Analysis of Total, Free, and Esterified Sterols and Triterpene Alcohols in Edible Oils using a Gas Chromatography-Flame Ionization Detector.

Abstract

Sterols and triterpene alcohols exist in free and esterified forms in edible oils. To date, only few studies have determined the content of free or esterified sterols and triterpene alcohols using gas chromatography-flame ionization detection (GC-FID). In this study, analytical conditions were optimized using free and esterified sterol standards. To analyze total sterol and triterpene alcohol (Method A), edible oil sample was saponified in the presence of an internal standard (IS, 5α-cholestan- 3β-ol). However, to analyze free sterol and triterpene alcohol (Method B), the sample was dissolved in hexane/ethyl acetate (90:10, v/v) in the presence of the IS, and the free sterol and triterpene alcohol fractions were isolated via silica gel chromatography. The fractions obtained from Methods A and B were derivatized separately as trimethylsilyl (TMS) ether and analyzed using GC-FID. The esterified sterol and triterpene alcohol contents of edible oil were calculated by subtracting the free sterol content (Method B) from the total content (Method A). The major sterols and triterpene alcohols in canola, soybean, rice bran oil, and lard were separated using a column coated with 5% diphenyl/95% dimethylpolysiloxane. The recovery rates of free sterols spiked into canola oil were 86-106% and 87-109%, while those of esterified sterols (sitosteryl palmitate) spiked into canola oil were 94-105% and －4-2% based on Methods A and B, respectively. The sterol and triterpene alcohol compositions of lard, canola, soybean, and rice bran oils were also determined using Methods A and B, and the results aligned well with those reported in the literature. Altogether, our methods can be successfully used to quantify the levels of sterols and triterpene alcohols in edible oils.