Optimization of Fermentation Process and Quality Analysis of Buckwheat Vinegar Fermented by Kombucha

In this study, buckwheat syrup was used as the raw material and was fermented by kombucha to produce the buckwheat vinegar. Based on the total acid content and the sensory score of buckwheat vinegar, the effects of different content of soluble solid, inoculation amount of kombucha and fermentation temperature on the quality of buckwheat vinegar were investigated, and the optimal process conditions for buckwheat syrup fermentation by kombucha were determined. Subsequently, the buckwheat vinegar was fermented under these optimal technological conditions, changes in pH value, total acids, total phenols, total flavonoids as well as organic acids of buckwheat syrup during the fermentation process were explored. The results showed that the optimal fermentation conditions of buckwheat vinegar by kombucha were as follows: Soluble solid content was 13%, kombucha fungus inoculation amount was 15%, fermentation temperature was 30 ℃. Under this optimized condition, during the fermentation process, pH was decreased, the total acid was increased, the reducing sugar content was increased first and then decreased, the total phenol content was increased, the flavonoid content was decreased first and then increased, the contents of acetic acid, lactic acid and succinic acid increased, while the contents of malic acid and malonic acid increased first and then decreased. After 9 days of fermentation, the total acid, total phenol and total flavonoid contents of the obtained buckwheat vinegar were 32.96, 1.72 and 2.55 g/L, respectively. The final vinegar had suitable acidity, soft taste, strong buckwheat aroma, and health care function.