Bioactive Compounds Responsible for Antioxidant Activity of Different Varieties of Date (Phoenix dactylifera L.) Elucidated by ¹ H- NMR Based Metabolomics

Several studies have demonstrated strong antioxidant activity of date fruits. Nevertheless, limited data is available for the bioactive compounds responsible for the activity. In this study, the antioxidant activity of five different date varieties (Ajwa, Anbara, Piyarom, Rabbi and Deglet Nour) extracted using 80% ethanol was determined using free radical scavenging (DPPH), ferric reducing power (FRAP) and antioxidant capacity (ABTS) assays. The 1 H- NMR was employed to profile the bioactive metabolites present in the dates. The obtained results demonstrated that the Piyarom extract had the highest total phenolic content (355 mg GAE/100g DW), total flavonoid content (57.07 mg/100g DW) and exhibited good antioxidant activity with IC 50 of 16.2 µg/mL, 26.38 mmol Fe (II)/g and 11.3 µg/mL for DPPH scavenging activity, FRAP antioxidant power and ABTS antioxidant capacity, respectively. The metabolites responsible for the variation between different date’s varieties were successfully identified using 1 H-NMR–based metabolomics. The principal component analysis (PCA) and partial least squares (PLS) analysis depicted clear and distinct separations into three clusters representing the five date varieties. The metabolites responsible for the separation were identified as sucrose, betaine, fructose, ascorbic acid, glycine, and arginine. Correlation study from PLS biplot revealed that glucose, ascorbic acid, epicatechin, gallic acid, and citric acid are responsible for the antioxidant activity measured.