Evaluation of the antioxidant activity in food model system of fish peptides released during simulated gastrointestinal digestion

In the last decade, increasing evidences of the occurrence of lipid oxidation during digestion have been reported, in either in vivo or in vitro studies (1,2,3). As a result, the nutritional quality and safety of foodstuffs could be affected by the decrease of certain lipidic compounds of interest and the generation of potentially toxic oxidation products. Regarding fish composition, the high content in polyunsaturated ω-3 acyl groups renders its lipids especially prone to oxidation. However, fish is also a major source of protein, which could greatly influence the extent of oxidation reactions taking place in the gastrointestinal tract. In fact, several studies have reported antioxidant activity of fish protein hydrolysates, coming from fish industry waste by-products (3,4). Thus, the potential release of peptides showing antioxidant properties during fish digestion cannot be ruled out. In order to shed light on these aspects, in vitro digestates of European sea bass were submitted to ultrafiltration using membranes with different cut off size. Afterwards, the potential antioxidant activity of the peptide fractions obtained was evaluated by comparing the oxidative stability of fish oil-in-water emulsions (5%), containing or not the isolated fractions (2 mg/ml final protein concentration). For this purpose, the occurrence of volatile markers of lipid oxidation, the tocopherol content, and the lipid composition of the emulsions during storage were studied. At day 12 of storage, emulsions made with digested protein fractions showed a higher content of docosahexanoic acyl groups and tocopherol than the emulsion control (without fractions), and also a lower content of volatile oxidation markers.