Effect of Frozen Storage on Biochemical Changes and Fatty Acid Composition of Mackerel (Scomber japonicus) Muscle

Abstract

The aim of the present work was to analyze the effect of frozen storage on biochemical characteristics in mackerel (Scomber japonicus). Fresh mackerel captured from Southwest Atlantic Ocean was frozen and then stored at -19 ± 1 ºC for one year. Biochemical analyses were done at established sampling times: total volatile basic nitrogen (TVB-N), fatty acid profile, thiobarbituric acid values (TBA-RS) and colour determinations. After twelve months TVB-N increase correlated (R2 : 0.888) with storage time indicating the effect of enzymatic activity. Lipid content presented high degree of unsaturation, EPA (eicosapentaenoic acid; C20:5 -3) and DHA (docosahexaenoic acid; C22:6 -3) acids prevail among total -3 acids. During frozen storage, polyunsaturated fatty acids, -3 and Polyene Index (EPA + DHA ⁄ C16) contents decreased. Frozen storage of whole mackerel caused important changes in fatty acid composition simultaneously with an increase in lipid oxidation in fillets, measured as TBA-RS. Dark muscle was more sensitive to lipid oxidation than the light muscle. Color analysis showed that L* value was the parameter which presented more changes during frozen storage indicating loss of lightness in the dorsal and ventral fish fillet areas. The increase in b* value on the ventral zone indicated the presence of yellow pigments as result of lipid oxidation. Although the frozen storage technique represents important changes in mackerel samples, the high values of PUFA in muscle are still high over other fish species making mackerel an important nutritional resource.