Camellia sinensis var. assamica is a major variety used to produce black tea. However, the core compounds influencing its aroma quality are unknown. In this study, Yinghong No. 9 black tea (YJBT), a distinctive black tea in South China, was analyzed. We detected 44 aroma compounds and identified seven key contributors, namely linalool, geraniol, trans -linalool oxide (furanoid), hexanal, methyl jasmonate, phenylacetaldehyde, and β-ionone. Linalool, which was generally more abundant in spring tea than in summer tea, contributed significantly to sweet and floral aromas. ( R )-Linalool was the primary linalool form in Yinghong No. 9, wherein it was highly abundant in high-quality tea leaves. The substantial expression of a linalool synthase gene and the relatively high catalytic efficiency of the encoded enzyme likely contributed to the accumulation of ( R )-linalool. This study identified the primary aroma compounds in YJBT, providing a foundation for advancing our knowledge of the aromatic quality of black tea.
Linalool is abundant in tea leaves and contributes greatly to tea aroma. The two isomers of linalool, (R)-linalool and (S)-linalool, exist in tea leaves. Our study found that (R)-linalool was the minor isomer in nine of Camellia sinensis var. sinensis cultivars. The (R)-linalool synthase of tea plant CsRLIS was identified subsequently. It is a chloroplast-located protein and specifically catalyzes the formation of (R)-linalool in vitro and in vivo. CsRLIS was observed to be a stress-responsive gene and caused the accumulation of internal (R)-linalool during oolong tea manufacture, mechanical wounding, and insect attack. Further study demonstrated that the catalytic efficiency of CsRLIS was much lower than that of (S)-linalool synthase CsSLIS, which might explain the lower (R)-linalool proportion in C. sinensis var. sinensis cultivars. The relative expression levels of CsRLIS and CsSLIS may also affect the (R)-linalool proportions among C. sinensis var. sinensis cultivars. This information will help us understand differential distributions of chiral aroma compounds in tea.
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