Characterization of the Key Odorants in a High-Grade Chinese Green Tea Beverage (Camellia sinensis; Jingshan cha) by Means of the Sensomics Approach and Elucidation of Odorant Changes in Tea Leaves Caused by the Tea Manufacturing Process

Sensory-guided analysis of the volatile fraction isolated from a freshly prepared green tea beverage (Camellia sinensis; type Jingshan cha) revealed 58 odor-active compounds after application of an aroma extract dilution analysis. Among them, 3-methylnonane-2,4-dione, (Z)-1,5-octadien-3-one, 3-(methylthio)propanal, trans-4,5-epoxy-(E)-2-decenal, methanethiol, dimethyl sulfide, and indole appeared with the highest flavor dilution factors. A quantitation of 42 aroma compounds by means of stable isotope dilution assays followed by the calculation of odor activity values (OAV; ratio of concentration to odor detection threshold) showed 27 key aroma compounds with OAVs ≥ 1. By far, the highest OAV of 458 was calculated for the asparagus-like/putrid smelling dimethyl sulfide followed by (E,E)-2,4-heptadienal (46). Finally, an aqueous recombinate containing all 27 aroma compounds in the concentrations measured in the beverage successfully mimicked the overall aroma profile of the tea infusion. Quantitative measurements were then performed on authentic tea material to elucidate changes in key aroma compounds during each processing step (fresh leaves, withering, pan-firing, rolling, and drying). The results indicated that dimethyl sulfide, one of the important aroma compounds, was significantly increased by withering of the fresh leaves, however, a major part was lost during drying. Linalool, geraniol, and hexanal showed the highest concentrations in the fresh tea leaves, while significantly lower concentrations were measured in the final tea. The same was observed for all lipid degradation products, such as (E,E)-2,4-heptadienal.