A fermented tea with high levels of gallic acid processed by anaerobic solid-state fermentation

• A high level of gallic acid in a fermented tea was produced up to 25.7 g/kg, similar to that in Galla chinensis.
• Thirty-day is the optimal fermentation time for the sensory quality of pickled tea.
• Most free amino acids in tea evidently increased through anaerobic solid-state fermentation.

Microbial tea products are widely welcomed for their unique quality characteristics. However, the quality characteristics of pickled tea, a microbial tea product traditionally consumed in most Asian countries remain unclear. Therefore, the quality characteristics of pickled tea processed using Camellia sinensis leaves through anaerobic solid-state fermentation were analyzed. During 60-d fermentation, the free amino acids, caffeine, and tea polyphenols in pickled tea kept much stable, the soluble sugar content showed significant and continuous decrease, but the water extract showed a continuously increasing trend. The optimal fermentation time for pickled tea was 30 d, at which its normal quality characteristics were formed: the sensory quality was the best, most free amino acids evidently increased, a high level of gallic acid was produced up to 25.7 g/kg, and volatile compounds were mainly alkanes such as heptadecane and hexadecane. It is the first report that high levels of gallic acid in a microbe-fermented tea processed by anaerobic fermentation reached to that levels in Galla chinensis, which will benefit development of a functional tea with high levels of active components and understanding the microbial transformation of tea components through anaerobic fermentation.