A new analytical procedure to differentiate virgin or non-refined from refined vegetable fats and oils

The effects of individual steps of industrial refining on the alteration of triacylglycerides (TAG) are reported. The level of dimer triglycerides, no rmally not present in crude oils, increased after each refining step, espec ially after steam-washing and desodorisation. A good correlation between th e applied temperatures and dimer triglycerides content was found. The formi ng of dimer triglycerides starts at 90 degrees C and increases correspondin g to the extension of thermal treatment like normal heating or desodorisati on. The data for various types of vegetable oils demonstrate that there is no clear-cut different tendency to form dimers. Heated oils with different contents of linoleic acid produced nearly the sa me amount of dimers. Other criteria, like the determination of trans fatty acids, steradienes, or the UV-absorption, were found not to be appropriate to detect a thermal treatment at temperatures below 150-170 degrees C. The formation of steradienes mainly depends on the total sterol contents, the p ercentage of added bleaching earth, and its acidity and moisture. Over 160 commercial vegetable oil samples were analysed to obtain a data ra nge on the content of dimerised triglycerides. Mostly, vegetable oils label led as non-refined (which may be steam-washed) did not exceed dimer content s of 0.1%. Virgin vegetable oils did not contain dimers (< 0.05%). The content of dimer triglycerides in vegetable oils was determined by a ne w method via clean-up on a short silica gel column, followed by size-exclus ion HPLC with refractive index detection.