Polyphosphate Treatment of Frozen Cod. 2. Effect on Drip, Yield, Lipid Hydrolysis and Protein Extractability in Twice-Frozen Newfoundland Summer Trap and Fall Cod

Abstract

Thaw-drip from once-frozen fall-caught Newfoundland cod (Gadus morhua L.), thawed after storage at -23[degree]C for up to 13 1/2 weeks, was equal to total drip from twice-frozen fish treated with sodium-tripolyphosphate between freezings. Treatment of twice-frozen cod before the first freezing only had no effect on reducing total thaw-drip below that from twice-frozen untreated samples and the yield, although higher in the former than in the latter, was no better than that from once-frozen untreated fillets. Yields from twice-frozen fish were improved greatly by dipping prior to the second freezing and by dipping before each freezing. Treatment between freezings gave yields close to 100% of initial fillet weight whereas losses with the untreated once- and twice-frozen product appear close to 7 and 15%, respectively. With summer-caught trap fish, characterized by higher thaw-drip values which were not affected by treatment, yields of twice-frozen cod were improved; however, losses were still about 12% in fish treated between freezings. Treatment of twice-frozen cod from the two sources did not appreciably affect lipid hydrolysis or protein denaturation. However, lipid content and free fatty-acid production were significantly higher in the trap fish samples as compared to the fall-caught cod.