Metabolome analyses of two varieties of Anhua dark tea

We performed volatile and nonvolatile metabolome analysis of Zhuyeqi (Z) and Baihaozao (B) dark teas during three stages of tea processing: (1) after withering and kneading (S), (2) after pile-fermenting (M), and (3) during drying and second kneading (Z). Our results indicate that the Z variety was rich in glycerophospholipids, isoflavonoids, morphinans, organic oxides, organic phosphonic acids, purines, and thiadiazines. A total of 427 metabolites were differentially accumulated between Z and B during three stages of processing (S, M, and Z). These metabolites were significantly enriched in ABC transporters, flavonoid biosynthesis, tyrosine metabolism, glutamic acid, linoleic acid metabolism, etc. Epicatechin, phenylacetic acid, (-)-cis-carveol, and neochlorogenic acid had higher levels in Z. Forty-three volatile compounds were differentially accumulated in BvsZ and their accumulation levels were affected by processing. The variety Z had a higher relative percentage of alcohols, and esters. Forty-six of the 75 substances contributed to the tea aroma. ZT had compounds with higher ROAV values such as furan (caramel-like and sweet fruity), 2-pentyl- (green beans, vegetable), heptanal (citrus, fatty, and rancid), and others. In total, 113 unique flavors were associated with substances that accumulated at higher levels in ZT. Our results suggest that Z offers a better composition and flavor profile than B due to the higher quantities of several health beneficial and taste-related compounds at the same processing stages.

本研究针对竹叶奇（Zhuyeqi, Z）与白毫早（Baihaozao, B）两个黑茶品种，在三大加工阶段——(1)萎凋与揉捻后（S）、(2)渥堆发酵后（M）以及(3)干燥与二次揉捻阶段（Z）——的挥发性与非挥发性代谢组开展了分析。结果表明，竹叶奇品种富含甘油磷脂、异黄酮类、吗啡烷类、有机氧化物、有机膦酸类、嘌呤类及噻二嗪类化合物；在三个加工阶段中，竹叶奇与白毫早间共鉴定得到427种差异积累代谢物，此类代谢物显著富集于ABC转运蛋白、黄酮类生物合成、酪氨酸代谢、谷氨酸代谢、亚油酸代谢等通路。表儿茶素、苯乙酸、(-)-顺式香芹醇及新绿原酸在竹叶奇中的含量更高；在白毫早与竹叶奇（BvsZ）的比较中，共有43种挥发性化合物存在积累差异，且其积累水平受加工过程影响。竹叶奇的醇类与酯类相对占比更高；75种挥发性物质中有46种对茶叶香气具有贡献。竹叶奇茶样（ZT）中部分化合物的香气活力值（Relative Odor Activity Value, ROAV）更高，例如2-戊基呋喃（类焦糖甜果香）、庚醛（柑橘、脂肪及哈喇味）等；总计113种独特风味物质与竹叶奇茶样中高积累的代谢物相关。本研究结果显示，相较于白毫早，竹叶奇在相同加工阶段中因含有更多有益健康及与风味相关的化合物，故而具备更优的组分组成与风味特征。