A Continuous High Pressure Carbon Dioxide System for Microbial Reduction in Orange Juice

A continuous high‐pressure carbon dioxide system, run at ambient conditions, was tested on its performance in reducing both natural and inoculated microbial loads. The prototype system continuously processes orange juice with carbon dioxide (CO 2 ) at high pressures. A central composite design was originally used to examine the variables of pressure, residence time, and CO 2 /juice ratio. For microbial reduction, residence time was the major factor followed by pressure. The CO 2 /juice ratio showed no influence on microbial load, and in this equipment, was difficult to control. The unit was able to cause a 5‐log reduction of the natural flora in spoiled juice, and could attain a 5‐log decrease in numbers of pathogenic Escherichia coli O157:H7, Salmonella typhimurium , and Listeriamonocytogenes . No viable cells of E . coli O157:H7 orS. typhimurium were cultured after the treated juices were stored at room temperature (22 °C) for 14 d. Thus, non‐thermal pathogen reduction is possible with this system.