THE INFLUENCE OF SOME TREATMENTS ON THE ANTIOXIDANT STABILITY IN CERTAIN EDIBLE OILS

Abstract

This study was designed to investigate the influence of refining steps i.e. degumming-neutralization, bleaching, polishing and deodorization of corn, sunflower and soybean oils on stability of various types of natural antioxidants containing these oils, such as tocopherols, phytosterols, polyphenols, chlorophylls, carotenoids and coenzyme Q10; also, the fat–soluble vitamins; besides, the physical and chemical properties and fatty acid composition of the tested oils. The refining process caused more significant changes in the chemical properties of the studied oils than the physical properties, which showed no or little changes, excluding the significant reduction of the yellow and red color. The free fatty acids, peroxide value, and the ultraviolet absorption at 232 nm and 270 were significantly reduced during the refining process. Also, significant decreases in the polyunsaturated linoleic and linolenic acids, together with palmitic acid, coupled with significant increases in saturated stearic and arachidic acids were taken place. A significant increase was happened too in trans fatty acids through the refining steps, especially deodorization. Concerning the bioactive components, the total phytosterols were the most abundant in the crude tested oils; the content of α-tocopherols came in the second order. However, these oils contained an inconsiderable concentration of coenzyme Q10 and polyphenols. The flavonoids and color pigments, i.e. carotenoids and chlorophylls, their levels were negligible. The industrial refining processes of oils caused a removal and alteration in these compounds; affecting their quality and oxidative stability. During refining, the loss in phytosterols content in oils was around 21%, while in α-tocopherol was between 11.91 and 22.44% of the initial values. The highest losses were taken place in flavonoids;