The Effect of antioxidative extracts on mitigating autoxidation of selected edible oils during deep frying

Abstract

The effect of extracts of pomegranate (Punica granatum L.) peel, rosemary and oregano on the oxidative stability of Coconut Oil (CO), Virgin Coconut Oil (VCO), Palm oil (PO), Sunflower Oil (SO) and Sesame Oil (SSO) during deep frying (170 ± 5 °C/10 min) was determined. These five locally available edible oils were used for frying standard size potato strips in the presence of three different antioixdative extracts namely, pomegranate pee, oregano and rosemary extracts at 2% (w/w) level. A sample of oil used for frying (10 mL) was collected into a glass vial, flushed with nitrogen and stored at -18°C until analysis. Frying was repeated twice more with the same oil. Oil devoid of any extract was used as the control. The samples were analysed for peroxide value (PV) and thiobarbituric acid reactive substances (TBARS). Results revealed that both PV and TBARS values gradually increased with the frying cycle across all oil systems tested indicating a gradual rise of oxidation of oils with use. The order of oxidative stability of oils followed the order: SO< SSO< PO< CO< VCO. A significant (p<0.05) inhibition of oxidation was observed in all oil systems tested as a result of the plant extracts incorporated into oils during deep frying. The least resistance against oxidation was observed in SSO which is predominantly rich in unsaturated fatty acids while VCO exhibited the highest level of resistance. Results further revealed that the pomegranate peel powder exerted the strongest antioxidant activity compared to that of the oregano and rosemary extracts.

Keywords

• deep frying, edible oils, oxidation, peroxide value (pv), thiobarbituric acid reactive substances (tbars)