This study is aimed to explore the effects of different full drying methods (far infrared, microwave, re-drying, carding, and rotary pot full drying) on the color and chlorophyll degradation of green tea. A method for the analysis of chlorophylls and their degradation derivatives in tea was established based on ultra-high performance liquid chromatography quadrupole orbitrap high resolution mass spectrometry (UPLC-Q-Exactive Orbitrap-MS). A total of 19 chlorophylls and degradation derivatives were detected within 20 min, and six pairs of epimeric chlorophylls and chlorophyll derivatives were well separated with simple sample pretreatments. For the purpose of the present study, this method was applied to analyze chlorophylls and their degradation products in green tea samples manufactured by the five different full drying methods, and the data were analyzed by orthogonal partial least square-discriminant analysis (OPLS-DA) and one-way analysis of variance (ANOVA). The results showed that compared to the other full drying methods, green tea prepared by microwave full drying had better sensory color and quality. The contents of chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll a’(Chl a’) and chlorophyll b’ (Chl b’) were the highest in green tea prepared by microwave full drying, while the contents of pyropheophorbide a (PyrPo a), pyropheophorbide b (PyrPo b), pyropheophytin a (PyrPhe a) and pyropheophytin b (PyrPhe b) were the lowest, indicating that microwave full drying resulted in the lowest degree of isomerization, magnesium removaland degradation reaction and decarboxymethylation. Therefore, microwave full drying is more beneficial to the protection of chlorophylls in green tea. This study can provide a theoretical basis and technical guidance for quality improvement and directed processing of green tea.

This research was undertaken to explore the effects of different rolling speeds (35, 45, 55 and 60 r/min) on the flavor quality and internal quality components of Congou black tea from the Jiukeng cultivar. Flavor attributes including taste and color were determined by sensory evaluation, color difference analysis and electronic tongue analysis. Quantitative analysis of tea pigments and theaflavin components were performed by systematic analysis and high-performance liquid chromatography (HPLC). In addition, metabolomics based on ultra-high performance liquid chromatography-quadrupole orbitrap high resolution-mass spectrometry (UPLC-Q-Orbitrap-MS) was used to determine the non-volatile compounds in Congou black tea. Partial least squares discriminant analysis (PLS-DA) and one-way analysis of variance (ANOVA) were used to investigate the effect of different rolling speeds on the internal quality components of Congou black tea. The results showed that a rolling speed of 45 r/min resulted in the best sensory quality of Congou black tea, especially in taste and aroma, as verified by color difference and electronic tongue analysis. Sixteen significantly differential metabolites were identified among the four tea samples, including procyanidin C₁, vitexin, isovitexin, asparagine, aspartic acid, gallic acid, malic acid, succinic acid, and gluconic acid. It was found that rolling speed showed a significant influence on phenolic acids, organic acids and tea pigments (theaflavins, thearubigins, and theabrownins), but had little effect on other metabolites. The contents of thearubigins, carbohydrates and aspartic acid and quality index were highest in Congou black prepared with a rolling speed of 45 r/min, and the contents of organic acids, phenolic acids and theabrownins were lowest, which indicated that this rolling speed was more favorable for the formation of the flavor quality of Congou black tea. This study is expected to provide a theoretical basis and technical guidance for the improvement of Congou black tea quality and the precise production of Congou black tea.

According to the results of sensory evaluation performed by experts, 14 black tea samples were divided into two groups based on their aroma quality: high-quality and quality-deficient black tea. Using fast gas chromatography-electronicnose (GC-E-Nose) and gas chromatography-mass spectrometry (GC-MS) combined with multivariate statistical analysis, discriminant analysis of the two groups were carried out, and the key differential components between these groups were selected. The results showed that 117-dimensional dataset was obtained by the fusion of the GC-E-Nose (44-dimensional) and GC-MS (73-dimensional) data and used to establish a model for accurate classification of the two types of black tea employing orthogonal partial least squares-discriminant analysis (OPLS-DA). The model’s explanatory and predictive capacity (R_Y² =0.976, Q²=0.959) were better than those of the model established based on the GC-E-Nose or GC-MS data. Based on variable important in projection (VIP) scores > 1.6 and P < 0.05, eight key aroma components including dimethyl sulfide (B3 and B25), β-ionone (A59), (3E)-4,8-dimethylnon-1,3,7-triene (A20), dihydroactinidiolide (A64), linalool (A17), phenylethyl alcohol (A19), δ-octyl lactone (A41) and γ-nonalatone (A45) were selected, which played an important role in the classification. These results showed that GC-E-Nose combined with GC-MS allows rapid and accurate discrimination between quality-deficient and high-quality black tea, which can be used as a supplement to traditional sensory evaluation, providing technical support for quality control and improvement of black tea.