Fatty Acid Composition in Ergosteryl Esters and Triglycerides from the Fungus Ganoderma lucidum

Free and esterified ergosterols are detected almost solely in fungi and are often employed as a biomarker of living fungi. In this work, the fatty acid composition and δ¹³C values of major fatty acids in triglycerides and ergosteryl esters from the fungus Ganoderma lucidum were analyzed by gas chromatography–mass spectrometer and gas chromatography–isotopic ratio mass spectrometer, respectively. The results showed that the fatty acid profiles varied in triglycerides and ergosteryl esters. The percentage of saturated fatty acids in ergosteryl esters was remarkably higher than that in triglycerides, where C ₁₈:₁ ∆⁹ᶜ was the predominant fatty acid and constituted 61.26 % of the total fatty acids. In contrast, C₁₆:₀ was the predominant fatty acid and constituted 71.88 % of the total fatty acids in ergosteryl esters. The study suggests that, after fungal death, free ergosterols in the cell membrane of the dead fungus were esterified with preferentially saturated fatty acids, mainly C₁₆:₀, from triglycerides and then stored in lipid particles for a longer period while free ergosterol markedly decreased. The δ¹³C values of C₁₆:₀, C₁₈:₀, C₁₈:₁ and C₁₈:₂ in ergosteryl esters exhibit a pronounced depletion in ¹³C compared with that in triglycerides within the range of −1.3 to −0.9 ‰, supporting the above inference. It is again suggested that free ergosterol in the cell membrane should be used as an indicator of living fungi, and ergosteryl esters in the lipid particles should not be included in the measurement of living fungal biomass.