Research team from Clemson University examines anti-listerial fruit coatings for risk reduction
Listeria monocytogenes is an important foodborne pathogen commonly found in the environment. Recent Listeria foodborne outbreaks have been linked to fresh produce including stone fruits. Contamination of stone fruits is problematic since these products are usually consumed without heating. In addition, some surfaces associated with packing operations (brushes, peach rollers) are inherently difficult to sanitize. In the packing house, these fruits are covered (brushed) with a wax-‐based coating, containing antifungal agents to prevent moisture loss and fungal infection. We propose to develop and compare alternative coatings based on edible components that have antilisterial properties in addition to their physical barrier and antifungal role. The coatings will be formulated to contain safe antimicrobial agents such as nisin, Listex P100, organic acids and or their combinations and could be applied as a spray reducing the risk of cross-‐contamination in the packing house. Experiments will be performed in laboratory settings and validated in challenge studies with inoculated stone fruits. The coating will prevent Listeria contamination on fruits and bacterial persistence on packing equipment. Results from this study will provide improved pathogen control in addition to the basic good agricultural practices, thereby helping fruit industry to produce safer produce for human consumption.
Technical Abstract: The number of human outbreaks associated with foodborne pathogens contaminating fresh produce has increased in the past decade. Stone fruits such as peaches and nectarines are usually consumed raw but these fruits were considered ‘safe ‘since they had not been implicated in major human outbreaks. In 2014, a stone fruit packing company issued the first recall of certain stone fruits because of concern about contamination with Listeria monocytogenes. Although limited with only 2 illnesses, this outbreak highlighted the potential of L. monocytogenes to cause outbreaks via foods that had been considered unlikely vehicles for this pathogen. Traditional preservation techniques such as heating, packaging or reduced water activity do not apply for these commodities. In the absence of any practices that prevent L. monocytogenes survival on stone fruit, the exposure of the fresh fruit to contaminated water or postharvest contact surfaces will increase the likelihood of contamination and foodborne outbreaks. In this project, we propose to investigate L. monocytogenes biofilm formation and transfer rate from surfaces typical for the packing house (rubber peach holders, stainless steel surfaces and cleaning and waxing brushes) to stone fruits (Objective 1). In addition to identifying problematic areas, biofilms will be inactivated with commonly used sanitizers and optimal conditions will be determined regarding sanitizer concentration and contact time. We also propose to design a novel fruit coating with antilisterial properties and intended for a hygienic application such as a spray or water flume. The coating will be formulated to contain antilisterial agents that can (i) inactivate L. monocytogenes on contact with equipment and, (ii) maintain the safety of the fruits (Objective 2). Furthermore, the coatings will be tested in challenge studies, regarding fruit preservation, antilisterial properties and consumer acceptability (Objective 3). Stone fruits will be coated with the antilisterial coating and with a commercially available wax for comparison purposes. A set of samples will be inoculated with a L. monocytogenes cocktail. Samples will be stored in conditions to mimic packing house and retail environment and survival of the pathogen over time will be determined by plate counts. Coated samples (antilisterial and wax) not inoculated with L. monocytogenes will be evaluated side-‐by-‐side for their consumer acceptability and shelf-‐life. We anticipate that results from research will point out practical preventive intervention strategies for safer fruit supply. This proposal will address the identified research area (Part3) “California Fresh Fruit Association”.