Comparison of Transesterification Methods for Fatty Acid Analysis in Higher Fungi: Application to Mushrooms

Abstract

This study evaluated the effectiveness of two commonly used transesterification methods for the preparation of fatty acid methyl esters (FAMEs) for gas chromatographic analysis. A combination of base followed by acid catalysis [potassium hydroxide/sulfuric acid/methanol (KOH–H2SO4–MeOH)] was compared to an acid-only catalyst [methanolic–boron trifluoride (BF3–MeOH)] for the quantification of the fatty acid content in mushrooms after preextraction of total lipids with chloroform/methanol (2:1 v/v). The mushrooms studied were commonly cultivated species, Agaricus bisporus (brown) and A. bisporus (white), and three wild medicinal mushrooms, turkey tail (Trametes versicolor), artist conk (Ganoderma applanatum), and tinder polypore (Fomes fomentarius). The major fatty acids identified were palmitic (C16:0), stearic (C18:0), oleic (C18:1), and linoleic acid (18:2n6) which constituted 80% to 90% of the total amount. Variation due to the FAME preparation methods was observed in both minor and major fatty acids. Another major observation made between the two methods was the total number of individual fatty acids (FAs) methylated. The base and acid transesterification procedure resulted in the identification of 42 FAMEs, whereas with the acid 38 FAMEs were observed. Therefore, the research recommends the use of a base–acid combination for preparation of FAMEs in mushroom lipids.