Associations Between Mineral Element Profiles, Biochemical Composition and Flavor Characteristics of Tieguanyin Oolong Tea Cultivated at Varied Altitudes

Mineral elements are components of metabolites in tea plants and directly contribute to taste formation in brewed tea infusions. Like quality-related compounds such as tea polyphenols and free amino acids, their accumulation and leachability are strongly influenced by growing conditions. To investigate the relationships between mineral elements and flavor quality, 56 Tieguanyin tea samples collected across different elevation gradients were analyzed. Unlike previous altitude-related studies that mainly focused on conventional metabolites, this study simultaneously examined mineral element contents in both dry tea leaves and brewed infusions, together with sensory evaluation and the quantification of tea polyphenols, free amino acids, caffeine, and catechin metabolites. Compared with low-elevation teas (300–400 m), high-elevation teas (600–800 m and above 800 m) exhibited superior flavor quality, with higher free amino acids and tea polyphenols, and lower phenol-to-amino acid ratios and caffeine contents, whereas catechin metabolites showed only a weak association with elevation. In dry tea leaves, analysis of total mineral elements indicated that higher magnesium (Mg) and phosphorus, together with lower aluminum, copper, manganese, and cobalt, were positively associated with both elevation and tea quality. In brewed tea infusions, Mg was positively correlated with quality, whereas sodium (Na) and potassium (K) were negatively associated. Notably, Na was 47% higher and K was 8% higher in teas from above 800 m than in those from 600–800 m, enabling further separation of the two high-elevation groups. These findings provide a scientific basis for improving Oolong tea quality through optimized cultivation practices and nutrient regulation.