Effects of different re-fermentation methods on the quality characteristics of kombucha beverages

The effects of different re-fermentation methods on the quality characteristics of kombucha beverages were investigated. The quality characteristics of kombucha beverages included the basic physicochemical indicators (pH, total acidity, reducing sugar, total sugar, organic acids, total phenolic compound, total flavonoid compound), antioxidant activity, volatile flavor substance and sensory evaluation of the beverages. The results showed the re-fermentation methods including the mixed fermentation and the step-by-step fermentation significantly decreased total acidity and various organic acids (P < 0.05) than traditional kombucha with no re-fermentation. In addition, the contents of total phenol compounds and total flavonoid compounds for the step-by-step fermentation were 184.70 and 338.33 mg/L respectively, and were higher compared with mixed fermentation and traditional kombucha with no re-fermentation. The antioxidant activity in the step-by-step fermentation was much stronger than that of mixed fermentation and traditional kombucha with no re-fermentation. Moreover, there were 53 kinds of volatile flavor compounds produced in the step-by-step fermentation, 14 of them were unique with good sensory quality. In conclusion, the re-fermentation methods for traditional kombucha (the step-by-step fermentation and mixed fermentation) had more active ingredients and better sensory quality, and the step-by-step fermentation was better than mixed fermentation.