Influence of Conventional Fermentation on Antioxidant Activity and Phenolic Contents of Two Common Dairy Products: Yogurt and Kefir

Abstract

During conventional fermentation of milk into yogurt and kefir, changes of antioxidant capacities (DPPH radical scavenging, ferrous chelating, reducing power, hydrogen peroxide/ H2O2 scavenging activity) and total phenolic content were investigated. Both products showed greater phenolic content, DPPH radical scavenging, and reducing power activities than was the case of their unfermented milk forms. But they were unable to scavenge H2O2. Chelating ability of milk increased by yogurt fermentation but decreased by kefir fermentation. In general, antioxidative capacity of milk improved throughout conventional yogurt and kefir fermentations and ripening periods (except chelating ability for kefir and H2O2 scavenging). This study is valuable since it evaluates the antioxidant power of yogurt and kefir produced by traditional fermentation with 5 different antioxidative approaches. In face of rapidly rising consumer demand for safe, healthy, functional but natural foods, revealed results might strengthen importance of conventional fermentation process and highlight the antioxidative contributions of mentioned products