Antimicrobial effect of mashua (Tropaeolum tuberosum) extract against pathogenic microorganisms

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Mashua (Tropaeolum tuberosum) is an ancestral tuber (root) original from The Andes, with high yields and low costs for its cultivation. It contains glucosinolates, which can inhibit pathogenic bacteria responsible for foodborne diseases. For this reason, in vitro antimicrobial capacity of mashua was evaluated, as followed: ethanolic extract of tubers (roots) against Listeria monocytogenes, ethanolic and aqueous extracts of leaves and stems against Staphylococcus aureus and Bacillus cereus. To evaluate the antimicrobial capacity of the tuber, tissues were lyophilized and extraction was performed by centrifugation using 70% ethanol as solvent, the solvent was then removed by a rotatory evaporation system and the process was completed in an oven at 40°C for 24 hours. The minimum inhibitory concentration was determined from the 1:2 1:4; 1:6 and 1:8 concentrations. For leaves and stems, following lyophilization, ethanolic and aqueous extracts (without ethanol) were prepared using the same methodology, although the stoving process lasted 48 hours, and total phenols were quantified by the Folin-Ciocalteu method. Antimicrobial activity of all extracts was determined by the Kirby-Bauer disk diffusion test. Tuber extract at concentrations of 1:2 and 1:4 (33 mg/ml and 20 mg/ml) inhibited growth of L. monocytogenes, whereas 1:6 and 1:8 concentrations showed no antimicrobial effect. For leaves and stems extracts tested concentrations did not present inhibitory effect on the microorganisms studied, possibly by migration of the glucosinolates of the aerial part of the plant to the tuber, nevertheless high levels of total phenols were obtained so it can be harnessed by its antioxidant activity. According to the results obtained, the ethanolic extract of the tuber is a potential alternative for the control of L. monocytogenes. However, its effect should be assessed in food matrices.