Effect of Cryoprotectants on the Functional Properties of Proteins from Tilapia (Oreochromis mossambicus) during Frozen Storage

Tilapia (Oreochromis mossambicus) whole fish (dressed), washed meat and washed meat with cryoprotectants were prepared, frozen and stored at -20 degrees C. The stored samples were drawn at 30 day intervals up to 360 days and samples were analyzed for various functional properties of proteins. Gel strength (g cm) decreased gradually for all samples during storage but washed meat showed drastic reduction from initial values of 431.46 to 125.66 g cm. This could be due to aggregation or denaturation of proteins, which lowered the gel forming ability of the meat during the storage period. The effect of freezing on the solubility was to the tune of 25-40% in different samples. The rate of decrease in protein solubility was higher in all the samples immediately after freezing and was minimum in dressed tilapia, where it decreased from 86.46 to 34.94% of total proteins. Free sulphydral group content increased immediately after freezing in all the three samples and subsequently declined, except for the meat with cryoprotectants, where the free sulphydral value remained constant throughout the storage period. Overall, the cryoprotectants were found to be less effective in minimizing deteriorative changes in tilapia meat during frozen storage.