Listeria research forces bacteria to jump hurdles
The microbiologist managing the project at the UK-based food research organisation, Greg Jones, said in a company podcast that the bacteria was a growing problem in Europe.
“The issue here is that listeria is on the rise. Particularly in Europe, we’re seeing more and more cases of listeria,” Jones said.
“And manufacturers are under pressure to remove inhibitory compounds from their products such as salt and preservatives in a bid for healthier and clean-label type products,” he added.
Sub-lethal stresses
Jones defined hurdle technology as “the application of a series of sub-lethal stresses to a food product”, to discover exactly what combinations of sub-lethal stress were inhibitory to listeria microflora.
According to the Campden BRI: “Previous work has shown that if different stress factors are applied to bacteria, the order in which they are applied will determine the potential for bacterial survival or death during subsequent storage.”
Campden BRI’s 3-year research programme – now underway for six months with first results expected at the year’s end – will examine a range of stresses used in hurdle technology, such as storage temperature, pH, salt, heat, process and preservatives.
Said Jones: “So you may add a little bit of salt, you might then chill the product. The combination of those two stresses might be enough to prevent the growth of listeria, whereas any one of those is not enough.”
Scientists at Campden BRI were using a broth-based system, Jones said, and analysing thousands of broths with different combinations of stresses in them to gather “growth or no-growth data” on listeria from each.
He said:“Then we can narrow that down and look at the order of the application of the stress, and also at exactly what levels of salt, for example, are going to be sub-lethal in combination with another stress.”
Cross-protection issue
Jones explained that the research would also examine "cross-protection", whereby one inhibitory hurdle might potentially protect listeria cells against other stresses.
“If a sub-lethal stress is applied then sometimes you get cross-protection to a second stress, sometimes you don’t,” he said.
"The way to figure that out is to look at a molecule called SigmaB in listeria. If cross-protection is going to happen SigmaB is produced, if it is not then it is not produced."
Jones added: “If we can find out which stresses make this molecule appear, we can predict that cross protection is either likely or unlikely to happen in response to a given sub-lethal stress.”
