Identification and analysis of essential oil components of the fruit peels of 6 mandarin orange species by GC-MS

Abstract：【Objective】China is the origin of mandarin orange with abundant resources. High frequency of natural variation and hybridization have increased the difficulty of identification and classification of mandarin orange species. The purpose of this study was to detect essential oil components of the fruit peels of 6 mandarin oranges in order to provide some information for citrus taxonomy and utilization of the resolved volatile compounds of citrus peel oil.【Methods】'Nanfeng tangerine' (C. reticulata) , Satsuma mandarin (C. unshiu) , 'No.3 ponkan' (C. reticulata) , 'Mangshanyegan' (C. mangshanensis) , tankan (C. tankan) and red tangerine (C. tangerina) were collected from Citrus Research Institute (CRI) . The peel essential oils of the fruit peels were extracted by steam distillation and investigated by gas chromatography-mass spectrometry (GC-MS) . SPSS 19.0 software was applied to conduct the principal component analysis (PCA) and hierarchical clustering analysis (HCA) .【Results】There were significant differences in the contents of essential oils ranging from 0.77% to 1.56%. A total of 55 volatile components were identified in the essential oil of the six species of mandarins, including 29 kinds of hydrocar-bons, 11 alcohols, 8 aldehydes, 3 esters, 1 ketones, 1 ethers and 2 phenols. The volatile components accounted for 99.5% of the essential oils.'Nanfeng tangerine', Satsuma mandarin, 'No.3 ponkan'and'Mangshanyegan'had 26 components. Tankan had 13 components and red tangerine owned 33 components. The fruit peel oil constituents of the 6 species were significantly different. D-limonene content varied from 66.91% to 91.51%, Tankan had the highest content (91.51%) of D-limonene, followed by Satsuma mandarin (82.65%) . Hydrocarbon compounds were the most abundant compounds in the essential oil constituents of mandarins, and the content of monoterpenoids was much higher than that of sesquiterpenes, and sesquiterpenes was only not found in tankan. Nine terpene alcohols were identified with linalool (0.1%-3.23%) being the most abundant compound. The content of linalool in'Nanfeng tangerine'was the highest (3.23%) , followed by tankan (3.19%) . Ketone was only detected in red tangerine. Ethers were only founded in'No.3 ponkan'. 1 R-α-pinene, β-phellandrene, β-myrcene, D-limonene, (Z) -β-ocimene, linalool, 4-terpineol, α-terpineol were commonly found in 6 mandarins. The occurrence of β-cubebene in the peel oil could be specific to the fruit peel oil of'Nanfeng tangerine'. Whileβ-pinene, α-caryophyllene, β-cadinene, decanal could be the typical compound of the Satsuma mandarin. The presence of α-bisabolene, citronelly acetate, neryl acetate, 2-methoxy-4-methyl-1- (1-methylethyl) -benzene seemed to be limited to the peel oils of'No.3 ponkan'. α-cubebene, β-terpinol, γ-eudesmol, α-methyl-α-[4-methyl-3-pentenyl] oxirane methanol, cis-α, α, 5-trimethyl-5-ethenyltetrahydro-2-furan-methanol could be specific to'Mangshanyegan'peel oil. Tankan could be distinguished from the other species by the occurrence of 3-carene, 2, 2'-methylene-cis [6- (1, 1-dimethylethyl) -4-methyl-phenol] and absence of γ-terpinene. Red tangerine had four specific components, including 8-isopropenyl-1, 5-dimethyl-cyclodeca-1, 5-diene, 1-octanol, (Z) -3-hexen-1-ol and nootkatane. The principal component analysis and the hierarchical cluster analysis indicated that the 6 species of mandarins could be divided into three groups according to three major chemotypes, limonene, limonene/γ-terpinene and limonene/β-myrcene.'No.3 ponkan'and red tangerine contained limonene and γ-terpinene as the main components, belonging to limonene/γ-terpinene chemotype.'Nanfeng tangerine', Satsuma mandarins and tankan were categorized as limonene chemotype with a very high amount of D-limonene.'Mangshanyegan'belonged to limonene/β-myrcene chemotype.【Conclusion】Satsuma mandarins, 'Nanfeng tangerine'and tankan were clustered as one group although the genetic relationship between Satsuma mandarins and'Nanfeng tangerine'were closer. The'No.3 ponkan'and red tangerine were clustered together, belonging to ancient cultivated varieties.'Mangshanyegan'formed an individual group as a wild mandarin germplasm.