Effects of rainbow trout freshness on n ‐3 polyunsaturated fatty acids in fish offal

The effects of rainbow trout cold storage on the quality of offal left after fish processing to fillets with skin were determined. The intact farmed rainbow trout were kept at 2 °C in ice for 0, 4, 7, and 14 days of storage. The offal was, immediately after processing, frozen at −20 °C and analysed after a month-long frozen storage; fillets (non-frozen) were analysed as well. Non-protein nitrogen, volatile bases, trimethylamine, lipid oxidation (peroxide value, anisidine value, UV-VIS spectra, and fluorescence) and fatty acid composition were determined. The offal consists in 15% of protein and in about 20% of chloroform/methanol-extractable lipids, with n-3 polyunsaturated fatty acids (n-3 PUFA) accounting for 20.37 ± 1.25% of the fatty acids. The fish storage duration was found to exert a significant (p = 0.05) effect on the changes in lipids and nitrogen compounds. No losses of long-chain n-3 PUFA in the offal were detected during the 2 wk of storage in ice plus 1 month at −20 °C. The rainbow trout offal is a valuable – rich and stable – source of n-3 PUFA.