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.
Highlights
Frying is one of the most popular culinary operations practiced in both industrial and domestic food preparation procedures which develop unique sensory characteristics in the food (Leong et al, 2015)
(P
Low peroxide value (PV) observed in the samples stabilized with pomegranate peel extract than Oregano and Rosemary is indicative of effectiveness of the peel extracts in the mitigating oxidation of oils
Summary
Frying is one of the most popular culinary operations practiced in both industrial and domestic food preparation procedures which develop unique sensory characteristics in the food (Leong et al, 2015). Oil undergoes a series of reactions namely hydrolysis, autoxidation, thermal oxidation, isomerisation, and polymerization (Abiona et al, 2011). These changes invariably bring about objectionable odours, flavours, colours, and altered texture of the fried product (Tian et al, 2000; Bopitiya & Madhujith, 2014). Synthetic antioxidants have quite often been used in order to retard oxidative deterioration of oils and fatty products (Kahl & Kappus, 1993), the use of synthetic antioxidants is negatively perceived by consumers due to potential toxicity and their connotation as chemicals in food (Ramadan et al, 2010). Their antioxidant effect was due to the presence of hydroxyl groups in their chemical structure (Vekiari, et al, 1993; Shahidi, et al, 1997; Shahidi, 2000)
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