基于代谢组学分析铁观音乌龙茶包揉过程中代谢物动态变化

Metabolomics Analysis of Dynamic Changes in Metabolites in Tieguanyin Oolong Tea during Wrapping-Twisting

为探明包揉对铁观音乌龙茶(简称“铁观音”)品质的影响,以铁观音揉捻叶为原料进行包揉处理,采用广泛靶向代谢组学技术和顶空固相微萃取-气相色谱-质谱联用技术,检测不同包揉阶段的非挥发性及挥发性代谢物。非挥发性代谢物测定结果表明:不同包揉阶段共鉴定出12类973种非挥发性代谢物,其中差异代谢物468种。包揉过程中,非挥发性代谢物总量呈下降趋势,尤其是具有苦涩味的黄酮醇糖苷类和酚酸类差异物质在包揉过程中含量下降,有利于茶汤苦涩感的减轻;脂质类差异物质在包揉过程中含量上升,为后期干燥过程中脂肪酸挥发物的转化提供有利条件。挥发性代谢物测定结果表明:不同包揉阶段共鉴定出6类47种挥发性成分。包揉过程中,具有脂肪香或青草味的β-红没药烯、庚醛、(E)-2-己烯基己酸酯和顺-3-己烯基异丁酸酯含量下降,呈花香或果香的茉莉酸甲酯、苯甲酸苄酯、香叶基丙酮和3,7-二甲基-1,5,7-辛三烯-3-醇含量上升。铁观音的主要呈香成分如芳樟醇、茉莉内酯、顺式茉莉酮、α-法尼烯和罗勒烯等,虽然在包揉过程中含量降低,但在包揉结束时其气味活度值仍然大于1。由此可知,包揉有利于纯化铁观音品质,促使滋味更醇和、花果香更显露,研究为乌龙茶包揉过程中代谢物变化和风味品质形成提供了新的见解。

In order to investigate the effect of wrapping-rolling on the quality of Tieguanyin oolong tea,non-volatile and volatile metabolites in rolled tea leaves before and after repeated wrapping-twisting for up to three times were analyzed by widely targeted metabolomics based on headspace solid-phase microextraction-gas chromatography-mass spectrometry(HS-SPME-GC-MS).The results showed that a total of 973 non-volatile metabolites belonging to 12 categories were identified,including 468 differential metabolites.The total amount of non-volatile metabolites showed a decreasing trend during the wrapping-twisting process.Particularly,the decrease in the content of differential metabolites such as flavonol glycosides and phenolic acids contributed to the reduction in bitterness and astringency during the wrapping-twisting process.The content of differential lipids increased,which provided favorable conditions for the conversion of volatile fatty acids during the subsequent drying process.A total of 47 volatile components belonging to six categories were identified.During the wrapping-twisting process,the contents ofβ-red myrcene,heptanal,(E)-2-hexenyl hexanoate and cis-3-hexenyl isobutyrate,responsible for fatty or grassy aroma,decreased,while the contents of methyl jasmonate,benzyl benzoate,geranyl acetone and 3,7-dimethyl-1,5,7-octatrien-3-ol,contributing to floral or fruity aroma,increased.It was noteworthy that the odor activity value(OAV)of the major aroma components in Tieguanyin oolong tea,such as linalool,jasmonolactone,cis-jasmonone,α-farnesene and basilene,were still greater than 1 at the end of the wrapping-twisting process although their contents decreased during this process.It could be seen that the wrapping-twisting process was beneficial to purify the quality of Tieguanyin tea,and provided it with a more mellow taste and more obvious floral and fruit aromas.This study provides new insights into the metabolite changes and the flavor formation of oolong tea during the wrapping-twisting process.