Comparative study of the antioxidant activity and phenolic compounds in green and processed yerba mate (Ilex paraguariensis)

LAURA COGOI, SEBASTIAN TURNER, SANTIAGO ISOLABELLA, GRACIELA FERRARO, CLAUDIA ANESINI, ROSANA FILIP

Montpellier, France

Conferencia; International Conference on Polyphenols; 2010

Ilex paraguariensis St. Hil., commonly named “mate” or “yerba mate”, is one of the species in South America most employed as a decoction or infusion due to its energizing, nutritional and medicinal properties. Antioxidant activity is attributed to Ilex species as are used as antirrheumatic and for gastrointestinal disorders for their eupeptic and choleretic properties. Yerba mate contains methylxanthines. Previous phytochemical studies carried out by HPLC demonstrated the presence of phenolic compounds (caffeoyl derivatives and flavonoids) which presented well documented antioxidant activity in different in vitro models, with a high correlation between the polyphenols content and the antioxidant activity. Growing knowledge about the health-promoting impact of antioxidants in everyday foods, combined with the assumption that a number of common synthetic preservatives may have hazardous effects, has led to increased investigations in the field of natural antioxidants. Yerba mate is not consumed as a raw material but instead it is processed before commercialization. The harvested fresh leaves and stems are dried over fire, milled and then the product is submitted to a forced aging process, where the material is stored under controlled temperature and humidity conditions during 30-60 days in order to acquire the desired taste, aroma and color.        By other way, the examination of the abilities for an antioxidant to scavenge DPPH radical and to inhibit lipid peroxidation has been traditionally and widely accepted to justify the antioxidant capacity.        Taking into account the reported antioxidant effect, the aim of this study was to evaluate if the industrial process can alter the antioxidant activity, specially, DPPH free radical and the prevention of lipid peroxidation of I. paraguariensis. Fresh leaves just harvested (green leaves: GL) and the commercial product obtained after the aging process (forced aging: FA) were analyzed.  Aqueous crude extracts were prepared and then lyophilized. The total polyphenols content was determined according to the Folin-Ciocalteu method and the main phenolic compounds, caffeoyl derivatives (chlorogenic and caffeic acids) and flavonoids (rutin) were quantified by HPLC with DAD.        Both extracts (GL and FA) presented scavenging action on free radical DPPH and preventive effect on lipid peroxidation in relation with the concentration. The maximum effect exerted was similar to that obtained by the antioxidant control ascorbic acid in both in vitro antioxidant models. Nevertheless, the GL extract was the most potent. The EC50 value obtained with GL extracts was between 1.8 to 1.99 times lower in the case of DPPH scavenging activity and between 1.62 to 1.78 times lower in the case of the prevention of lipid peroxidation, in comparison with EC50 values obtained with FA extracts.             On the other hand, total polyphenols content of FA extracts was higher than that obtained for GL. The comparative quantitative analysis by HPLC indicated that the FA extracts possess higher content of chlorogenic acid (2.03 ± 0.05) % and rutin (1.30 ± 0.03) % when compared with green leaves (chlorogenic acid: 1.84 ± 0.04 % and rutin: 0.98 ± 0.05 %). No significant differences were found for caffeic acid among samples (p< 0.05 according to one way ANOVA and Dunnett´s test).                         The results obtained in this work demonstrated for the first time that the industrial processing decreases the antioxidant activity of I. paraguariensis extracts, despite an increase in the polyphenol content was observed. These results suggest the presence of compounds with pro-oxidant activity which should be investigated.