Antimicrobial Delivery Systems to Improve Food Safety

There are four major approaches to ensure food safety and prevent foodborne diseases:
<ol> <li>Asceptic handling of foods,
<li>Removing microorganisms through washing or filtration,
<li>Destroying microorganisms with heat, pressure or irradiation or
<li>Inhibiting growth through addition of antimicrobials. Food antimicrobials or preservatives synthetic or biologically derived, naturally occurring ssubstances when brought in contact with microorganisms reduce the ability of pathogens to grow or survive. </ol>
<p>
The major problem with all antimicrobial agents is their low activity in food that consists of many different components. A lack of suitable delivery systems and an incomplete understanding of their mode of action currently prevents their widespread use in the food industry. The objective is to develop encapsulation systems that are able to protect food antimicrobials from interfering food components and improves delivery of the food antimicrobials to the site where they can be active, that is the cell surface of the microorganisms. We plan to evaluate three different encapsulation technologies and evaluate their use in foods.
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<ol>
<li>Determine encapsulation mechanism and inhibitory efficacy of phytophenol antimicrobials in food emulsifier nanaparticles. The influence of antimicrobial and emulsifier properties and environmental conditions on production of antimicrobial nanoparticles will be determined and the impact of nanoparticle characteristics on their antimicrobial efficiency in microbiological and model food systems will be identified.
<li>Determine delivery mechanism and inhibition efficacy of phytophenol antimicrobials in colloidal dispersions. The optimum formulation and preparation conditions required to prepare stable emulsion-based delivery systems for phytophenol antimicrobials that have the highest activities in microbiological and model food systems will be identified.
<li>Determine stability of liposomes containing polypeptide antimicrobials (lysozyme and nisin) and their efficacy to inhibit growth of pathogens. Lipid-antimicrobial combination will be optimized to reduce rate of leakage of liposomes to increase concentration of encapsulated antimicrobials. Antimicrobial efficiency of liposomes to inhibit growth of pathogens in model and selected food systems will then be evaluated.</ol> </p>
<p>
Phytophenols such as carvacrol (from oregano) and eugenol (from cloves) are components of plant essential oil extracts that have potential antimicrobial activity. However, they are generally insoluble or poorly soluble in the water phase of foods. The objectives of a study were to determine the antimicrobial and physical stability properties of phytophenols in nanoscale surfactant micelles. Carvacrol and eugenol containing micelles were prepared by dispersing Surfynol 485W or 465 in water at room temperature. Nanoparticles were effective against Escherichia coli O157:H7 and Listeria monocytogenes. E. coli O157:H7 was more sensitive than L. monocytogenes. This is unusual in that gram-negative bacteria are generally more resistant to essential oils because of the protective effect of the lipopolysaccharide (LPS) layer. Antimicrobial activity of the nanoparticles was stable to changes in pH and temperature. Solubilization in micellar systems has potential to improve application of phytophenols as antimicrobials in food systems. The objectives of a project were to encapsulate a nisin and lysozyme in phosphatidylcholine (PC) based liposomes of various lipid ratios and determine the physicochemical properties of the capsules. Efficacy of encapsulated antimicrobials against Listeria monocytogenes was determined. Inhibition was highest for PC and PC:cholesterol liposomes. Inhibition was lower when lysozyme was encapsulated. Liposomes could be used as suitable delivery systems for antimicrobials. Increased antimicrobial stability and efficacy through protection of antimicrobials from interaction with food components could result in cost savings. In a related study, the objective was to determine stability of liposomes as a function of pH, temperature, and phospholipid composition. Liposomes demonstrated encapsulation capabilities with low temperature- or pH-dependent release of entrapped contents, thus indicating liposomes have potential for long-term storage stability. DSC analysis indicated that addition of antimicrobials to PC liposomes did not significantly degrade liposomes. With proper lipid formulations, antimicrobial-entrapping liposomes may prove useful tools for preventing growth of spoilage and pathogenic microbes. The purpose of another project was to attempt encapsulate antimicrobials in the biodegradable polymer polylactic acid (PLA). A method was developed for creating nanoparticles in the laboratory and the effect of empty PLA nanoparticles on the growth of L. monocytogenes was determined.This was done using an emulsification-diffusion method. Nanometer-sized empty PLA particles were produced with a wide range of sizes. Empty PLA nanoparticles had little to no effect on the growth of four strains of L. monocytogenes. Thus, PLA will not interfere in future antimicrobial assays. </p>
<p>
The greatest drawback to the use of naturally occurring antimicrobials is their lack of activity in foods. This is due to their interaction or binding with food components such as lipids and proteins reducing or eliminating the antimicrobial activity of the compounds. Research in this project thusfar has shown that encapsulation of naturally occurring antimicrobials in surfactant-based nanoparticles, liposomes or polymer nanoparticles has excellent potential as an application strategy to reduce interaction with food components and increase activity against microbial pathogens. Surfactant-based nanoparticles in particular are attractive because of their ability to allow incorporation of relatively large amounts of lipid soluble antimicrobial compounds into aqueous systems. One of the major goals of encapsulation is to make naturally occurring antimicrobial compounds more water soluble, thereby improving their applicability in food systems. Microorganisms likely localize in the water phase or at oil-water interfaces. Therefore, encapsulation has the potential to increase the activity of natural antimicrobials against pathogenic and spoilage bacteria in foods.</p>