Journal of Tea Science Research, 2024, Vol.14, No.5, 249-261 http://hortherbpublisher.com/index.php/jtsr 253 5.2 Chemical composition and health benefits The chemical composition of tea, including its polyphenols, amino acids, and other bioactive compounds, is profoundly affected by fermentation conditions. For example, fermentation temperature has been shown to influence the levels of polyphenols, polysaccharides, and catechins in black tea. Lower fermentation temperatures can enhance the antioxidant activities and inhibitory effects on enzymes such as α-glucosidase, contributing to the health benefits of tea (Qu et al., 2020). Oxygen-enriched fermentation can also modify the non-volatile metabolites in black tea, reducing bitterness and astringency while enhancing umami intensity by altering the levels of catechins, flavonoid glycosides, and phenolic acids (Chen et al., 2021). Furthermore, the use of specific microorganisms during fermentation can improve the nutritional value and functional components of tea, such as increasing the content of amino acids and reducing caffeine levels (Li et al., 2018; Cui et al., 2021). 5.3 Consumer preferences and quality perception Consumer preferences and quality perception of tea are closely linked to its sensory attributes, which are influenced by fermentation conditions. Sensory evaluations have shown that black tea fermented at optimal temperatures, such as 28 °C, received higher scores for aroma and taste compared to those fermented at higher temperatures (Qu et al., 2020). The reduction of bitter and astringent metabolites through oxygen-enriched fermentation also contributes to a more favorable taste profile, enhancing consumer satisfaction (Chen et al., 2021). Additionally, the fermentation of autumn green tea with specific fungi has been found to improve its aroma and reduce astringency, making it more appealing to consumers (Xiao et al., 2021). The optimization of fermentation conditions, including temperature, time, and pH, can thus lead to the production of tea with superior sensory qualities and higher overall acceptability (Tang et al., 2018). By understanding and optimizing the fermentation conditions, tea producers can significantly enhance the physical attributes, chemical composition, and sensory qualities of tea, ultimately improving its marketability and consumer satisfaction. 6 Case Studies 6.1 Optimized fermentation in black tea production Optimizing fermentation conditions is crucial for enhancing the flavor and quality of black tea. Various studies have explored different parameters to achieve the best results (Figure 2). For instance, oxygen-enriched fermentation has been shown to significantly improve the taste of black tea by reducing bitter and astringent metabolites. This process involved a 10%-30% decrease in catechins, flavonoid glycosides, and phenolic acids, and a 5% increase in theaflavins, glutamate, and glutamine, which collectively enhanced the umami intensity and reduced astringency and bitterness (Chen et al., 2021). Another study identified that fermenting black tea at 28 °C yielded the best sensory quality, with the highest scores for aroma and taste, and also demonstrated strong antioxidant activities (Qu et al., 2020). Additionally, re-rolling treatment during fermentation has been found to improve the aroma quality of black tea, imparting floral and fruity scents by altering the levels of various VOCs (Chen et al., 2023). The plots for Theaflavin (A, B, C) showed that its levels were significantly influenced by fermentation time and temperature, with optimal conditions leading to higher concentrations. Similarly, Thearubigin (D, E, F) levels were affected by all three factors, showing complex interactions that required precise control for desired outcomes. High Polymeric Substances (G, H, I) and Total Liquor Color (J, K, L) were also sensitive to these variables, impacting the overall quality and appearance of the tea. Total Phenolic Content (M, N, O) showed less variation with changes in conditions, suggesting a more stable component during fermentation. Finally, the TF to TR ratio (P, Q, R) was crucial for determining the balance of astringency and color in tea, highlighting the importance of optimizing fermentation conditions for the best sensory attributes.
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