Bagged greens

Produce growers are trying to find better ways to make sure that bagged greens are free of illness-causing organisms. (Ricardo DeAratanha, Los Angeles Times / January 26, 2012)

Earthbound Farm of San Juan Bautista, another Salinas-area salad powerhouse, also is investing heavily in food safety.

The company faced a steep climb to win back consumer confidence. In 2006, it processed the spinach, sold under the Dole label, that spread the deadly E. coli to 26 states.

Besides the five people who died, 31 people developed a serious illness linked to E. coli that can cause kidneys to fail. The illness,hemolytic-uremic syndrome, or HUS, is most common in children, and 29% of those sickened after eating Salinas Valley spinach were younger than 18.

Investigators traced the E. coli to a single 50-acre field at the Paicines Ranch in San Benito County. Wild pigs may have tracked it from cattle grazing nearby, since E. coli typically lives in mammals' intestines, officials said.

That a portion of a single field could sicken so many people was a harsh lesson for the bagged salad industry. Will Daniels, Earthbound's senior vice president for food safety, believes that the E. coli may have been contained in a single 500-pound lot of spinach.

So scientists are delving deep into the biology of leafy greens to learn exactly how a pathogen clings to a leaf, and how to get it off.

That's tougher than it might seem.

Most companies treat their salad wash water by adding an antimicrobial agent, typically chlorine. Ideally, a rinse in clean, chlorinated water would whisk off those pathogens and prevent them from migrating to other leaves. But tiny amounts of pathogens can survive those washes and taint clean leaves.

Taylor Fresh's T-128 has been shown in studies to boost the power of chlorinated water. Fresh Express, meanwhile, developed its own Fresh Rinse, a chlorine alternative, and Earthbound is testing chlorine-free cleansers with a citrus base, citing concerns about the potential environmental problems linked to chlorine.

Even so, a simple rinse can't easily remove pathogens if they've become embedded in so-called biofilms — thin, microscopic layers that can be formed by bacteria like E. coli and salmonella.

"You have this gooey mass, like frosting on top of a cantaloupe surface or a leaf surface," said Trevor Suslow, a UC Davis food safety researcher. "They're hard to penetrate by antimicrobials. They're glued on pretty tightly."

And so "biofilm disrupters" are a popular topic among researchers trying to pull pathogens from greens.

Daniels of Earthbound Farm is especially enthusiastic when he describes high-power ultrasound tests his firm is funding at the Institute for Food Safety and Health, part of the Illinois Institute of Technology.

The institute outside Chicago is one of only a handful of U.S. food safety centers with a test processing plant ranked Biosafety Level 3, or BSL-3, in which scientists must wear moon suits for certain experiments and are decontaminated before they leave the lab. It's designed to test the behavior of live, potentially lethal pathogens on foods, be they sprouts, eggs or ready-to-eat meals.

The high-power ultrasound works like a factory-scale bubbling denture cleanser. Researchers use it to create millions of tiny bubbles that cover leaf surfaces. When the bubbles burst, they release enormous energy that can dislodge pathogens into water treated with highly acidic citrus cleanser — a one-two punch that Daniels says is yielding promising results.

Gas washes are also catching the attention of food companies, perhaps applied while post-harvest greens are stored in coolers before processing.

Even the best research can't reduce the risk of contaminated greens by 100%, scientists said. At Earthbound, Daniels says the ultimate goal is to achieve what scientists call a "5 log reduction," the equivalent of pasteurizing milk. In short, if an unwashed lettuce contained 100,000 pathogens, the perfect wash system would knock off five "0s" and reduce the pathogen count to 1.

Plenty of money is being tossed at the problem of tainted greens. The Center for Produce Safety at UC Davis, founded in response to the spinach outbreak as an industry-public partnership, has pumped more than $9 million into 54 research projects at 18 universities, according to Executive Director Bonnie Fernandez-Fenaroli.

But even if the perfect wash-treatment combo emerges, some experts wonder how much companies would be willing to pay for it.

Microbiology professor Michael Doyle, director of the Center for Food Safety at the University of Georgia, has consulted with some of the nation's leading food companies for decades.

"There's an elite group that's committed to food safety," he said. "Then there are others that don't want to spend a lot on food safety unless they're forced to by theMcDonald'sof the world."

Deborah Schoch is a senior writer at the California HealthCare Foundation Center for Health Reporting, an independent news organization devoted to reporting about health care issues that concern Californians. The Center is based at the USC Annenberg School for Communication & Journalism. It is funded by the nonpartisan California HealthCare Foundation, one of two health foundations created by the privatization of Blue Cross of California in 1996.