Deterioration of High-Oleic Safflower Oil Heated in Low Oxygen Atmospheres with Water-Spray.

Abstract

High-oleic safflower oil was heated at 180°C while spraying water in the atmosphere at four levels of oxgen concentration (2,4,10,20%) modified with nitrogen gas to assess the effects of atmospheric oxygen levels on the oxidative deterioration of deep-frying oils. Acid value, carbonyl value, polar material, linoleic acid and tocopherol content, and oxidative stability were measured to evaluate the qiality of heated oils. In general, all these indices correlated with both heating time and the atmospheric oxygen concentration. The increase in acid and carbonyl values and polar material content, and the decrease in linoleic acid and tocopherols in heated oils were almost proportional to the atmospheric oxygen concentration. Compared with heating without water as reported previously, spraying water accelerated the oxidative deterioration of heated oils in all indices. The acid value in particular changed remarkably, but hydrolysis of triacylglycerols did not occur without oxidation. The increase in the acid value was suggested to be due tu thermal oxidation rather than to simple hydrolysis of triacylglycerols. The oxidative stability of the heated oil at 2% and 4% O2 was well maintained. These results suggested that the rate of oxidative deterioration in deep-frying oil is nearly proportional to the atmospheric oxygen concentration.