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Protein oxidation in muscle foods: mechanisms, effects and development of antioxidant strategies

Final Activity Report Summary - Pox-MUSCLE (Protein oxidation in muscle foods: mechanisms, effects and development of antioxidant strategies)

The ‘POX-MUSCLE’ Marie Curie project was devoted to the study of the occurrence and factors influencing oxidative reactions in proteins from muscle foods.

Before this project was designed and fully accomplished, the precise mechanisms involved in the oxidation of muscle proteins in model systems and the susceptibility of muscle proteins to undergo oxidative reactions were mostly unknown. The elaborated research started following a mechanistic approach, which initiated with understanding the intrinsic mechanisms involved in the onset of the reactions in simple model systems. The purpose of the first step was to evaluate the susceptibility of myofibrillar proteins (MP) from porcine muscle to suffer oxidative reactions in an oil-in-water emulsion environment. According to the obtained results, myofibrillar proteins were considerably resistant to protein oxidation compared to other well-known animal proteins such as bovine serum albumin (BSA).

Apart from theoretical oxidation mechanisms, POX-MUSCLE considered practical issues such as managing protein oxidation. For that reason, in a second step, the antioxidant effect of selected phenolic compounds against the oxidation of oil-in-water emulsions containing one percent MP, was investigated. According to the results, gallic acid, cyanidin-3-glucoside and genistein were the most efficient inhibitors of lipid and protein oxidation.

In a third step, we approached one of the most challenging issues of the project, i.e. the characterisation of protein oxidation products using high-pressure liquid chromatography (HPLC) techniques. The purpose of this study was to develop a procedure for the accurate detection of two protein oxidation carbonyls, namely a-aminoadipic and ?-glutamic semialdehydes (AAS and GGS, respectively). AAS and GGS were used as indicators of the oxidative deterioration of MP. We reported the detection, for the first time, of both semialdehydes in oxidised food proteins, such as myofibrillar, BSA, lactalbumin and soy proteins. According to our results, both compounds could serve as reliable and specific protein oxidation markers in foods.

The purpose of the fourth step was to study the suitability of using AAS and GGS as protein oxidation markers in real meat products, including minced meat, dry-cured sausage, dry-cured ham, dry-cured loin, cooked sausage and liver pâté. A lack of consistency was observed between the MS results for AAS and GGS and the values obtained by the conventional dinitrophenylhydrazine (DNPH) method and the fluorescence spectroscopy. Unlike the last two methods, AAS and GGS measurements proved to be unaffected by the composition or the food matrix structure providing precise information about the fate of particular amino acids during processing of muscle foods.

During the fifth step, we deepened our knowledge on the formation of AAS and GGS in oxidised myofibrillar proteins. The aim of the final sixth step was to investigate the involvement of the proteins semialdehydes, AAS and GGS, in further reactions. These results proved, however, that protein carbonyls could also contribute to the formation of Strecker aldehydes, with these semialdehydes playing an active role in the development of the odour and flavour of muscle foods. Finally, all POX-MUSCLE project results were published in six journal articles.