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Development of postharvest UV treatment to reduce fungal toxins in stored wheat and corn

Principal Investigator: Tatiana Koutchma

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

Timeline: November 2015 – March 2018

Objectives:

  • Develop, adapt and validate methodologies for evaluating antifungal activity of ultraviolet (UV) treatment on mycotoxin-producing fungi and analyzing mycotoxins in wheat and corn kernels.
  • Adapt the UV unit experimental set-up and develop methodologies to optimize exposure of kernels to UV irradiation, measure UV dose and effect of critical process parameters such as UV surface intensity, air humidity, and grain characteristics.
  • Establish the UV dose to achieve a 90% reduction of microorganisms and mycotoxins.
  • Establish the processing concept and conditions to achieve targeted degradation of fungi and mycotoxins in stored wheat and corn.

 Impacts:

  • The use of UV light treatment has the potential to be effective in degrading mycotoxins in contaminated stored grain and may effectively kill/suppress spoilage and mycotoxin-producing fungi on wheat and corn grains.
  • The development of a UV light treatment will allow Canadian grain farmers to maintain the quality and safety of their grain products and remain competitive in the global market.

Scientific Summary:

Although levels can vary greatly across year and geography, mycotoxin accumulation in wheat and corn occurs in pockets every year in Ontario and across Canada. Contaminated grain not only causes significant economic loss to farmers due to price discounts but it can also add significant cost and complexity to the downstream supply chain that needs to comply with food safety regulations. Certain strategies have been used at harvest to reduce mycotoxin accumulation in grain, such as adjusting combine settings to minimize the number of infected kernels harvested and setting equipment parameters to keep tip kernels on the corn cobs. Mycotoxin accumulation in grains is still a great challenge to grain producers and more effective post-harvest treatments are needed to reduce fungal toxin accumulation in stored grains. Short-wavelength ultraviolet (UV-C) irradiation is widely applied in the food industry and for water treatment. Several reports have indicated that UV irradiation could kill or supress microorganisms adhering to grain and reduce the levels of certain Fusarium toxins; however, previous studies have not been conducted on naturally contaminated grain.

Postharvest strategies are an integral step in controlling mould development once field crops have been harvested. This project studied the feasibility of a 3D UV-C illumination strategy at 253.7 nm to reduce mycotoxin and fungal loads on the surface of corn and wheat kernels. The choice of UV treatment at 253.7 nm was justified by its promise as a non-ionizing postharvest strategy for the reduction of fungal and mycotoxin loads on both artificial and grain surfaces, and growth of regulatory-approved UVC light applications for food and feed.

The feasibility of UV-C light at 253.7 nm on the reduction of both fungal and mycotoxin loads on flat model surfaces as well as on corn and wheat kernels using 2D and 3D illumination was shown. Reduction of Penicillium verrucosum (98.6%) and Fusarium graminearum (88.8%) on agar was achieved using a UV-C dose of 100 mJ cm-2. Naturally occurring Penicillium growth on corn was reduced by 79% after exposure to 5,000 mJ cm-2. Similarly, Fusarium growth on corn was reduced by 60% with 1,000 mJ cm-2. On wheat, no significant reduction of Fusarium growth occurred and Penicillium was not detected. The reduction of DON (30%; 14%), ZEN (52%; 42%), and OTA (17%; 6%) on corn and wheat, respectively, was achieved after exposure to a UV dose of 15,000 mJ cm-2 in static conditions and was lower than in model systems.

Additionally, it was concluded that postharvest UV-C treatment of corn kernels is feasible for reducing Fusarium and Penicillium growth at different points of the grain production chain which could decrease eventual mycotoxin accumulation and, at higher UV doses, decrease ZEN by ~50%. Despite the fact that no effect of UV dose was found on germination and grain protein, the established values of UV dose at 253.7 nm are an order of magnitude higher than UV doses typically used in other food and feed treatment applications and will require long exposure time. In order to reduce treatment time and efficiency of UV light, in the next phase of the project the anti-fungal and anti-toxin effects of high power monochromatic UV, polychromatic UV and pulse light will be explored solely on corn kernels. The effects of polychromatic UV and pulse light on fungal and mycotoxin reduction will be tested in a dynamic regime to test the technology for further commercialization.

Integrating 3D UV light illumination in a dynamic regime using a conveyer system or other transportation means with light sources at the higher intensity levels should test the industrial feasibility of this method. Also, the polychromatic emission spectrum in 200 -1000 nm range and higher power output produced by medium pressure mercury or pulsed lamps can be more effective at reducing mycotoxin levels as the wider range of emitted wavelengths can increase the possibility of overlap with mycotoxin absorbance peaks.

The cost of the technology is quite affordable. But more discussions are needed with the grain sector to identify how they could be applied.

External Funding Partners:

Growing Forward 2 Agri-Innovation Program (AIP).

Funding for this project has been provided by Agriculture and Agri-Food Canada through the Growing Forward 2 (GF2) Agri-Innovation Program.

Project Related Publications:

Koutchma, T. 2018. Shining a light on problem fungi: A feasibility study shows ultraviolet light reduces fungi and fungal toxins on harvested corn and wheat. Top Crop Management. February.

Popovic, V. 2018. Feasibility of UV-C treatment to mitigate fungal and mycotoxin loads on post harvest grain. UV for Food. June.

Popovic, V., Fairbanks, N., Pierscianowski, J., Biancaniello, M., Zhou, T., and Koutchma, T. 2018. Feasibility of 3D UV-C treatment to reduce fungal growth and mycotoxin loads on maize and wheat kernels. Mycotoxin Research. 34 (3) : 211-221.

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