Carbon dioxide, the stuff that makes soft drinks fizzy, can also make fresh fruit juice safer to drink, according to researchers at the University of Florida. The findings were reported at the 220th national meeting of the American Chemical Society, the world’s largest scientific society.
Treating juice with carbon dioxide works as well as heat pasteurization to eliminate bacteria without altering the flavor, according to Stephen Hill and Dilek Kincal, graduate students at the university. They conducted their research under the direction of Maurice Marshall, Ph.D., and Murat Balaban, Ph.D., professors at the University of Florida Institute of Food and Agricultural Sciences.
“Tasters could not tell the difference between fresh-squeezed orange juice and carbon dioxide-treated juice,” Marshall says. An added benefit of the carbon dioxide treatment is that it also improves the appearance of fresh squeezed orange juice. The process deactivates an enzyme that causes the juice to separate into a transparent, watery layer at the top and a pulpy mass at the bottom. Ninety-eight percent of juices in the United States are heat pasteurized, the same method used to treat milk, according to the U.S. Food and Drug Administration (FDA). Less than two percent of juices do not get pasteurized and can cause food poisoning.
“Right now heat pasteurization is the only game in town to minimize pathogens in juice. The heat required for pasteurization has the effect of making fruit juice taste ‘slightly cooked’,” according to Marshall. Other alternative methods to pasteurization -- UV radiation, high pressure and pulsed electric fields -- also raise the temperature of the juice, but for a much shorter period of time.
Using carbon dioxide instead of heat preserves the flavor of the juice while still killing pathogens. Pressurize liquid carbon dioxide is added to the juice at room temperature. After ten minutes, the mixture is depressurized. The carbon dioxide turns into a gas and escapes, leaving behind a pure, non-fizzy juice.
To test the effectiveness of the treatment, the researchers inoculated sterile orange juice and apple cider with Salmonella, E.coli and Listeria monocytogenes, another bacteria commonly found in food, and then treated the contaminated juice with the pressurized CO2. The treatment reduced the bacteria population from more than 1,000,000 organisms per milliliter to zero. The researchers do not know precisely how the carbon dioxide destroys the microbes but suspect that the reduction of oxygen in the system and high pressure might play a role.