Plant location and extraction procedure strongly alter the antimicrobial activity of murta extracts

Abstract

Leaves and fruits of Murta (Ugni Molinae Turcz.) growing in three locations of Chile with diverse climatic conditions were extracted by using ethanol/water mixtures at different ratios and the antimicrobial activity was assessed. Extracts containing the highest polyphenolic content were from murta plants grown nearer to the mountain (58 mg GAE/g murta), subjected to extreme summer/winter-day/night temperature changes and rainy regime. Extracts from leaves collected in the valley and coast contained 46 and 40 mg GAE/g murta, respectively. A mixture of 50% ethanol/water was the most efficient in extracting polyphenols, showing pure solvents—both water and ethanol—a lower extraction capacity. No correlation between antioxidant capacity and polyphenolic content was found. Extracts from Murta leaves provoked a decrease in the growing of Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus, and showed no activity against the beneficial, probiotic bacteria. A significant correlation between polyphenol content and antimicrobial activity on harmful bacteria was found. Myricetin glucoside and quercetin glucoside/glucuronide/dirhamnoside presumably contributed to the antimicrobial activity of the extract. The higher antimicrobial activity of leaves extracts compared to the fruits could be attributed to flavan-3-ols and other flavonol glycosides. Quercetin glucuronide, myricetin xyloside and flavan-3-ols in polymeric form were tentatively identified for the first time in murta extracts. Both extracts showed an antimicrobial activity similar to some commercial antibiotics, suggesting their suitability to replace synthetic antimicrobials in food.