Influence of fatty acids of different unsaturation in the oxidation of purified vegetable oils during microwave irradiation

Abstract

Purified vegetable oils (soya bean, safflower and rapeseed) containing stearic, oleic, linoleic or linolenic acid at different levels (05-100 g kg-I), were exposed to microwave irradiation for several periods of time to study the contribution of fatty acids of different unsaturation to the oxidative stability of these oils. The evaluation of the oils was based on peroxide value or carbonyl and anisidine values as an indicator for the primary or secondary oxidation products, respectively. A pro-oxidative effect of the added fatty acids was established. The extent of this effect depended on the degree of unsaturation of added fatty acids and/or purified vegetable oils. During microwave treatment the oxidative rate of purified vegetable oils was rapid in the presence of the unsaturated fatty acids, but comparatively lower for the corresponding saturated fatty acid or hydrocarbon. The oxidative state of the oils was lower in the rapeseed oil than in the soya bean oil or safflower oil. In assessing the propensity to oxidation particular attention should be paid to not only the type of free fatty acids, but also the difference of glyceride structure in the purified vegetable oils.

Effects of free fatty acids on the oxidative processes in purified olive oil

“…A singular exception was observed for peroxide value, whose increase was more marked when adding less unsaturated fatty acids: this was explained with the hypothesis of a more rapid decomposition of hydroperoxides catalyzed by unsaturated fatty acids, yielding secondary products. No clear effect was observed for the level of added fatty acids, so that only data for 0.05-0.5% (Yoshida et al, 1992a) and 0.5% (Yoshida, 1993) levels were reported. A significant effect was observed, instead, for the type of purified oil.…”

“…Other researchers studied the interaction of FFA with the oxidative processes in purified oils during microwave heating (Yoshida, 1993;Yoshida, Kondo, & Kajimoto, 1992a). As stated by the Authors, microwave energy effects could differ significantly from those of conventional cooking.…”

Microwave heating of different commercial categories of olive oil: Part II. Effect on thermal properties

“…Po showed higher content of linoleic acid, PUFA and TAG esterified with this fatty acid (LLL + LLPo, OLLn, LLP + OLnO, OLP + OOPo) than EVOo (Table 1). Vegetable oils with high degrees of unsaturated fatty acids were found to be more sensitive to the effect of microwave energy (Farag, Hewedi, Abu-Raiia, & El-Baroty, 1992;Yoshida, 1993). Albi, Lanzó n, Guinda, Pé rez-Camino, and Leó n (1997b) observed that thermal degradations of TAG were more abundant than were oxidative ones, especially after microwave heating, and this effect was more evident for highly unsaturated vegetable oils.…”

Oxidative changes of vegetable oils during microwave heating

“…High levels of oxidation were observed in model systems containing sunflower, soybean, and virgin olive oils during microwave heating, while lipid hydrolysis was only moderate (CAPONIO et al 2001). Oxidative changes depend on the unsaturation degree of oils, therefore, rapeseed oil was found more stable than soybean or safflower oils because of its lower polyenoic acid content (YOSHIDA 1993). Free fatty acids present in oil enhance the oxidation ( YOSHIDA 1993), which may be important if cold-pressed unrefined oils are used in microwave treated systems.…”

“…Oxidative changes depend on the unsaturation degree of oils, therefore, rapeseed oil was found more stable than soybean or safflower oils because of its lower polyenoic acid content (YOSHIDA 1993). Free fatty acids present in oil enhance the oxidation ( YOSHIDA 1993), which may be important if cold-pressed unrefined oils are used in microwave treated systems. Similar results were obtained on comparison of sunflower, soybean, and peanut oils, and a mixture of soybean and peanut oils (HASSANEIN et al 2003).…”