Diversity of antioxidant properties and phenolic content of date palm (Phoenix dactylifera L.) fruits as affected by cultivar and location

Abstract

Fruits of the date palm are very commonly consumed in many parts of the world and are a vital component of the diet. Date fruits were found to be a good source of antioxidant components. The antioxidant properties of date fruits vary depending on their content of phenolic components, vitamin C and flavonoids. Fruits of ten cultivars from USA and fruits of five cultivars from Saudi Arabia were collected in 2006 and 2007 to characterize and compare total phenolics content and antioxidant activities among them and to study the difference between ABTS and DPPH methods in measuring antioxidant activity in addition to the effect of growth location on antioxidant activity and phenolics content. Fruits of cultivars collected from Saudi Arabia had higher dry matter content than those collected from USA. In most of the tested cultivars, total phenolics contents were significantly higher during the second year of the study. Ranking of tested cultivars for total phenolics content indicated that SA4 (Gur) cultivar had the highest total phenolics content (507.0 mg GAE/100 g FW) during the second year of the study followed by US3 (Deglet Noor) cultivar which had a total phenolics content of 488.0 mg GAE/100 g FW during the same year. The lowest content was found in US9 (225.0 mg GAE/100 g FW) followed by US8 (Khalasa) (241.9 mg GAE/100 g FW) and US1 (258.4 mg GAE/100 g FW). US3 cultivar had higher antioxidant activity during the second year as compared to the first year of the study while SA5 (Khunizi) had higher antioxidant activity during the first year of the study. Over all cultivars, the second year samples had higher antioxidant activity than those of the first year as measured by either ABTS or DPPH. In general, US3, SA5 and SA4 had the highest antioxidant activity over all cultivars while US8, US9 (Medjool) and US2 (Barhee) had the lowest antioxidant activity over all cultivars. Although ABTS analysis indicated a higher antioxidant activity as related to the total phenolics contents in most cultivars, concordance correlation analysis indicated that DPPH analysis had higher reproducibility. Over all cultivars tested from both years, the antioxidant activity as related to total phenolics content was higher in samples collected from Saudi Arabia which indicate the higher efficiency of their phenolics content in free-radical-scavenging activity. In conclusion, the fruits of different date palm cultivars have different physical and chemical characteristics including dry matter content, total phenolics content and antioxidant activity. Total phenolics assay may be good indicator to evaluate antioxidant properties in date fruit.