Polysaccharide-based Oil-in-water Emulsion Systems for the Prolonged Efficacy of Hydrophobic Antimicrobial Compounds

Abstract

Prevalence of foodborne pathogens and its associated disease outbreaks are major causes of concern for public health globally. Significant efforts have been taken to resolve this issue, among which the use of antimicrobials is a major approach. Antimicrobial compounds have been used alone or in combinations to achieve enhanced functionality within food systems. Natural antimicrobials such as essential oils used in food preservation by conventional techniques are prone to rapid depletion owing to their volatile nature, hydrophobic properties, enzymatic hydrolysis, specific interactions with surrounding food components and alteration of flavor profile at higher usage levels. One strategy for prolonged protection of antimicrobial compounds is through designing a suitable carrier vehicle. In this study, the overall goal is to design oil-in-water emulsion systems for the sustained protection of various antimicrobial compounds against targeted foodborne pathogens. The first part of the work was carried out in model testing system such as Brain heart infusion (BHI) broth, where the effective concentration of antimicrobial emulsions prepared through ultrasonication and stabilized with gum arabic were evaluated. The oil phase of formulated emulsions was constituted with geraniol and carvacrol, incorporated at various ratios of 1:0, 2:1, 1:1, 1:2, and 0:1 (v/v). These emulsion systems were characterized for mean particle diameter, polydispersity index (PDI), ζ-potential, storage stability, creaming index, and microstructural parameters (confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM)). In addition, Time-kill assay for the formulated emulsions was tested against model bacterial pathogens, Gram-positive bacteria B. cereus MTCC 430 and Gram-negative bacteria Escherichia coli MTCC 443. The results demonstrated that among all the formulations, higher stability was displayed by combined oil, geraniol: carvacrol (1:1) emulsion with no visible separation of cream. Further, the microstructural analysis confirmed the presence of stable emulsion. Analysis of time-kill assay showed prolonged antibacterial efficacy for the combined essential oil-based emulsion against both the model bacterial pathogens. In the second part of the work, the antimicrobial emulsions incorporated with geraniol and carvacrol at the selected oil phase ratios were stabilized with Tween 80 and Gum arabic (coating solution). These emulsion-based coating solutions were used to extend the shelf life of goat meat. They were characterized for mean particle diameter, PDI, ζ-potential, storage stability and creaming index, and microstructural parameters. Evaluation of the antimicrobial activity of the functional emulsions was carried out against Gram-positive bacteria B. cereus MTCC 430 and Gram-negative bacteria Escherichia coli MTCC 443. The study showed that the emulsion-entrapped formulations could prolong the antimicrobial efficacy of geraniol and carvacrol till nine days as compared to treatments performed with non-emulsion formulations on a goat meat model. The final part of the work was focused towards using two volatile essential oils, d-limonene and trans-cinnamaldehyde stabilized by Tween-20 and Starch-Octenyl Succinic Anhydride (OSA), for the preparation and characterization of oil-in-water type emulsions (coating solution). The impact of this delivery system on the antimicrobial retention was studied against the model bacterial pathogens using fresh-cut papaya as the model food. It was found that the emulsion-based coating solutions could prolong the antimicrobial efficacy of d-limonene and trans-cinnamaldehyde against both B. cereus MTCC 430 and Escherichia coli MTCC 443 on fresh-cut papaya. Overall, the emulsion-based carrier systems demonstrated effective retention of antimicrobials in the model testing system (BHI broth) and a potential application of these delivery systems to extend the shelf-life of goat meat and fresh-cut fruits was identified.