Abstract:In order to realize the rapid detection of volatile flavor substances in oolong tea samples from different producing areas, the gas chromatography-ion mobility (GC-IMS) technique combined with the stoichiometry was employed to study the volatile compounds in 29 samples of oolong tea from 4 different origins. The IMS maps of oolong tea samples from different origins showed significant differences in volatile substances. The citrus limonene content was the highest in the oolong tea from Guangdong Province, and the contents of heptanal, hexanal and 3-octanone with characteristic components of herbaceous aroma in the oolong tea from southern Fujian were obviously higher than those of oolong tea from other producing areas. The oolong tea from Taiwan Province had more fruit aroma characteristic components, such as 2-hexanone, propionic acid, γ-butyllactone, n-hexanal and so on. The oolong tea from northern Fujian had more baked fragrance like trans-2,4-heptyl diene aldehyde, p-ethyl phenol and 5-methyl furfural. The peak strength of 43 kinds of volatile compounds screened by the differential spectrum method were set as the variables, and dimension reduction was done by the principal component analysis (PCA), which could distinguish oolong tea from different producing areas. The contribution of PC1 and PC2 were 54.2% and 19.4%, respectively, and the cumulative contribution rate was 73.6%. The results of partial least squares discriminant analysis (PLS-DA) showed that the contribution rate of PC1 and PC2 were 54.2% and 19.3%, respectively, and the cumulative contribution rate was 73.5%, which had good distinguishing effect on the oolong tea from different producing areas. The linear discriminant analysis (LDA) could effectively distinguish oolong tea from different producing areas with the discriminant rate of 100%. The experiment showed that GC-IMS technology could be effectively applied to detect the volatile substances in oolong tea and rapidly identify their origin.
