Effects of Fermentation and Storage on Bioactive Activities in Milks and Yoghurts

Fermentation of milk enhances its nutritional value through improved bioavailability of nutrients and production of bioactive substances which have biological functions. The goals of this research were to study the effect of fermentation and storage on antioxidant and antimicrobial activities in buffalo, goat and cow milks and yoghurts. Samples of buffalo, goat, cow milks and their yoghurts during their fermentation and storage were determined for proximate analysis and bioactive activities including antioxidant activities of DPPH, ABTS and reducing power assays, and antimicrobial activities against Staphylococcus aureus, Bacillus cereus, Salmonella typhimurium and Escherichia coli. Results showed that buffalo, cow and goat yoghurts had antioxidant activities in all assays and their activities significantly increased during their fermentation. Pasteurization did not affect the antioxidant activities. The activities of all yoghurts remained unchanged after a storage time of 21 days at 4 °C. For the antimicrobial activities, only yoghurts from buffalo, cow and goat milks had the activities, while all milks did not show any activities. However, buffalo yoghurt could inhibit only Gram positive strains (S. aureus and B. cereus), while goat and cow yoghurt inhibited all tested strains. A chemical responsible for antimicrobial activities in yoghurts was lactic acid formed by lactic acid bacteria. However, bioactive peptides produced by protein digestion during milk fermentation by lactic acid bacteria could not be ruled out for antioxidant and antimicrobial activities present. The antimicrobial activities of all yoghurts remained constant during their storage. It is concluded that all yoghurts would retain milk nutrition and bioactive functions during their storage in a refrigerator and may be served as a functional food with benefits from those activities for consumers.