Effect of some plant extracts in reducing oxidation of selected edible oils during deep frying

Abstract

The repeated use of edible oils leads to oxidative degradation of lipids which results in the development of objectionable odours, flavours, colours and more importantly, generates toxicants. The objective of the present study was to examine the efficacy of natural anti- oxidative extracts obtained from rosemary, oregano and pomegranate peel in mitigating the oxidation of coconut oil (CO), virgin coconut oil (VCO) and sunflower oil (SO). These edible oils were used for frying standard-sized potato strips in the presence of three different anti- oxidative extracts; namely, pomegranate peel powder, oregano and rosemary extracts, at 2% (w/w) level. A sample of oil (10 mL) was collected into a vial, flushed with nitrogen and stored at -18⁰C until analysis. Frying was repeated twice more with the same oil. Oil devoid of any extract was used as the control. The samples collected 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 in all oil systems tested, indicating a gradual oxidation of oils with time. A significant (P < 0.05) inhibition of oxidation due to incorporation of additives was observed in all oils. The stability of oils increased in the order: sunflower oil < sesame oil < virgin coconut oil. Generation of primary as well as secondary oxidative products was higher in sunflower oil (PV: 1.33 - 5.38 meq/kg, TBARS: 68.27 - 104.12 meq MA/kg) than in SSO and VCO. The inhibition exerted by anti- oxidative extracts against development of primary oxidative products as measured by PV was significantly (P < 0.05) higher in SO followed by VCO and SSO. The inhibition exerted against development of TBARS was higher in VCO as compared to SO and SSO. It can be concluded that anti-oxidative extracts such as pomegranate peel powder, oregano and rosemary can be effectively used to mitigate oxidation of edible oils during accelerated storage.