Effect of NaCl on the oxidation and hydrolysis of lipids in salted sardine [Sardinops melanostictus] fillets during storage

Effects of NaCl on the oxidation and hydrolysis of lipids in salted sardine Sardinops melanostictus fillet, iwashi hirakiboshi, during storage were investigated. Salted sardine fillets with NaCl contents of 0.39, 2.83, 5.36 and 9.19% were prepared and stored at 5°, -3°, -20° and -35°C. The degree of lipid oxidation of the samples was evaluated. When the peroxide value of the extracted lipid and the content of highly unsaturated fatty acid (HUFA) remained unchanged, the extent of lipid hydrolysis was measured by the acid value. During salting and drying processes, carotenoid and tocopherol contents in the lipids decreased with increase of NaCl content of the sample. At -3°, -20° and -35°C, lipid oxidation in the samples with NaCl contents of 2.83, 5.36 and 9.19% commenced immediately after storage, while that of 0.39% began 5-30 days after storage, depending upon temperature. The rates of lipid oxidation increased with increase of NaCl content. Lipid hydrolysis occurred during storage at 5°, -3° and -20° and the rates of hydrolysis depended upon the NaCl content and storage temperature: the lower the NaCl content was, the faster hydrosis proceeded. The hydrolysis may be attributed to endogenous enzyme system in sardine meat. In the samples stored at -35°C, little lipid hydrolysis occurred throughout the entire 180-day storage period, regardless of NaCl content of the sample. From these findings, it is clear that NaCl accelerates lipid oxidation and inhibits lipid hydrolysis in the salted sardine fillet during storage, though the degrees of accelerative and inhibitory effects of NaCl depend on the NaCl concentration and the storage temperature.