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When fatty fish are transformed into surimi, lipid oxidation takes place, decreasing the quality of the product. This study was aimed to identify the critical stages of the process in terms of the development of lipid oxidation. Horse mackerels were transformed into surimi on a pilot line and samples taken (hand-skinned fillets = minced fillets, mince, washed and refined minces, paste, surimi and washing water). Most of the lipids were removed during the process and neutral lipids were lost in higher proportion than polar lipids. As a consequence, total lipids of surimi contained more polyunsaturated fatty acids (338 ± 19 g kg −1 ) than total lipids of the minced fillets (220 ± 8 g kg −1 ). Thiobarbituric acid reactive substances (TBARS) was higher in the minced fillets than in the mince because less subcutaneous fat and dark muscle were removed during hand-mincing, indicating that the settings of the skinning-deboning machine can strongly influence the final quality of the product. Concentrations of lipid oxidation products increased significantly during the next stages of surimi processing. The increase was more pronounced for TBARS than hydroperoxides. Concentrations in hydroperoxides were similar in mince and washed mince (15.3 ± 2.8 and 16.6 ± 2.8 mmoles kg −1 lipid) and increased in refined mince (29.6 ± 2.8 mmoles kg −1 lipid). TBARS accounted for 2.7 ± 1.0 mg kg −1 lipid in mince, 40.4 ± 2.3 mg kg −1 lipid in washed mince and 237 ± 7 mg kg −1 lipid in refined mince. Hydroperoxides and TBARS were found in appreciable amounts in washing water (76.9 ± 4.7 mmoles kg −1 lipid and 479 ± 8 mg kg −1 lipid respectively), when they decreased in surimi (27.3 ± 3.8 mmoles kg −1 lipid and 44.2 ± 0.8 mg kg −1 lipid respectively) compared with refined mince. This shows that the last dewatering stage is crucial to ensure surimi quality.

Lipid oxidation causes deterioration of the quality of fatty fish during processing and storage. Its development should be evaluated by measurement of several oxidation products, among them the hydroperoxides. However, most of the methods for determining hydroperoxides already in use failed when tested on fatty fish. The objective of this study was to adapt the ferrous ion xylenol orange assay (FOX) for easy and sensitive measurement of hydroperoxides in fatty fish such as small pelagics during their storage and processing. The proposed procedure is based on the assay developed by Hermes‐Lima et al. that consists of a colourimetric assay performed directly on the methanol extract from minced fish. The reactant was replaced by Wolff's reagent (FOX2 reagent) to improve the solubility of the extract and to simplify the procedure. It was shown that absorbance should be measured at 560 nm instead of 580 nm. The method is valid between 0.3 and 0.6 absorbance units. The modified method is easy, sensitive and allowed differentiation between fresh horse mackerel samples and those stored for 12 h at 17 °C on the basis of their hydroperoxide levels.

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Fatty fish have been recognized as potential raw material for the production of surimi; however, they can easily oxidize. The ability of antioxidants added in the washing water to reduce oxidation during the washing and subsequent storage needs to be evaluated. Horse mackerel ( Trachurus trachurus ) mince was washed three times with 3 volumes of cold water (W) or the antioxidant solutions caffeic acid (CA) or propyl gallate (PG), at concentrations of 100 mg/kg, or spermine (SP), at a concentration of 400 mg/kg. Accumulation of antioxidant in the mince at each washing step was evaluated. The obtained washed minces were characterized and stored for 5 days at 5 degrees C. Lipid oxidation was followed by measuring primary and secondary lipid oxidation products (peroxides and volatiles, respectively). Characterizations of the physicochemical properties of protein and protein oxidation were also performed. Results indicated that the antioxidants were accumulated differently, but all antioxidants tested were able to prevent lipid oxidation in fatty fish mince during washing and subsequent storage. The ranking in terms of oxidative stability of the washed minces was CA = PG > SP > W. The antioxidants tested also showed some protection of the protein during processing and storage,; however, the results were more difficult to explain and indicated complex interactions between protein and antioxidant. The chemical structures of the antioxidant and its functional groups, its properties, and its interaction with the protein matrix are important parameters that need to be carefully evaluated to reveal to what extent antioxidants are able to protect protein from oxidative damage.

Summary :Increase the consumption of long-chain omega 3 polyunsaturated fatty acids (LC ω3 PUFA) is highly recommended for their health benefits. However, these fatty acids are very prone to oxidation, which can impair sensory, nutritional and functional properties of foods. In this paper the various ways that increase LC ω3 PUFA stability during processing and storage of food products are reviewed. To efficiently protect LC ω3 PUFA during processing and storage of foods, a combined strategy, taking into account both the matrix and the process should be undertaken. First the quality of the raw materials should be rigorously controlled by, for example, increasing contents of in situ antioxidants and decreasing length of storage. Then, during processing and storage of LC ω3 PUFA concentrates and LC ω3 PUFA enriched foods all pro-oxidant factors, such as oxygen and temperature, has to be carefully managed. An other way is to encapsulate the oils and add antioxidant substances, but the influence of the structure of the matrix and its organisation on antioxidants partition and their activity and on the oxidability of the fatty material as function of its chemical structure should be also taken into account.