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Further research on nonthermal alternatives.

In helping ensure the safety of products while maintaining their quality, USDA-ARS researchers have investigated several nonthermal processing technologies, including high-pressure processing (HPP). This treatment involves applying 80,000 to 130,000 pounds per square inch of pressure to a sample.

Scientists found that HPP treatment at 25 C can significantly reduce E. coli populations in tomato juice and liquid whole eggs. Their research also suggested that several brief high-pressure treatments were more effective than one lengthy treatment using continuous pressure for the same amount of time.

While HPP can eliminate vegetative microorganisms, it is not effective at killing microbial spores. And at a cost of up to 10 cents per pound of product treated, it is too pricey to be practical. Researchers hope to develop pressure technology that is less expensive and more effective against spores.

USDA scientists also have investigated pulsed electric fields (PEFs) used to kill yeasts, molds and vegetative bacteria in liquid foods. These intensive electric pulses break down the cell membranes of the microorganisms. One effort explored the feasibility of using PEFs to make shelf-stable salad dressings.

A model salad dressing was formulated by Kraft Foods. ARS scientists inoculated the dressing with L. plantarum, a very heat-resistant spoilage bacterium. The sample was then treated either by PEFs alone or by PEFs followed by mild heat.
 While the PEF treatment alone significantly reduced L. plantarum
 levels, the dressing retained microbial shelf stability only when it
 was refrigerated. PEFs combined with exposure to mild heat, however,
 produced shelf stability at room temperature.

Another study involved subjecting applesauce to PEFs. This was followed by a mild heat treatment. The processed applesauce was aseptically packed in plastic cups and stored at room temperature. The applesauce maintained its quality during 470 days of storage. That's a longer shelf life than is currently used in commercial practice. This research showed that following PEF treatment, mild heat may be used in producing high-quality, shelf-stable applesauce products.

Scientists also treated apple cider with ultraviolet (UV) light. The sample had been inoculated with bacteria. The UV treatment reduced populations of E. coli and L. innocua by more than 99% without changing the liquid's flavor. On another front, researchers combined UV and heat treatments to kill E. coli in liquid egg whites. Whites infected with E. coli O157:H7 were processed using a UV system consisting of a low-pressure mercury lamp surrounded by a coil of UV-transparent tubing. The scientists found that UV treatment at room temperature can significantly reduce the heat subsequently required to pasteurize liquid egg whites.

Further information. Howard Zhang, USDA-ARS Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038; phone: 215-233-6583; fax: 215-233-6406; email:
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Publication:Microbial Update International
Date:Dec 1, 2006
Previous Article:Chives inhibit E. coli O157:H7, Salmonella in culture medium.
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