Atividade antibacteriana e antioxidante de extrato de araçá (Psidium cattleianum Sabine): influência da temperatura, do genótipo e estudo do mecanismo antiestafilocócico

Abstract

Araçá is a fruit with high levels of bioactive compounds whose antimicrobial potential is still little explored. The aim of this study was to evaluate the antibacterial and antioxidant activities of araçá fruit extracts (AEs), verify the influence of genotype and temperature on their bioactivity and elucidate the mechanism of action of AEs against Staphylococcus aureus. The AEs were prepared with yellow and red araçá genotypes. The antibacterial activity of the AEs was evaluated by disk diffusion, minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) tests using ATCC strains of S. aureus, Listeria monocytogenes, Escherichia coli, Salmonella Typhimurium and Campylobacter jejuni. Antioxidant activity was determined using the DPPH radical scavenging method. Total phenolic content was determined by spectrophotometry and the quantification of individual phenolic compounds was performed by HPLC-MS, with all determinations carried out before and after heat treatments. The thermostability was evaluated by exposing the AEs to temperatures between and 100 ºC, for 1 h at each temperature. The antistaphylococcal mechanism of action was determined by kinetics of antibacterial action, cell membrane integrity bacterial (releasing of macromolecules and nucleic acids, scanning electron microscopy and confocal laser scanning microscopy), as well as by testing the interaction of AEs with bacterial DNA (fluorescence spectrophotometry). The AEs showed antibacterial activity against all microorganisms, with inhibition halos diameter ranging from 11 to 17 mm. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values ranged between 9 and 147 mg mL-1 and 18 and 294 mg mL-1 , respectively. The lowest MIC and MBC values were found against S. aureus. There was no difference in antibacterial activity between yellow and red genotypes and the antioxidant activity was higher than 90%, before and after the heat treatment in all AEs evaluated. The total phenol content ranged from 414 to 465 mg 100 g-1 , with higher values in red AEs than in yellow AEs. Gallic, ferulic, and cumharic acids were idenfied in all AEs. The heat treatment of the AEs increased 2 to 4 times the MIC and MBC values and there was a reduction in the concentration of phenolic compounds. In addition, the heat treatment caused partial losses in phenolic compounds, with exception of ferulic and cumharic acids in red AEs, in which did not have significant losses. In the study of the mechanism of antistaphylococcal action of AEs the bacterial multiplication was inhibited by AEs within 24 h of contact when the MBC was used. The bacterial cell membrane was compromised, losing its integrity, and releasing important cellular constituents. AEs also showed the ability to intercalate with bacterial DNA, indicating that its antistaphylococcal activity of AEs occurs by modification in cell membrane integrity and by causing damage to the DNA of S. aureus. This study shows promising and unpublished results and demonstrates that AEs have antibacterial and antioxidant potential, regardless of genotype to be used as a natural adjuvant in food preservation, including thermally processed foods.