Method Development for the Determination of Free and Esterified Sterols in Button Mushrooms (Agaricus bisporus)

Ergosterol is the major sterol in button mushrooms (Agaricus bisporus) and can occur as free alcohol or esterified with fatty acids (ergosteryl esters). In this study, gas chromatography with mass spectrometry in the selected ion monitoring mode (GC/MS-SIM) was used to determine ergosterol and ergosteryl esters as well as other sterols and steryl esters in button mushrooms. Different quality control measures were established and sample preparation procedures were compared to prevent the formation of artifacts and the degradation of ergosteryl esters. The final method was then used for the determination of ergosterol (443 +/- 44 mg/100 g dry matter (d.m.)) and esterified ergosterol (12 +/- 6 mg/100 g d.m.) in button mushroom samples (n = 4). While the free sterol fraction was vastly dominated by ergosterol (similar to 90% of five sterols in total), the steryl ester fraction was more diversified (nine sterols in total, ergosterol similar to 55%) and consisted primarily of linoleic acid esters.