Abstract

In industrial fish filleting, around 30–70 % of the total weight of the fish end up as side streams (often called by- or co-products), such as the head, backbone, caudal fin, skin, and intestines. Currently, these fractions are dedicated to low value uses as fodder meals or mink feed, even if they contain significant amounts of protein, long chain (LC) n-3 polyunsaturated fatty acids (PUFA), and other nutrients such as vitamins and minerals. However, most fish processors mix their side streams, not least when it comes to small pelagic species like herring. This practice limits use of the side streams for food production since the raw material gets very complex, and since blood, enzymes and lipids from e.g., the viscera and head parts easily contaminate the cleaner parts like the backbones and tails, accelerating e.g., their oxidative or enzymatic degradation. In the present study, lipid oxidation in ice-stored sorted and minced herring fractions (head, backbone, viscera+belly flap, tail, fillet) from spring and fall, and its association with endogenous pro-oxidants, antioxidants and lipid substrates were investigated. Peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) had increased significantly in all fractions after 1 day, but for both seasons, the most rapid PV and TBARS development occurred in head, which also had highest hemoglobin (Hb) levels and lipoxygenases (LOX) activity. Viscera+belly flap was overall the most stable part, and also had the highest -tocopherol content. Pearson correlation analyses across all five fractions confirmed a significant impact of Hb, LOX and -tocopherol on the lipid oxidation susceptibility, while content of total iron, copper, lipids or PUFA provided no significant correlation. Overall, the study showed which pro-oxidants that should be inhibited or removed to succeed with value adding of herring filleting side streams along with the fillet itself.

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