The Impact of Brewing Water pH on Green Tea Infusion Flavor Quality: A Microstructural Perspective of Tea Leaves

The pH of brewing water plays a significant role in shaping the microstructure of tea leaves, thereby affecting the flavor profile of green tea infusions. In this study, green tea was brewed using water with seven different pH levels to examine microstructural alterations and their impact on flavor quality. Results showed that the contents of total volatile compounds, tea polyphenols, and soluble sugars initially decreased and then increased with rising water pH, a trend consistent with changes in the degree of tea leaf damage. This indicates that the damage status of the leaves considerably influenced the release of these flavor components. Sensory evaluation revealed notable differences among infusions: T1, derived from the most severely damaged leaves, exhibited the strongest floral aroma, while T7 had the most intense chestnut aroma along with a dull odor. Both T1 and T7 also showed prominent bitterness and astringency. Partial least squares discriminant analysis (PLS-DA) identified 19 key flavor compounds contributing significantly to aroma profiles. Further partial least squares regression (PLSR) analysis correlated high concentrations of 1-hexadecanol, dodecanal, acetic acid, and nonanal in low-pH infusions with clean, refreshing, and flowery aroma, whereas diisobutyl phthalate was associated with dull odor. These findings offer important insights into how brewing water pH modulates the physicochemical and sensory properties of green tea.