A meta-analysis of dynamic changes of key aroma compounds during black tea processing

Black tea aroma is composed of volatile flavour compounds at different concentrations generated during the manufacture of black tea. The common process of black tea production consists of four stages: withering, rolling, fermentation, and firing. However, no systematic review and meta-analysis study on the volatile components during black tea processing was conducted. The present study evaluated the changes of the volatile compounds in black tea processing through a systematic review and meta-analytic approach. The results revealed that the content of phenylacetaldehyde and (E)-2-octenal significantly increased during the withering process, which was attributed to glycoside hydrolysis and amino acid reactions. During the rolling process, the content of (E)-2hexenal increased, which may be due to the oxidation of fatty acids. During the fermentation process, the content of phenylacetaldehyde, (E)-2-octenal, and trans-beta-ionone increased through enzymatic and oxidative effects. The withering, rolling, fermentation, and drying processes played crucial roles in the formation of black tea aroma and had significant effects on the key odorants in black tea. These findings provide important insights into optimizing processing parameters in commercial black tea production.