Effect of enzyme concentration on cryoprotective activity of gelatin hydrolysates in freshwater crayfish actomyosin subjected to freezing and thawing process

In this study, gelatin hydrolysates were produced from the skin of farmed beluga sturgeon and their cryoprotective effects on freshwater crayfish actomyosin subjected to six freeze-thaw cycles was investigated. Gelatin was extracted from beluga sturgeon skin and hydrolyzed with alcalase (1-5%). H-5:100 had the higher 2,2-diphenyl-1-picryl hydrazyl (DPPH) and 2,2'-azinobios-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging activities compared with H-1:100-4:100(P<0.05). Lipid oxidation was impeded as evidenced by the lower formation of thiobarbituric acid-reactive substances (TBARS) after six freeze-thaw cycles. The decrease in Ca2+-ATPase activity and total sulfhydryl group content was noticeable in natural actomyosin after six freeze-thaw cycles (P<0.05). Natural actomyosin incorporated with H-5% had higher Ca2+-ATPase activity with the coincidental higher content of total sulfhydryl groups, indicating protection of myosin heavy chain against freeze denaturation. H-5:100 was consisted of numerous peptides and those corresponding to molecular mass of 1436.72, 1579.82, 1627.74, 1716.80 and 2135.07 Da were the dominant peptides as determined by MALDI-TOF MS spectrometry. Results indicated the potential of H-5:100 with specific size of peptides in protection of freshwater crayfish natural actomyosin during freeze - thaw cycles.