Characterization and mitigation of food safety risks associated with waxing roller brushes

Characterization and mitigation of food safety risks associated with waxing roller brushes

Jan. 1, 2024 - Dec. 31, 2025

2024CPS09

University of California, Davis

$407,384.00

Luxin Wang, Ph.D.
University of California, Davis

Gang Sun, Ph.D.

Waxing roller brushes play an important role during the application of waxes onto fruit and vegetable surfaces. However, food safety risks associated with waxing roller brushes have not been well characterized, and the cleaning and sanitizing of roller brushes have been challenging for the industry. To address the above knowledge gap and challenge, the team will first evaluate the impact of waxes and wax residues on the survival of pathogens on roller brushes made with different materials. Second, the team will perform a microbial sampling at operating packinghouses to generate firsthand information about the native microbial loads of commercially-used waxing roller brushes. Third, the team will characterize the physical and chemical properties of wax residues, and compare, optimize, and validate the efficacy of commonly-used roller brush cleaning and sanitizing protocols. The optimized protocols will be validated at two pilot facilities for both clean-out-of-place and clean-in-place usages. Results of this study will be summarized in CPS reports, presented at CPS meetings, and published in peer-reviewed journals. Outcomes will directly assist the design, optimization, and validation of protocols used for the removal of waxes, wax residues, and microorganisms from waxing roller brushes, thus mitigating microbial safety risks associated with waxing.

Technical Abstract

In recent years, the impact of waxing on the microbial safety of fresh produce has received increased attention. During the waxing process, waxing roller brushes play a significant role as they come into direct contact with fruit surfaces and allow for the rolling and turning of the fruit. Unfortunately, while the wax-saturated brushes ensure optimum waxing, they pose challenges to cleaning and sanitizing protocols. Waxes and the waxing roller brush materials have different affinities due to their chemical natures. Horsehair brushes, for example, tend to be harder to clean compared to other materials. Unremoved or built-up waxes make the waxing roller brushes even harder to clean and sanitize. Current cleaning reagents and cleaning frequency, as well as the cleaning protocols used for waxing roller brushes by packinghouses, differ significantly. Protocols range from soaking brushes in household-brand ammonia solution for different durations (for as long as overnight, clean-out-of-place) to the spraying application of branded detergent or cleaning products manufactured by wax suppliers. Sometimes, simply hot water (clean-in-place) is used. The hydrolyzed waxes after cleaning can be water-insoluble, and even harder to clean. The recovery of Listeria monocytogenes (LM) in waxing areas highlights the need for science-based information to comprehensively characterize the microbial food safety risks associated with insufficiently cleaned waxing roller brushes and to develop references for the design and implementation of efficient cleaning and sanitizing protocols. To address this need, this proposal aims to deliver three objectives. In the first objective, the team will investigate the behavior of LM on waxing roller brushes in the presence of fresh and built-up waxes. Different wax build-up times will be tested to better represent the different production and cleaning schedules followed by different commodity groups. In the second objective, indigenous microbial populations present on commercial waxing roller brushes will be evaluated by culture-dependent and culture-independent approaches. This will provide first-hand information about the microbial loads of commercial waxing roller brushes. In objective 3, the team will characterize the physical and chemical properties of wax residues, and compare, optimize, and validate the efficacy of commonly used cleaning and sanitizing protocols. The validation will be conducted at pilot scale at the Lindcove Research and Extension Center for clean-in-place validation and by working with a newly-developed clean-out-of-place machine at the industry collaborator’s pilot plant. Outcomes of this study will bridge knowledge gaps about the impact of build-up waxes and wax residues on the survival of LM on waxing roller brushes and the physical and chemical properties of hydrolyzed waxes and wax residues. Information about the efficacy of different commercially available cleaning and sanitizing agents for the removal of different waxes, wax residues as well as microorganisms will facilitate the design, modification, and implementation of waxing roller brush cleaning and sanitizing protocols. The inclusion of different waxing roller brush materials, waxes (different wax bases or solvents), and cleaning reagents (generic/household brand and specialized wax cleaning products) will ensure the broader application of this research, thus mitigating the food safety risks associated with waxing roller brushes in packinghouses.