High Pressure Eliminates Need for Heat Sterilization

Food processes promise greener processing, cleaner labels and higher-quality food

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From its first applications in the early 1990s on Japanese jams and jellies to the commercialization of high-pressure vessels in mid 1990s, high-pressure processing (HPP) has proven a winner. It kills foodborne pathogens and extends shelf life without heating the product and degrading taste or quality. And it's fast; an hour in a retort might equate to a six-minute HPP cycle.

Early on, HPP-treated guacamole was shown to retain the taste of a freshly made dip while extending shelf life from days to up to two months, in the process freeing formulators to exceed the traditional 4.6 pH acidic standard.

Today, HPP's inroads extend to the meat industry with sliced and whole-muscle meats with shelf-life beyond 100 days. Hormel Foods and Perdue Farms, both users of systems from Avure Technologies, Kent, Wash. (www.avure.com), are leading examples.

Elsewhere, Goose Point Oyster Co. in Bay Center, Wash., applies 43,000 lbs. of pressure for 90 seconds to kill pathogens and extend shelf life to 17 days for its fresh, in-the-shell oysters. “You would really, really have to be a connoisseur” to discern a change in the product, says Jeri Joy, marketing director.

While there are batch and continuous systems, throughput hasn't reached the stage where the technology can compete with low-cost, high-speed commodity processes. However, horizontal machines with a 350-liter vessel have roughly doubled the capacity of vertical machines, and can typically process 500 or more lbs. of product per cycle, depending on the packaging configuration.

To justify the cost, some companies turn to contract packers such as Milwaukee-based American Pasteurization Co. (APC), whose president, Justin Segel, notes HPP is “not irradiating things, it’s not better living through chemistry. It’s just the physics of putting something under pressure and decompressing it.”

The top candidates for HPP tend to be premium products, products with critical food safety needs and those in need of extended shelf-life for deeper supply chain penetration.

“Companies that have adopted the technology have ended up purchasing additional equipment, because they were able to market their products in different areas of the country or even internationally,” says Errol Raghubeer, vice president for microbiology & food technology for Avure.

There are application limitations to HPP, namely products with low moisture; the common comparison is that of a marshmallow, which will be squished under pressure vs. a grape, which comes out fine. Still, ongoing research may lead to new applications. HPP has been proven to extend the shelf life of milk from 15 or 20 days under refrigeration to 45 days at room temperature. And Raghubeer has presented research on sterilizing herbs using HPP to preserve their heat-sensitive bioactive phytochemicals and essential oils.

In addition to safety, taste and shelf-life benefits, the energy savings and an ability to reduce or eliminate chemical additives make HPP a technology to watch as trends develop.

Separately, the FDA in February accepted a pressure-assisted thermal sterilization, or PATS, process to sterilize low-acid foods. This followed four years of consortium research led by the National Center for Food Safety and Technology and Illinois Institute of Technology, which filed the petition, and Avure, as well as Basic American Foods, Baxter Health Care, ConAgra Foods, General Mills, Hormel Foods, Mars Inc. and Unilever.

By the way, NC Hyperbaric (www.nchyperbaric.com) of Burgos, Spain, has produced similar systems, some of which have appeared in the U.S.

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