Comprehensive analysis of the flavor and color characteristics of light-fermented sour tea mediated by aspergillus Niger RAF106

Light-fermented sour tea (ST) was produced by fermenting the Yunnan large-leaf variety of sun-dried green tea (GT) with Aspergillus niger RAF106. The flavor characteristics of both ST and GT were analyzed using GC–MS, HPLC, and LC-MS/MS. The results indicated that 58 volatile compounds were identified after fermentation, including linalool, benzaldehyde, geraniol, and (+)-limonene (odor activity value, OAV > 1). A total of 66 non-volatile compounds were identified, including caffeine, gallic acid, epicatechin, and epigallocatechin (degree over threshold, DoT >1). The content of non-ester catechins, theanine, L* (luminosity), b* (yellowness), theaflavins, and thearubigins significantly increased. The changes in volatile and non-volatile compounds contributed to ST its rich floral aroma, sweet aftertaste, and bright yellow color of the soup. These results enhance the understanding of the flavor characteristics of ST and the effect of A. niger RAF106 fermentation on tea flavor, highlighting the crucial role of microorganisms in tea flavor development.