Generalized Method to Quantify Glycidol Fatty Acid Esters in Edible Oils

Abstract

We previously reported a method to quantify five species of glycidol fatty acid esters (GEs) in edible oils which used a combination of a double solid-phase extraction (SPE) and liquid chromatography-mass spectrometry (LC-MS) using fast HPLC. To expand its application, we established a new method using conventional HPLC, which is applicable not only to liquid oils but also to solid ones. The optimized LC-MS conditions using conventional HPLC were useful for standard GEs but not for oil samples because of the insufficient accuracy during sequential runs. Thin-layer chromatographic studies revealed that co-existing diacylglycerols were not sufficiently removed by the original SPE procedure due to excessive amounts of oil applied to the normal-phase SPE, which disturbed the quantitative and stable detection only when conventional HPLC was employed. The amount of oil applied was decreased tenfold (100 mg ? 10 mg), which resulted in stable LC-MS measurements. Furthermore, the use of chloroform/acetone, instead of acetonitrile, prior to the SPE treatment expanded its applicability to solid oils, with recovery values ranging from 102.7 to 109.5% for three oil samples (two liquid and one solid oils). This method can form the basis of a standardized method for the quality control of GEs in edible oils.

Comparison of Indirect and Direct Quantification of Glycidol Fatty Acid Ester in Edible Oils

“…3.1 Comparison of GE levels as measured by indirect and direct methods The GE levels in edible cooking oils and fat spreads from a local market were determined by both the indirect method 3 and the direct LC-MS method 6 , as shown in Table 3.…”

“…By using the direct LC-MS method 5,6 , a summed level of five species of GE in the oils was determined. Thus, as standard materials, reagent grade GS was used for C18:0-GE while other GEs such as C16:0-GE, C18:1-GE, C18:2-GE, and C18:3-GE were synthesized and used 5 .…”

“…Thus, as standard materials, reagent grade GS was used for C18:0-GE while other GEs such as C16:0-GE, C18:1-GE, C18:2-GE, and C18:3-GE were synthesized and used 5 . The GErich extracts of test oils obtained by double SPE treatment were carefully dissolved in methanol/2-propanol 1:1 by vol for LC-MS analysis, which was performed under the absolute same conditions as in prior work 6 . Phenyl boronic ester derivatives of polyols were then analyzed using GC-MS Option A .…”

“…The other method is one reported by Masukawa et al, which directly quantifies five species of GE in edible oils with a combination of a double solid-phase extraction SPE and liquid chromatography-mass spectrometry LC-MS . This direct method has been validated in terms of the trueness and precision of the quantitative values produced by a spike and recovery study of GEs using triacylglycerol TAG -and/or diacylglycerol DAG -rich oils 5,6 . In comparing the indirect and direct methods, using the same samples, we noticed that the indirect method produced lower GE level estimates for some oil compositions.…”

Chiral separation of glycerolipids by high-performance liquid chromatography

“…The concentrations of palmitate, stearate, oleate, linoleate, and linolenate were 6.6, 2.6, 74, 118, and 49 µg/g, respectively. The total amount of GE (250 µg/g) was less than that reported previously (295 µg/g), where a combination of double SPE and reversed-phase HPLC-MS was used 26) . As with GE, fatty acid esters of racemic 3-chloro-1,2-propanediol (Fig.…”