Composition of supercritical fluid extracts of some Xanthium species from China

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The genus Xanthium (Compositae) is represented by 25 species in the world and 3 species and 1 variety in China [1]. These are X. sibiricum Patr. (X. strumarium L.), X. mongolicum Kitag., X. inaequilaterum DC., and X. sibiricum var. subinerme (Winkl.) Widder. Xanthium species have been used as traditional herbal medicines for the treatment of nasal sinusitis, headache caused by wind-cold, urticaria, and arthritis for a long time in oriental countries [2]. The chemical composition of ent-kaurane diterpenoids, sesquiterpene lactones, caffeoylquinic acids, and thiazinediones from this genus (leaves or fruits) has been reported [3–8]. Chemical examination of the essential oil from the leaves of Xanthium strumarium showed that the main components of the essential oil were d-limonene and d-carveol, with a relative content of 35% and 25% (w/w), respectively [9]. The composition of the fruit essential oil of Xanthium sibiricum Patr. was reported in 1994 [10], and showed that saturated paraffin hydrocarbons such as eicosane and nonadecane were the major components. The fruit oil of Xanthium obtained by crushing were reported to have anti-thrombus effects and to decrease blood-fat in civil use [11], which were referred to the lipophylic extracts of Xanthium fruits. The purpose of this research was to conduct a comparative analysis on the fatty oil composition from samples belonging to three Xanthium species growing in China: X. sibiricum, X. sibiricum var. subinerme, and X. mongolicum. The collected location and date of the three Xanthium species used for supercritical fluid extraction (SFE) and GC-MS analysis are listed in Table 1. This is the first report on the lipophylic extracts prepared by SFE of the three Xanthium species. The results of the fatty acid analysis by GC-MS and the oil yield of the taxa are presented in Table 1. The extraction of essential oil components using solvents at high pressure, or supercritical fluids, has received much attention in the past several years, especially in the food, pharmaceutical, and cosmetic industries, because it presents an alternative to conventional processes such as organic solvent extraction and steam distillation [12, 13]. By comparing the composition of the product with hydrodistilled oil [14], higher levels of the volatile components such as d-limonene and d-carveol were found by using the hydrodistillation method [9]. However, these compounds were not found in the SFE products. In contrast, the fatty acids linoleic acid, palmitic acid, stearic acid, and some sterols were found in the SFE products, whereas negligible amounts were present in the distilled oils. In this study, a total of 37 compounds of three Xanthium species in China was determined, of which aromadendrene, α-phellandrene, globulol, norphytane, tomentosin, etc. were identified from Xanthium genus for the first time. The fatty oil composition of the studied Xanthium genus was not uniform but overlap. A considerable content of linoleic acid and palmitic acid was noted in all samples, but small quantitative differences were also found. Linoleic acid was the predominant constituent of the studied fruit oil and had the relative content of 80.24% (X. sibiricum), 70.75% (X. sibiricum var. subinerme) and 77.71% (X. mongolicum), respectively. The amount of linoleic acid is important with respect to the quality of the oils consumed as a food resource [15]. Therefore, the fruits of the three studied Xanthium species can all be regarded as a new resource for linoleic acid production. Stearic acid, linolenyl alcohol, n-tetracosane, n-pentacosane, and n-nonacosane, were present in both X. sibiricum var. subinerme and X. mongolicum fruit oil. The X. sibiricum var. subinerme oil composition was characterized by a large variation of the long-chain diolefins, including n-heptadecane, n-docosane, and all the linear-chain diolefin froms n-tetracosane to n-nonacosane. Only nine compounds of X. mongolicum fruit oil were determined, of which diisooctyl phthalate was the special component.