Adding omega-3 rich fish oils into functional food products by substituting it for some of the original fat in foods could be a way to increase the amount of long chain omega-3 in our diet. However the problems involved with incorporating fish-oils in food products are well established. The main problem with introducing fish oils such as omega-3 to into food products is that it brings oxidative instability and can lead to potential ‘off-flavor’ formation.
Research that assessed the feasibility of such enrichment in dairy products found that yogurt with added omega-3 fatty acids are less susceptible to oxidation then milk containing the same amount of omega-3.
The new study, reported in the journal Food Chemistry, aimed to investigate the reason for such big differences in oxidative stability, with differences suggested to be due to the different protein composition of milk and yogurt.
The research measured the antioxidant properties of protein fragments formed when milk is fermented into yogurt. Samples of yogurt proteins of various sizes (3kDa, 10kDa, and 30 kDa), were tested for antioxidant activity by investigating DPPH radical-scavenging activity, Fe2+ iron-chelating activity, and reducing power.
The study observed that the smaller fraction peptides (<10kDa) were more effective antioxidants than larger fractions, especially in terms of Fe2+-chelanting activity and reducing power – of which Fe has previously been suggested to be important catalyst in fish-oil oxidation.
The smaller proteins with high antioxidant properties were then tested in omega-3 enriched milk which usually has a low oxidative stability, and were found to offer protection against oxidation of fish-oil enrichments.
The study’s findings suggest that the higher oxidative stability of yogurt might be due to antioxidant peptides released during the fermentation of milk by lactic acid bacteria, and that these peptides could be used to offer oxidative stability to fish-oil enriched food products.
Further work is now needed to identify exactly which peptides have the observed benefits on oxidative stability. The researchers wrote: “Since the antioxidant activity of the peptides depends on amino acid compositions, sequence and configuration of peptides, we cannot explain the exact mechanism for the observed findings”
Further purification and characterization of these [protein] fractions may offer an explanation for the discrepancies in the active peptides”.
With indications that current diets are highly deficient in omega-3 fatty acids, the greater oxidative stability provided by adding natural antioxidant peptides to an omega-3 enriched functional food could make omega-3 enrichment in foods more straightforward.
The study concludes: “These results also demonstrate the applicability of these naturally-occurring antioxidant peptides as an ingredient in foods enriched with fish oils to increase their oxidative stability.”
Antioxidant activity of yoghurt peptides: Part 1-in vitro assays and evaluation in ω-3 enriched milk
Authors: K.H. Sabeena Farvin, Caroline P. Baron, Nina Skall Nielsen, and Charlotte Jacobsen