Effect of microwave heating of linseed oil on the formation of primary and secondary oxidation products

Abstract

The purpose of the present study was to explore the influence of microwave heating for different periods on the primary and secondary oxidation, total oxidation as well as conjugation of stripped and non-stripped linseed oils. Color index of the oil samples was also evaluated to show changes of color during periodical heating. It was generally found that a significant increase in peroxide value, p-anisidine, total oxidation, conjugated diene and conjugated triene for microwave heating periods of 1,2,3,4 and 5 min. Two samples (stripped and non-stripped) of linseed oil (microwave treated) were analyzed individually in triplicate, and the results were reported as mean ±SD. Statistical significance of the differences between mean values was assessed by one-way ANOVA. It was found that stripped linseed oil (absence of antioxidants) is prone to heat effect than the non-stripped oil (with antioxidants). Generally, it is recommended that polyunsaturated oils have to be prevented from heat treatment for cooking purposes (e.g. soybean and linseed oils), since they contain linoleic and linolenic acids which are sensitive to oxidation.

Enhancing Oxidative Stability of Sunflower Oil during Convective and Microwave Heating Using Grape Seed Extract

“…Based on Figure 2 , it can be seen that oxidative degradation was greater in the microwave heating time than in the convective heating at comparable temperatures. Data obtained in this study are in agreement with others reported by Dostalova et al [ 6 ], Megahed [ 34 ], Erkan et al [ 35 ] that concluded that even a short period of microwave heating accelerates the formation of some undesirable and harmful compounds (e.g. oxidation products, transformed pigments) due to interactions between electromagnetic field with the chemical constituents of oil.…”

“…This effect was assessed in this study in parallel with convective heating under comparable temperatures. On this topic, there was controversy regarding free radical formation when oils and fatty food are subjected to microwave treatment [ 6 , 34 , 35 ]. Based on Figure 2 , it can be seen that oxidative degradation was greater in the microwave heating time than in the convective heating at comparable temperatures.…”

Oxidative changes in hazelnut, olive, soybean, and sunflower oils during microwave heating

“…Lampi et al [3] indicated that the amount of unsaturated fatty acids and their degree of unsaturation are the most important factors affecting oxidation and other factors, such as the position of unsaturated fatty acids in the triacylglycerols and the presence of anti-and pro-oxidants controlling oxidizability. Some researchers investigated the effects of microwave heating directly applied on oils [4][5][6][7][8][9][10] and others evaluated the effects of microwave application on oils extracted from microwaved seeds. [11][12][13][14][15][16] Jittrepotch et al [11] indicated that 0, 2.5, 3.5, 4.4, 5.5, and 6.5 min exposure to microwave heating significantly increased (p < 0.05) the peroxide value (PV), anisidine, and free fatty acid (FFA) of the peanut seeds oil.…”

Effects of Microwave Pre-treatment on the Quality of Kenaf (Hibiscus cannabinus L.) Seed Oil

“…Studies have shown that pre-treatment of hazelnuts with microwaves can increase the oil extraction yield, and increasing the treatment time also had a positive effect on the oil extraction yield [7]. In addition, microwaves heat treatment caused changes in composition and oxidative stability of the oils [8]. Microwave roasted rapeseed oils showed a markedly improved oxidative stability due to the increase of phenolic antioxidants [9].…”