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 (HSSPME-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 of β-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.

The aroma and taste profiles of Qingxiang Tieguanyin tea from different regions were determined through sensory evaluation and quantitative descriptive analysis of sensory attributes. By gas chromatography-mass spectrometry (GC-MS), biochemical composition analysis, ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) and metrological statistical analysis, the aroma and taste constituents of the tea were determined. The correlation between aroma and taste components and aroma and taste attributes was explored by correlation analysis and regression analysis, and the correlation between taste components and taste attributes was verified through experiments. The results showed that the sensory quality of Qingxiang Tieguanyin tea had regional characteristics and the aroma composition was dominated by terpenoids, followed by esters. Water content, water extract content, total tea polyphenols content and theaflavins content were the major biochemical factors responsible for the taste quality.