Identification and quantification of important steryl esters in aspen wood

Steryl esters make up a major portion of the total lipids in aspen wood, an d contribute significantly to pitch deposit problems during pulping. Fungal treatment of aspen is an attractive method for removing these compounds be cause it is inexpensive and environmentally acceptable; however, the mechan ism of steryl ester removal remains unclear. Identification of the steryl e sters will lead to a better understanding of how they are removed by fungi. The steryl ester fraction from aspen wood was obtained by acetone extracti on then further purified by silica gel column chromatography and argentatio n-silica gel column chromatography. This led to the isolation of three majo r fractions: fraction I, fraction II, and fraction III. The major steryl es ters of fractions I and ii were identified by gas chromatography, gas chrom atography-mass spectroscopy, and proton nuclear magnetic resonance analysis of the intact fraction as well as sterol and fatty acid moieties obtained after base hydrolysis. Identification of the steryl esters was carried out by mass spectra comparisons with steryl ester standards synthesized in the laboratory and comparison with mass spectra libraries (Wiley and NIST) by m ass fragmentography. Fraction I contained primarily the palmitate, stearate , and eicosanoate esters of alpha- and beta-amyrin. Fraction II consisted m ainly of the palmitate, stearate, and eicosanoate esters of tirucalla-7,24- dien-3 beta-ol and lupeol.