Fermented or not fermented: a comparative study of the biological activities and microbiomes of a non‐fermented green tea and a five‐year‐old fermented tea prepared from young leaves of Shan tea

Summary Camellia sinensis var. shan is a special tea variety in Vietnam that is in high demand, especially its fermented products. This study compared the total polyphenol content (TPC), antioxidant activity, cytotoxicity, and microbiome of a green Shan tea and a five‐year‐old fermented Shan tea. Folin–Ciocalteu, DPPH and SRB assays were used for TPC, antioxidant activity and cytotoxicity evaluation. The isolated microbes were morphologically and molecularly identified. The TPC (126.59 mg g −1 ) and antioxidant activity (IC 50 of 284.82 μg mL −1 ) of the green tea were significantly higher than those of the fermented tea. However, the latter showed a significantly higher cytotoxicity against liver cancer cells (inhibiting 73.84% cells at 1 mg mL −1 ). Notably, the green tea had a negligible number of microbes, but the fermented tea had a much richer microbiome with Aspergillus restrictus (4.7 × 10 4 CFU g −1 ), A. ruber (1.76 × 10 3 CFU g −1 ), A. pseudoglaucus (1.32 × 10 3 CFU g −1 ), A. cibarius (8.8 × 10 2 CFU g −1 ), Bacillus cereus (1.13 × 10 4 CFU g −1 ), Peribacillus frigoritolerans (4.0 × 10 2 CFU g −1 ) and B. amyloliquefaciens (2.0 × 10 2 CFU g −1 ) present. These microbes are either harmless or beneficial, except for B. cereus (can cause food poisoning at >10 6 CFU g −1 ). The fermented tea would appear to have some advantages over the green tea. However, the presence and density of B. cereus should be monitored.