Effect of microwave heating with different exposure times on the degradation of corn oil

Abstract

In the present work, the influence of microwave power and heating times on the quality degradation of corn oil was evaluated. Microwave heating test was carried out using a domestic microwave oven for different periods at low- and medium-power settings for the corn oil sample. The changes in physicochemical characteristics related to oil degradation of the samples during heating were determined by standard methods. In this study, refractive index, free fatty acid content, peroxide value, p-anisidine value, TOTOX value, viscosity and total polar compound of the oils all increased with increasing heating power and time of exposure. In GLC analysis, the percentage of linoleic acid tended to decrease, whereas the percentage of palmitic, stearic and oleic acids increased. The C18:2/C16:0 ratio decreased in all oil samples with increasing heating times. Exposing the corn oil to various microwave power settings and heating periods caused the formation of hydroperoxides and secondary oxidation products. The heating reduced the various tocopherol isomers in corn oil and highest reduction was detected in ?-tocopherol. Longer microwave heating times resulted in a greater degree of oil deterioration. Microwave heating caused the formation of comparatively lower amounts of some degradative products in the oil samples heated at low-power setting compared to medium-power setting. The present analysis indicated that oil quality was affected by both microwave power and heating time.