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Practical application of postharvest continuous UV and pulse light treatments to reduce fungal and vomitoxin (DON) loads in corn

Principal Investigator: Tatiana Koutchma

Research Institution: Agriculture and Agri-Food Canada (AAFC)

Timeline: March 2020 – March 2023  

Objectives:

  • To determine the appropriate practical application of continuous and pulsed UV-C polychromatic light and LEDs as post-harvest treatments to reduce existing fungal loads on corn and to reduce ingress and spreading of fungi and DON.
  • To investigate contamination vectors and determine the most appropriate UVC treatment points: a) to reduce existing fungal loads, and b) to reduce ingress and spreading of fungi through cross contamination.
  • To evaluate the efficacy of polychromatic UV light (pUV) emitted by medium pressure mercury lamp to reduce Fusarium graminearum and mycotoxin (DON) on the surface of corn and contact surfaces in a static regime. The effects of pUV on inoculated and naturally occurring fungi will be tested.
  • To evaluate the efficacy of polychromatic light emitted by pulsed lamp (PL) to reduce F. graminearum and the DON mycotoxin on the surface of corn and contact surfaces in a static regime. The effects of PL on inoculated and naturally occurring fungi will be tested.
  • To evaluate the efficacy of UVC light emitted at 275-280 nm using LEDs to reduce F. graminearum and the DON mycotoxin on the surface of corn kernels and contact surfaces in a static regime. The effects of 275-280 nm UVC LEDs on inoculated and naturally occurring fungi will be tested.
  • To develop a testing unit to integrate monochromatic and polychromatic light source with dynamic delivery of the kernels to the source. The light delivery to kernels in dynamic motion to achieve 3D exposure to light photons will be conducted.
  • To design and build the pilot unit(s) with monochromatic and/or polychromatic light sources based on the above experimental results; to measure the efficacy of the units in reducing F. graminearum and the DON mycotoxin on the surface of the corn.
  • To determine the most appropriate practical UVC treatment post-harvest and recommended practices for contact surfaces, air and corn via study and piloting.

Impacts:

  • The development of a successful pilot scale UV treatment system and practices that could help reduce postharvest losses and improve the quality of corn for sale by Ontario grain farmers.

Scientific Summary:

Gibberella ear rot in corn has long been a serious problem for farmers in Ontario. The disease can reduce grain yield, causing economic loss, but its causative pathogen, Fusarium graminearum, can also produce mycotoxins, deoxynivalenol (DON) in particular, resulting in food safety burdens and market value reduction. In the first study, the feasibility of continuous ultraviolet (UVC) treatment at 253.7 nm was explored to reduce fungal (Penicillium verrucosum and F. graminearum) and mycotoxin loads on model surfaces, corn and wheat kernels. Reduction of F. graminearum (88.8%) on agar was achieved at UVC dose of 100 mJ cm-2 whereas naturally occurring Fusarium growth on corn was reduced by 60% with 1,000 mJ cm-2. The reduction of DON by 30% and 14%, ZEN by 52% and 42%, and OTA by 17% and 6% on corn and wheat, respectively, was achieved after exposure to 15,000 mJ cm-2 in static conditions. It was shown that postharvest UVC treatment of corn is feasible at small scale for reducing Fusarium at different points of the grain production, which could decrease mycotoxin accumulation. Despite no reported effect of UVC treatment on germination and protein content of grains, the established UV doses were an order of magnitude higher than exposures used in food and feed applications and hence require long exposure time. The long exposure requirement limits the practicality of the technology for bulk grain handling systems.

To reduce treatment time and efficiency of UV light, this second project proposed to explore the anti-fungal and anti-toxin effects of UVC LEDs, polychromatic UV (pUV) and pulse light (PL) on corn kernels, contact surfaces and air. The effects of LEDs, pUV and PL on fungi and DON reduction was tested in a dynamic regime to evaluate the UV technology for further commercialization.

The practical applications of UV treatment in corn harvest and post-harvest processing was also explored. Optimization of UV exposure was considered to maximize efficiency of the treatment thereby maximizing fungi-mycotoxin reductions. In addition, the practical application investigated where ingress of fungi occurs and determined harvest and post-harvest control points via UVC exposure to reduce fungal growth and toxin accumulation.

Results

Activity 01-1: Analyze postharvest corn production and storage practices; investigate contamination vectors and determine the most appropriate light treatment points.

The fast procedure “Vertu Touch” to measure DON concentration in kernels was developed and validated by the National Research Council. High DON variability in corn presented a real challenge during experimentation. A procedure of corn sampling to reduce this variability between samples was developed and used in pilot testing.

Activity 02-2: Measure the efficacy of polychromatic UV light (pUV) and pulsed light (PL) to reduce Fusarium graminearum and vomitoxin (DON) on the surface of corn and contact surfaces in a static regime.

Cathode ray or electron UV tubes used in the tests are the next generation of pulsed light UVC (eUV) technology that uses luminescent phosphors to produce germicidal UVC photons. Electron pulsed UV lamps have potential commercial advantages for mitigating the risk of microbial and chemical contamination in food and grain applications because of combined action of at least 4 wavelengths, shorter treatment time, low energy consumption and cost. Testing of eUV lamps was done in a static mode using a single lamp mode and continues in continuous treatment mode using a UV processing conveyor where 2 panels with 4 eUV lamps each are installed. The testing demonstrated that from the four UV sources including eUV, 222 nm (excimer lamp), 254 nm (low pressure mercury) and 275 nm (UV-LED), the lowest fluence required to achieve 1-log and 5-log reductions of E. coli P 36 was observed using the eUV lamps (0.9 and 1.4 mJ/cm2, respectively) followed by 277, 253.7 and 222 nm wavelengths. The lowest photo-reactivation of UV inactivated cells was observed following a 3 h treatment using 222 nm light followed by eUV, 253.7 and 277 nm. In the case of DON reduction on filter paper, eUV was the most effective followed by 222, 253.7 and 277 nm treatments.

Activity 03-3: Measure the efficacy of UVC light emitted at 265-280 nm using LEDs to reduce F. graminearum fungi and DON mycotoxin on the surface of corn and contact surfaces in a static regime.

UVC LEDs treatment at 280 nm and 500 mJ/cm2 had an effect on Fusarium graminearum growth on corn kernels. However, due to their low level of irradiance, UV LEDs cannot be used for DON control on corn. More tests are needed to measure the LEDs’ effect on DON contamination on contact surfaces.

Activity 04-4: Develop testing units to integrate light sources with dynamic way of kernels delivery. To conduct performance testing of the dynamic delivery to the light source and to measure efficacy of pUV and PL to reduce F. graminearum and DON.

Commercial potential of the UV treatment and the most effective UVC light source for use in the grain industry will be estimated when pilot experiments using 4 novel UV sources are completed. However, it was found that UV light treatment is more effective against fungal load than for reduction of natural DON on corn kernels. There is a lot of interest in using UV control microbial load in brewing and on pulses in the production of plant protein ingredients.

Activity 05-5: Design and build the pilot unit(s) and test the efficacy, using the most effective UV light source and delivery mode, to reduce F. graminearum fungi and DON mycotoxin on the surface of the corn.

It was found that natural DON in whole kernels is very resistant to UV treatments because of the irregular shape and size of whole kernels. The exact location of DON in kernels is not known and can be under the outer layer of the kernels where light cannot penetrate. The highest reduction effect was found after exposure to polychromatic MPM lamps. The higher DON reduction was achieved when corn was ground before the UV treatment. MPM lamps were the most effective due to their polychromatic spectrum and higher output power.

Because of the delivery issue we were not able to test novel electronic pUV lamps that are polychromatic and can achieve UV treatment in a shorter time. The remaining results will be reported after completion of these tests.

Conclusion: Due to the complexity of UV treatment and the requirement for long UV treatment durations and surface contact with contaminated grain, the practical application of UV technology to reduce DON levels in contaminated grain within bulk grain handling systems is limited.

External Funding Partners:

Agriculture and Agri-Food Canada (AAFC)

Funding for this project has been provided by Agriculture and Agri-Food Canada.

Project Related Publications:

Jaiswal, M., Debbarma, M., Makroo, H., Srivastava, B., Koutchma, T. 2023. Chapter 3: Food Preservation Using Ultraviolet Light. CRC Press. Emerging Technologies in Food Preservation.

Koutchma, T. 2022. Chapter in book: Evolvement of Ultraviolet Light (UV) Technology for Microbial and Viral Control in Food Applications. Elsevier. Reference Module in Food Science.

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