Quantitative Determination of Polymerized Triacylglycerols in Frying Oils and Fats by Size Exclusion Chromatography : A Collaborative Study

Acid, peroxide and carbonyl values are often used for assessment of the deterioration of frying oils and fats in Japan. But in some cases, these indexes don’t provide adequate evaluation. In many European countries, amounts of polymerized triacylglycerols, which are major components of deterioration, serve as a more accurate index for this assessment. A standard method to determine these amounts should thus be established and applied in this country. To that end, a collaborative study was conducted to quantify polymerized triacylglycerols in oils and fats using size exclusion chromatography (SEC) with refractive index detection. Analytical conditions such as column, sample concentration and injection volume were optimized so as to achieve accurate and reproducible results. From these results, an adequate standard method was established. The study findings are follows: 1) The column (TSKgel G2500HXL) with a size exclusion limit at a molecular weight of 2 × 104 (polystyrene standard) was found most effective for separating polymerized triacylglycerols from triacylglycerols. 2) A sample concentration of 0.5% and an injection volume of 50μL were best for achieving reproducible result. CVR was 2.4 with heated rapeseed oil containing approximately 2.5% polymerized triacylglycerols. 3) Several peaks appeared between polymerized triacylglycerols and triacylglycerols in used oils and fats, but the separation was insufficient because hydrolysis occurred during frying. In such cases, the use of several columns connected together was found to bring about adequate separation.