Study on the Accumulation Mechanism of Amino Acids during Bruising and Withering Treatment of Oolong Tea.

Amino acids are very important for oolong tea brisk-smooth mouthfeel which is mainly associated with bruising and withering treatment (BWT). In this study, metabolome and transcriptome analyses were performed to comprehensively investigate the changes in abundance of amino acids and the expression pattern of relevant genes during BWT of oolong tea manufacturing. Levels of most amino acids increased during BWT in the leaves harvested from 4 cultivars, while expression of the relevant function genes responsible for synthesis and transformation of amino acids up-regulated accordingly. Upstream hub genes including receptor-like protein kinase IKU2, serine/threonine-protein kinase PBL11, MYB transcription factor MYB2, ethylene-responsive transcription factor ERF114, WRKY transcription factor WRKY71, aspartate aminotransferase AATC, UDP-glycosyltransferase U91D1, and 4-hydroxy-4-methyl-2-oxoglutarate aldolase 2 RRAA2, were predicted to be involved in regulation of the function genes expression and the amino acids metabolism through weighted gene coexpression network analysis. A modulation mechanism for accumulation of amino acids during BWT was also proposed. These findings give a deep insight into the metabolic reprogramming mechanism of amino acids during BWT of oolong tea.

Formation mechanism of the oolong tea characteristic aroma during bruising and withering treatment.

To elucidate formation mechanism of oolong tea aroma, the released and remaining volatiles during bruising and withering treatment were analyzed using head space solid-phase microextraction/gas chromatography-mass spectrometry. An increase in proportion of the released terpenoid volatiles (TVs) along with a decrease in proportion of the released C6 green leaf volatiles (GLVs) was observed in both cultivars 'Zhejiang139' and 'Foshou'. Proportion of remaining TVs also fluctuated reversely with GLVs although the level of these volatiles increased remarkably. High ratio of TVs to GLVs was the key chemical foundation of oolong tea characteristic aroma and could be regarded as a good indicator in screening cultivar for suitably producing high quality oolong tea. Combining with transcriptome analysis, increased TVs and GLVs during the treatment might be largely generated through de novo synthesis and modulated at transcript level through up-regulation of genes involved in terpenoids metabolism and enzymatic cleavage of long-chain fatty acids.

Studies on the mechanism of efficient extraction of tea components by aqueous ethanol.

Effect of solvent on the extraction yield and its relevant mechanism have been studied in this paper. Compared with extraction by water, catechins and caffeine could be easily extracted from green tea by aqueous ethanol, but hardly at all by absolute ethanol. Results of the vacuum-assisted extraction, solubility determination of EGCG and caffeine, as well as swelling ratio analysis of the infused leaves, indicated that an excellent leaf-matrix-swelling effect and high solubility of tea components might be the key mechanisms for high extraction efficiency by the aqueous ethanol. These mechanisms were further confirmed by the pre-swelling extraction. This is a first report on the mechanism of efficient extraction by aqueous organic solvent. Application of pre-swelling extraction is also discussed.