Throughout the research process, Nitin said they have received industry input, which has been invaluable. “Without that industry input … it would be very difficult to design even the proposal,” he said.
The researchers are looking at coatings with different properties to address the varying physical attributes of surface materials. For plastic surfaces – which are hydrophobic and repel water – they initially looked at yeast-derived particles charged with chlorine and deposited using a beeswax coating.
Charging particles took about 15 seconds at high chlorine levels and was based on findings of previous work Nitin conducted.
In laboratory experiments, they treated coupons – or disks – of various materials with the yeast and wax coating, then exposed them to a known quantity of E. coli. The goal was at least a 3-log reduction in pathogen levels in two minutes, which was achieved. The researchers also plan to test the coating against Listeria monocytogenes.
They also measured the potential for cross-contamination using spinach leaves to simulate contact with contaminated surfaces that might occur during harvest. In addition to being stable in water and in the presence of organic matter, the beeswax coating also reduced cross-contamination of baby spinach by more than 2 log.
The coating did not appear to affect the texture or other quality characteristics of the baby spinach, Nitin said. The researchers haven’t yet completed testing the spinach leaves for potential residues transferred from the coating.
In addition, they are examining a chlorinated soy protein-based hydrogel. In laboratory tests, the hydrogel inactivated 10 million colony forming units of E. coli within 5 minutes of contact and reduced biofouling – the accumulation of microorganisms.
As part of the project, Nitin said they’re also developing a coating using the corn-derived protein zein or shellfish-derived chitosan.
“The protein-based coatings worked well on stainless steel or related surfaces,” Nitin said. “The zein protein may be more adaptable to the plastic or conveyor surface.”
One challenge with conveyors is that crevices, joints and cracks are difficult to sanitize and pose obstacles when spraying protein-based coatings.
The researchers’ next step will be to test the coatings on knives and conveyors under simulated field conditions. Nitin said they hoped to work through industry partners and facilities, including the food science pilot plant and UC Davis Vegetable Crops fields, to conduct the trials.
