Analysis of High Molecular Weight Autoxidation Products Using High Performance Size Exclusion Chromatography: II. Changes during Processing

Abstract

High performance size exclusion chromatography (HPSEC) was used for analysing the quality of vegetable oils during the industrial refining process. The main interest focused on the contents of high molecular weight autoxidation products: oxidized triacylglycerols (PTAG) and triacylglycerol dimeric compounds (TGD). The diacylglycerol and free fatty acid contents of the oils were also monitored. Three vegetable oils (sunflower oil, soya bean oil and low erucic acid rapeseed oil) were used as test materials. In crude oils, the content of PTAG compounds ranged from 5.3 to 9.0 g/kg of oil and that of diacylglycerols from 6.1 to 12.6 g/kg, indicating the different autoxidative and hydrolytic qualities of the raw materials. No dimeric or higher oligomeric TAG compounds were detected in crude oils. The major change during the refining process detected by HPSEC analyses was the increase in TGD content after bleaching and deodorization. In refined oils, the TGD content ranged from 1.2 g/kg for rapeseed oil to 2.3 g/kg for sunpower oil. A slight decrease in PTAG content after bleaching was detected in each of the samples. The content of PTAG compounds in refined oils was comparable to that in crude oils. The decrease in free fatty acid content after neutralization was clear but there was no change in the diacylglycerol content during the processing. HPSEC analysis is a suitable method for monitoring the level of high molecular weight autoxidation products during the processing of edible oils and for analysing the autoxidative quality of oils after industrial refining.