Mechanisms of single and mixed microbial fermentation to improve summer-autumn green tea.

To investigate the effect of individual and collaborative fermentation on summer-autumn green tea (SAGT) quality. Liquid fermentation with individual inoculation of Aspergillus cristatus (ACFT), Aspergillus niger (ANFT) and mixed inoculation of A. cristatus / A. niger (MFT), respectively, with SAGT extracts (CT) as raw materials. The volatile organic compounds (VOCs), characteristic non-volatile compounds and sensory evaluation of tea samples were determined. The results showed a significant decrease in the content of tea polyphenols, carbohydrates and nongalloylated catechins (C, EC) and a significant increase in the amount of VOCs in MFT compared to ANFT and ACFT. The results of metabolic pathway analysis and sensory evaluation showed that ACFT went through the terpene and phenylpropanoic acid metabolic pathway, which produced large amounts of α-terpineol, phenethyl alcohol, and methyl salicylate, which in turn conferred ACFT with distinctly sweet, floral, and herbal aroma. ANFT produces large amounts of linalool oxides I and II, mainly through the linalool oxide metabolic pathway, making ANFT a distinctive aged and woody aroma. MFT may be due to the strong woody aroma of linalool oxides masking other weaker and better aromas, thus giving MFT a significant woody, herbal and stale aroma. This study provides new insights and a theoretical basis for mixed fungal fermentation to improve the quality of SAGT. [Display omitted] • Mixed fermentation is expected to be a new way to improve the quality of summer-autumn green tea. • Synergistic action of microorganisms produces more volatile organic compounds. • Mixed fungi fermentation is better in nongalloylated catechins (C, EC) degradation. • Differences in key VOCs synthesis pathways between A. cristatus and A. niger. [ABSTRACT FROM AUTHOR]