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

ABSTRACT

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. 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. 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. 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