Oxidative stability of edible oils via addition of pomegranate and orange peel extracts

The main objective of the present study was to improve the oxidative stability of sunflower oil (SFO) and soybean oil (SBO). The aqueous ethanol extracts (80% ethanol) of pomegranate and Baladi orange peels were used as natural antioxidants at concentrations of 800 and 1,200 ppm in SFO and SBO in comparison to butylated hydroxytoluene (BHT). Their antioxidant activities were estimated via the Rancimat method and over 24 days of storage at 65°C. The effect of extracts on the stability of sunflower and soybean oils during the storage period was studied by measuring the peroxide value (PV), conjugated dienes (CD) at 232 nm, conjugated trienes (CT) at 270 nm, free fatty acids (FFAs), iodine value (IV), and the refractive index (RI). A great difference in PVs was observed between the control sample and the oil samples containing natural extracts which slowed the rate of peroxide formation. Generally, the results showed that during the storage period at 65°C, the conjugated diene formation followed a similar pattern relative to PV accumulation. The PV, CD, CT, FFA, and RI values of SFO and SBO containing a pomegranate peel extract (PPE) and Baladi orange peel extract (BOPE) at concentrations of 800 and 1,200 ppm were lower than those of SFO and SBO containing 200 ppm BHT, and this trend became apparent during the storage period. The rate of reduction of IV in the control was higher than that in SFO and SBO containing both synthetic and natural antioxidants. These findings confirmed that the natural antioxidants under investigation could be used as alternatives to synthetic antioxidants to improve the oxidative stability of edible oils in the food industry.