By Dr Sukhvinder Pal (SP) Singh senior research scientist, NSW DPI

The NSW Department of Primary Industries (NSW DPI) recently delivered a project (CT20005) to examine microbial food safety risks along the citrus supply chain and develop management strategies.

The project was aimed at mitigating microbial food safety risks associated with the production, postharvest handling and supply of citrus to consumers in domestic and export markets.

The success of Australia's citrus export industry hinges on several key factors, including free trade agreements with importing nations and our reputation for delivering clean, green, and safe citrus products to global markets.

In order to maintain our competitiveness and safeguard our market share, it is imperative that we consistently supply safe fruit and strive for zero product recalls.

While citrus fruit inherently poses a relatively low microbial food safety risk to consumers due to its inedible peel, the detection of pathogens on the fruit surface by regulatory bodies could have significant repercussions, including product recalls, damage to our reputation, and jeopardised trade relationships with export markets.

This project delivered a national snapshot of the industry’s current food safety practices and identified potential gaps to be addressed.

The project followed a whole-of-chain approach to identify potential hotspots for microbial contamination and cross-contamination along the supply chain.

Each link within the supply chain was examined, starting with field production and postharvest processing through to retail by collecting fruit and environmental samples (2257) to detect the target foodborne bacterial pathogens (Listeria monocytogenes, Salmonella species and pathogenic Escherichia coli).

Associating industry practice with microbial risk mapping proved to be an effective strategy towards microbial risk identification and development of targeted interventions to manage these risks.

The project achieved remarkable success in engaging more than 50 citrus packers throughout Australia, representing a substantial network of over 750 growers.

Through microbial mapping analysis along the supply chain, it was revealed that Listeria monocytogenes emerged as the primary environmental pathogen of concern, with Salmonella and pathogenic E. coli posing minor risks.

Insights derived from the prevalence and distribution data indicate that Listeria monocytogenes was present in citrus orchard soils, which could lead to the potential contamination of fruit on trees through dust storms.

The whole genome sequencing of Listeria isolates confirmed harvested fruit could serve as the primary carrier of the pathogen from the field into packing facilities.

The pathogen could establish itself in the postharvest processing equipment and premises, including harvest bins, conveyor belts, brushes, and eventually could reach cool rooms via forklifts and workers’ movements (for a summary of best practice recommendations see the break out panel).

To uphold consumer confidence, satisfy regulatory requirements and ensure continued market access and expansion, it is essential for the citrus industry to adopt proactive measures in managing fruit quality and safety.

The industry has robust microbial food safety preventative controls during both production and postharvest handling operations.

However, continuous improvement and change of some practices were recommended during fruit production, harvest and postharvest operations.

The project's effectiveness in garnering significant industry interest has played a pivotal role in raising awareness about microbial risks.

Based on the current industry practice, microbial risk mapping and available scientific literature, Best Practice Guidance was developed as a technical resource to achieve the microbial risk management objectives.

The Citrus Microbial Food Safety Best Practice Guide offers expert advice and recommendations on best practices for fruit production, harvest techniques and postharvest handling, enabling us to effectively mitigate the risk of microbial pathogens.

This comprehensive guide is designed to serve as a practical and targeted resource for citrus growers, packers and all stakeholders involved in the citrus supply chain, offering invaluable insights into the assessment and management of microbial food safety risks.

This guide is a culmination of the collaborative efforts of industry stakeholders and has been made possible through the generous contributions of more than 50 citrus packers who shared their insights and facilitated microbiological sampling from production fields and packing facilities.

The guide is now available for download on the NSW DPI website at https://www.dpi.nsw.gov.au/agriculture/horticulture/food-safety

In conclusion, the project's success was dependent not only on its ability to engage citrus growers and packers but also in uncovering novel insights into the prevalence, distribution, and pathways of microbial contamination.

The identified gaps in industry practices serve as opportunities for improvement and addressing them will contribute significantly to safeguard the food safety record of the citrus industry.

Acknowledgement: This project has been funded by Hort Innovation, using the citrus industry research and development levy and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

Further details from Dr Sukhvinder Pal (SP) Singh, senior research scientist, NSW Department of Primary Industries, at sp.singh@dpi.nsw.gov.au or 0420 593 129.

BREAKOUT BOX:

Best practice recommendations

• Organic soil amendments, dust storm-mediated pathogen dispersal, irrigation water, water used in the chemical spray application and wildlife incursions are the major sources and/or routes of microbial contamination during citrus fruit production.
• Citrus orchards in proximity to livestock operations and high wildlife pressures should revisit their food safety plans to understand the pathogen load and dispersal pathways affecting their operations, especially during extreme weather events such as duststorms, floods and bushfires.
• Raw animal manures or partially composted manures in citrus orchards should not be used. Dust-suppression agronomic practices including the use of perennial windbreaks is recommended. Spray water quality should be assessed before its application.
• Trailer mounting of harvest bins, avoiding ground contact, is the best practice to mitigate microbial food safety risks. Cleaning and sanitisation of harvest bins after each use are the best practice recommendations to mitigate microbial food safety risks associated with harvesting.
• Immediately after harvesting, citrus fruit should be drenched with a sanitiser followed by drenching with a fungicide. This ‘two-step’ drenching operation will minimise the cross-contamination risks and maximise the efficacy of both types of chemicals. Their concentrations should be monitored regularly along with the changes in the frequency of replacing drenching solutions adjusted according to the organic matter load on the fruit.
• Maintaining cool chain after harvest is critical to maximise food safety, storage and transportation potential of fruit with minimum quality and fungal decay losses.
• Clean and sanitise the fruit receival area after each shift so that environmental pathogen transfer continuum is interrupted. Dry dumping with careful unloading of fruit onto the conveyor belt is relatively lower risk than wet dumping in large volumes of water.
• Eliminating/sorting out rotten, mouldy and damaged fruit before washing and sanitisation process is a cost-effective strategy to minimise mould spore load in the fungicide tanks/packing shed and improve the food safety outcomes.
• All brush rollers should remain covered under the sanitised wash water along with daily cleaning and sanitisation schedule at the end of the shift to remove organic matter and debris from the core and sides of the rollers.
• Treat the wash water to drinking quality before it is used/re-used for fruit washing to mitigate the microbial contamination risks to the lowest level. Alternately, single use wash water (run-to-waste) system is recommended, but it may not be an environmentally sustainable option.
• The citrus packers should be avoiding the use of chlorine-based sanitisers due to their negative impact on the environment. The selection of PAA in postharvest wash water is recommended due to its efficacy, low environmental impact, and its action is least influenced by the presence of organic matter. Other alternative options such as electrolysed water, cold plasma and ozone should be explored to meet sustainability requirements with minimal environmental impact.
• Automation of sanitiser dosing and its digital monitoring and logging are strongly recommended to eliminate human errors. Furthermore, verification of sanitiser concentration should be conducted at regular intervals using digital measurement tools.
• Frequent cleaning and sanitisation of  fungicide tanks to remove bacterial contamination and compatibility of sanitisers and fungicides should be confirmed before mixing them in fungicide tanks.
• Conveyor belts/rollers connecting washing and waxing zones should be cleaned and sanitised with utmost care to avoid any contamination opportunities between two steps. Also, the importance of washing and sanitisation step is reiterated as a control mechanism.
• There is significant opportunity to uplift the hygiene of packhouses through proper cleaning and sanitisation tools and processes. It is recommended that the industry should be aiming to popularise the environmental monitopring program (EMP) among citrus packers and highlight the benefits linked to the EMP costs.