Comparison of Enzymatic Hydrolysis and Acid Hydrolysis of Sterol Glycosides from Foods Rich in Δ7-Sterols

In this study, we present the difference in sterol composition of extracted steryl glycosides (SG) hydrolyzed by either enzymatic or acid hydrolysis. SG were analyzed from foods belonging to the plant families Cucurbitaceae (melon and pumpkin seeds) and Amaranthaceae (amaranth and beetroot), both of which are dominated by Delta(7)-sterols. Released sterols were quantified by gas chromatography with a flame ionization detector (GC-FID) and identified using gas chromatography/mass spectrometry (GC-MS). All Delta(7)-sterols identified (Delta(7)-stigmastenyl, spinasteryl, Delta(7)-campesteryl, Delta(7)-avenasteryl, poriferasta-7,25-dienyl and poriferasta-7,22,25-trienyl glucoside) underwent isomerization under acidic conditions and high temperature. Sterols with an ethylidene or methylidene side chain were found to form multiple artifacts. The artifact sterols coeluted with residues of incompletely isomerized Delta(7)-sterols, or Delta(5)-sterols if present, and could be identified as Delta(8(14))-sterols on the basis of relative retention time, and their MS spectra as trimethylsilyl (TMS) and acetate derivatives. For instance, SG from melon were composed of 66 % Delta(7)-stigmastenol when enzymatic hydrolysis was performed, whereas with acid hydrolysis only 8 % of Delta(7)-stigmastenol was determined. The artifact of Delta(7)-stigmastenol coeluted with residual non-isomerized spinasterol, demonstrating the high risk of misinterpretation of compositional data obtained after acid hydrolysis. Therefore, the accurate composition of SG from foods containing sterols with a double bond at C-7 can only be obtained by enzymatic hydrolysis or by direct analysis of the intact SG.