Analysis of Volatile Compounds in the Manufacturing Process of Eucommia Ulmoides Leaves Fu Brick Tea Based on Gas Chromatography-Ion Mobility Spectrometry Method

In order to examine the variation of volatile components of Eucommia ulmoides leaves Fu Brick Tea during processing, Gas Chromatography-Ion Mobility Spectroscopy (GC-IMS) was employed. The volatile compounds fingerprints of Eucommia ulmoides leaves Fu Brick Tea were plotted using Gallery Plot software. The differences between the samples from the six stages during processing and principal component analysis were assessed, respectively. The results showed that a total of 70 volatile compounds were detected in each sample of the six stages, including raw material screening, piling fermentation, steam and forming stage (the 0th day of flowering), the 8th day, the 25th day of flowering and the 1st year of aging stage. Among these compounds, qualitative analysis of 51 kinds of components were determined, including aldehydes, ketones, alcohols, esters, pyrazines, acids, terpenes, furans, ethers and sulfur compounds. PCA analysis showed that PC1 was 47%, PC2 was 27%, and the cumulative contribution rate was 74%, which was better reflected the influencing factors of the differences of volatile components among different tea samples. The tea samples at different stages were separated on the PCA chart, indicating that there were differences in the volatile components contents of tea samples at different stages in the processing. The relative contents of several kinds of pyrazines, aldehydes and ketones with grass flavor and earthy aroma in tea samples gradually decreased with the processing, while the relative contents of alcohols, aldehydes and esters with medicinal aroma, fruity aroma and mellow aroma gradually increased. Finally, the medicinal, fruity and fungus aroma of Eucommia ulmoides leaves Fu Brick Tea was formed. Moreover, the relative contents of 2-ethyl-3, 5-dimethylpyrazine dimer in the pile fermentation samples, 2, 4-heptadienal and 3-methylthiopropanal in the flowering stage samples, and 5-methylfurfural, butyl acrylate monomer, butyl acrylate dimer, furfural dimer, 2, 3-butanediol in the aging stage samples were higher than compared to other stages. Therefore, these compounds might be the potential indicators of the assessment of the piling fermentation, flowering and aging stage of Eucommia ulmoides leaves Fu brick tea, thus providing a tool for the regular monitoring of aroma components on the manufacturing process of Eucommia ulmoides leaves Fu brick tea.