Effect of the harvesting period on the phenolic content and on antioxidant activity of two Algerian olive cultivars

Because of their antioxidant and anti-free radical capacities, the phenolic compounds of olives gained growing interest. The aim of this work is to determine the harvest optimal period of two Algerian olive varieties (Chemlal and Blanquette de Guelma) harvested at four stages of maturity which will allow the best equilibrium between the olives' composition in phenolic compounds and their antioxidant activities. Phenolic compounds were determined by colorimetric methods and by UPLC-PDA. The antioxidant activity of olive extracts was assessed by measuring the reducing power, the antiradical activity toward DPPH radical and ABTS. Results confirm that the process of maturation and the variety of olives affect considerably the phenolic compounds and their antioxidant activity. As a consequence, a significant decrease in the antioxidant activity (reducing power and antiradical activities) of the olive fruits is observed. The relative antioxidant capacity index (RACI), which represents the mean scores of the antioxidant activities, showed that the highest indices were obtained by the green stage for Chemlaland spotted green stage for Blanquette de Guelma. The harvesting can occur when the olives are in the spotted green stage, corresponding to the middle of December. This period allows a good combination between the phenolic content and antioxidant activity.