Infusions of Portuguese medicinal plants: dependence of final antioxidant capacity and phenol content on extraction features

BACKGROUND: Aqueous extracts of most medicinal plants traditionally employed in Portugal (at the ratio of 1 g plant: 110 mL water) have been assayed for total antioxidant capacity and phenol content, in order to elucidate their claimed medicinal features. RESULTS: The antioxidant activity was assessed by the ABTS^•+ method; the ascorbic acid equivalent values ranged from 1.4280 ± 0.1261 g L^-1 for avocado (Persea americana (Lauraceae)) obtained by infusion of powder, down to 0.0027 ± 0.0012 g L^-1 for olive (Olea europaea (Oleaceae)) obtained by infusion of leaves. Total phenol content was determined by the Folin-Ciocalteu procedure; the gallic acid equivalent values ranged from 0.5541 ± 0.0289 g L ^-1 for avocado obtained by infusion of powder, down to 0.0053 ± 0.0014 g L^-1 for olive obtained by boiling leaves. A good correlation between total antioxidant capacity and total phenol content was found. CONCLUSION: The method of powder infusion should be chosen if high concentration of antioxidants are sought. On the other hand, a high antioxidant capacity and a high phenol content correlate well with the empirically established (and widely publicised) capacity to treat respiratory infections.