properties of the heat-set unfrozen and freeze-thawed surimi gels were characterized (results shown in Table 4). Addition of the hydrolyses and SuSo to the surimi led to an initial increase in hardness and chewiness of the resulting unfrozen gels, while springiness and cohesiveness of the samples were not affected before freeze-thaw treatment. After six freeze-thaw cycles, the textural properties of control sample exhibited a marked increase in hardness, springiness, cohesiveness, and chewiness. However, similar to addition of SuSo, incorporation of the hydrolyses (PH-2 and PH-4) to the surimi demonstrated protective effects on the textures of the heat-set gels against freeze-thaw abuse. The gels of freeze-thawed surimi containing SuSo, PH-2 and PH-4 did not show significant differences in textural properties compared to the gels prepared from unfrozen control, which suggested preservation of initial qualities of surimi gel. The AH-2 group showed similar hardness, chewiness, and cohesiveness, but not springiness, to the unfrozen control gel after freeze-thaw treatments. PH-6, AH-4, and AH-6 groups showed relatively significant changes in textural properties after freeze-thaw treatments. Therefore, addition of certain amount of the hydrolyses could slow surimi protein denaturation and decrease the degree of protein aggregation, leaving these proteins available for subsequent gel network formation during heat processing, and thus, improving the gel-forming capacity and textural structure of freeze-thawed surimi gels. Similar observations were also reported upon the addition of fish protein hydrolysate prepared from Pacific have on natural actomyosin gel [14]. These results indicated that the hydrolyses could potentially be used to maintain product quality in terms of textural properties during temperature fluctuation abuse or frozen storage.  
Our results demonstrated that PH are more effective in cryoprotection of the actomyosin samples than AH. Possible reasons were as follows: firstly, PH is comprised of more peptides with relatively higher molecular weight (2027 Da), which is not available in AH. Small molecular peptides in AH are preferentially concentrated in aqueous phases and therefore, may not be available to impede protein aggregations in the process of freeze-thaw treatments [9]; secondly, the contents of free Lys plus Arg, Glu and Asp in PH are much higher than those in AH (\(P<0.05\)), resulting in PH being better at hydrating actomyosin and binding free water [26]; and, thirdly, PH contains relatively more hydrophobic amino acid residues than AH, which can provide remarkable cryoprotective abilities by maintaining textures of fish mince [5]; finally, the intrinsic structural properties of the hydrolyses, such as net terminal charge and terminal composition, are different between PH and AH due to differences in the enzyme type employed, which can possibly affect the cryoprotective effects of the  
Figure 5: Surface hydrophobicity of actomyosin from different surimi samples during freeze-thaw cycles. SuSo (surimi added with sucrose-sorbitol blend); PH-2, PH-4 and PH-6 (surimi with addition of 2, 4, and 6 g of the hydrolysate prepared by Protamex hydrolysis, respectively); AH-2, AH-4 and AH-6 (surimi with addition of 2, 4, and 6 g of the hydrolysate prepared by Alcalase hydrolysis, respectively); and control (surimi without cryoprotectant). The reported data represent mean values from three replications. Bars represent standard deviations.  
hydrolysates [(10)]. Future research should aim to elucidate the influence of various peptide properties and amino acid compositions of the hydrolyses on the cryoprotective effects and mechanism.