Cryoprotective effect of gelatin hydrolysate from shark skin on denaturation of frozen surimi compared with that from bovine skin

Gelatin hydrolysate from blue shark skin (SSGH) was prepared using alcalase to determine its cryoprotective effects on frozen surimi. The hydrolysis time of 15 min and 90 min was used to define the degree of hydrolysis since it provided different peptide species and distribution in hydrolysate. SSGH hydrolyzed for 90 min (SSGH-90) was composed of a higher amount of low molecular weight peptides. SSGH hydrolyzed for 15 min (SSGH-15) and 90 min (SSGH-90) were studied for their cryoprotective effects. The SSGH was added to surimi at a ratio of 5 % (w/w), and then the surimi was frozen at −25 °C for 135 days. The gel-forming ability, Ca-ATPase activity, and amounts of liquid water were monitored as indicators of protein denaturation in the frozen surimi. Those properties were compared between surimi without cryoprotectant and with bovine skin gelatin hydrolysate (BSGH) hydrolyzed for 30 (BSGH-30) and 120 (BSGH-120) min. The presence of gelatin hydrolysates helped delay the decrease in breaking the gel strength of frozen surimi and reduced aggregation in myofibrillar protein structure due to the increase in liquid water. Within 15 days of frozen storage, the breaking gel strength was decreased to 21.54–28.47 % after addition of gelatin hydrolysate regardless of the source, but the decline was less than surimi gel without additive (35.66 %). Suppression in freezing-induced denaturation of surimi was similar by addition of SSGH-90 or BSGH-120, as well as was the amino acid content of both gelatins. They were more effective than SSGH-15 and BSGH-30.