What was it all about?

Foodborne illness outbreaks linked to fresh produce adversely affect consumers, the healthcare system, growers and industry. Microbial pathogens such as Salmonella species and Listeria monocytogenes continuously pose a problem for horticultural industries from a food safety and cost standpoint. Preharvest and postharvest risks of microbial contamination of fresh produce can be mitigated with best management practices, but these risks cannot be eliminated. Current postharvest sanitisation processes have limitations due to limited effectiveness against pathogens, chemical residues, and environmental regulatory issues. Consequently, a global push towards zero chemical residues and assurance of food safety has created a technological gap that could be filled with an innovative decontamination process acceptable to the industries, consumers and regulators.

Cold plasma has emerged as a leading decontamination technology in the last ten years, with applications expanding into the food and healthcare sectors. This project investigated using cold plasma to decontaminate fresh horticultural produce to mitigate the risk of food safety incidents and boost consumer confidence. Cold plasma is an ionised air stream capable of killing or inactivating a broad range of microorganisms such as bacteria, moulds, yeasts, and viruses. It can be generated at ambient conditions by applying electrical current to normal air or a specific gas. The reactive oxidising species in the ionised air can kill or inactivate microbial pathogens on produce surfaces, improving food safety and postharvest decay control.

This project has developed, scaled up, validated and demonstrated the potential application of cold plasma technology in several horticultural products. The foodborne bacterial pathogens inoculated on the produce surfaces were killed or inactivated by plasma treatment, depending upon the exposure duration and other variables. A dry postharvest treatment with cold plasma has shown promising results for apples, citrus, strawberries, and blueberries. In addition to the dry plasma treatment, the plasma stream was also infused in the wash water to achieve sanitisation during postharvest processing of products such as leafy vegetables. The antimicrobial potential of the plasma-activated water and its stability was established for its potential application in the sanitisation of postharvest water.

To scale up and validate the technology, prototype equipment was designed, constructed, and tested for its performance to simulate postharvest processing operations. The prototype was designed to demonstrate the capability of the technology and its potential for retrofitting in the packing operations. The validation of the prototype not only evaluated the performance of plasma in killing pathogens but also its effect on the sensory and nutritional quality of treated products. Comprehensive datasets were generated on the responses of various pathogens and treated products, leading to a greater understanding of the technology and overcoming its application limitations. Further evaluation of the technology in commercial settings is required for positive outcomes.

The development of this novel postharvest technology offers industry the potential option of a rapid, chemical-free, non-thermal, environmentally friendly, and effective antimicrobial solution for food safety and decay control in horticultural products. Adopting this technology in the horticulture sector could lead to better food safety outcomes, mitigate postharvest losses, and reduce the reliance on chemicals used in postharvest processes, resulting in improved environmental health and sustainability. This technological intervention will enable the industry to maintain a competitive advantage by consistently supplying safe and healthy fresh produce to consumers in domestic and export markets.