Impact of Different Aspergillus Fermentation Combinations on the Quality Components and Color of Summer and Autumn Tea Infusion

To enhance the economic value-added of summer and autumn teas, this study conducted separate and combined liquid-state fermentation of the tea infusions using Aspergillus niger and Aspergillus oryzae, followed by a detailed analysis of changes in quality components and color during fermentation, as well as the correlation between tea pigments, pH, and chroma values. The results indicated that the individual inoculation of Aspergillus niger had the most significant degradation effect on tea polyphenols and caffeine (P<0.05), with a reduction of 1261.17 μg/mL in tea polyphenols and 61.52 μg/mL in caffeine content. Whereas the individual inoculation of Aspergillus oryzae helped to preserve more catechins and gallic acid. Mixed fermentation was conducive to the synthesis of theabrownin, with its content reaching up to 1779.12 μg/mL after 48 hours. Sensory evaluation and chroma value measurements showed that Aspergillus fermentation could rapidly transform the tea infusion color from light yellow to dark reddish-brown, with a significant decrease in L^* and a marked increase in a^* and b^* (P<0.05). Correlation analysis revealed that theaflavins were significantly and positively correlated with L^* (P<0.05). Thearubigins were also significantly and positively correlated with L^*, but significantly and negatively correlated with a^* and b^* (P<0.05). In contrast, theabrownin showed a significant negative correlation with L^*, but a significant positive correlation with a^* and b^* (P<0.05), indicating that an increase in theabrownin content would reduce the brightness of the tea infusion and enhance the reddish-brown tone. Furthermore, pH was significantly and positively correlated with theabrownin synthesis (P<0.05), indicating that an increase in pH was beneficial for promoting the synthesis of theabrownin. In summary, this study provides a scientific basis for the development of diversified products of summer and autumn teas and is of significant importance for promoting the sustainable development of the tea industry.