Effect of deep-fat frying on fat oxidation in soybean oil.

The frying performance and stability of pure soybean oil (PSBO), soybean oil blended with palm kernel olein and PSBO with an antioxidant mixture of butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate and citric acid were compared. The oils were subjected to intermittent frying (up to 15 fryings, without any 'topping up') of potato slices, at 180 degrees C for a period of and 337 min. Analytical determinations on the oils included the peroxide value (PV), iodine value (IV), free fatty acid (FFA) value, saponification value (SV) and the refractive index (RI). Changes in the product at the sensory level were also assessed. Results showed that (1) fat oxidation hence, reduction of unsaturated fatty acids, as indicated by changes in the IV, was non-significant in the treated oils, (2) hydrolysis of fats, as shown by changes in the FFA value from the first to last frying, was lowest in the blended oil but highest in PSBO, (3) the same trend as above was observed for PV, an indicator of fat oxidation and rancidity, (4) changes in SV were non-significant in the treated soya oils while PSBO with the antioxidant showed the least change in RI, (5) treated oils exhibited no visual increase in viscosity or turbidity and (6) PSBO with the antioxidant had the lightest colour at the end of the frying period. Taste panellists were unable to discriminate between products fried in the treated oils and in PSBO. Sensory assessment showed an improved quality of the chips fried in the blend. Chips fried in PSBO scored the lowest ratings. Thus, the overall results showed an improved behaviour and quality of the treated oils in terms of themal stability during frying.