Antioxidant Peptides Discovered in Yogurt

Yogurt is considered a healthy food making it a good candidate for fortification with other healthful ingredients such as omega-3 fatty acids, and helping it reach an estimated $4.1 billion market in 2009 according to Mintel. But it’s essential the finished product retain a desirable taste and long shelf life when working with oxidation-prone omega-3 PUFAs (polyunsaturated fatty acids).

Researchers at the Technical University of Denmark, Lyngby, Denmark conducted a study was to investigate factors that contribute to the oxidative stability of fish-oil-enriched yogurt, particularly the possible antioxidative effects of peptides generated from the breakdown of dairy proteins during yogurt fermentation.

They removed the sugars and lactic acid from yogurt samples and then fractionated tem via ultrafiltration. The various yogurt fractions were tested for antioxidant activity by investigating the inhibition of oxidation in a liposome model system, radical-scavenging activity, iron-chelating activity, and reducing power.

The scientists found that the lower-molecular-weight peptide fractions were more-effective antioxidants than the fractions with higher molecular weights. These lower-molecular-weight fractions were then studied as antioxidants in fish-oil-enriched milk. Based on the measures of the milk’s peroxide value, volatiles, tocopherol and sensory characteristics, the lower-molecular-weight fractions (3 to10 kDa and less than 3 kDa) protected the test dairy product against oxidation of fish oil to the same extent as caseinophosphopeptides. In addition, the oxygen content of the yogurt was found to be lower than that of milk.

The researchers say these findings suggest that the higher oxidative stability of yogurt might result from antioxidant peptides developed during the fermentation of the milk by lactic acid bacteria and/or by the lower oxygen content of yogurt (which reduces the oxidative stress on the unsaturated fatty acids in the fish oil.). They believe that antioxidant peptides might also be added as an ingredient to fish-oil-fortified foods to increase their oxidative stability.