Recent challenge studies carried out by Monaghan Mushrooms and researchers in Teagasc Food Research Centre, Moorepark, indicate that Listeria monocytogenes does not grow on refrigerated, pre-packed whole mushrooms during the shelf-life period.
Traditionally, the bacterium has not been an issue for mushroom growers, but in early 2014 L. monocytogenes was detected on a mushroom sample from one producer. The number of L. monocytogenes was not determined, and a concern arose that growth would occur and the numbers would exceed the regulations during the shelf life of the mushrooms.
A previous study conducted at retail level by the Food Safety Authority of Ireland in 2006 showed that 99 per cent of mushrooms were free of Listeria. In the remaining 1 per cent, the levels were within regulations and therefore safe for consumers.
This raised the question as to whether mushrooms support the growth of L. monocytogenes under normal shelf-life conditions, to the extent that the pathogen could grow above the safe level, according to Dr Juan Valverde, Research and Development Manager for Monaghan Mushrooms.
The company decided to conduct studies on the growth of L. monocytogenes on whole mushrooms, and to use conditions specified in a European Union Reference Laboratory for Listeria monocytogenes Technical Guidance Document published in June 2014.
The study was a safefood mini project and funded by the safefood Knowledge Networks. It was carried out with Dr Kieran Jordan, the Listeria Knowledge Network facilitator, who works at Teagasc, Moorepark.
The results showed that refrigerated fresh whole closed cap prepackaged mushrooms (Agaricus bisporus) did not support the growth of L. monocytogenes under these test conditions.
“As a result, detection of L. monocytogenes on a mushroom sample is not sufficient as the numbers will not increase during the shelf-life,” says Dr Jordan. “Instead it is necessary to determine the actual numbers and the relationship between these numbers and the regulatory limit.”
The results were presented at the safefood Listeria Knowledge Network conferences in Dublin (September 2014) and Belfast (November 2014) by Dr Avelino Alvarez-Ordonez (Teagasc) and Dr Juan Valverde.
Juan says the results were welcomed, as it shows that Monaghan Mushrooms produce a safe product, but he cautions against complacency. “We have set a standard, and now we have to keep up to it,” he says.
Since the occurrence of L. monocytogenes on mushrooms in 2014, the mushroom industry has taken the issue seriously and embarked on a strategy to address the issue, notes Kieran.
That includes creating awareness about L. monocytogenes in all parts of the mushroom production chain; challenge studies to determine the ability of L. monocytogenes to grow on mushrooms; a survey of the occurrence of L. monocytogenes at growing facilities and supporting a research project under the Food Institutional Research Measure to look at novel methods for control of L. monocytogenes in mushroom-growing facilities.
Comments