Influence of gamma radiation on the antimicrobial activity of crude extracts of anacardium occidentale rich in tannins

Abstract

Anacardium occidentale L. Anacardiaceae, known as cashew, commonly found in northeastern of Brazil, has high levels of secondary metabolites, particularly tannins, used as raw material for herbal medicines. An efficient alternative to decontaminate plant products is the total sterilization or reduction of the initial microbial count, the process of gamma irradiation with 60Co. The objective of this study was to analyze the antimicrobial activity of crude extracts of bark and leaves of A. occidentale, based on the quantification of total phenols and tannins, before and after exposure to gamma radiation from 60Co. The extracts were obtained in the laboratory by cold maceration in ethanol, filtered and dryness. They were divided into non-irradiated control group (0 kGy) and irradiated: groups exposed to gamma radiation at doses of 5, 7.5 and 10 kGy. The total phenols was obtained by the Folin-Ciocalteau method and tannins, by the precipitation of casein. The antimicrobial potential activities of these extracts were also evaluated. The results showed that gamma radiation doses employed in this study did not influence statistically the percentage of total phenols and tannins in the bark extracts, at levels ranging from 5.73±0.14 and 5.20±0.14, respectively. The levels of metabolites in the leaves were statistically (p<0.05) influenced by radiation, observed average total phenols between 3.13±0.04 (0 kGy) and 3.50±0.08 (10 kGy), and tannin between 2.47±0.06 (0 kGy) and 2.93±0.04 (10 kGy). The extracts of bark and leaves were active against Staphylococcus aureus, Micrococcus luteus, Bacillus subtilis, Enterococcus faecalis, Mycobacterium smegmatis, Candida albicans. Gamma radiation caused an increase in antimicrobial activity of extracts against Staphylococcus aureus (Gram positive), with average inhibition zones for shells: 14.33±058 (0 kGy) and 22.33±0.58 (10 kGy), and leaves: 11.33±0.58 (0 kGy) and 19.00±1.00 (10 kGy). Exposure to radiation caused changes in physical and chemical constituents of phenolic extracts of leaves of cashew, increasing levels of tannins.