Managing microbial food safety risks in the Australian citrus industry (CT20005)

This project is aimed at mitigating microbial food safety risks associated with the production, postharvest handling and supply of citrus to consumers in domestic and export markets. To map the microbial food safety risks along the supply chain, 1641 fruit and environmental samples from citrus packing sheds and retail have so far been collected and analysed for target foodborne bacterial pathogens such as Listeria monocytogenes (Lmono), Salmonella species and E. coli O157:H7. The positive detections were cultured, isolated and subjected to whole-genome sequencing (WGS) to better understand the prevalence and transmission of target pathogens. Results showed that harvest bins, fruit receival area and cool rooms were the potential hotspots for harbourage and transmission of Lmono onto the fruit surface and processing equipment. The WGS data supported the hypothesis that harvested fruit was the principal vehicle for transmission of Lmono from the field to postharvest packing facilities.

The industry practice data from 50 packing sheds has been collected and collated to identify the gaps and develop best practice recommendations to bridge these gaps. There is scope for improvement in food safety practices in citrus packing sheds. As supported by the microbial mapping data, harvest bins and the fruit receival area in packing sheds are the major transmission routes with the harvested fruit as a vehicle for the entry of environmental pathogens such as Listeria into the packing operations. Recirculation of wash water with inadequate and inconsistent levels of sanitisers is a common practice.

A lack of digital monitoring of sanitiser concentrations and manual dosing systems are widespread in the industry and is leading to suboptimal fruit washing and sanitisation procedures. There is a strong need to undertake packhouse environmental monitoring and management plans across the industry.

To determine the potential survival and persistence of foodborne bacterial pathogens on the fruit surface during the simulated supply chain conditions, the experiments were conducted on various cultivars of oranges, mandarins and lemons stored at 2.8°C for 4 weeks and then removed to ambient conditions for shelf-life simulation (20°C). The postharvest export chain simulation trials showed that citrus fruit (oranges, mandarins and lemons) surfaces did not support the multiplication of environmental pathogens (Lmono and Salmonella), but these could survive on the surface with a slight reduction in their populations during 3-4 weeks of cold treatment (2.8-3.0°C), which is the major phytosanitary treatment for citrus export from Australia.

A draft best practice guide has been developed which will be further improved, finalised and peer-reviewed before its final release. On-site visits to citrus packers, microbiological surveillance reports and technical articles have been ongoing extension activities in this project to enhance the industry's food safety capacity and influence food safety practices to mitigate microbial food safety risks associated with the citrus supply chain.