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Pasteurization in a flash

January 15, 2007
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A burst of steam and a jigger of bactericide in a high-speed packaging machine might provide hot-dog packers with a Listeria monocytogenes silver bullet.

Steam pasteurization is accomplished in the chamber immediately before the discharge zone (right) in RapidPak’s horizontal form/fill/seal packaging systems. Five years of development work preceded this year’s expected commercial introduction of the pasteurization component. Source: Alkar-RapidPak


On the fear factor index, E. coli 0157:H7 tops the charts of foodborne pathogens. But despite multiple headline-grabbing events in late 2006, Escherichia coli has a relatively low incidence rate compared to other pathogens, and the lethality rate is 3 percent. Listeria monocytogenes, on the other hand, is an efficient killer. The Centers for Disease Control and Prevention peg the fatality rate from L. monocytogenese at 23 percent, highest of all foodborne pathogens. Deaths in 2002 from listeriosis numbered 500, with another 2,500 serious illnesses. The pathogen is most often associated with ready-to-eat meats and hot dogs, which may receive no or insufficient reheating to kill the bacteria. To address the risk, public health officials created a three-class system in 2003 to prioritize oversight efforts. Plants with a post-lethality treatment or an antimicrobial step to arrest Listeria qualify for Alternative 2 status, one level above the minimum; facilities doing both rate Alternative 1 status, which relieves them of the otherwise required microbial testing program.

Post-packaging sterilization with hot water or steam is a common post-lethality treatment, and the steady decline in Listeria infections can be at least partially attributed to its effectiveness. But the process takes up to 20 minutes, results in package purge and adds heat to the product that must then be removed. It also requires somewhat thicker package film to withstand the sterilization treatment, adding cost as well as time.

Engineers at Lodi, WI-based RapidPak proposed past packaging pasteurization to Sara Lee Inc.’s Bil Mar Foods in the early stages of 1998’s Listeria outbreak at the Zeeland, MI, plant. By the time the problem was resolved, Bil Mar had recalled 15 million lbs. of hot dogs and other RTE meats. The Centers for Disease Control and Protection linked Bil Mar products to 15 deaths and 100 serious illnesses.

Although he drafted a 1998 memo outlining a post-packaging pasteurization step to Bil Mar, Robert E. Hanson eventually shifted his focus to a flash pasteurization step that could be executed immediately before packaging film is sealed in packages of hot dogs and other vacuum-packaged meats. Such a system could be incorporated into the servo-driven horizontal form/fill/seal machines his former company began fabricating in 1990. When RapidPak merged with an oven manufacturer to form Alkar-RapidPak Inc., development work began in earnest. In 2002, the first of two patent applications were filed for a module that could be incorporated into the firm’s packaging web system to deliver a quick burst of pressurized steam before the film was sealed, sterilizing the frank and the film before recontamination could occur. To help processors achieve Alternative 1 status, an antimicrobial application was later incorporated into the design.

Hanson, who served as vice president-research & technology at Alkar-RapidPak, left the firm last spring after Middleby Corp., an Elgin, IL, a manufacturer of foodservice ovens, acquired it. Before he left to cultivate his skiing skills, Hanson discussed the development of flash pasteurization. Company officials say the unit should reach commercialization this year.

FE: How does the system work?

Hanson: As with our original machine, an indexing advancement system is used to load the product and form the upper and lower web of film into a package that is sealed downstream. The difference is the pasteurization chambers that are incorporated in the forming area. Each chamber is outfitted with nozzles where a mixture of steam and water heated to 250

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