Characterization of ganoderma spore lipid by stable carbon isotope analysis: implications for authentication

The ratios of stable carbon isotopes (¹³C/¹²C) of ganoderma fruiting body, ganoderma spore, ganoderma spore lipid (GSL) and individual fatty acids in GSL were determined by gas chromatography–stable isotope ratio mass spectrometry and elemental analysis–stable isotope ratio mass spectrometry. These values fall into a range from −26.9 to −23.3‰, suggesting that the cut log as the Ganoderma-cultivated substrate in Fujian, China, may belong to C3 plants. Eighteen fatty acids were identified and their abundances measured by gas chromatography–mass spectrometry in the six GSL samples with C_16:0, C_18:0, C_18:1 and C_18:2 as major constituents, and C_16:1 is evidently enriched compared with the other edible vegetable oils. On the basis of the compositions of fatty acids and stable carbon isotopes in GSL, we have developed a novel method to detect the adulteration of GSL products with cheaper edible vegetable oils. An example of ideal blending between GSL and C4 or C3 vegetable oil is further provided to expound the discrimination procedures and corresponding sensitive indicators. Simultaneously, the carbon isotope fractionation in the biosynthesis of individual fatty acids was observed, revealing that the formation of C_18:0 from C_16:0 in ganodema spores had no conspicuous ¹³C enrichment of +0.4‰ for Ganoderma sinensis spore and +0.1‰ for G. lucidum spore; the desaturation of C_18:0 to C_18:1 resulted in a distinct ¹³C depletion of −1.4‰ for G. sinensis spore and −0.9‰ for G. lucidum spore; and the next desaturation from C_18:1 to C_18:2 displayed no evident ¹³C fractionation of −0.1‰ for G. sinensis spore and −0.2‰ for G. lucidum spore. Figure Ganoderma lucidum has been widely used in traditional Chinese medicines. Ganoderma spore lipid (GSL) extracted from the spores of G. lucidum has been approved as a health food supplement. However, because of rarity, GSL has become a target for adulteration with cheaper vegetable oils.