## 4 Discussion  
### Non-Volatile Signatures and Taste Differentiation  
Taste constitutes the most critical quality indicator for NGBT, accounting for 30% of its sensory evaluation score [29; 39], with non-volatile compounds serving as primary determinants of taste attributes. Among these, theanine, catechins, and caffeine are established as the most influential factors governing tea taste perception [40; 41; 42]. Although the five investigated NGBT cultivars share comparable growing environments, genetic differences  
Figure 8: Correlation analysis of sensory evaluation and characteristics of taste and aroma in 5 NGBTs. Statistical significances are denoted by * for \(p<0.05\) and ** for \(p<0.01\). (**A**) Correlation analysis of sensory evaluation and 15 important factors of taste in 5 NGBTs. (**B**) Correlation analysis of sensory evaluation and 8 important volatile compounds of aroma in 5 NGBTs.  
emerge as the dominant factor driving compositional variation in these compounds [20; 34]. Our HPLC quantification revealed significant inter-cultivar differences in theanine, catechin, and caffeine levels, while OPLS-DA modeling identified total catechins, simple catechins, CG, EGCG, esterified catechins, and EGC as discriminative non-volatile markers, establishing a direct linkage between chemical signatures and sensory profiles.  
Sensory evaluation confirmed distinct taste characteristics among the cultivars. Theanine, a known sweet-tasting compound, activates umami receptors while suppressing bitterness perception [13; 31; 43; 44]. Notably, JSH and YH] exhibited significantly elevated theanine content compared to other NGBTs, correlating with their superior sweetness and freshness scores. Conversely, DXE's low theanine content aligned with its reduced performance in these attributes. Correlation analysis further demonstrated significant positive relationships between theanine and freshness, as well as between theanine and sweetness, while revealing a significant negative correlation with astringency--mechanistically explaining DXE's pronounced astringency. Catechins, recognized contributors to bitterness and astringency [45], showed an inverse pattern: JSH and YH]'s lower total catechin levels, combined with negative correlations between total catechins and both sweetness (\(p<0.05\)) and freshness (\(p<0.05\)), collectively enhanced their sweetness/freshness perception while reducing astringency. While caffeine and theobromine typically impart bitterness that compromises sweetness and freshness [46], their unexpected correlation patterns here likely reflect the combinatorial nature of taste perception, where individual compounds rarely dictate overall quality in isolation.  
Critically, the T/F ratio emerged as a fundamental biochemical indicator for taste balance, sharply distinguishing JSH and YH] from DXY, DXE, and QTZ and explaining the former group's characteristic fresh-sweet profile. The observed compositional differences are governed by multiple factors: Catechins undergo oxidation into theaflavins/thearubigins during processing [47], with their accumulation further influenced by seasonal variations and bud-to-leaf ratio at harvest. Meanwhile, theanine biosynthesis is regulated by glutamine synthetase, glutamate synthase and glutamate dehydrogenase enzyme activity, and _CsTS1_, _CsAlaDC_, and _CsGS_ gene expression [44]. These factors collectively determine the elevatedanine-catechin ratio in JSH and YH]. Consequently, strategic optimization of processing protocols, harvest season, plucking standards, and cultivar selection is essential for enhancing the taste quality of NGBTs.