Investigation on antioxidant activities of some fermented milk products

Fermented milks are one of the oldest and the most important components of our diet. The aim of the milk fermentation is to produce products having a characteristic aroma and viscosity which have a longer shelf life than raw milk itself.Milk is a complex matrix that naturally comprising many antioxidative factors like proteins, peptides, enzymes, vitamins. Recently, with the increasing consumer interest to the fermented milk products and natural antioxidants; also a necessity to identify the antioxidant capacities of these products has been arised. Additionaly; fermentation provides some metabolic and cellular components that have beneficial effects to consumer.In this study; the antioxidant capacities (total phenolic content, Fe+2 chelating, reducing power, H2O2 inhibition and DPPH free radical scavening) of milk and some fermented milk products like yogurt, white cheese, kefir, kumis which are consumed daily in our country. Also in order to identify the fermentation effect; the antioxidant activity alteration is observed during the traditional yogurt and kefir fermentation.The commercially purchased UHT milk, yogurt, white cheese, kefir and kumiss possessed an significant antioxidant activity and these antioxidant activities differed responsively (in conformity) with the dissolved protein content among the products.Yogurt that produced traditionally with milk, showed higher total phenolic content, Fe+2 chelating, reducing power and DPPH scavening, but lower H2O2 inhibition antioxidant activities than milk.At the end of the kefir fermentation; total phenolic content, reducing power and DPPH scavening activity was measured as higher than those of milk, on the other hand; H2O2 inhibition and Fe+2 chelating activity was measured as lower than the milk.These results suggests that; with their antioxidant properties; milk and fermented milk products can be consumed as natural antioxidants. Also, some antioxidative peptides and aminoacids as hydrolyzates of these milk proteins can be used to prevent oxidation reactions in food industries.Key words: milk, fermentation, antioxidant activity, kefir, kumiss.