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Supplementing food antimicrobials in commercial edible coatings to enhance the safety and extend the shelf-life of stone fruits


Stone fruits are commonly considered as low-risk commodities but have been linked to multi-state outbreaks and recalls including a 2020 Salmonella outbreak. Stone fruits are usually waxed to preserve freshness and reduce decay, but the fungicides used in commercial coatings (“waxes”) are not active against foodborne pathogens and are strictly regulated by the US Environmental Protection Agency. Many novel coatings have been studied for fruits, but their feasibility has not been proved commercially. To facilitate transfer of project findings to the industry, the goal of the present project is to implement commercial, generally-recognized-as-safe food antimicrobials in commercial stone fruit coatings to enhance the microbial safety and extend the shelf-life of stone fruits. We hypothesize that implementing appropriate types and amounts of commercial food preservatives in commercial stone fruit coatings will maintain the characteristics of coatings to preserve fruit quality and effectively inhibit foodborne pathogens and spoilage microorganisms on stone fruits. The hypothesis will be tested in two objectives. In the first objective, the proximate composition of five commercial stone fruit coating dispersions and their coating properties before and after adjusting to pH 3.0-7.0 will be first characterized. Selection of antimicrobials will then be studied for the combination of polar (lauric arginate; benzoic, propionic, sorbic acids and their salts) and non-polar (parabens) antimicrobials, which may have synergistic antimicrobial activities and may maintain water vapor permeability of coatings. This will include the determination of the minimum inhibitory and minimum bactericidal concentrations of individual antimicrobials, and the fractional inhibitory concentration index to study the combination of lauric agrinate and the most effective organic acid with synergistic activity and the combination of lauric arginate/organic acid mixture and methyl- and propylparagens (2:1). Films will then be prepared with 15 antimicrobial coating dispersions to evaluate physical, mechanical, and antimicrobial properties. Five formulations leading to films with physical and mechanical properties similar to those without antimicrobials, as well as good antimicrobial activities, will be identified for coating the fruit. In the second objective, the effectiveness of antimicrobial coatings inhibiting Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica cocktails inoculated at 5 or 3 log CFU/fruit on yellow peaches and white nectarines, as well as total populations of native yeasts and molds/fungi and total aerobic bacteria, will be evaluated during storage at ideal and simulated retail conditions. Antimicrobial coating treatments will be compared to controls of the uninoculated and uncoated fruits, fruits inoculated with bacteria but uncoated, and those with the corresponding commercial coating and fungicide. The quality, gloss, and decay of fruits during storage will also be evaluated. The project success will be evaluated for the absence of detectable pathogens during storage and the properties of antimicrobial coatings preserving the quality and reducing the decay of stone fruits. Findings from the project will directly enhance the microbial safety and extend the shelf-life of stone fruits and can be adopted to enhance the safety and sustainability of many other fresh produce commodities.

Qixin Zhong, Ph.D.; Thomas G. Denes, Ph.D.
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