Food Colloids As Carrier Systems For Antimicrobials

Colloidal dispersions such as oil-in-water or water-in-oil emulsions have found widespread use in the food industry. Oil-in-water emulsions consist of three principal components i.e. oil dispersed in the form of droplets, water surrounding the droplets as the continuous phase, and emulsifiers comprising the interface. Because of the complicated interaction among components, it is often difficult to predict the physicochemical properties and final functionalities of emulsions. Nevertheless, the structural and functional features of emulsions allow scientists to create many unique emulsions that may serve as suitable carriers for lipophilic functional compounds. These functional compounds may include antioxidants, flavors, colors and antimicrobials, the latter which is the principal topic of this thesis. Incorporation of food antimicrobials in emulsions could create value-added emulsions that may improve the safety and quality of a variety of foods, but to date, few systematic studies on their formulation have been reported. The objective of this thesis was therefore to formulate food emulsions that are physicochemically stable and able to deliver antimicrobial compounds to microbial target sites. Two antimicrobial agents, N-α-lauroyl-L-arginine ethyl ester monohydrochloride, (LAE) and eugenol were used as model compound to be incorporated into the colloidal food dispersion. The two antimicrobials were selected because they are either amphiphilic (LAE) or predominantly lipophilic (eugenol). When emulsions were formulated with eugenol, an essential oil component, it was found that O/W emulsions were only stable when emulsions were formulated with other lipids (hexadecane, dodecane, tetradecane, and corn oil). Above a critical loading of the carrier lipid with eugenol, Ostwald’s ripening led to rapid destabilization while above this critical loading concentration, the ripening rate was greatly reduced and depended on type of carrier lipid and concentration of eugenol. Alternatively, when emulsions were formulated with LAE as emulsifier, results indicated that emulsions were not stable to aggregation and coalescence. Consequently, LAE had to be combined with a nonionic surfactant (Tween 20) to improve the emulsion stability. Higher Tween20 composition led to more stable emulsions droplets. Both systems (emulsions with either eugenol or LAE) had high antimicrobial efficacies and were able to completely inhibit microbial growth at concentrations that depended on the type of microorganisms and formulation of the emulsions. Generally, eugenol were able to more effectively inhibit the growth of E.coli O157:H7 while LAE containing emulsions were more effective against L.monocytogenes. Finally, a food emulsion was formulated that contained both antimicrobial agents; eugenol in the lipid phase and LAE in the droplet interface. Interestingly, stability of these emulsions depended both on the LAE and eugenol loading. The antimicrobial activity in this double antimicrobial emulsion was high but was principally influenced by the interfacial formulation that is the ratio of LAE to Tween 20. The combined emulsion similar to the LAE stabilized emulsion more effectively inhibited growth of L.monocytogenes