Green tea, a widely consumed beverage, is valued for its health benefits and complex taste profile, where bitterness and astringency are key sensory attributes. Tea polyphenols, including catechins and phenolic acids, significantly influence these tastes. Catechins, particularly galloylated catechins like ECG and EGCG, strongly correlate with bitterness and astringency. Phenolic acids, such as gallic acid (GA), chlorogenic acid (CGA), and caffeic acid (CA), contribute sourness and astringency, with their concentrations impacting taste intensity. Flavonol glycosides, like Que-rut, also influence taste, imparting a soft astringency. Previous research highlights taste interactions within green tea, with EGCG synergistically enhancing bitterness and astringency of caffeine while inhibiting sucrose sweetness. However, the individual contributions of phenolic acids and Que-rut to green tea's taste profile remained unclear. This study aimed to investigate the contributions of phenolic acids and Que-rut to the bitterness and astringency of green tea infusion, aiming to provide a theoretical foundation for improving green tea's taste.

Existing literature establishes the importance of polyphenols in green tea's sensory qualities. Studies show strong correlations between catechin concentrations, especially galloylated catechins (ECG, EGCG), and both bitterness and astringency. Research on phenolic acids indicates their contribution to sour and astringent tastes, with GA and CGA showing positive correlations with bitterness and astringency in white tea. Flavonols, particularly Que-rut, have also been identified as contributors to the astringent taste of tea, particularly black tea. Prior work has examined taste interactions; for instance, EGCG's interaction with caffeine and sucrose. However, a comprehensive understanding of how phenolic acids and Que-rut influence green tea's bitterness and astringency remains limited, prompting this study.

Sixteen green tea samples were collected and their infusions prepared using a standard brewing method. Sensory evaluation, involving five trained panelists, assessed the bitterness and astringency on a ten-point scale (0-10). The concentrations of major polyphenols, including catechins, flavonols (including Que-rut), and phenolic acids (GA, CGA, CA), were determined using HPLC and UPLC-QE-Orbitrap-MS. Correlation analysis examined relationships between polyphenol concentrations and sensory scores. Dose-over-threshold (Dot) factors were calculated to quantify each component's contribution to taste. Taste interactions were analyzed by comparing sensory scores of mixtures of EGCG with phenolic acids/Que-rut and comparing these scores to the sum of individual component scores. Similar interactions were analyzed between green tea infusions and phenolic acids/Que-rut at various concentrations. Statistical analysis involved one-way ANOVA (SPSS Version 22.0) to determine significant differences (p<0.05).

Sensory evaluation revealed bitterness scores ranging from 3.00 ± 0.07 to 6.03 ± 0.04 and astringency scores from 2.95 ± 0.07 to 6.00 ± 0.00. A strong correlation (r=0.931, p<0.01) existed between bitterness and astringency. Correlation analysis showed significant positive relationships between total tea polyphenols, individual catechins (especially ECG and EGCG), flavonols (including Que-rut and its related compounds), phenolic acids (GA, CGA), and both bitterness and astringency intensities. Dot factor analysis identified ECG and EGCG as major contributors to bitterness, while EGC, ECG, EGCG, Kae-rut, Que-rut, and several other flavonols were major contributors to astringency. Que-rut exhibited the highest Dot factor (average 4113.99). Concentration-taste intensity curves for phenolic acids and Que-rut fit cubic functions (R² >0.998). Studies of taste interactions with EGCG showed that GA, CGA, CA, and Que-rut enhanced EGCG's bitterness, but had a more complex effect on astringency. At lower concentrations, CA, CGA, and Que-rut inhibited EGCG's astringency, while at higher concentrations, a synergistic effect was observed. GA consistently enhanced EGCG's astringency across all concentrations. Interactions between green tea infusion and phenolic acids/Que-rut showed synergistic enhancement of bitterness and astringency, increasing with concentration. Low concentrations of CA, CGA, and Que-rut inhibited EGCG astringency, yet enhanced astringency in the green tea infusion, possibly due to interactions with other compounds or increased mouth sensitivity in the complex mixture.

The findings confirm the critical roles of phenolic acids and Que-rut in shaping green tea's taste profile. Their synergistic effects with other polyphenols, particularly EGCG, highlight the complexity of taste interactions in this mixed system. The differing effects of phenolic acids and Que-rut on EGCG's astringency, compared to their effects in the complete green tea infusion, suggest that these compounds may interact differently with other components in the mixture, or the overall sensitivity of the mouth to these compounds may change in a complex mixture. These findings support the idea that astringency in green tea is not solely determined by catechin concentration. The concentration-dependent synergistic effects emphasize the potential for manipulating these compounds to optimize green tea's taste.

Phenolic acids (GA, CGA, CA) and Que-rut significantly contribute to the bitterness and astringency of green tea. These compounds interact synergistically with EGCG and other components in the infusion, enhancing bitterness and astringency. Future research should explore the specific interactions of these compounds with other taste components in green tea to further refine our understanding of taste development and to guide strategies for improving green tea quality.

The study used a limited panel of trained tasters, which might limit the generalizability of the findings. Further investigation using larger panels and diverse green tea varieties is recommended. The study focused primarily on bitterness and astringency; exploring other taste attributes (umami, sweetness) and their interactions with phenolic acids and Que-rut would provide a more comprehensive understanding of the overall sensory experience.