Putting the squeeze on produce to kill germs

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WASHINGTON (AP) — Could food producers literally squeeze the salmonella out of a jalapeno? Or zap the E. coli from lettuce without it going limp?

Headline-grabbing food poisonings from raw foods are prompting new interest in technology — from super-high pressure to irradiation — to get rid of some of the bugs. It won't be a panacea: Far better to prevent contamination on the farm than to try to get rid of it later.

"This is never an excuse for a dirty product," warns University of Minnesota infectious disease specialist Michael Osterholm.

But it's impossible to prevent all contamination in open fields. And increasingly popular ready-to-eat foods — salads already washed and bagged, fruit peeled and sliced — allow another processing step where a single slip-up can introduce pathogens.

Washing, even with chlorine or other chemicals, only gets rid of surface contaminants, not germs that sneak inside the fruit or vegetable. Enter high-tech options.

At a Virginia Tech laboratory this summer, food scientists subjected small grape tomatoes to what's called "high pressure processing" to see if they could squeeze salmonella to death.

It's been known for decades that massive pressure — the equivalent of two African elephants standing on a dime is how Tech microbiologist Robert Williams puts it — can destroy certain pathogens. The question is how to kill the bugs without smushing the food they're in.

Key is to choose a water-packed food with few air pockets. Put it in a container of water and apply pressure evenly to all sides. Air pockets will collapse but waterlogged tissue is more resistant.

Grape tomatoes emerged fine, says Tech food scientist George Flick.

But bigger beefsteak-style tomatoes cracked under the pressure. There's more air inside the regular tomatoes than their tiny cousins.

Foods treated by high-pressure processing, or HPP, already are on the market — particularly raw oysters treated to kill the vibrio germs that proliferate in warmer waters, and processed meats treated to kill dangerous listeria.

For more delicate raw produce, sliced fruits and vegetables seem to be HPP's main niche, says Errol Raghubeer of Avure Technologies, the Kent, Wash.-based company that makes high-pressure food processing equipment sold under the trade name "Fresher Under Pressure."

First on the market: Sliced avocadoes and guacamole, when companies realized that HPP treatment killed spoilage germs that rapidly turned cut avocadoes brown, thus extending the products' shelf life.

Whole large tomatoes don't fare well but diced ones can if they're processed in certain ways, Raghubeer says — and a number of HPP-treated salsas are hitting the market.

Also arriving are ready-to-assemble fajita meal kits with little bags of HPP-treated fresh, sliced jalapenos. Raw jalapenos have become the prime suspect in the nationwide salmonella outbreak that sickened more than 1,200 people this summer.

A whole jalapeno goes limp when HPP treated because of its hollow center, but diced jalapenos emerge just as crisp, says Raghubeer.

Simple physics is behind high-pressure processing. A different approach under consideration by the Food and Drug Administration is irradiation, zapping fruits and vegetables with enough electron beams or other radiation to kill germs.

Irradiated meat has been around for years; it's considered particularly useful in the ground beef that is a favorite hiding spot for E. coli. And while irradiated foods initially caused some consumer concern, government scientists make clear that the food itself harbors no radiation.

But early on, irradiation left lettuce and spinach limp and made tomatoes mushy. That's changed, says Minnesota's Osterholm: "It's like talking about the TV sets of the 1970s versus flat screens of today," he says of improved irradiation delivery.

In studies of bagged salads, tailored irradiation doses killed E. coli on nine different types of lettuces without harming the texture, or affecting the taste of accompanying ingredients like tomatoes and cucumbers, says Jeffrey Barach, director of the Grocery Manufacturers Association's food laboratory. Killing salmonella takes a little more energy, so producers would customize the beam to the need.

Barach's trade association has petitioned the FDA to allow the irradiation levels, somewhat lower than meat requires, for produce pathogen and other ready-to-eat foods, and hopes for approval by year's end.

Both high-tech options add to foods' cost, meaning they'd always be something of a niche product. But parts of the population are particularly vulnerable to food poisoning because of age or health conditions, a natural market.