Comparison of chemical constituents of Eurotium cristatum-mediated pure and mixed fermentation in summer-autumn tea

Eurotium cristatum, isolated from the unique stage of "fahua" in Fuzhuan brick tea, contributed greatly to aroma formation of fermented tea. This study aimed to characterize the main amino acids, tea polyphenols, volatile organic components (VOCs) and sensory qualities both in pure (E. cristatum) and mixed fermentation (E. cristatum, Aspergillus niger and Penicillium oxalicum) with summer-autumn tea as substrate. Amino acid content increased by 10.7% and 14.3% both in pure and mixed fermentation, respectively. Differently, tea polyphenols decreased rapider in pure fermentation (6%) than mixed fermentation (2.7%). Venn diagram indicated that more kinds of VOCs (286) were produced by synergetic effect of mixed strain compared with pure fermentation. PCA was performed to visualize the differences of VOCs, 2,6-dimethyl-1,5-heptadiene (93) and 2-ethyl-1-hexanol (95) were closely related to mixed fermentation, whilst, trans-linalool oxide (furanoid) (118), acetone (120), d-limonene (123) and diazene, dimethyl- (125) were closely related to pure fermentation. Moreover, two-way ANOVA exhibited that the effect of starters (F, 7940.846) on VOCs is more significant compared with fermentation time (F, 421.813). Mixed fermentation product provided better sensory proterties with the higher yield of 11.83% and score of 87.81 than pure fermentation. In summary, mixed fermentation of E. cristatum combined other strains may be a new channel to develop wasted summer-autumn tea.