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Fakin’ it: fighting Listeria through simulation

By Rod Addy , 28-Jan-2013

Listeria may not be completely killed off by standard heat treatments
Listeria may not be completely killed off by standard heat treatments

Manufacturers can test the Listeria-killing potential of heat treatments in factories by using the enzyme amylase to simulate the behavior of the pathogen, scientists have discovered.

The industry uses heat treatment as an additional safeguard to kill off pathogens in products such as ready-to-eat foods, which involve minimal cooking after processing.

Amylase has the same rate of degradation when subjected to heat as Listeria and is harmless if ingested. Research fellow Sonja Gronqvist at Norwegian food research institute Nofima devised the method as one of two ways to test the reliability of heat treatment methods in eliminating Listeria monocytogenes in food.

The other procedure involved examining the effect of heat treatments on actual Listeria microbes encapsulated in alginate beads. However, because this involves the use of a pathogen, food safety rules dictate that it can’t be used on production lines.

More trustworthy picture

By contrast, the simulation method could be and consequently provided a more trustworthy picture of Listeria control under plant conditions, Nofima researcher Jan Thomas Rosnes told FoodProductionDaily.com. The organization partnered a fish cake manufacturer on the research.

Burgers and fish cakes were often fried or grilled on both sides, but this was still not sufficient to completely kill all Listeria microbes, he said.

“Manufacturers validate their own lines in an incomplete way. Many measure the core temperature at the end of the line, but that may not be safe. You need to see if there are cold spots in some of the burgers.”

Alginate beads

Nofima had also been testing the survival rate of Listeria microbes encapsulated in alginate beads after microwave heat treatment in a lab context, he said. “We can’t introduce Listeria directly in line,” Rosnes explained.

Nofima states: “It is easier to use a harmless enzyme when conducting research in real production lines, as this avoids contamination of the processing equipment and foods.

“This method was tested in full-scale production of grilled fish cakes, and showed that this type of TTI (time temperature indicator) was simple to use and is useful in documenting that secure targets are achieved for heat treatment in complicated heat processes.”

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