Physico-chemical changes in rice bran oil during heating at frying temperature

Rice bran oil was subjected to static heating at 180 + 2°C in a domestic fryer for 8 h in this process 150 ml of the heated oil samples were drawn, at intervals of every 2 h, to study the changes in the physico-chemical characteristics. Results indicated that the peroxide value and free fatty acid content increased gradually from 0.2 to 2.9 Meq.O2/kg of oil and 0.25 to 0.63% respectively. The oil became darker as given by the colour value (5R + Y) 63 Lovibond units. Tocopherol content was found to decrease from 48 mg/100gram to 5 mg/100gram at the end of 8 h of heating whereas, oryzanol was fairly stable (1.59 to 1.40%). The p-anisidine value and Total polar compound (TPC) increased from 5.04 to 18.30 and 1.0 to1.8% respectively, showing the formation of secondary oxidation products. Rice bran oil is a non-Newtonian fluids having shear thinning behavior. Heating was found to cause an increase in the flow behavior index. Fatty acid composition did not show significant changes except for the linoleic acid content which decreased from 29.4 to 27.1%.