Decoding the Flavor Code of Ninghong Black Tea: A Metabolomic-Sensory Integration Revealing Hierarchical Signatures of Key Aroma and Taste Compounds

To elucidate grade-dependent flavor patterns of Ninghong black tea (NBT), an integrated method combining metabolomics, sensory evaluation with multivariate analysis was employed. Chromatographic analyses resolved 73 volatile and 31 non-volatile compounds. Eighteen key volatile compounds were screened based on variable importance in projection (VIP > 1, p<0.05). Among these, 11 components, notably β-ionone, linalool, geraniol, and (2E,4E)-2,4-heptadienal, had OAV > 1, significantly contributing to floral and fruity aroma. For non-volatile compounds, 11 metabolites (caffeine, epigallocatechin, gallic acid, epicatechin gallate, epigallocatechin gallate, theanine, arginine, glutamic acid, tryptophan, serine, and gallocatechin) were identified as key taste contributors, with the first eight compounds exhibiting TAV > 1, identifying them as the primary drivers of​ bitterness, astringency, and umami. Multivariate analysis (Principal Component Analysis, PCA; Partial Least Squares Discriminant Analysis, PLS-DA; hierarchical clustering; fold change) of 29 marker compounds clearly differentiated four quality grades into Jinhao and Congou categories. The differential abundance patterns of key symbolic metabolites (e.g., β-ionone, ECG, and GC with FC differences), which mark the significant metabolic differences between categories, were consistently mirrored in sensory evaluations. Premium NBT characteristics included: tightly twisted leaves with golden pekoe, bright orange-red liquor, tender floral aroma, brisk/mellow taste, and reddish-bright uniform buds. This study deciphers the hierarchical chemical signatures underlying the sensory quality of NBT grades, and provides a theoretical basis for flavor quality evaluation, with symbolic metabolites serving as objective indicators for grade differentiation and quality control in the tea industry.