Performing Well “Under Pressure”

There is a new and emerging technology, called high hydrostatic pressure (HHP) processing, that the retail and foodservice industry should be aware of. The technology involves the use of very high pressure, sometimes accompanied by heat, to lessen the amount of pathogenic and spoilage microorganisms in foods. The positive outcomes from this technology can include safer food products, extended product shelf-life, fresher appearing products, and cleaner labels with more “natural” food ingredients. Today, the market for HHP processed foods is over $2.5 billion dollars annually. HHP is currently being used effectively for foods such as ready-to-eat whole muscle and sliced meats, processed fruits and vegetables, fresh juices and smoothies, deli salads and dips, and shellfish.

I recently had the opportunity to visit Sandridge Foods in Medina, OH to have a closer look at this technology. The company has recently installed one of the largest HPP processing systems in the U.S. At this plant location, Sandridge Foods uses the technology for refrigerated deli-salads that are commonly displayed and sold in grocery stores and salads that are part of meals sold through foodservice.

In many ways, I felt like I was entering a scene from the original Star Wars movie. The food product is placed into plastic bags or single-use plastic containers and then placed into the high pressure chamber. Less than 5 minutes later, after being processed at over 87,000 psi, the product leaves the chamber. The end result was a very high quality, fresh deli salad with an extended shelf-life.

The benefits to product appearance and taste were obvious compared to traditionally prepared salads that would either be thermally processed and/or acidified. In many ways, Sandridge Foods is a pioneer in the movement toward the use of new technologies for refrigerated food products sold at retail. One of the company’s main goals is to produce foods that are “free from bacteria.” While not there yet, use of new and novel technologies may provide a path forward toward their goal.

HHP, also known as ultra-high pressure processing (UHP), is highly effective at eliminating bacterial contaminants without the use of chemical additives or subjecting products to heat. The structure of many foods processed at ultra-high pressures is not damaged because equal pressure is applied to all surfaces of the product from all directions. High pressure processing can be completed at ambient or refrigerated temperatures. After the product (within plastic packages) is placed into the chamber, the desired pressure is obtained (normally takes about 2-3 minutes), and then the product is exposed to the high pressure for a dwell time of usually 3-5 minutes. HHP processing works best on high water-content foods and pressures are often at 87,000 psi or higher but can also be as low as 25,000 psi. HPP products have a shelf-life that is comparable to heat processed pasteurized foods and foods that have been acidified. The use of refrigeration helps to extend shelf-life by maintaining microbial stability and prevents spore growth.

Some of the benefits of HPP foods include:

Safer foods. HPP has been shown to be effective for inactivation of many foodborne pathogens including Listeria monocytogenes, Escherichia coli and Salmonella spp., with little or no change in organoleptic properties or nutritional value.

Fresher foods. HHP is effective in lessening microorganisms that cause spoilage, naturally preserving the freshness of packaged foods. In many cases, the shelf-life of foods can be doubled.

There are many examples of recent research that has justified the use of this technology from a microbial perspective. Post processing control for Listeria monocytogenes in prosciutto ham leads to a > 5 log reduction when processed at 90,000 psi. Treatment of raw oysters is done to controlVibrio parahaemolyticus, Vibrio cholera, and Vibrio vulnificus, processed at 25,000 psi that leads to a >6 log reduction (lower pressures are used so the oysters do not open). In general, yeasts and molds are more sensitive to HHP, which makes this technology effective for enhancing shelf life of many foods. HHP has been shown to also inactivate viruses including the feline calicivirus, coxsackievirus, and human parechovirus. Similar to heat processing, bacterial spores are far more resistant to HHP processing. Some spores have been shown to survive at >250,000 psi for 45 minutes. To eliminate spores, often a synergistic treatment with heat is needed. Other controls methods for preventing spores from outgrowing include refrigerated storage, pH adjustment, and use of preservatives.

More natural foods. HHP can allow food processors to substantially reduce or eliminate the use of chemical preservatives, cutting costs while creating the clean-label, all-natural and organic products that many consumers are demanding.

Better tasting foods. Many HHP foods retain more of their fresh taste, texture, color and nutrients because there is no need for heat processing.

The use of HPP is in its infancy. As consumers become more aware of the many benefits of HHP processing technology, it is likely they will come to prefer and demand it. HHP poses none of the potential risks inherent in irradiation or artificial chemical preservatives. HPP also avoids heat degradation of vitamins, enzymes, flavors and texture as is found in cooking and pasteurization. The use of HPP is not inexpensive, with HPP services running about 20-30 cents per pound of treated food. However, many think this is a small price for consumers to pay when they are shopping for peace-of-mind along with quality nutrition.

From a microbiological perspective, HHP processing is a technology that has great potential. As we learn more about HHP and the costs of the technology can be decreased, I expect to see a great increase in the amount of HHP processed foods.

So what does this mean for those of us that work in the retail food industry? We should all be aware of this emerging technology, as well as many other new technologies, that may hold promise for creation of a safer food product with longer shelf-lives. I have identified a few resources that may be helpful in your pursuit to learn more about this emerging technology.

For more information:

http://grad.fst.ohio-state.edu/hpp/faq.html – Fact Sheet on HHP processed foods from The Ohio State University.

http://maria-blanco.suite101.com/the-role-of-hpp-technology-in-food-safety-a393197 – Fact sheet on the role of HPP technology in food safety from Engineering 101.

Hicks, D. T.; Pivarnik, L. F.; McDermott, R.; Richard, N.; Hoover, D. G. & Kniel, K. E. Consumer awareness and willingness to pay for high-pressure processing of ready-to-eat food. Journal of Food Science Education 2009, 8(2), 32-38

Heinz, V. & Buckow, R. Food preservation by high pressure. Journal of Consumer Protection and Food Safety 2010, 5(1), 73-81.

Patterson, M. F. A Review: Microbiology of pressure-treated foods. Journal of Applied Microbiology 2005, 98(6), 1400-1409.