Black Tea Quality is Highly Affected during Processing by its Leaf Surface Microbiome

Microbiomes can greatly affect the
quality of fermented food and
beverages, including tea. In this study, microbial populations were
characterized during black and green tea manufacturing, revealing
that tea processing steps can drive both the bacterial and fungal
community structure. Tea leaves were found to mostly harbor Proteobacteria,
Bacteriodetes, Firmicutes, and Actinobacteria among bacteria and Ascomycetes
among fungi. During processing, tea microbial populations changed
especially between sterilized and unsterilized samples. The surface
sterilization of fresh leaves before processing can remove many microbes,
especially the bacteria of the genera Sphingomonas and Methylobacteria, indicating that
these are mostly phylloplane microbes on tea leaves. The surface sterilization
removed most fungi, except the Debaryomyces. We also observed a fluctuation in the content of several tea quality-related
metabolites during processing. Caffeine and theanine were found in
the same quantities in green tea with or without leaf surface sterilization.
However, the sterilization process dramatically decreased the content
of total catechins and theanine in black tea, indicating that microbes
on the surface of tea leaf may be involved in maintaining the formation
of these important metabolites during black tea processing.