Quality and stability of canola and sunflower oils blended with palm olein during frying and microwave heating

Abstract

The aim of this study was to evaluate the changes in quality and oxidative degradation of canola oil (CO) and sunflower oil (SFO) and their blends with comparatively low priced palm olein (PO) during frying and microwave heating. The oil blends were prepared by blending PO with CO and SFO in the volume ratios of 20:80 (PC1 and PSF1) and 40:60 (PC2 and PSF2). Refractive indices of the samples increased insignificantly as the heating time performed by the oils increased. The amounts of free fatty acids were found to be higher in PO and in blends compared to the substrate oils. Peroxide values during frying or microwave heating of all the samples were increased until a maximum is reached and then decreased until the end of the heating. Other quality indices such as p-anisidine value, polymer content, viscosity, specific extinctions, food oil sensor and color unit values increased significantly in most of the samples as heating time progressed with increase in the blends being lower than those of the substrate oils. The amount of total polar compound in all the oil samples increased significantly with the time increment. During frying and heating, progressive decreases in iodine value and oxidative stability index were detected. However, PO addition to CO or SFO decelerated the formation of primary and secondary oxidative products and polymeric compounds during heating. In Gas Liquid Chromatography (GLC) analysis, the percentage of linoleic and linolenic acids tended to decrease, whereas the percentage of palmitic, stearic and oleic acids increased in most of the samples during frying and microwave heating. The decreased amounts in C18:2/C16:0 ratios from the initial values were observed for PO, CO and SFO in frying and microwave heating; being higher than those of their blends. In differential scanning calorimetry (DSC) analysis, addition of PO altered the shapes of endo- or exotherm peaks of CO and SFO. In this study, most of the degradation indicators suggested that the degradation was the fastest in CO or SFO as compared to their blends. Overall, it can be concluded that addition of PO to CO or SFO slowed down the oxidative degradation rate of the substrate oils. Blend PC2 and PSF2 showed slightly better frying performance compared to PC1 and PSF1.