Infusions of Portuguese medicinal plants: Dependence of final antioxidant capacity and phenol content on extraction features Maria S Gi ˜ ao, 1 Maria L Gonz ´ alez-Sanjos ´ e, 2 Maria D Rivero-P ´ erez, 2 Cl ´ audia I Pereira, 1 Manuela E Pintado 1 and F Xavier Malcata 1∗ 1 Escola Superior de Biotecnologia, Universidade Cat ´ olica Portuguesa, R. Dr. Ant ´ onio Bernardino de Almeida, P-4200-072 Porto, Portugal 2 Department of Biotechnology and Food Science, Burgos University, E-09001 Burgos, Spain Abstract 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. Keywords: Persea americana (Lauraceae); powder; leaves; ABTS •+ ; Folin–Ciocalteu INTRODUCTION Antioxidants have been extensively employed in the food industry, mainly as preservatives. Crude extracts of fruits, herbs, vegetables and cereals, as well as derived products, are particularly rich in phenolic compounds, so they have been a focus of attention by industry, because they can retard oxidative degradation of lipids, for example, and thereby improve quality and nutritional value of lipid-containing foods. 1 Phenolic compounds have been commonly found in both edible and non- edible plants, in which they exhibit a multiplicity of biological effects, including anti-inflammatory capacity, cholesterol regulation, vascular problem healing and antioxidant activity. The latter activity lies in their capacity to act as reducing agents, hydrogen donors, singlet oxygen quenchers and metal chelators. 2 Further to such preservation features, antioxidants are now increasingly sought in the human diet because of their benefits upon health. In this regard, antioxidants are viewed as compounds that protect cells against oxidative stress, which might otherwise lead to cell damage. 3–6 Coronary heart diseases, ulcers, cancer and neurodegenerative diseases (e.g. Parkinson’s and Alzheimer’s), besides overall ageing, are but a few examples of diseases and conditions that can be prevented (or at least delayed) via regular and balanced inclusion of antioxidants in the human diet. 7,8 There is a long history of medicinal properties ascribed to plants that grow wild in nature, and such plants still constitute a major source of pharmaceutical and healthcare products. The active roles of several herbal infusions in disease prevention (and even cure) have been attributed, at least in part, to antioxidant properties of their constituent (liposoluble) vitamins A and E, (water soluble) vitamin C, and several amphipathic molecules, which are broadly termed phenolics. 9 A whole range of plant-derived dietary supplements, phytochemicals and pro-vitamins, which that have been claimed to assist in maintaining good health and fighting disease, are now described as ∗ Correspondence to: F Xavier Malcata, Rua Dr. Ant ´ onio Bernardino de Almeida, P-4200-072 Porto, Portugal E-mail: fxmalcata@esb.ucp.pt Contract/grant sponsor: Funda ¸ c˜ ao para a Ci ˆ encia e a Tecnologia, Portugal; contract/grant number: SFRH/BD/19601/2004 Contract/grant sponsor: Ag ˆ encia de Inova ¸ c˜ ao, Portugal; contract/grant number: EXTRAVIDA, 13-05-04-FDR-00020