Antioxidant activities of ethanolic extracts of four Tunisian olive varieties

Abstract

Olive leaves extracts of four olive varieties from Tunisian origin: Chitoui, Chimlali, Sahli and Zarrazi were studied for their phenolic contents, antioxidant activities and their effect on corn oil stability. The amounts of total polyphenolics, flavonoids and proanthocyanidins were determined by spectrophotometry. The antioxidant activities of extracts were evaluated and compared with butylated hydroxytoluene (BHT) using a             β-carotene bleaching assay and a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging method. Chimlali ethanol extract showed the highest total phenolics, flavonoids and proanthocyanidins contents expressed respectively in gallic acid, in quercetin  and catechin equivalent per gram of dried matter 245.5; 9.12 and 40.92. Chimlali ethanol extract showed the highest antioxidant activity coefficient (AAC) of 863.636 at 200 mg/ml by the β-carotene bleaching method and the highest scavenging activity of 7.5 µg.mL^-1 at 0.1 mg/mL by the DPPH method. The obtained results showed that the variety Chimlali is the richest in phenolic compounds, flavonoids, and proanthocyanidins and  the most potent of antioxidant activity. Analysis of the oxidation results of corn oil, heated to 110°C and during frying, showed a significant antioxidant effect of ethanolic olive leaves extracts relative to the BHT. Olive leaves extracts from varieties Chimlali and Sahli showed the highest antioxidant activity. The synthetic antioxidant BHT exhibits a lower antioxidant power than the extracts from varieties Sahli and Chimlali but is comparable to other varieties. The results suggest the introduction of olive leaves extracts in food preparation, both during storage or heating food, for better preservation.