Effects of Different Full Drying Methods on the Chlorophyll Degradation in Green Tea as Analyzed by UPLC-Q-Exactive Orbitrap-MS

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.