Quantification of phenolic compounds, evaluation of physicochemical properties and antioxidant activity of four date (Phoenix dactylifera L.) varieties of Oman

Abstract

Abstract Objectives This study aimed to evaluate the antioxidant activity and to quantify the phenolic compounds by colorimetric and High Performance Liquid Chromatography (HPLC) analytical methods of four dates palm varieties cultivated in Oman. Methods The sun-dried mature fruits (Tamer stage) of Bunarinja, Khasab, Fard and Khalas date cultivars were collected from Al-Dakhiliya and Al-Sharqiya regions, Oman at the beginning of the 2013 harvest season. The antioxidant activities of date fruits were investigated by 1,1 diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging method. Folin-Ciocalteau colorimetric and HPLC methods were used to determine the total phenolic content (TPC) and to quantify the phenolic acids, respectively in the hydroalcoholic date fruit extracts. Results A preliminary HPLC analysis of the date fruits showed the presence of phenolic acids like Gallic acid, Vanillic acid, Caffeic acid, p-Coumaric and Syringic acid in different proportions. The TPC of all four varieties ranged from 32.24 mg to 35.84 mg Caffeic acid equivalents/100 g of fresh weight. All varieties exhibited significant free radical scavenging activity (28.78-70.62%) in a concentration dependent manner. Conclusion The present study confirms that Omani dates are a rich source of phenolic compounds and posses good antioxidant properties. HPLC also revealed the Gallic acid as the predominant phenolic acid in all date cultivars.