Combatting Listeria on Two Fronts

OnionsThis article by Melanie Jackson originally appeared in a publication by Oklahoma State University’s Division of Agricultural Sciences and Natural Resources.

Outbreaks of foodborne illnesses are reported in the news almost daily. And while some foodborne pathogens are inconvenient, others are lethal. Listeria monocytogenes is the lethal kind – it kills 1 in 5 victims. Researchers at DASNR’s Robert M. Kerr Food & Agricultural Products Center are working to transform this statistic, committing to both conducting research and working with industry partners to develop methods and processes for reducing listeria.

Laboratory successes

Under the leadership of Peter Muriana, FAPC food microbiologist, a research team has developed a new method to reduce listeria without using heat. This type of process is useful for ready-to-eat products that aren’t heated before consuming, such as deli meat, ice cream and vegetables.

“Listeria monocytogenes is notorious for being found in meat- processing facilities and especially those that produce ready-to-eat meats such as deli luncheon meats or hotdogs,” Muriana said. “It produces biofilms that prevent sanitizers from killing the pathogen and allows the bacteria to hang around and persist a lot longer than other organisms.”

Muriana’s team has been able to use compounds called bacteriocins to slow the growth of listeria on ready-to-eat foods. Bacteriocins are antimicrobials produced by some types of bacteria that can kill other harmful bacteria strains. Naturally-occurring bacteriocins are found in probiotics in yogurt.

“[The bacteriocins we studied] are the same type of bacteria, except you can select some of them and make an additional bacteriocin,” Muriana said.

Muriana and his team combined various bacteriocins to create bacteriocin cocktails, and then they applied them to hot dogs. The researchers saw an immediate reduction in listeria, which was maintained through 14 weeks of shelf-life storage and even survived heat treatment.

“Not only can we add them on the product, but they also are heat stable so they can be added in the product, and their biological activity against listeria survives cooking,” Muriana said.

As a result of the research, FAPC has been able to license eight of the bacteriocin cocktails as antimicrobials for potential commercial use through Chr. Hansen Inc., a global bioscience company that develops natural solutions for the food, nutritional, pharmaceutical and agricultural industries.

“[The commercialization of the cultures] is proof that food safety lethality steps backed up with scientific evidence are in demand for products that can be contaminated with pathogens,” said David Howard, president and chief executive officer of Unitherm Food Systems, a company that produces innovative equipment for pasteurization, cooking and chilling food products.

Industry partnerships

The extent of Muriana’s listeria research extends beyond the lab through industry partnerships. Howard’s company, Unitherm, has been a particularly valuable ally. Unitherm regularly donates equipment to FAPC for third-party evaluation of antimicrobial effectiveness.

“The Unitherm-FAPC relationship is interdependent,” Howard said. “FAPC uses our support for different food safety studies, and we use that information to generate business.”

Most recently, Muriana has helped the company validate the effectiveness of a gas-fired flame grill designed to reduce bacteria in ready-to-eat products. The grill moves items along a conveyor, slightly grilling the surface and killing pathogens but leaving the product composition mostly unchanged.

The grill first was used for ready-to-eat meats, but Unitherm recently expanded its offering to include other products like onions, so they turned to Muriana for further validation.

This system is beneficial because the onions are cleaned without physical manipulation or yield loss.

“They can provide intact onions with the outer layers removed that can be shipped or further processed in a safer manner than if you were to cut pieces off,” Muriana said.

The research team looked at yeast, mold and listeria on red, yellow and white onions and quantified how much bacteria remained after going through the system.

Collaboration with industry helps FAPC create intellectual property and provide even more impact to Oklahoma’s value-added food industry, said Roy Escoubas, FAPC director.

“We are grateful for Unitherm’s support of FAPC’s mission and especially the important food safety work conducted in our microbiology lab by Dr. Muriana,” Escoubas said. “This kind of support drives success in the food industry and provides valuable information to help our food supply be even safer.”

Read more in OSU Research Matters 2017.

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