Putting the squeeze on produce to kill germs

WASHINGTON — 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 smashing 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, a company based in Kent, Wash., that makes high-pressure food-processing equipment sold under the trade name "Fresher Under Pressure."