Recent headlines about contaminated peanut butter and tainted meat have raised concerns about our nation’s food supply. For food safety researchers at Oregon State University, these alerts are a renewed call to action; for some it means working under pressure.
J. Antonio Torres works with extremely high pressure … to kill microbes. The pressures exceed 100,000 pounds per square inch, 6,000 times greater than atmospheric pressure and almost 10 times greater than pressure in the deepest ocean.
“Dairies and all food processors use heat to inactivate microorganisms that are naturally present in foods,” Torres explained. “But heat is the enemy of freshness and nutrition. It breaks down chemical bonds, changing the taste, color, and nutrients in foods.”
Pasteurization uses 161-degree heat for 15 to 20 seconds to kill most of the microbes in food, and can reduce nutrition and flavor in the process. By exposing food to 100,000 psi, Torres has been able to pasteurize foods without heat. In addition, when pressure is applied during pasteurization at temperature lower than the standard 161 degrees, food lasts three to four times longer and suffers less chemical damage than when processed by conventional technologies.
“With milk, we found that pressure inhibits the formation of ‘off’ flavors. We are working on high pressure combined with lower sterilization temperatures to produce shelf-stable milk that tastes like fresh milk.”
Torres began exploring pressure-processing technologies in the mid-1990s. Early interest in high-pressure food preservation came from outside the food processing industry. A Seattle-area company named Flow International, Inc., which makes high-pressure pumps to inject water into oil wells, enlisted OSU’s help to adapt pressure technology to food processing. “They knew pumps,” Torres recalled, “but they didn’t know food. That’s why they came to us.”
When the first Gulf War began, military planners saw the need for improved food preservation in the blazing heat of the Middle East and adopted high-pressure methods to treat foods after they are sealed in the package.
“You’ve probably been eating pressure-treated food and didn’t even know it,” Torres said. “It is used to preserve sliced meats. If you buy avocado paste, it was treated with high pressure; there is no other way to preserve it without ruining its taste.”
Torres examines chemical changes in foods produced by this new technology, called pressure-assisted thermal processing (PATP), and has formed an international group to examine nutrient retention and possible toxic risks in PATP foods. “Our job is to confirm the absence of risks before food reaches consumers,” Torres says.
There remains one group of pathogens that are resistant to heat and virtually immune to pressure. To understand these resilient spores, Torres turned to Mahfuzur R. Sarker, a food safety microbiologist at OSU. Sarker was given the Presidential Award for Early Career Scientists and Engineers in 2004 for his research with Clostri-
dium perfringens spores.
Clostridium perfringens is less famous than its relative, Clostridium botulinum, which produces one of the most toxic poisons known and is the source of the wrinkle-fighting cosmetic Botox. C. perfringens is, however, the third-leading cause of food poisoning in the U.S. Its spores are everywhere—in the ground, wafting in the air, and carried into food processing plants on shoes, clothing, and supplies. The tiny, dormant spores can germinate and return to life in just 20 minutes after being consumed, sometimes killing elderly and immune-compromised people. Usually C. perfringens makes healthy victims too sick to work.
“Killing the spores is one of the biggest challenges in the food industry,” Sarker explained. “The economic loss was important to the government; the USDA provided funds to understand how the bacteria produces spores and how we can kill them.”
Sarker’s five-year study showed that the spore’s core of DNA—the genetic code—was tightly bound to and protected by a small, acid-soluble protein. Sarker, the microbiologist, and Torres, the high-pressure processing expert, are collaborating to crack the spore’s defenses. Their goal is to inactivate the protein to reach the DNA, in hopes of finding a preventive that can be sprayed on meat products to stop germination of the spores.
The research has yet to overcome the obstacles, but the researchers discovered that the spores can be tricked into germinating by either asparagine or potassium chloride. If Sarker and Torres can find ways to trigger germination and kill the microbes with high pressure, the result should be food that is safe and fresh, but Torres remains cautious.
“We haven’t studied all the effects of high pressure on the chemical composition of the food,” Torres said. “There may be new chemistry happening here. We are looking out for other chemicals that we have not seen before.”
OSU scientists are committed to averting food crises, as well as extending the freshness of perishable food products. Take strawberries, for example. Oregon is a leading berry-producing state, and berry juice is a high-value product. To deter contamination of strawberry juice by strains of E. coli and Salmonella, food scientist Yanyun Zhao and her research associate Jingyun Duan are using natural essential oils from cinnamon leaf and lemongrass.
She’s focused on the germ-fighting properties of essential oils as an all-natural alternative to pasteurization, which reduces Vitamin C and other nutrients in berry juice. “Less heat could mean higher quality and more health benefits for berry juice,” she said.
Down the hall from Zhao’s office in the OSU Food Science and Technology Department, Mark Daeschel has succeeded in finding ordinary alternatives to chemical preservatives. With the motto “keep it simple,” Daeschel has shown that raisins can help preserve beef jerky and wine in a spray bottle can be used as a disinfectant. He discovered that an enzyme called lysozyme, which is found in egg whites, can be used as a natural preservative in beer and wine.
“We’ve used chemical preservatives in the past because they work well to keep food from spoiling,” Daeschel said. “But now our strategy is to use a series of obstacles that cumulatively wear down microbes without chemicals and without affecting the quality of the food.”