Evaluation of fermented tea (kombucha) quality

Abstract

The research was done at Aleksandras Stulginskis University (Vytautas Magnus University Agriculture Academy since 2019) in 2017–2018. The research object was kombucha beverage brewed from Camellia sinensis L. black, green, oolong, pu-erh tea and fermented for 9 and 22 days by microorganisms at different room lighting conditions. The soluble solids content, active acidity and titratable acidity were determined in teas fermented for 22 days. The total amount of phenolics compounds, antioxidant activity, yeast colonies and sensory evaluation of tea were determined in teas fermented for 9 days. The research results showed that the quality of fermented tea was dependent on the tea species, but fermentation conditions were not essential. During the fermentation the soluble solids content of tea decreased by an average of 0.60% and the content of acetic acid increased by 0.34%. The highest content of acetic acid was found on the 22nd day of fermentation in all species of teas. The active acidity (pH) of all investigated species of teas decreased significantly during the fermentation process. The total content of phenolic compunds in all species of teas during the fermentation increased from 20 to 57% regardless of fermentation conditions. The highest content of total phenolic compounds was established in teas fermented for 9 days. The antioxidant activity of teas fermented for 9 days varied depending on the fermentation conditions. For black and green teas fermented in the light the antioxidant activity decreased, for oolong and pu-erh teas fermented in the dark the antioxidant activity increased. The number of yeast colonies increased in all tea samples during the fermentation. The best taste was fixed for pu-erh tea, which scored the highest (11.4) in sensory evaluation.