In recent years the consumption of yoghurt has increased rapidlyowing to the fact that it fulfils many current dietary needs. Consumptionof yoghurt has been reported to exert a number of healthbenefits like increased bone mineralisation (Schaafsma, Dekker, &de Ward, 1988), gut associated immune responses (Puri, Rattan, Bijlani,Mahapatra, & Nath, 1996) and laxation (Strandhagen et al.,1994). Furthermore, yoghurt has proved to be an excellent vehiclefor the production of functional foods, especially those containingprobiotic bacteria (Meance et al., 2003). One major characteristicof yoghurt, which distinguishes it from many other foods, is thepresence of beneficial lactic acid bacteria. The fermentation of themilk by lactic acid bacteria releases a large number of peptidesand amino acids with varying biological actions such as angiotensin-converting enzyme (ACE) inhibitory (Hernandez-Ledesma,Miralles, Amigo, Ramos, & Recio, 2005; Nielsen, Martinussen, Flambard,Sørensen, & Otte, 2009), immune modulatory (Coste et al.,1992), opioid (Meisel, 1986) and antioxidant activities (Pena-Rasmos,Xiong, & Arteaga, 2004).Yoghurt has also been shown to be a good matrix for enrichmentwith omega-3 fatty acids (Nielsen, Debnath, & Jacobsen,2007). In contrast to omega-3 enriched milk, yoghurt enrichedwith omega-3 fatty acids had a very good oxidative stability (Let,Jacobsen, & Meyer, 2007). As there is no difference in gross compositionbetween yoghurt and milk, which could explain the high oxidativestability of yoghurt, it is assumed that compounds liberatedduring fermentation, namely peptides and free amino acids play asignificant role. It has been reported that free amino acids areformed during fermentation of yoghurt and it is well known thatsome free amino acids possess antioxidative properties (Marcuse,1960). Therefore, an attempt was recently taken to explore thecontribution of amino acids and peptides to the higher oxidativestability of fish oil-enriched yoghurt when compared to milk(Farvin, Baron, Nielsen, & Jacobsen, 2010). The amino acids andpeptides from yoghurt were isolated and separated according totheir molecular weight by ultrafiltration (>30, 10–30, 3–10 and<3 kDa). The antioxidant activities of the obtained fractions weretested in both in vitro assays and in fish oil-enriched milk. All theisolated fractions showed high to moderate DPPH-radical-scavengingactivity, and especially the low molecular weight fractionsshowed higher reducing power and iron-chelating activity in theassays. The low molecular weight fractions were as effective ascaseinophosphopeptides in preventing lipid oxidation in fish oilenrichedmilk and even better at preventing formation of fishy flavourand odour in the milk emulsion.Although our previous study (Farvin et al., 2010) yielded interestingresults concerning the antioxidant activity of these differentpeptide fractions, the exact amino acid compositions of the
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