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

The murta, also known as the Chilean guava or the strawberry myrtle, is a shrub native to Chile and adjacent regions of southern Argentina. In Chile, it grows in three locations that have diverse climatic conditions.

Chilean scientists extracted the leaves and fruit of the shrub by using ethanol-water mixtures at different ratios. Then they assessed the antimicrobial activity of the extracts. Extracts containing the highest polyphenolic content came from murta plants grown near the mountain regions. These plants were subjected to extreme summer-winter and day-night temperature changes and a rainy regime. Extracts from leaves collected in valleys and along the coast contained 46 mg and 40 mg gallic acid equivalent per gram of murta, respectively.

A mixture of 50% ethanol and water was the most efficient solvent for extracting the polyphenols. Pure solvents, both water and ethanol, had a lower extraction capacity. The researchers found no correlation between antioxidant capacity and polyphenolic content.

Extracts from murta leaves generated a decrease in the growth of P. aeruginosa, K. pneumoniae and S. aureus. They showed no activity against beneficial probiotic bacteria. The scientists found a significant correlation between polyphenol content and antimicrobial activity on harmful bacteria.

The researchers believe that myricetin glucoside, quercetin glucoside, glucuronide and dirhamnoside contributed to the antimicrobial activity of the extracts. Quercetin glucuronide, myricetin xyloside and flavan-3-ols in polymeric form were tentatively identified for the first time in murta extracts. The higher antimicrobial activity of extracts from the leaves, compared to extracts from the fruit, could be attributed to flavan-3-ols and other flavonol glycosides. The extracts showed an antimicrobial activity similar to some commercial antibiotics, suggesting that they have potential to replace synthetic antimicrobials in food.

Further information. Monica Rubilar, Departamento de Ingenieria Quimica, Centro de Genomica Nutricional Agroacuicola Unidad de Tecnologia de Procesos, Universidad de La Frontera, Av. Francisco Salazar, 01145 Temuco, Chile; phone: 45-744232; email:
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Publication:Microbial Update International
Geographic Code:3CHIL
Date:Dec 1, 2011
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