Analysis of Composition Differences between Huazhou Citri Grandis Exocarpium and Guangxi Citri Grandis Exocarpium Based on Portable GC-MS and HS/SPME-GC×GC-TOF MS

The volatile components of Citri Grandis Exocarpium from Huazhou (CGEH) and Guangxi (CGEG) were analyzed by portable gas chromatography-mass spectrometry (GC-MS) and comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOF MS) combined with headspace solid-phase microextraction (HS/SPME). Due to its limited separation ability, the portable GC-MS can identify only 8 chemicals in CGEH and 4 chemicals in CGEG and is not able to determine any marker compounds which can distinguish CGEH over CGEG. While the merit of GC×GC-TOF MS is strong separation ability, allowing the identification of 304 chemicals in CGEH and CGEG, of which 261 chemicals are reported for the first time. Among them are 52 compounds only detected in CGEH, 81 ones unique in CGEG, and 171 detected in both CGEH and CGEG. The volatile components in CGEH and CGEG are classified into 17 and 19 types, respectively. The contents of alkene aromatics, hydrocarbons and alcohols in both CGEH and CGEG are relatively high. The principal component analysis (PCA) and orthogonal partial least squares (OPLS-DA) were further performed on the MS data obtained by GC×GC-TOF MS. The results indicated that there is basically no difference from different batches of fruits in the same region, while have obvious differences between CGEH and CGEG. Among these different components, 10 compounds including 3,4-diethyl-1,1'-biphenyl, 1-methyl-4-(1-methylethenyl)-1,2-cyclohexanediol, 1-dodecanol, α-ethylidene-benzeneacetaldehyde, 3,8-dimethyl-undecane, tetradecanal, 2-methyl-tridecane, 5-methyl-2(5H)-furanone, tetraethylene glycol, sabinol in CGEH are screened out with the values of Pearson correlation coefficient |p(corr)|>0.9, |p|>0.06 and variable influence on projection (VIP) value>1.1. On the other hand, several marker compounds, such as cedrane, hibaene, 1,3,5-tris(methylene)-cycloheptane, (E)-longipinane, 1,1,6,6-tetramethylspiro4.4nonane, 2-(4a,8-dimethyl-1,2,3,4,4a,8a-hexahydro-2-naphthalenyl)-2-propanol, γ-gurjunene, 1S-(1α,4α,7α)-1,2,3,4,5,6,7,8-octahydro-1,4,9,9-tetramethyl-4,7-methanoazulene, (2R,5S)-2-methyl-5-(prop-1-en-2-yl)-2-vinyltetrahydrofuran, copaene, spathulenol, β-elemene, sativene, N-4-bromo-n-butyl-2-piperidinone, eremophilene, 10α-eremophilane, oleyl alcohol, trifluoroacetate, and selinane are picked up in CGEG. These results proved that GC×GC-TOF MS can identify markers of Citri Grandis Exocarpium, while portable GC-MS can not. These markers can help to distinguish CGEH from others and provide references to quality evaluation of Citri Grandis Exocarpium.