FRACTIONATION OF OLIGOMERIC TRIACYLGLYCERIDES AND THE RELATION TO REJECTION LIMITS FOR USED FRYING OILS

Precipitates enriched in oligomeric triacylglycerides were separated f rom thermally oxidized olive residue oil, conventional and high-oleic sunflower oils, and soybean oil by solvent fractionation in methanol/a cetone at 4-5 degrees C for 16 h. Different fractionation conditions w ere evaluated in an effort to isolate the oligomeric triacylglycerides (OTC), OTG, formed in frying oils upon heating at low concentations, were not de tectable with conventional methods to determine polymeric compounds. The best conditions found from the different assays were th e following: (i) weight of oil sample-to-solvent volume ratio of 1:20; and (ii) solvent system methanol/acetone 10:90 (vol/vol) for monounsa turated oils and 15:85 (vol/vol) for polyunsaturated oils. Precipitate s, enriched in oligomers, were formed when heated oils and used frying oils contained more than 27% polar compounds, a value which is widely accepted as the upper limit for use of frying oils.