Application of Central Composite Design to evaluate the antilisterial activity of hydro-alcohol berry extract of Myrtus communis L.

The antimicrobial activity of the hydro-alcohol extract of Myrtus communis L. (ME) berries was investigated against six Listeria monocytogenes strains (2 type strains and 4 isolates). Sub-lethal ME concentrations reduced L. monocytogenes counts by at least 2 log cycles. A Central Composite Design was used to investigate the combined effects of sub-lethal concentrations of ME (0.039–0.195 mL/100 mL), NaCl (0–2.0 g/100 mL) and pH (5.0–7.0) on strains growth. ME affected growth parameters, generally extending lag phase length and reducing maximum growth, sometimes with interactive effects with pH. The highest ME concentrations (0.117–0.195 mL/100 mL) combined with the lowest pH values (5.0–6.0) strongly reduced or even inhibited strains growth. Total phenolic content (TPC) and radical scavenging activity were also determined. ME had a TPC of 5315 ± 20 mg/kg of gallic acid equivalent, and malvidin-3-O-glucoside was the most abundant anthocyanin. In vitro radical scavenging activity, determined by TEAC assay, was stable during 70 days of refrigerated storage. In conclusion, low ME concentrations, combined with salt and pH, were effective in reducing or containing cell growth. This antilisterial effect has interesting perspectives on industrial application; ME hydro-solubility can be considered a useful feature when antilisterial strategies are applied in food formulation.