Analysis of Volatile Components in the Manufacturing Process of Eucommia ulmoides Leaves Fuzhuan Tea Based on Headspace Solid Phase Microextraction/Gas Chromatography-Mass Spectrometry Method

In order to examine the variation of volatile components of Eucommia ulmoides leaves Fuzhuan tea during the production process, the combination of headspace solid phase microextraction (HS-SPME) with gas chromatography-mass spectrometry (GC-MS) was applied to explore the changes of volatile components of tea products during the production process. The results showed that 152 volatile components were identified in the production process of Eucommia ulmoides leaves Fuzhuan tea. Among these volatile components, the relative contents of acids, esters, ketones, alcohols were high and may be the main volatile components of Eucommia ulmoides leaves Fuzhuan tea during the production process. Principal components analysis (PCA), hierarchical cluster analysis (HCA) and partial least squares discriminant analysis (PLS-DA) were used to effectively distinguish the different processing stages of Eucommia ulmoides leaves Fuzhuan tea. The composition and structure of volatile components, such as acids, alcohols, ketones and esters, altered significantly during the production process of Eucommia ulmoides leaves Fuzhuan tea, whereas the contents of the volatile components with irritant, green, spicy and bad smell volatile components such as propanoic acid, acetic acid and 2-hexenal showed a decreased trend. Moreover, linalool, dodecanoic acid, tetradecanoic acid, hexadecanoic acid ethyl ester, 4-hydroxy-5-methyl-3(2H)-furanone, acetaldehyde and other volatile components with fungus fragrance, woody fragrance, flower fruit fragrance and frankincense presented a increased trend. Based on VIP value, 64 markers of differential volatile components during the production process were identified. For instance, the relative contents of 5-methyl-1H-Indole, dotriacontane and 1-dodecanol in the raw material samples, 3-amino-phenol, oxacyclohexadecan-2-one and 5-hydroxy-3-methyl-1-indanone in the piling fermentation samples, benzoic acid, 2-methoxy-4-vinylphenol and 1-hexen-3-ol in the steam and forming stage samples, 6,10,14-trimethyl-2-penta- decanone, 1H-pyrrole-2-carboxaldehyde and 2-hydroxy-cyclopentadecanone in the 8th day of flowering stage samples, and ethosuximide, 1-methoxy-4-propyl-benzene in the 25th day of flowering stage samples were relatively higher compared with other stages. Therefore, these compounds might be the potential indicators for the assessment of the raw material screening, piling fermentation, steam and forming, different stages of flowering of Eucommia ulmoides leaves Fuzhuan tea. In the finished product, hexadecanoic acid methyl ester, (R)-5,6,7,7a- tetrahydro-4,4,7a-trimethyl-2(4H)-Benzo-furanone, dodecanoic acid, 6,10,14-trimethyl-2-Penta-decanone, β-ionone and other volatile components were relatively higher compared with the content of aromatic volatile components, which might be the main material basis of fragrance of Eucommia ulmoides leaves Fuzhuan tea. The results can provide the material basis for identifying the aroma characteristics and regulating the formation of aroma of Eucommia ulmoides leaves Fuzhuan tea during processing.