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Continuous C[O.sub.2] processing uses moderate pressures.

The continuous pressurization of fluid milk using carbon dioxide (C[O.sub.2]) as a preservation strategy is under investigation by Cornell University scientists as an alternative to ultra-high-pressure processing (UHP) technology. The UHP--400 MPa to 1000 MPa--of milk can be effective. It can have a minimal impact on a product's flavor, visual characteristics and nutritional value. However, UHP processing may be prohibitively expensive for milk and many other products.

The use of moderately pressurized--less than 50 MPa--continuous flow dense C[O.sub.2] systems for pasteurizing fluid products provides benefits when it comes to processing fruit juices. Continuous C[O.sub.2] processing technology may potentially be applied to milk that is used for cheesemaking as well as to bulk raw concentrated milk destined for export. The technology also may be useful in reducing spore populations in fluid milk prior to further processing, such as ultra-high-temperature pasteurization or spray-drying.

The Cornell researchers are investigating a process that uses pressurized dense C[O.sub.2] within the range of 7 MPa to 34 MPa at 10 C to 60 C for treating milk. Results show that pressures between 1500 psi and 3000 psi at 25 C can lead to a 2-log to 3.5-log reduction of raw milk bacteria. These are comparable to effects the investigators achieved using high-temperature short-time (HTST) pasteurization--72 C for 15 seconds--with few detectable changes in milk quality, such as protein precipitation, undesirable flavor development or changes in opacity or color.

The scientists are investigating optimum C[O.sub.2] pressure and temperature treatments that would yield the necessary milk microbial spoilage and pathogen inactivation levels as well as milk quality parameters. Their goal is to design a process equivalent to that of HTST pasteurization. They're also investigating oscillatory treatments that destabilize and reduce the number of bacterial spores, typically the most environmentally resistant population.

The investigators are also exploring the C[O.sub.2] pressure continuous-flow system as a component of a multi-process system that includes physical separation and heat treatment technologies that might significantly extend fluid milk shelf life beyond the current 21-day expected maximum to as much as 60 to 90 days.

Further information. Joseph Hotchkiss, Department of Food Science, Cornell University, 119 Stocking Hall, Ithaca, NY 14853; phone: 607-255-7912; fax: 607-254-4868; email:
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Publication:Microbial Update International
Date:Jun 1, 2004
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