Far UVC light effective against fungal contamination in cereals

Fungal contamination can have an impact on cereal market prices and lead to revenue loss for cereal farmers. Furthermore, when contaminated grain is downgraded to animal feed, the health problems associated with mycotoxins - such as immune deficiency, cancer, kidney damage, and foetal development effects - are shifted to livestock.

“Light-based technology is easy to use, and the cost is minimal compared to many other methods. However, conventional UVC lamps emit light at a wavelength of 254 nm, which can cause skin or eye damage to humans, so it’s not safe to use when workers or consumers are around,” said Yi-Cheng Wang, an assistant professor in the Department of Food Science and Human Nutrition, part of the College of Agricultural, Consumer and Environmental Sciences at Illinois. “So instead, we are using a technology called microplasma-based far-UVC light. It emits light at 222nm, a wavelength other studies have found to be safe for humans, even at prolonged exposure. We wanted to see if it can also be used to mitigate fungal contamination.”

Conventional 254nm light disinfection works by damaging cells’ DNA, whereas the shorter 222nm wavelength is mainly absorbed by peptide bonds and amino acids. Wang said this means far-UVC causes cell damage to microorganisms, but cannot penetrate humans’ outermost layer of dead skin cells or the tear layer of their eyes.

Study co-author Wang and lead author Zhenhui Jin tested the efficacy of far-UVC light against two fungi, Aspergillus flavus and Fusarium graminearum. Both fungi affect grains in the field; they can lead to substantial losses in grain quality and produce mycotoxins.

First, the researchers suspended the fungi’s spores in a liquid buffer and treated them with various doses of far-UVC light. They found that, at the highest treatment doses, 99.999 per cent of the spores of Aspergillus and Fusarium were inactivated via changes to the cells’ membranes and their mitochondria. 

The next step was to test the far-UVC light treatment against the two fungi’s mycelia, a network of threadlike strands that invade host plants’ tissues after spores germinate. On agar plates, the growth of mycelia for both fungi was successfully inhibited.

“For the liquid and agar, we could just put the lamp above the petri dishes containing the fungi. However, food products are three-dimensional. Therefore, we constructed a treatment system with six lamps that shine light over and around the grains,” Wang said in a statement.

The researchers tested the system on sweetcorn kernels and wheat grains. The treatment reduced over 90 per cent of both fungi. The surface roughness of the cereal grain was likely the reason for lower treatment effects than in liquid buffer, Wang said. However, the results were comparable to, or even better than, previously published studies in which cereals were treated with conventional 254nm UVC light.

The team also investigated whether the light treatment affected the quality of the grains. They found no significant effect on moisture content in either the sweetcorn or the wheat, and no significant change in the percentage of the wheat that germinated within seven days after treatment. However, for the sweetcorn kernels treated with the highest dosage of light, there was a 71 per cent increase in germination over the same period. This could have been because the light treatment increased the corn cells’ permeability, facilitating their uptake of water, but Wang said this idea will need to be tested through future research.

Wang envisions grain would be treated at the processing facility after harvest, before it reaches the food production system.

The team’s findings are detailed in Food Research International.