Fatty acids, essential oils, and squalene in the spore lipids of Ganoderma lucidum by GC-MS and GC-FID

Abstract

Spores of Ganoderma lucidum contain a large amount of bioactive components such as polysaccharides and lipids and have a higher bioactivity than the fruit bodies [1, 2]. It was reported that 24.82% (w/w) yield of spore oil was obtained from sporoderm-broken spores of G. lucidum by supercritical CO2 fluid extraction (SFE-CO2) [3]. But if the crude spores were not superfine-pulverized, the yield of spore oil was only 3.96% (w/w) even under the optimal condition of SFE-CO2 [4]. This result was evidenced that sporoderm-broken was a necessary technical step before SFE extraction that enables the endo-substances such as lipids to be easily extracted. Table 1 shows the results of analysis of 15 kinds of fatty acids in the spore lipids by GC-MS. The main components were palmitic acid (16:0, 16.12%), stearic acid (18:0, 4.97%), oleic acid (18:1, 67.11%), and linoleic acid (18:2, 9.63%). The totaled relative contents of unsaturated fatty acids were 77.84% (mass fraction), including 16:1, 18:1, 18:2, and 20:1. Among them, 9,12-octadecadienoic acid and (Z)-9-octadecenoic acid (total up to 76.74%) were the major compounds in the spore lipids of G. lucidum. The GC-MS results also showed that the chemical compositions of essential oils (from separator II) were different from the fatty acids (from separator I). At least 39 compounds were analyzed; among them 11 compounds were identified (see Table 2), including terpenoids (such as -pinene, D-limonene), aromatic aldehydes (such as nonanal, (E)-2-heptenal, (E)-2-decenal, (E,E)-2,4-decadienal), and several alkanes (see Table 2). In addition, squalene in the spore lipids was isolated together with fatty acids from separator I and was separately determined by GC-FID with a standard substance (tR/min 23.062 and 22.863) purchased from Sigma-Aldrich. The content of squalene was 0.43 mg/g. It is known that squalene exists in codliver oil, olive oil, and other major oil products and can improve the in vivo activity of superoxide dismutase, enhance immunity and improve sexual function, and has anti-aging, anti-cancer, and other physiological functions [5]. According to early reports, there were 20 kinds of fatty acids (C14–C25) from spore oils of G. lucidum obtained by GC-MS/LC-MS, and the major compounds were oleic acid (18:1, 63.28%), linoleic acid (18:2, 6.59%), and palmitic acid (C16:0, 20.73%) [6]. In our preliminary study, nine kinds of known fatty acids were determined by GC, and their main constituents were also oleic acid (18:1, 57.5%), linoleic acid (18:2, 13.4%), and palmitic acid (16:0, 19.6%) [7]. There are four types of components (lipids, terpenes, aromatics, and heterocyclic) in spore essential oil [8]. Moreover, some other reports have indicated that spore oils or lipids extracted from Ganoderma lucidum have antioxidant activity [4], and show positive antitumor effects in vitro and in vivo [9, 10]. The aim of this study was to use different operational conditions of SFE-CO2 from those reported previously for extracts of spore lipids and essential oils [3]. The conditions were 30 MPa of extract pressure, 40 C extract temperature, 25 L/h of CO2 flux, and 2.0 h of extract time. The spore lipids were collected from separator I (at 8 MPa and 45 C) with an average yield of 24.16% (w/w), and the essential oils were collected from separator II (at 5.0–5.5 MPa, 32 C) with an average yield of 0.64% (w/w). The chemical components of the spore lipids and essential oils were analyzed by GC and GC-MS, respectively.