Effect of microbial fermentation on the sensory characteristics and chemical compositions of Chinese sweet tea (Lithocarpus litseifolius (Hance) Chun)

Sweet tea, which has hundreds of years of use among in Chinese folk, is a traditional herbal tea with pleasant sweetness, bitterness and astringency. In the current study, we used traditional microbial fermentation to improve sensory characteristics of sweet tea, especially for the reduction of bitterness and astringency. The dynamic changes of non-volatile, volatile compounds and microbial community were investigated during microbial fermentation. The contents of polyphenols, flavonoids, soluble sugar, soluble protein, catechins and dihydrochalcones decreased significantly while the tea pigments, free amino acids and gallic acid content inversely increased during microbial fermentation. A total of 61 volatile compounds were identified and quantified in sweet tea, of which 20 key compounds were identified as odor active compounds (OAV), including 3 aldehydes, 1 ketone, 4 alcohols, 9 esters, 4 alkenes and 3 other compounds. In addition, eight fungi and four bacteria were considered as core microorganisms, such as Aspergillus, Alternaria, Cladosporium, Epicoccum, Itersonata, Penicillium, Periconia, Wallemia, Aureimonas, Enterobacter, Klebsiella and Stenotrophomonas, which were significantly correlated with non-volatile compounds and flavor compounds. These results provided theoretical guidance for processing of fermented sweet tea.