A special “Golden Flower” fungus with yellow cleistothecium: Its impact on the flavor of golden flower loose tea produced from summer-autumn tea

Summer-autumn tea leaves are abundant, yet their utilization remains low. Our study enhances the quality and flavor of Golden Flower loose tea (GFLT) from fresh summer-autumn tea leaves by using a special “Golden Flower” fungus (strain ACF-2). The strain ACF-2, identified as Aspergillus cristatus with yellow cleistothecium and isolated from Fu Brick Tea, was characterized by colony morphology, microstructural analyses, and phylogenetic examination using a 3-gene dataset (BenA, CaM, RPB2). Inoculation of raw dark tea products with A. cristatus led to a significant increase in tea water extract and a reduction in tea polyphenols, soluble sugars, flavonoids, and total amino acids, thereby enhancing the quality and flavor of GFLT. HS-SPME-GC-MS analysis of GFLT aroma revealed that A. cristatus substantially improved the tea’s aroma profile. 9 volatile compounds—(Z)-jasmone I, β-cyclocitral, linalool oxide I, linalool, hexanal, 1-octen-3-ol, (Z)-citral, citral, and methyl salicylate, were found to be significantly elevated in GFLT compared to the controls. Our findings provide both theoretical and practical insights into optimizing the utilization of summer-autumn tea leaves, identifying the “Golden Flower” fungus, and understanding its impact on GFLT quality. In summary, fermenting A. cristatus to produce GFLT may be a new channel to utilize summer-autumn tea.