Title: Oxidation of lipids on mackerel fillets during cooking

Mackerel rich in n-3 PUFA is one kind of popular fish in Iceland and China. Lipid changes of mackerel fillets cooked for 6 min and 30 min were studied, in which lipid composition and oxidation were evaluated. Results showed lipid and PL content significantly increased after cooking, while FFA decreased. Not many changes of FAC were detected after cooking, except C22:0 increased 6 folds dramatically, which responded to slight decrease of C22:5n3, and C18:0 increased responding to C18:3n3 reduced. Higher lipid oxidation level was determined with PV and AV after 30 min cooking, which shown marked difference from raw fillets. Furthermore, 12 volatile compounds closely related with lipid oxidation were detected in the three groups. It was found that the content of propanal and (E,Z)-2,6-Nonadienal derived from n-3 PUFA increased dramatically after steaming, especially for (E,Z)-2,6-Nonadienal, which content after cooking was more than 19 fold higher than the raw material. In addition, pure lipid changes during heating were evaluated, in which effect of other components was removed. In pure lipid system, PL content decreased and FFA from different groups had no difference. The change of FAC were similar with FAC in fillets, C18:3n3 and C22:5n3 reduced after heating. But PV was lower after cooking, and AV was detected. It is noteworthy that heating induced darker lipids, which should be studied further to analyse the oxidation products.