WEST research investigates the use of light technologies to enhance food safety

Contamination of fresh produce during harvest and in food processing environments remains a substantial problem for growers and producers of food crops in Arizona and elsewhere. Many traditionally used disinfectants and sanitizers are applied via spray and most have limitations. For example, many disinfectants such as chlorine and other oxidizers interact with organic matter and are no longer able to act upon microorganisms. Additionally, some chemicals are not safe to use on produce or food contact surfaces; some have reduced efficacy under refrigerated conditions; and some are damaging to human health outright or because of harmful disinfectant by-products (DBPs).
 

While spray sanitizers do have efficacy and are used to their best effect, light technologies have been used in conjunction with traditional practices to improve sanitation and decrease both water and chemical use. Specifically, germicidal ultraviolet light (UV-C) with a wavelength of 254 nm has been used as a disinfectant in many applications. Light with this wavelength damages microbial proteins and nucleic acids. It also has the advantages of being unaffected by organic matter, not producing DBPs, and being non-corrosive and non-residue producing. While effective against a wide variety of microorganisms (e.g., bacteria, viruses, protozoa, and molds), 254-nm UV-C light nevertheless has an important disadvantage. It is harmful to human tissues such as the eyes and skin and can only be safely used in unoccupied spaces. 
 

Given this important limitation, WEST Center researchers are investigating the use of two other types of light for use in food harvest and processing disinfection: 1) FAR UV-C with wavelengths of 200 to 230 nm, and 2) Blue light with wavelengths of 400 to 470 nm (visible light range).

1. FAR UV-C: New FAR-UV-C technologies utilize wavelengths at the far end of the UV-C spectrum (200 to 230 nm). This range of light has the advantages of traditional UV-C light and has been shown to be effective against most pathogens in water (Ma et al., 2022). Importantly, this wavelength is also considered safe for eyes and skin tissues and is thus useable in spaces with active workers.

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   In the current study, researchers at WEST Center are investigating the effectiveness of 222-nm FAR UV-C on foodborne bacterial pathogens and a foodborne virus surrogate. The impact of this light treatment is being further tested on a variety of surface materials found in the fresh produce harvesting and processing environments; for example, on workers’ hands (gloved), cardboard boxes, plastic produce bins, and stainless-steel harvesting tools (e.g., knives). Pathogens included in the study include field irrigation water isolates of Escherichia coli and Salmonella, and food outbreak strains of E. coli, Salmonella, and Listeria monocytogenes.

2. Blue light: The antimicrobial effect of blue light against many pathogens under various conditions has been reported, though many studies have focused on decontamination of hospital rooms or other medical applications (Murdoch et al. 2012, Bache et al. 2012; Maclean et al. 2010). Likewise, while the application of blue light for food safety has been documented (Guffey et al. 2016, Srimagal et al. 2016), research has been limited.

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   In the second study at WEST Center, researchers are exploring the efficacy of blue light as a disinfectant against field and outbreak strains of Listeria monocytogenes. Unlike most foodborne bacterial pathogens, L. monocytogenes not only survives, but is able to grow under the refrigerated conditions found in fresh produce processing, shipment, and storage environments. Therefore, this pathogen is of particular concern for commodities that are typically consumed raw, such as leafy greens and melons. Like the study of FAR UV-C, researchers at WEST will investigate blue light’s effectiveness against the pathogen on a variety of surfaces. 

The objective of both studies is to develop a disinfectant dose-response curve* for each technology relative to the selected pathogens. Results will provide valuable information for specialty crop growers/producers on the effectiveness of each disinfectant technology, and light technologies may provide enhanced options when other disinfectants have limited efficacy or disadvantages. 
 

The principal investigator for both projects is Dr. Kelly Bright. Each project is being conducted as a one-year study, with work funded by the Arizona Department of Agriculture (AZDA). 
 

* The term “dose-response curve” here describes the relationship between a disinfectant’s dose and the targeted microbe’s survival rate.

References:

Bache et al. (2012) Clinical studies of the High-Intensity Narrow-Spectrum light Environmental Decontamination System (HINS-light EDS), for continuous disinfection in the burn unit inpatient and outpatient settings. Burns 38(1): 69-76.

Guffey et al. (2016) Inactivation of Salmonella on tainted foods: Using blue light to disinfect cucumbers and processed meat products. Food Sci Nutr 4(6): 878-887.

Ma et al. (2023) UV inactivation of common pathogens and surrogates under 222 nm irradiation from KrCl* excimer lamps. Photochemistry and Photobiology 99(3): 975-982.

Maclean et al. (2010) Environmental decontamination of a hospital isolation room using high-intensity narrow-spectrum light. J Hosp Infect 76(3): 247–251.

Murdoch et al. (2012) Bactericidal effects of 405 nm light exposure demonstrated by inactivation of Escherichia, Salmonella, Shigella, Listeria, and Mycobacterium species in liquid suspensions and on exposed surfaces. Sci World J 2012: 137805.

Srimagal et al. (2016) Effect of light emitting diode treatment on inactivation of Escherichia coli in milk. LWT- Food Sci Technol 71: 378-385.