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Emulsions and microemulsions as antimicrobial delivery systems
Phytophenols are antimicrobials that may inhibit the growth of foodborne pathogens. However, their antimicrobial activity is low because of low water solubility. The objective of this study was to formulate emulsion and microemulsion and test their efficacy as antimicrobial delivery systems. Eugenol was solubilized into cationic-nonionic (Mirenat-N® -T-Maz®80K or LAE-TM) and nonionic surfactant mixtures (T-Maz®80K-Surfynol®485W or TM-S485). Formulation of emulsions using eugenol is challenging due to Ostwald ripening. Eugenol was mixed with hydrocarbons to decrease Ostwald ripening rate using compositional ripening. Physicochemical characterization included surface tension, particle size, charge and solubilization capacity. Antimicrobial efficiency was tested using spot inoculation against four strains of Listeria monocytogenes and Escherichia coli O157:H7. The antimicrobial activity of eugenol micelles in ultra-high temperature pasteurized milk containing different percentages of milk fat was investigated. Nonionic mixed surfactant micelles showed no inhibition against both pathogens but the individual surfactants showed inhibition with 8mM of eugenol. The antimicrobial efficiency of cationic-non-ionic micelles was high since LAE alone inhibited the growth of E. coli O157:H7 and Listeria. Micelles inhibited all microbial the growth with exception of the TM:LAE (5:1) ratio. Addition of eugenol at 3mM inhibited the growth of Listeria and 7 mM inhibited the growth of E. coli O157:H7. When microemulsions were tested in a food system (milk), the antimicrobial efficiency varied depending on the fat level. Microemulsions completely prevented growth of Listeria and E. coli O157:H7 in skim and 2% milk but not in 4% fat in milk. Therefore, food composition, especially fat level, may affect the efficiency of targeting of foodborne pathogens by surfactant-encapsulated antimicrobials. The stability and antimicrobial efficacy of 5% oil-in-water emulsions formulated with eugenol and hydrocarbons was evaluated. Eugenol and lipids were mixed at different eugenol:lipid ratios. Corn-oil emulsions loaded with eugenol were the most stable and inhibited the growth against E. coli O157:H7 strains depending on loading ratio but failed to inhibit growth of Listeria strains. When surfactants are used as transport vehicles, selection of surfactant and mixing ratios is of crucial importance. Microemulsion and emulsions have substantial potential as new preservation systems for foods since they were completely composed of GRAS compounds.
Gaysinsky, Sylvia, "Emulsions and microemulsions as antimicrobial delivery systems" (2007). Doctoral Dissertations Available from Proquest. AAI3289244.