Effect of different cooking techniques on total moisture, total lipit and fatty acid composition of fish fillets of leer (Lichia amia) and mahi̇-mahi̇ (Coryphaena hippurus)

In this study, the effects of frying in vegetable oils such as corn oil, sunflower oil, olive oil and hazelnut oil and cooking methods other than frying such as cooking in oven and microwave oven, grilling and steaming; on total moisture, total lipid, fatty acid composition in total lipid and fatty acid composition in phospholipid and triacylglycerol fractions of leer (Lichia amia) and lambuka (Coryphaena hippurus) fish were investigated. The total moisture content was determined as 73.36% in raw leer and 74.95% in raw mahi-mahi. All cooking methods reduced the total moisture content of the fillets of both fish species. The decrease in the total moisture content in the fillets of both fish was determined in cooking with the least steaming. Total lipid amount was determined as 1.89% in raw leer and 1.58% in raw mahi-mahi. Total lipid content of leer and mahi-mahi fillets fried in vegetable oils increased. The least percentage increase in total lipid in both fish species was determined in fillets fried in olive oil. In our study, it was seen that the dominant components determined in the fatty acid analysis in total lipids in leer and mahi-mahi fillets were similar. The major of these fatty acids are; 16:0 from saturated fatty acids, 18:1n-9 from monounsaturated fatty acids, 22:6n-3 from polyunsaturated fatty acids was to be seen. However, the percentage contents of these fatty acids were found to be different in both fish species. It was determined that cooking methods changed the fatty acid composition in total lipid of leer and mahi-mahi fillets. In leer and mahi-mahi fillets fried separately in vegetable oils such as hazelnut oil, olive oil, corn oil and sunflower oil compared to jointly control; 16:0, 18:0 and ∑SFA percentages decreased significantly, 18:1n-9 and ∑MUFA for fillets fried in olive oil and hazelnut oil; on the other hand, 18:2n-6 and ∑n-6 PUFA percentages and PUFA/SFA ratios increased significantly in those fried in sunflower oil and corn oil. In raw (control) leer and mahi-mahi fillets; 20:4n-6, 20:5n-3, 22:5n-3, 22:6n-3, ∑n-3 PUFA levels and n-3/n-6 ratio, it was seen that they were significantly higher than fillets fried in different vegetable oils. Compared with control and other cooking techniques; 18:1n-9 and ∑MUFA in oven cooking; a slight decrease in the percentages of 16:0, 22:6n-3, ∑PUFA, ∑n-3 PUFA and n-3/n-6 was recorded in steaming. In mahi-mahi fillets cooked in the oven; compared to control, microwave and steam cooking methods 18:1n-9, 18:2n-6, ∑MUFA, ∑n-6 PUFA increased, DHA, ∑PUFA, ∑n-3 PUFA percentages were found to be significantly lower. According to the results obtained; in leer and mahi-mahi fillets cooked by steaming, jointly showed a decrease of 16:0. The examined cooking methods did not change the n-3/n-6 ratio of leer much. In mahi-mahi, cooking methods other than microwave, cooking methods, especially in the oven and on the grill, it reduced the n-3/n-6 ratio very significantly. The atherogenic and thrombogenic indices (AI and TI) obtained from the fatty acid composition in the total lipid of leer and mahi-mahi cooked with different cooking methods were found within the ranges recommended by the diet experts. Some common findings were determined regarding with the effect of frying technigues in various vegetable oils on the phospholipid fatty acid composition of leer and mahi-mahi fillets. For example, in fillets of both fish species fried in hazelnut oil, compared to control and other cooking methods 18:1n-9 and ∑MUFA increased, ∑SFA was decreased in those fried in corn oil. In addition, EPA, 22:6n-3 percentages and n-3/n-6 ratios in raw samples of leer and mahi-mahi were found to be higher than those fried in oils. The n-3/n-6 ratio in both fish fillets fried in olive oil was detected to be higher than those fried in other vegetable oils. In both types of fish cooked in the oven, compared to control fillets 22:6n-3, ∑PUFA, ∑n-3 PUFA levels were determined to be higher. In the triacylglycerol fraction of both fish species fried in olive oil, compared to those fried in other oils 16:0 and ∑SFA, in those fried in olive oil and hazelnut oil 18:1n-9 and ∑MUFA, whereas those fried in sunflower oil and corn oil 18:2n-6, ∑PUFA, ∑n-6 PUFA were determined to be at higher levels. Also, in raw fillets of leer and mahi-mahi 16:0, 18:0, ∑SFA, 20:4n-6, 20:5n-3, 22:5n-3, 22:6n-3 and ∑n-3 PUFA percentages with n-3/n-6 ratio, was detected to be significantly higher than fillets fried in all other oils. The common finding in both fish species, when cooked by steaming 18:1n-9 and ∑MUFA levels were found to be high. In our study, it was determined that the fatty acid compositions in the phospholipid and triacylglycerol fractions of the leer and mahi-mahi fillets, which we used as research material, were different. For example, in the phospholipid fraction of leer fillets fried in both control and different oils; with fatty acids such as 16:0, 18:0, 20:4n-6, 20:5n-3 and 22:6n-3; fatty acid groups ƩSFA, Ʃn-3 PUFA and n-3/n-6 ratio is higher than triacylglycerol; with unsaturated fatty acids such as 18:1n-9 and 18:2n-6; ƩMUFA, one of the fatty acid groups, was found in lesser percentages. It has been seen that the phospholipid and triacylglycerol fatty acid contents of mahi-mahi fillets fried in different vegetable oils are also different. For example, phospholipid fraction compared to triacylglycerol fraction; with fatty acids such as 16:0, 18:0, 20:4n-6, 20:5n-3, 22:5n-3, 22:6n-3; richer in fatty acid groups such as ƩSFA, Ʃn-3 PUFA; with fatty acids such as oleic acid, linoleic acid; Ʃn-6 was determined to be poorer in terms of PUFA. The n-3/n-6 ratio in the phospholipid fraction of both fish fillets, both raw and cooked with different cooking methods, was significantly higher than that of triacylglycerol. Keywords: Cooking methods, Fatty acid composition, Leer, Mahi-mahi.