Refractive index as an objective method for evaluation of rancidity in edible oils and fats

Common edible oils and fats (refined peanut oil, seasame oil, safflower oil, and butter oil, ghee) were exposed to direct sunlight, fluorescent light and Schaal Test. Data collected on refractive indices (N D 25 ) show an increase of the order of 0.001±0.0003 at the stage of development of perceptible rancid odor. The pattern of changes in refractive indices and peroxide values of these edible oils, autoxidized at 100±5 C, show that refractive indices indicate more precisely the termination of the induction periods than peroxide values.