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

Abstract

SummaryCamellia 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 (IC50 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 × 104 CFU g−1), A. ruber (1.76 × 103 CFU g−1), A. pseudoglaucus (1.32 × 103 CFU g−1), A. cibarius (8.8 × 102 CFU g−1), Bacillus cereus (1.13 × 104 CFU g−1), Peribacillus frigoritolerans (4.0 × 102 CFU g−1) and B. amyloliquefaciens (2.0 × 102 CFU g−1) present. These microbes are either harmless or beneficial, except for B. cereus (can cause food poisoning at >106 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.