What was it all about?

Beginning and ending in 2019/20, this investment worked to better understand the causes of outbreaks of listeria in rockmelons, and explored potential risk management strategies.

After conducting a comprehensive review of both Australian and international listeria outbreaks, and looking at methods that are being used or proposed to manage the risk post-harvest, the project team reported:

• Outbreaks are rare. While the bacteria that causes listeriosis, Listeria monocytogenes, is common in the natural environment and can colonise food processing plants, outbreaks from whole rockmelons are rare. Only three outbreaks associated with whole melons have been reported in international literature over the last 40 years.
  
  
• Contamination often occurs in the packhouse. While a range of factors can contribute to outbreaks, it was suggested colonisation of the packhouse – likely undetected for many weeks – was a factor in the contamination of melons in two of the largest outbreaks investigated. In a 2011 United States outbreak, colonisation was suspected to be caused by failure to use sanitiser spray on melons, or contamination from trucks, or the introduction of contaminated food processing equipment. It was also suggested that high-prevalence but low-level contamination of melons occurred in the field in the 2018 Australian outbreak after adverse weather events, and was not eliminated during processing in the packhouse.
  
  
• More work is needed to confirm the optimal use of sanitisers. While they play an important role in product safety, the researchers revealed limited evidence to determine the efficacy of sanitisers under the conditions currently used in Australia to kill or remove Listeria monocytogenes from the surface of whole melons.
  
  
• Alternative sanitisation methods are promising, but not all are relevant for the Australian industry. From their review, the researchers found evidence that a range of technologies can be effectively used to reduce Listeria monocytogenes from the surface of rockmelons, including X-rays, hot water, superheated steam, dry steam and chemicals including octenidine and dihydrochloride.

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See the full final technical report

The project has developed a summary of essential information for the industry, which is available here. The team has also worked closely with other levy-funded programs, including Food safety training, extension and capacity for the melon industry – phase 2 (VM18003), to ensure that their findings are easily accessible.