Abstract
The present study was undertaken to investigate the effect of heating, reheating and exposure to microwave radiation on some biophysical and biochemical properties of edible oils. In homes and restaurants, vegetable oils used for cooking are usually heated to very high temperatures, and may be reused several times to save costs. The recycling process involves repetitive heating of the oils may be bad for health. In this study used four samples of edible oils such as olive oil, cotton seeds oil, supply oil and corn oils in which used two kilograms for each sample and were collected from the origin of production in the local market and considered as fresh oils. The biophysical results showed that viscosity, refractive index of edible oils increase with the increase of heating frequency, this increase is higher in case of normal heating than microwave heating, the color intensity increased with normal heating and decreased with microwave exposure. The biochemical results revealed that the saponification number, the acid and peroxide values increased with increasing frequency of heating by both methods and the iodine number decrease by increased heating by the two methods. From this results it is concluded that the normal heating for four times induced biophysical and biochemical changes that must be taken in consideration, using microwave exposure induces minor changes in biophysical and biochemical properties and the olive oil showed the lowest level of changes which may be due to its high content of monounsaturated fatty acids, which may be the reason of its least autoxidation of rancidity