Comparative Study of Vegetable Oils Oxidative Stability using DSC and Rancimat Methods

Abstract

A comparative study was carried out to evaluate and compare the oxidative stability of vegetable oils (olive, corn and sunflower) in Egypt, through evaluation of accelerated oxidation at four different isothermal temperatures (110, 120, 130, 140 °C) using two different instruments: a differential scanning calorimeter (DSC) and a Rancimat instrument, taking into account the physicochemical quality characteristics and relationships between oxidative stability and fatty acid composition of oils. The Rancimat instrument was set at the four different isothermal temperatures with an air flow 20 L/h and measures the induction period (IP) of the selected oils. The differential scanning calorimetry (DSC) technique involved accelerated oxidation of oil samples in an air flow of 60 ml/min in DSC cell set at four different isothermal temperatures. A rapid increase in evolved heat was observed with the appearance of a sharp exothermic curve during initiation of the oxidation reaction. From the resulting exothermic curve, the onset of oxidation time (To) was determined graphically by the DSC instrument. There was an excellent correlation (p < 0.0001) found between DSC (T0) values and Rancimat (IP) measurements where the Pearson correlation coefficient (>0.98) between the two methods with coefficient of determination (R2 >0.89) for DSC independent of the vegetable oil source, imply that DSC can be recommended as an alternative appropriate objective method for assessing the oxidative stability of vegetable oils because of its simplicity, absence of toxic chemicals, small amount of sample and time-saving nature and could be easily used for routine analysis in oils and fats industry.