The Effect of Fermentation Time and Yogurt Bacteria on the Physicochemical, Microbiological and Antioxidant Properties of Probiotic Goat Yogurts

Abstract

In this study, monocultures of L. casei, L. acidophilus, B. lactis and their combination with yogurt starter culture were used with goat yogurt. Yogurts containing only probiotic bacteria were observed for 12 hours of fermentation, and yogurts containing both probiotic bacteria and yogurt bacteria were followed for 8 hours of fermentation. The use of yogurt culture increased the lactic acid contents, hardness values and antioxidant activities – using ABTS (2,2-azino-di-(3-ethylbenzothialozine sulfonic acid) and DPPH (2,2-Diphenyl-1-picrylhydrazyl) methods – and exhibited a shortened fermentation time. DPPH radical scavenging activity of all probiotic yogurt samples without yogurt culture decreased significantly at the end of fermentation (after 8 hours) compared to the beginning of fermentation (p<0.05). Across all the samples, L. acidophilus and B. lactis-containing yogurts exhibited the maximum viability at the end of fermentation. L. casei could not maintain viability at the end of the 8 hour fermentation. A high positive correlation was determined between antioxidant activity (ABTS) and the free amino acid results of probiotic yogurts containing yogurt culture. In this study, it was concluded that antioxidant activity, probiotic viability and amino acid content of probiotic goat yogurts changed with fermentation time.

Key words
goat milk; probiotic yogurt; fermentation; antioxidant activity; free amino acid content