Polyunsaturated Fatty Acids in Tuna Phospholipids: Distribution in the sn-2 Location and Changes during Cooking

Fatty acid composition with a special stress on polyunsaturated fatty acids (PUFA) was studied in the sn -2 location of tuna phospholipids (PL) in eight commercial species. Comparison with the sn -1 location and changes of both positions ( sn -1 and sn -2) during cooking were also analyzed. When the sn -1 and sn -2 locations in albacore tuna were compared, some differences were noted. The sn -1 position showed higher contents in saturated (16:0 and 18:0) and 18:1ω7 fatty acids; in contrast, higher proportions in PUFA (22:6ω3, 20:5ω3, and 20:4ω6) and in 18:1ω9 were obtained in the sn -2 location. The comparative study of the sn -2 position of PL showed a similar pattern of distribution in the different tuna species. In all cases the main fatty acid was 22:6ω3, followed by 18:1ω9, 20:5ω3, 16:0, 20:4ω6, and 24:1ω9. A high ω3/ω6 ratio was found in all cases, although great differences were noted between the highest (bonito and yellowfin) and the lowest (little tunny and skipjack) values; ratios between the most abundant PUFA belonging to the ω3 and ω6 series (22:6ω3/20:4ω6 and 20:4ω6/20:5ω3) showed similar differences. The behavior of both positions ( sn -1 and sn -2) in albacore PL was studied during cooking. As a result of the thermal treatment, some changes in the fatty acid composition were seen in both locations. The sn -2 position showed a decrease in 22:6ω3 and an increase in 18:1ω9. On the contrary, a decrease in 18:0 was obtained in the sn -1 position, along with an increase in 22:6ω3 and 20:4ω6.