Improving antimicrobial activity of lauric arginate by combination with essential oils for novel applications

Lauric arginate (LAE) and essential oils (EOs) are highly efficacious in broth media but are required at much higher concentrations in food products to inhibit foodborne pathogens. Because high levels of LAE and EOs affect organoleptic properties of food products, this dissertation was studied for the potential of lowering their usage concentrations by using them in combination. Antimicrobial activities of LAE and EO used alone or in combination were characterized in Chapter 2. Synergistic and antagonistic effects of LAE-EO combinations and cinnamon leaf oil/eugnol/thymol were observed for inhibiting Gram-positive Listeria monocytogenes and Gram-negative Salmonella Enteritidis and Escherichia coli O157:H7, respectively. To overcome the antagonistic effect, the antimicrobial activities of LAE-cinnamon oil (CO) combination with and without ethylenediaminetetraacetic acid (EDTA) were investigated in Chapter 3. EDTA significantly enhanced antimicrobial activities against both Gram-positive L. monocytogenes and Gram-negative S. Enteritidis and E. coli O157:H7 that showed the increased permeability of outer membrane. Because microscopy studies showed the severe damage of bacteria cell membranes by CO and the induced assembly of DNA by LAE, it was hypothesized that the increased membrane permeability by EDTA facilitated the penetration of LAE and CO targeting intracellular and extracellular matters, respectively, to enhance the activity against Gram-negative bacteria. The LAE-CO-EDTA combination was then studied as coatings to improve the safety and quality of whole cantaloupes. To predict properties of coatings, chitosan-based films containing LAE, CO, and EDTA were characterized for physical and antimicrobial properties in Chapter 4. The chosen formulation, with 0.1% LAE, 0.1% EDTA and 1% CO, was studied on whole cantaloupes in Chapter 5. These chitosan-based coatings significantly inhibited the growth of foodborne pathogens inoculated on whole cantaloupes and natural molds and yeasts and delayed the ripening of whole cantaloupes during 14-day storage at room temperature (21°C). The last study in Chapter 6 was focused on emulsifying EOs with LAE for use in aqueous systems. Cosurfactant lecithin facilitated the formation of stable nanoemulsions but reduced the antimicrobial activity at the studied conditions. Overall, the combination of LAE and EO after supplementing EDTA can provide novel applications in various consumer products.