Purpose: The purpose of this project was to develop a chitosan-based, antimicrobial-coupled microparticle to be applied through immersion, drench or spray on fresh and fresh-cut fruits and vegetables. Studies were conducted to determine antagonistic or additive effect when combining chitosan microparticles with other antimicrobials.
Methods: Plain chitosan microparticles (~270nm) were produced by adding sodium tripolyphosphate (TPP) to chitosan solution. The mixture was centrifuged and microparticles were resuspended in water and checked for size and zeta-potential. Antimicrobial activity was tested at neutral and acidic pH in TSB against Gram-positive and Gram-negative bacteria. Studies were performed in water at pH 6 using particles and chitosan solution. A panel of antimicrobials commonly used in food (e.g., EDDS, nisin and lauric arginate) were also evaluated and, based on their Minimal Inhibitory Concentration (MIC), were tested in tandem with chitosan microparticles.
Results: The MIC of the particles was found to be > 2mg/ml at neutral pH for most strains, at lower pH the MIC was reduced for G(+) bacteria; e.g. L. monocytogenes (~0.9 mg/ml). Chitosan solution and particles elicited an effect on the survival of G(+) bacteria within 30 min of exposure, and both inhibited the growth of L. monocytogenes and Salmonella over a 24h period.
Significance: The microparticles can be used independently or in conjunction with sanitizing wash to inactivate foodborne pathogens on fresh produce immediately prior to packaging, providing a food-safe and low-cost alternative to control foodborne pathogens.