Characteristic Aroma Components of Guangnan Dixu Black Tea and Their Changes During Processing

Aroma is a key factor in evaluating tea quality.To investigate the dynamic evolution of aroma compounds during the processing of Guannan Dixu black tea, this study utilized headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS),to systematically analyze changes in volatile compounds at five processing stages: fresh leaves (XY), withering (WD), rolling (RN), fermentation (FJ), and dried tea (GC). Aroma-active values (OAV) and principal component analysis (PCA) were used to identify key aroma compounds at each processing stage. A total of 96 volatile compounds were identified, including alcohols, aldehydes, esters, ketones, alkanes, olefins, and others.The aroma components undergo significant dynamic changes during processing. At the withering (WD) stage, the content of alcohols (such as linalool) decreases, while some aldehydes begin to form. During the rolling (RN) stage, the total amount of volatile compounds increases the most. Aldehydes (such as (E)-2-hexenal), ketones (such as β-ionone), and some alkenes increase significantly. In the fermentation (FJ) stage, aldehydes (such as nonanal) and some esters (such as methyl salicylate) continue to increase in concentration. However, during the drying stage, the total amount of esters sharply decreases due to high-temperature volatilization. At the dried tea (GC) stage, certain alcohol oxides (such as (E)-linalool oxide (pyran)) and aldehydes (such as (Z)-3-nonen-1-ol) reach their peak concentrations. Principal component analysis (PCA) showed that samples from the rolling stage were clearly separated from those of other stages, indicating that rolling is a critical process for aroma formation in Guannan Dixu black tea. In the final dried tea samples, nine key aroma compounds with an odor activity value (OAV) greater than 10 were identified: 2-methylbutanal, heptanal, phenylacetaldehyde, trans-linalool oxide (furan type), nonanal, linalool, (Z)-3-nonen-1-ol, (E)-linalool oxide, and benzaldehyde. Among these, 2-methylbutanal, nonanal, linalool, (Z)-3-nonen-1-ol, and benzaldehyde (all with OAVs greater than 100) made particularly significant contributions. Together, they form the characteristic aroma profile of Guannan Dixu black tea, which features intense floral, sweet, fruity, and fresh grassy notes.