Non-targeted Metabolomic Analysis of Aroma Metabolites of Black Teas from Different Production Regions in China

Non-targeted metabolomics based on headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS), multivariate data analysis and odor activity value (OAV) were integrated to clarify the aroma metabolites in representative black tea samples from different production regions of China and also to determine their key aroma compounds. The results indicated that a total of 140 aroma metabolites were identified in this study, which were classified into 12 types based on their chemical structures, including alcohols, esters, aldehydes, acids, ketones and alkenes. The proportion of alcohols in the total aroma compounds was quite high, ranging from 22.90% to 47.16%. Jiangsu black tea had the highest content of alcohols, followed by Jiangxi, Hubei, Guangdong, Zhejiang, and other regions, while Shandong tea samples had the lowest value. Esters accounted for 2.75% to 26.30% of the total aroma compounds, with the relative content of esters being significantly higher in China Taiwan black tea than tea samples from other regions. Sensory evaluation revealed that all black tea samples shared the common characteristic of sweet aroma, yet each had unique characteristics, presenting a diverse range of aromas, such as medicinal sweet, ripe sweet, roasted sweet, fruity sweet and honey sweet aromas. Black tea samples from Luokeng, Guangdong had a rich almond-like aroma and received the highest score of 96.0 in sensory evaluation. Partial least squares-discriminant analysis (PLS-DA) allowed clear differentiation black tea samples from different regions of China, and 27 differential aroma metabolites were identified based on variable importance in projection (VIP) values > 1.0, among which seven including linalool, phenylethanol, phenylacetaldehyde, methyl salicylate, hexanoic acid, 1-methylnaphthalene, and geraniol had aroma activity with OAV > 1. Methyl salicylate in China Taiwan black tea, as well as phenylacetaldehyde in Guangdong black tea could serve as a marker aroma metabolite to differentiate them from those produced elsewhere. This study offers a scientific basis for identifying the aroma quality of black tea from different regions of China.