Effect of drying processes on the occurrence of lipid oxidation-derived 4-hydroxy-2-hexenal and 4-hydroxy-2-nonenal in Spanish mackerel ().

In this study, dry-cured Spanish mackerel (, DCSM) was prepared via three different methods (hot-air drying, cold-air drying, and sun drying). The content of 4-hydroxy-2-hexenal (HHE) and 4-hydroxy-2-nonenal (HNE) derived from lipid oxidation in whole processes was investigated by HPLC-MS/MS. The changes in fatty acid composition were detected by GC-MS, and the degree of lipid oxidation was evaluated by the levels of acid values (AV), peroxide values (POV), and thiobarbituric acid-reactive substances (TBARS). The results showed that the drying process significantly accelerated lipid oxidation in DCSM. The contents of HHE and HNE were significantly increased after processing. The content of HHE was higher by 18.44-, 13.45-, and 16.32-folds compared with that of HNE after three different processes, respectively. The HHE and HNE contents fluctuated upward during the hot-air and cold-air drying process. However, the contents of HHE and HNE increased time-dependent during the sun drying process, with the highest values of 86.33 ± 10.54 and 5.29 ± 0.54 mg/kg fish among the three different processes. Besides, there was a significant positive correlation between HHE contents and n-3 fatty acids content in hot-air drying and sun drying processes (Pearson's  = .991/.996), and HNE occurrence was closely related to n-6 fatty acid content in sun drying process (Pearson's  = .989). Regression analysis indicated that the content of HHE and TOTOX values in DCSM showed good linear relationships ( value = .907), which suggested that the content of HHE could be used to estimate the oxidative deterioration of dry-cured fish products.