Determination of the effects of olive wastewater and pomace extracts on the oxidative stability of refined sunflower oil

In the present study, the effect of olive wastewater and pomace extracts on the oxidative stability of refined sunflower oil during deep frying and under accelerated oxidation conditions were investigated. The 2,2?-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, ferric ion reducing antioxidant power and the antioxidant activity, which was determined by the conjugated diene method and the ß-carotene method in linoleic acid emulsion, of the wastewater extracts at different concentrations were all determined to be higher than those of the pomace extracts. An increase in the extract concentration resulted in an increase in antioxidant activity. The Trolox-equivalent antioxidant activity of wastewater extracts was determined to be in the range of 6.8-26.0 µM whereas that of pomace extracts was determined to range between 6.7 µM and 27.1 µM. The wastewater extract at a concentration of 3 mg/mL was determined to have a higher reducing power than the butylated hydroxyanisole (BHA) that was used at a concentration of 0.2 mg/mL. The addition of extracts increased the induction periods of the sunflower oil and its triglycerides. The use of lecithin along with the extracts was shown to be more effective and higher protection factor values were achieved. The E232 values of the sunflower oil with extract (1 mg/g) and lecithin (5 mg/g) was lower than that of BHA and oil samples containing ?-tocopherol in the oxidation test conducted in the incubator at 60 °C. The E232 values of the triglycerides increased after the 9th day and those of wastewater containing samples increased after the 12th day. Wastewater extract was more efficient in lowering the conjugated acid content of the sunflower oil samples than the pomace extract during the oxidation test conducted at 180 °C. The sunflower oil containing wastewater extract and lecithin was shown to have lower p-anisidine values, higher tocopherol content and higher induction periods than that containing butylated hydroxytoluene (BHT) at the end of 40 hours. The oil samples with wastewater extract and lecithin were determined to have lower conjugated diene content, p-anisidine value, polar material content, viscosity and b* values than the control samples during deep frying. However, lecithin caused an increase in the free fatty acid content of the oil and darkening of the color. Key Words: Wastewater, pomace, antioxidant activity, induction period, accelarated oxidation, deep frying