Chemical Composition Characteristics And Identifiability Of Agarwood In Different Producing Zones

Agarwood is a natural mixed substance composed of xylem tissue and its secretions formed during the growth of Aquilaria spp.,which is a traditional medicinal material and a precious flavour that is valued by consumers and is a high value-added forest product.Agarwood resources are mainly distributed from the northeast of the South Asian subcontinent to the Indonesian Islands and Papua New Guinea Islands.Agarwood is generally divided into three producing zones: Guan-Xiang Zone,Hoi-An Zone and Sin-Chew Zone.It is quite different in quality and prices among three producing zones,and the phenomenon of counterfeiting in producing zones is common,which seriously disrupts the market order.In addition,Agarwood is an appendix II of the CITES Convention.Therefore,studying the chemical composition characteristics and identifiability of Agarwood in different producing zones will provide basic theoretical basis and technical support for traceability and quality evaluation of Agarwood.This study analyzed 95 wild agarwood samples from three producing zones by using modern gas / liquid chromatography and mass spectrometry combined with chemometric methods to obtain the basic physical and chemical properties and chromatographic fingerprints of samples from different producing zones.And the signature chemical components that characterize the information of the producing zones were screened and verified to determine the characteristics of the chemical composition of agarwood and explore their identifiability of agarwood from different producing zones.In addition,this study also conducted a preliminary analysis on the odor characteristics of agarwood from different producing zones.The main research conclusions are as follows:(1)The basic physical and chemical properties of agarwood in different producing zones had common characteristics and certain differences.The macro and micro structures of agarwood wood were basically the same,but there were some differences in the shape of tube holes,the number of intact phloems,the length of rays and the distribution of agarwood secretions.The ethanol extract content of 95 agarwood samples from different producing zones was between 10%and 60%,with no obvious regional differences.The color difference of the sublimation reaction of ethanol extract could be used as an auxiliary method to identify agarwood producing zones.(2)The average relative content of sesquiterpene compounds in agarwood samples from three production areas was found to be higher than 50%,and the average relative content of volatile 2-(2-phenethyl)chromone compounds was 32%～42%,and other compounds were less than 4%,the aromatic compounds were less than 0.3%.The relative ratios of sesquiterpenes and volatile chromone compounds in the same producing zones were Guan-Xiang Zone 1.3,Hoi-An Zone 1.5,and Sin-Chew Zone 1.9,respectively,with increasing trends.It was found that OPLS-DA can effectively distinguish three groups based on GC-MS analysis combined with chemometric analysis,with a discrimination accuracy of greater than 80%,and the discrimination accuracy of Sin-Chew Zone samples was 100%.The 22 GC-MS characteristic peak variables could be used as the marker compounds of agarwood from different producing zones.(3)It was found that 2-(2-phenethyl)chromone compounds showed a certain regional characteristics.Similarly,Guan-Xiang Zone and Hoi-An Zone samples were more similar than the Sin-Chew Zone.The average relative content of Flidersia type 2-(2-phenethyl)chromone(FTPECs)in agarwood from different producing zones accounted for more than 65%in the three producing zones;the average relative content of 5,6-epoxy-2-(2-phenethyl)chromone(EPECs)was the lowest,less than 4%.The 5,6,7,8-Diepoxy-2-(2-phenethyl)chromone(DEPECs)were relatively high in samples of Guan-Xiang Zone.The average content of agarotetrol was 1.97% in the Sin-Chew Zone sample,which was much higher than the other two groups,and might become an important feature of Sin-Chew Zone agarwood.It was found that OPLS-DA can effectively distinguish three groups based on HPLC analysis combined with chemometric analysis,with a discrimination accuracy of greater than 80.0%,and the discrimination accuracy of Sin-Chew Zone sample was 100%.The 33 HPLC characteristic peak variables could be used as the marker compounds of Agarwood from different producing zones.(4)A total of 66 compounds were identified from agarwood smoke using HS-GC-MS,including 38 aromatic compounds,19 sesquiterpenes,5 esters,3 salts,and 1 alkenes;the proportions of the relative contents of the five types of components had a small difference,the highest content of which was sesquiterpene compounds(65.87% ～ 69.10%),aromatic compounds(27.01 %～30.21 %);other three types of compounds account for less than 5%.(-)-nootkatene and Styrene might be characteristic ingredients of Guan-Xiang Zone;cis-α-Copaene-8-ol and(-)-Globulol might be characteristic ingredients of Sin-Chew Zone;4-methoxy-benzaldehyde might be a volatile component common to Guan-Xiang Zone and Sin-Chew Zone samples;10-epi-γ-Eudesmol and 2-Furanmethanol were common components to Guan-Xiang Zone and Hoi-An Zone,10-epi-γ-Eudesmol might be the key compounds that the two groups of Guan-Xiang Zone and Hoi-An Zone smell sweeter than Sin-Chew Zone.(5)GC-MS was suitable for the analysis of volatile compounds of Aquilaria,and had a standard mass spectrometry library,which was conducive to the identification of compounds,but the specific 2-(2-phenethyl)chromones of agarwood could not be completely isolated by GC-MS,which was characterized by HPLC efficiently and stably in contrast.In addition,HS-GC-MS directly heated agarwood powder on the basis of GC-MS,and was an effective method to explore the odor components of agarwood.In this study,based on the properties of agarwood components and the characteristics of different chromatographic techniques,each of them focused on the relationship and differences in the chemical composition of agarwood in different producing zones.The chemical composition characteristics of agarwood from Guan-Xiang Zone and Hoi-An Zone proved to be more similar,while agarwood from Sin-Chew Zone was significantly different from the former two.The main reason for the difference in the chemical composition of agarwood in the three producing zones was the tree species.And geographical location and ecological environment also had a certain impact.