Improved method for the determination of wax esters in vegetable oils

Abstract

In this work a modified International Olive Council (IOC) method for wax determination involving a double-adsorbent layer of silica gel and silver nitrate-impregnated silica gel is presented (SN method). Column chromatography by the SN method did not show retention of wax esters standards with an even number of carbon atoms (C34-C44), observing recovery percentages higher than 90% even for unsaturated wax esters. All wax fractions were lower by the SN method than by the IOC method, resulting in a percentage decrease in the total wax content (olive oils: 20-50%, crude sunflower oil: 38%, crude soybean oil: 58% and crude grape seed oil: 13%). Olive oils analysed by the SN method showed increases of up to 27% in C40 relative percentage with respect to the IOC method. Additionally, decreases were observed by the SN method in the relative percentages for odd-carbon atom waxes for the seed oils in comparison to the IOC method (crude sunflower oil: 27%, crude soybean oil: 28% and crude grape seed oil: 13%). The main advantages of the proposed modification consist in its easy implementation and a better determination of wax esters (C34-C60) by controlling their complete recovery and removing interfering substances. The method is suitable for quality control and for authentication of olive oil and seed oils as well as in processing monitoring.