Lipid oxidation in fillets of herring (Clupea harengus) during frozen storage. Influence of prefreezing storage.

Fillets of herring (Clupea harengus) were kept on ice for 0, 3, 6, and 9 days prior to storage at -18 degrees C for 0, 21, 42, 63, and 84 days. At each storage point, peroxide value (PV), absorbance at 268 nm (A(268)), fluorescent products (FP), alpha-tocopherol, glutathione peroxidase (GSH-px) activity, and ascorbic acid were measured. As shown by regression analyses, samples held for 6 days on ice formed oxidation products at the highest rate during frozen storage, followed by, for PV and FP, the 9-day samples. These data indicate that severe changes that negatively affect the oxidation process took place in the herring muscle between 3 and 6 days after catch. Both the initial antioxidant levels and the rate of antioxidant loss at -18 degrees C decreased with increased prefreezing holding time, the latter being most obvious for GSH-px activity and ascorbic acid. alpha-Tocopherol showed the largest losses and had disappeared entirely from the 6- and 9-day samples at the end of the frozen storage. Partial least-squares regression analysis of the data showed that ice storage had a greater effect than frozen storage on changes in PV, A(268), FP, alpha-tocopherol, and ascorbic acid. For GSH-px activity, frozen storage had the greatest effect.