QUANTITATION AND DISTRIBUTION OF ALTERED FATTY-ACIDS IN FRYING FATS

The distribution and quantity of polar compounds and altered fatty aci ds in used frying oils, collected by Food Inspection Services of the J unta de Andalucia in Spain, was measured. Additional samples evaluated were sunflower oil, high-oleic sunflower oil, and palm olein that wer e subjected to thermoxidation and frying in laboratory experiments. A combination of adsorption and high-performance size-exclusion chromato graphy was applied to the oil samples both before and after transester ification. Through analysis of fatty acid methyl ester derivatives, di fferentiation of four groups of altered fatty acids (oxidized monomers , nonpolar dimers, oxidized dimers, and polymers) could be attained. E valuation of real frying samples with polar compound levels around the limit for fat rejection (21.1-27.6% polar compounds) gave values of t otal altered fatty acids ranging from 8.1 to 11.3%, and levels higher than 20% were found in the most degradated samples. The results obtain ed clearly support the need for control and improvement of the quality of used fats in fried-food outlets.