Purpose: The objective of this study was to determine the efficacy of edible antimicrobial coatings to control Lm on fresh cheese (Queso Fresco) applied before (precoated; PC) or after (preinoculated; PI) surface contamination.
Methods: Coating solutions were formulated to contain 2% chitosan and either 5% hydrogen peroxide (HP), 5% lauric arginate (LAE), 10% sodium caprylate (SC), 25% acidified calcium sulfate (ACS), or combinations of SC with either LAE or ACS at pH ~4.5. Fresh cheese samples (25 g) were inoculated with Lm (104 CFU/g) prior to or following coating application, vacuum packaged, and enumerated, weekly, throughout storage at 7°C for 35 days.
Results: In general, there was no effect of coating application type (PI vs. PC) on Lm counts for all treatments except LAE+SC combinations (P=0.0002). There was a significant effect of chitosan coating, alone, on Lm counts for both applications when compared to control over time (P<0.0001), reaching >7 log CFU/g after 35 days. Overall, HP was the most effective bactericidal coating with counts <1 log CFU/g after 35 days. Although the effect of singular treatment of LAE did not differ from chitosan alone, singular treatments with ACS (P≤0.021) as well as combination treatments of both compounds with SC resulted in significantly lower Lm counts over time (P≤0.0026). Both LAE+SC coating applications were bacteriostatic while counts in both ACS+SC applications were ~5 log CFU/g at 35 days.
Significance: The identification of bactericidal and bacteriostatic edible antimicrobial coating applications that are effective when applied before or after contamination events provides a new tool for the control of Lm on fresh cheese for enhanced food protection.