Pressure, carbon dioxide kill pathogens, extend shelf life of juice.

Thermal pasteurization is a common preservation technology used to extend the shelf life of juices. But the thermal process causes a loss of the fresh flavor of the juice and also imparts a cooked aftertaste to the product.

Consumers want a fresh-tasting juice, and scientists at Praxair are evaluating a variety of technologies to achieve what consumers want. The company has licensed a carbon dioxide process from the University of Florida that kills microorganisms and extends the shelf life of juices while retaining freshness and nutrients. Praxair is commercializing the technology under the Better Than Fresh[TM] trademark.

The process uses carbon dioxide as a processing aid. The technique entails continuously pumping freshly extracted raw juice and liquid carbon dioxide by separate pumps in predetermined ratios into a closed mixing chamber. This mix is pressurized between 1500 psi and 5000 psi and held in a retention tube for a while.

Then the mix is brought to atmospheric pressure during a controlled depressurization step, which releases most of the carbon dioxide. The juice is collected in a decarbonation tank to remove any residual carbon dioxide.

Investigators undertook process validation studies by inoculating fresh orange juice with various bacteria. All pathogens were acclimated to the low pH of the orange juice prior to the treatment. The process consistently yielded more than a 5-log reduction of all of the pathogens tested in inoculated single-strength orange juice using carbon dioxide concentrations ranging from 8% w/w to 12% w/w. In the U.S., juice HACCP regulations require that processes deliver more than a 5-log reduction of targeted pathogens for a specific product.

Besides reducing the number of pathogens, the process also decreases the number of spoilage bacteria, mold and yeast. In this manner, it is able to extend the shelf life of the product. Results of sensory tests showed that consumers could not differentiate between raw and treated juice. Analysis using gas chromatography confirmed that there were no significant differences between the raw and treated juices. There was no loss of vitamin C and foilic acid. The treated juice didn't experience any changes in pH, Brix, Brix-to-acid ratios or total antioxidant values.

Praxair researchers continue to investigate combining carbon dioxide with high pressure on other juices, juice blends and low-acid beverages. Preliminary results show similar benefits, such as extending shelf life while preserving fresh flavors and nutrients.

Further information. Nari Nayini, Praxair Inc., 7000 High Grove, Burr Ridge, IL 60521; phone: [phone]; email: [e-mail].