TORONTO - Maple Leaf Foods is assessing a recently approved preservative for meat products that inhibits the growth of Listeria following a deadly outbreak linked to one of its plants that's claimed 20 lives across the country.

Health Canada gave the go-ahead on Sept. 20 for food processors in Canada to use sodium diacetate as a preservative in meat, poultry and fish products. When used in combination with sodium lactate, the preservative can curb the growth of Listeria monocytogenes.

Spokeswoman Linda Smith said Maple Leaf is aware of the approval and is "assessing it."

The iconic food producer shut down a meat processing plant in Toronto on Aug. 20 after Listeria contamination was detected and linked to the nationwide listeriosis outbreak.

The plant underwent an intensive sanitization and production resumed on Sept. 17. Initial product runs were still being tested and not shipped to the public for consumption when, on Wednesday, more Listeria was detected.

CEO Michael McCain held a press conference the following day to stress the prevalence of Listeria, after the most recent positive findings. It's everywhere, he said, and reasonable to assume most people consume it every day.

It is however dangerous in very high levels, and food scientists say should low levels of Listeria exist on equipment in processing plants the preservatives could ensure it never multiplies to dangerously high levels.

Food scientist Martin Wiedmann said sodium diacetate can completely prevent the growth of Listeria or slow it down, depending on several factors such as the type of food. But he cautioned against viewing it as a "magic bullet" solution.

"It's one piece of an effective total strategy to reduce the risk of Listeria contamination," he said.

Wiedmann is a food science professor at Cornell University and researches Listeria contamination on ready-to-eat products. Tests he has conducted have found Listeria on sidewalks, wheels of carts in supermarkets, in playgrounds and in rivers -- in short, everywhere.

"(People) usually expect food to be free of bacteria. Well, no, you shouldn't," he said. "You can't. We've evolved over millions of years to co-exist with bacteria and we have defence mechanisms against it."

However, there are ways for food processes to protect, as best they can, against Listeria contamination, he said. The first is trying to ensure as little as possible enters the facility.

Wiedmann said some plants have people walk through sanitizers or antimicrobial foam to kill bacteria on shoes, some have people change their shoes or even their clothing.

Companies also conduct tests to detect Listeria and have sanitization processes. Some problems arise there, Wiedmann said, because of issues with the equipment.

Maple Leaf believes the "most likely" explanation for the deadly Listeria contamination in the summer was an accumulation of bacteria deep within its meat slicing equipment. Wiedmann said it's a common problem.

"We've seen issues with slicing machines before in the U.S. and all over the world...if you do research on slicers and Listeria it's endless," he said.

There are several ways food processes can reformulate food, such as adding sodium diacetate and sodium lactate, to slow the growth of any bacteria that may have made it onto the food.

Irradiation briefly exposes food to gamma rays or electron beams and can kill harmful bacteria. It is approved for use on meat and poultry in the United States, but in Canada is limited to onions, potatoes, wheat, flour, whole wheat flour, and whole or ground spices and dehydrated seasonings.

Lowering the pH, therefore increasing acidity, also controls Listeria, as would heat-treating the final product, Wiedmann said.

"It's not one thing," he said. "You can't look at one plant saying, `You didn't do your job."'

Once it leaves the company's control and is purchased by a consumer, Wiedmann said it's up to individuals to ensure they don't do anything to encourage bacterial growth.

Listeria does continue to grow in refrigerated food, but lower temperatures are still ideal. Wiedmann said under 4 C is preferable.

"To you and me it might not sound like a big difference if they refrigerate it at seven degrees or at three degrees -- to Listeria it makes a big difference," he said.

Outside of a fridge on a hot day Listeria can double every 30 minutes, Wiedmann said. If that same food is stored at 4 C, it takes 24 hours to double.