Biochemical and physical changes of grass carp (Ctenopharyngodon idella) fillets stored at -3 and 0 °C.

The objective of this study was to investigate the effect of superchilling at -3 °C compared with ice storage at 0 °C on the biochemical and physical properties of grass carp fillets. Fillets stored at -3 °C showed significant changes in whiteness, drip loss and textural hardness, while changes in pH, total volatile basic nitrogen and TCA-soluble peptides were slowed down. Partial denaturation of myosin as demonstrated by differential scanning calorimetry differed between fillets stored at -3 and 0 °C in that the transition peak showed a left shoulder at -3 °C and sharpened at 0 °C. Detachments between muscle cells and formation of cracks within cells were accelerated during storage at -3 °C, and from 10 days on, clear spaces between and within cells were observed with the concurrent appearance of white spots on the surface of fillets, suggesting the formation of both extra- and intracellular large ice crystals.