Phenological Stages as Quality Determinants of Phenolics Content and Antioxidant Activity of Seven Date Varieties Grown in Algeria

In the present study, the methanolic extracts of fruits of seven date palm varieties (Deglet-Nour, Mech-Deglet, Ghers, Arechti, Ytima, Taouri, Tantboutche) grown in Biskra, Algeria were assessed for their total phenolics, and flavonoid content and antioxidant activity at three edible maturity stages namely Khalal, Rutab and Tamar according to the standard Iraqi Arabic nomenclature.  Polyphenols expressed as mg of gallic acid equivalents (GAE) per g of dry matter (DM) were found to be relatively higher in Khalal (1.705 - 8.620), from 0.303 to 4.787 in Rutab, and from 0.161 to 1.993 in Tamar. On the other hand, the flavonoids content calculated as quercetin equivalents (QE) per g of DM was found to vary between 0.282 and 0.627 in Khalal, from 0.210 to 0.491 in Rutab and from 0.008 to in 0.075 in Tamar. Moreover, the antioxidant activity was conducted using DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical assay.   Important scavenging ability was recorded with almost all varieties in the Khalal and Rutab stages (average IC₅₀ of 30.417 µg/ml for Khalal and 30.415µg/ml for Rutab), however the Tamar fruits displayed the weakest activity (average IC₅₀=107.00 µg/ml). A positive correlation was observed between total phenolics and antioxidant ability in different stages and varieties suggesting that phenolics were the main contributor to this activity.