Comparative assessment of total phenolics content and in vitro antioxidant capacity variations of macerated leaf extracts of Olea europaea L. and Argania spinosa (L.) Skeels

Abstract

The present study aims to ascertain the potency of Olea europaea L. and Argania spinosa (L.) Skeels leaves extracts in natural phenolic compounds of variable antioxidant properties. The obtained extracts were investigated for their total phenolic and total flavonoid content, total antioxidant activity (TAC), as well as evaluated for their ferric reducing capacity (FRAP), β-carotene bleaching inhibition capacity, and for the radical scavenging activity through the extent of their abilities to scavenge the DPPH• and ABTS+ radicals. Antioxidant contents and capacities were expressed as mg/g DW, IC50, and as (%) inhibition in percentage. Total phenolic content was ranged between 378.10 ± 2.05 to 22.51 ± 0.07 mg/g DW in argan samples and from 226.50 ± 1.32 to 15.02 ± 0.04 mg/g DW in olive samples, expressed as gallic acid equivalents and shown in the decreasing order: methanolic extracts > aqueous extracts > ethyl acetate extracts. Moreover, for both plant species; the highest reducing and antiradical power as well as the greatest total antioxidant capacities, were obtained by the methanolic leave extracts. Whilst the most distinguished β-carotene bleaching inhibition was observed for aqueous extracts of olive (90.67%) and argan (87.39%) macerated leaves. With this highly revealed antioxidant power of the extracts, it was significantly linked to the important correlations between the in vitro executed assays and the total phenolic (TP) and total flavonoid (TF) contents detected. Based on the obtained results, it could be concluded that argan and olive leaves display promising antioxidant capacities to potentially serve as rich sources of phenolic compounds with variable antioxidant properties.