Analysis of the Physicochemical Quality and Key Aroma Components of Yihong Congou Black Tea in Different Seasons

To investigate the physicochemical properties and key aroma compounds of Yihong congou tea across different seasons, a multidisciplinary methodology was employed, integrating sensory evaluation, colorimetry, standardized physicochemical assays, headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS), and gas chromatography-olfactometry (GC-O). Samples of spring-, summer-, and autumn-harvested teas from high-altitude regions were systematically analyzed. Results showed that significant seasonal differences were found in physicochemicals. Spring tea exhibited the highest amino acid content (4.13%, P<0.05) and sensory evaluation scores, along with the highest volatile compound concentration (1633.68 μg/kg, P<0.05). Summer tea had the more content of polyphenols (10.76%, P<0.05), while autumn tea showed increased soluble sugar content (5.69%, P<0.05). 63 volatile compounds were identified across seasons, including 40 common to all samples. Orthogonal partial least squares-discriminant analysis (OPLS-DA) and variable importance in projection (VIP) identified 7 key discriminators (VIP>1, P<0.05): Nerol, linalool, methyl salicylate, (E)-2-hexenal, nonanal, linalool oxide I, and citral. GC-O analysis detected 18 aroma-active compounds. Phenylacetaldehyde, linalool oxide II, linalool, and β-ionone demonstrated high aroma intensity (AI>2.5). A comparative analysis of the aroma components in Yihong Gongou tea across different seasons showed notable seasonal differences in phenethylaldehyde, a key element of floral sweetness. Higher aroma levels of linalool oxide II, and (E)-furanoid linalool oxide were found in spring tea. In summer tea, higher aroma intensity values were observed for linalool, N-butyric acid (trans)-2-hexenyl ester and α-phellandrene. The woody aroma compound α-terpineol was only found in autumn tea. Integrated analysis of GC-O and relative odor activity value (ROAV) established linalool (ROAV>10, AI>3.0), nerol (ROAV>10, AI>2.5), β-ionone (ROAV>1, AI>2.5) and nonanal (ROAV>1, AI>2.0) were the key aroma compounds. These findings could provide a theoretical foundation for enhancing the quality of Yihong Congou tea and the utilization of fresh leaf resources.