Antimicrobial effectiveness of Phenyllactic acid against foodborne pathogenic bacteria and Penicillium and Aspergillus molds
Natural antimicrobials from plant, animal, or microbial sources have the potential to increase food safety, improve shelf life and promote the idea of &ldquonatural foods.&rdquo The overall objective of this research was divided into two parts. The aim of the first part was to evaluate the antimicrobial efficacy of phenyllactic acid alone or in combination with phosvitin against four human enteric pathogens. The aim of the second part was to evaluate the efficacy of phenyllactic acid (PLA) against selected mold species. Growth inhibition of Listeria monocytogenes, Salmonella enterica, Staphylococcus aureus, or Escherichia coli O157:H7 by PLA used singly or combined with phosvitin in brain heart infusion (BHI) broth (35 °C) was evaluated over a 24&ndashhour period using a Bioscreen C Turbidometer (OD 600nm). Subsequently, selected concentrations of the antimicrobials were evaluated for antimicrobial effectiveness in controlling growth of the pathogenic bacteria in cream of chicken soup at 12 °C and 35 °C. Growth inhibition of Aspergillus ochraceus, Aspergillus spp., Penicillium roqueforti, Penicillium glabrum, and Penicillium spp. by phenyllactic acid in brain heart infusion (BHI) broth (25 °C) was also evaluated over a 5-day period using a Bioscreen C Turbidometer (OD 600nm).
In cream of chicken soup, at both temperatures, phenyllactic acid (5 mg ml-1) alone exerted the greatest bactericidal effect against all four pathogens throughout storage. At 12 °C and 35 °C, phosvitin combined with PLA (3.75 or 5 mg ml-1) did not offer enhanced antibacterial effect above that provided by PLA (5 mg ml-1) used alone. PLA had the greatest growth inhibitory effect on all the mold species at the lowest pH tested (pH 3.8). The minimum inhibitory concentration (MIC) of PLA at pH 3.8 against all the mold species was 15 mg ml-1. Based on results of the present studies it is concluded that: i) PLA (5 mg ml-1) has good potential for controlling the growth of foodborne pathogenic bacteria in cream of chicken soup and ensuring the microbial safety of this potentially hazardous food product, ii) PLA and phosvitin combinations are far less effective for inhibiting growth of pathogens in soup, iii) PLA has the potential to control Penicillium and Aspergillus molds if used in an acidic environment.