New approach also keeps juice tasting fresh
Washington D.C., August 21 -- 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 here today 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, say 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. 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," Marshall says.
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. Pressurized 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 lysteria 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 100,000 organisms per milliliter to zero, according to Marshall.
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.
The research was funded by Praxair, a carbon dioxide manufacturer in Danbury, Conn., and the U.S. Department of Agriculture.
The paper on this research, AGFD 38, will be presented at 10:40 p.m., Monday, Aug. 21, at the Convention Center, Room 7.
Stephen Hill is a graduate student in food science at the University of Florida in Gainesville, FL.
Dilek Kincal is a graduate student in food science at the University of Florida in Gainesville, FL.
Murat Balaban, Ph.D., is a professor in the Institute of Food and Agricultural Sciences at the University of Florida in Gainesville, FL.
Maurice Marshall, Ph.D., is a professor in the Institute of Food and Agricultural Sciences at the University of Florida in Gainesville, FL.
A nonprofit organization with a membership of 161,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals and databases, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.