1. Determine the spectrum of activity of combinations of caprylic acid and nisin against a wide variety of Listeria monocytogenes strains inoculated into queso fresco. </P>
2. Determine the effect of combinations of caprylic acid and nisin on growth and survival of Salmonella and Escherichia coli O157:H7 strains in queso fresco. </P>
3. Enhance the antimicrobial effect of caprylic acid and nisin on Salmonella and Escherichia coli O157:H7 using additional antimicrobial GRAS ingredients. </P>
4. Assess the effect of two effective antimicrobial combinations on shelf life and quality of queso fresco.
Foodborne disease caused by contaminated soft-style fresh Hispanic cheeses is a major concern for the dairy industry. Queso fresco is the most popular fresh Hispanic cheese, but it could be susceptible to contamination of pathogenic bacteria such as Listeria monocytogenes, Salmonella and Escherichia coli O157:H7 because it is minimally processed. Previous work by this researcher showed that the combined effect of two GRAS substances (nisin and caprylic acid) had great potential for controlling L. monocytogenes in queso fresco. </P>The goal of the current project was to expand their work by testing the antimicrobial ingredients against Salmonella and E. coli O157:H7. Researchers conducted a series of experiments with Queso fresco inoculated with representative bacterial strains and treated with different concentrations of GRAS ingredients. Results from this study show that combinations of nisin, caprylic acid (CA), and trans-cinnamaldehyde controls the growth of Listeria monocytogenes in queso fresco with relatively little impact on the natural flora of cheese. The nisin/CA had no effect on Salmonella and had limited effect on E. coli O157:H7. Cinnemaldehyde alone inhibited growth of L. mono, Salmonella and E. coli. Trans-cinnamaldehyde (CN) effectively inhibits Salmonella enterica and E. coli O157:H7 at concentrations of 0.3 ? 2 g/kg. These antimicrobial combinations could eventually be used to manufacture safer queso fresco.