The cryoprotectant effect of shrimp chitin and shrimp chitin hydrolysate on denaturation and unfrozen water of lizardfish surimi during frozen storage

Shrimp chitin and shrimp chitin hydrolysate prepared from black tiger (Penaeus monodon), endeavour (Metapenaeus endeavouri) and giant freshwater (Macrobrachium rosenbergii) prawns were added to lizardfish surimi, and it was frozen and stored at −25 °C for 6 months to evaluate freeze-induced protein denaturation. Changes in total Ca-ATPase activity and the amount of unfrozen water in samples were periodically determined during frozen storage. The surimi containing shrimp chitin showed the same freeze-denaturaion rate (K_D) as the surimi without cryoprotectants (control), and the amount of unfrozen water was lower than that of control. However, surimi containing shrimp chitin hydrolysates showed K_D values equal to surimi containing sucrose or glucose but lower than the control, and the amount of unfrozen water was increased compared to control. The results revealed that shrimp chitin hydrolysates retarded the effects on freeze-induced denaturation by stabilizing the hydrated water molecules that surround the protein.