Degradation Kinetics of the Antioxidant Activity in Date Palm (Phoenix dactylifera L.) Fruit as Affected by Maturity Stages

Fruits of three date palm (Phoenix dactylifera L.) cultivars, namely Berhi, Khalas and Khawaja were evaluated for their total antioxidant activity, total phenolics and ascorbic acid at four ripening stages; full-color, just-ripe, half-ripe and full-ripe. The total antioxidant activity was estimated by the ferric reducing ability of plasma (FRAP). FRAP values, ascorbic acid and total phenolics were all higher at full-color unripe state. Khawaja possessed the highest FRAP values (expressed as mmol/100 g dwb): (18.9 +/- 0.95), followed by Khalas (12.0 +/- 0.82) and Berhi (3.4 +/- 0.49) cultivars. Similar ranking was observed for total phenolics (expressed as mg GAE/100 g dwb): 434.3 +/- 20.7, 397.2 +/- 14.3 and 283.3 +/- 5.4, respectively. As the ripening proceeded, FRAP values, total phenolics and ascorbic acid progressively declined. The kinetic studies revealed that the decline of the FRAP values, total phenolics and ascorbic acid essentially followed a pseudo-first order reaction. The rate constants and half-life of these parameters are calculated and the probable role of total phenolics and ascorbic acid is further discussed.