Food Product Design: New Technologies - July 2004 - Under Pressure

July 2004

Under Pressure

By Amy SchauweckerContributing Editor

Although this is not recommended -- or even humanly possible -- if you were to scuba dive in the deepest proclaimed section of the world's oceans -- the Marianas Trench -- you would be subjected to pressures of 16,000 psi. High-pressure processing (HPP) commonly processes food at 87,000 psi.

HPP is a novel commercial technology that food manufacturers utilize to improve food safety, extend shelf life, increase viscosity and alter destructive enzymes. They primarily choose HPP over traditional processing means because it has minimal influence on raw flavors and nutrients.

Stacking on the pounds We have known of HPP for over a century, but the equipment has only become more available and reliable over the last two decades. HPP can be used in either continuous or batch systems. While continuous systems require pumpable products, batch systems can process both liquid and solid products. "Batch processing is most suited to our key target areas: ready-to-eat meats, shellfish, processed fruits and vegetables," explains Terry Anstine, marketing director, Avure Technologies Inc., Kent, WA.

In an HPP vessel, the hydrostatic pressure is uniformly and instantaneously distributed on all sides of the flexible packaged food product through a pressure-transmitting fluid, usually water. One way the extreme pressure loads are accounted for on the HPP vessels is by a wire-wound, prestressed cylinder and frame.

Anstine says: "It's taken ongoing work to develop new systems that are reliable and with adequate processing volumes to get HPP costs down to current state. We are starting to see a real understanding by food processors, retailers and food distributors of the value that HPP can bring to premium foods."

Fleeting microbes and mad cows Researchers theorize that HPP kills microorganisms by breaking noncovalent bonds, resulting in disruption of microorganism cellular functions. Widely held theory also suggests that protein compression and denaturing are principle mechanisms for microbial inactivation in HPP foods. Evidence suggests that when the HPP system releases pressure, it shocks large molecules (like proteins), but it leaves the smaller molecules (like flavor compounds and antioxidants) intact.

HPP products found in the marketplace have demonstrated that the process can be used in meeting FDA and USDA requirements for pathogenic reduction. HPP has met pasteurization requirements for juice HACCP regulations and for ready-to-eat (RTE) foods at risk for Listeria monocytogenes. HPP can achieve increased shelf-life results by reducing deteriorative enzymes, yeast and mold, and spoilage activities in foods. The National Institutes of Health (NIH) recently conducted a study using HPP to inactivate infectious prions responsible for bovine spongiform encephalopathy (BSE). While HPP treatment of meats could ensure greater safety from infectious BSE, it should not be used as a remedy for poor-quality meat ingredients. "You cannot put quality in by HPP alone. You need to start off with quality in order to preserve quality," warns Edmund Ting, Sc.D., R&D vice president for Avure.

Circling the globe and beyond A wide number of studies have determined that suitable food products for HPP are nonporous, have high water activity (aw), tend toward heat sensitivity and have a high-value perception in the market. Current HPP products are refrigerated, and many do not require preservatives. A growing array of commercial offerings exists in the RTE, seafood, juice, fruit and vegetable categories.

Avomex International, Keller, TX, one of the front-runners in utilizing HPP technology, was named in Houston-based Sysco Corporation's top 10 suppliers for 2003. "We can achieve a 30-day refrigerated shelf life in guacamole without the use of preservative and a 45-day shelf life on salsas made with all fresh vegetables," states Marcia Walker, Ph.D., vice president, technology and microbiology, Avomex.

According to Ting, the shelf life extension is typically three times longer for high-acid foods and two times longer for low-acid foods, such as cold cuts.

Avomex is currently launching a new HPP line of fruit-juice smoothies and RTE meal kits, including chicken and beef fajitas, chicken chipotle, chicken enchiladas and chicken quesadillas. The chicken fajita prepared meal kit is approximately six servings at a suggested price of $7.99. "We are more expensive than typical retort or canned foods, however, many of the products we run cannot be thermally processed. The foods that we produce are value-added and do command a higher price in the markets that we are in. Consumers are willing to pay more for safer, more freshlike quality," explains Walker.

RTE foods that are post-processed with HPP have emerged in the marketplace more frequently than ever. Ting and Anstine attribute the increased commercial interest to the new USDA Food Safety Inspection Service (FSIS) rules that mandate manufacturers use a post-lethality intervention method for Listeria in prepackaged RTE meats, such as deli meats. The USDA approved HPP as an effective intervention method. Mainstream companies, such as Perdue Farms, Horsham, PA, and Hormel Foods, Austin, MN, are utilizing HPP in prepackaged RTE deli meats.

Oysters are another HPP success story. Researchers have proven the ability to kill Vibrio vulnificus pathogens in oysters at 35,000 to 45,000 psi pressure ranges. HPP relaxes the oyster adductor muscle and shucks the oyster from its shell, eliminating the need for further processing steps. Flavor profiles remain the same as raw oysters, according to sensory results. More oysters have been treated by HPP since California passed a law that requires processing of post-harvested oysters retrieved from the Gulf in summer months.

Product developers sometimes struggle with increasing viscosity without adding additional ingredients at the customer's request. With HPP, this may no longer be an issue. HPP is effective in thickening yogurt products and gelatinizing egg products and sauces containing ingredients with natural pectin. Researchers at Washington State University, Pullman, recently used HPP to make cheese and increased yields by 8% to 11%.

HPP products are available around the world, including in Europe, Australia, Japan, Asia, Mexico and Canada. The European Space Agency (ESA), Paris, is reportedly experimenting with various HPP Mediterranean foods in outer space. If the ESA can maximize the flavor and nutritional shelf life of the food, it will provide their astronauts with a healthier diet.

Staying out of trouble The ability for food manufacturers to market products as "fresh" provides great leverage over conventional convenience foods. Title 21 of the Code of Federal Regulations (CFR), Part 101, Section 95 dictates the labeling guidelines for the term. John Larkin, Ph.D., FDA Chief Process Engineering Branch, Summit-Argo, IL, interprets the regulation to HPP. "As current labeling regulations for 'fresh' are written, an HPP food product could not be labeled as 'fresh' since the food item is processed outside of those allowed within 'fresh' labeling regulation," he says. However, many industry members utilizing advanced technologies, such as HPP, challenge this regulation because some products are processed at ambient or refrigerated temperatures.

Manufacturers also question how HPP differs from 21 CFR Pt. 179 Sec. 26, whereby raw food treated with ionizing radiation is an exception to the "fresh" regulation. Larkin explains, "A few years ago the Agency did ask the industry to provide it with data to allow the Agency to review the labeling regulation for 'fresh,' and this review is still ongoing."

HPP products are permitted to use "fresh" on labels as long as they indicate that the food was processed. The "fresh" restriction is inspiring many companies using HPP to label products with a creative twist to get the fresh flavor and processing points across to consumers. Avomex markets to consumers that their products are Fresherized(TM). Avure markets Fresher Under Pressure® technology to food manufacturers.

Symbiotic squeeze Combining pressure with temperature, pulsing, chemical and/or gas techniques may enable processors to get more bang for their buck. An HPP processing aid to extend refrigerated food shelf life might be to add modified atmosphere packaging (MAP) technology or gas mixtures. "We have seen a two to four log increase in the death of spoilage and pathogenic microorganisms when the food is additionally treated with a modified gas environment compared to HPP treatment under the same conditions," states Vasuhi Rasanayagam, food safety & technology research assistant, Air Liquide America, Countryside, IL.

The food was processed with a 1:1 food to supercritical gas ratio at 40,000 psi and less than 40?C for one minute. "The HPP alone can kill the harmful microorganisms, but the gas functions by providing a harsher environment for enzymes and microbes that spoil food, thereby reducing the severity of the HPP treatment and potentially improving the quality and shelf life of the raw and RTE meats," states James Yuan, Ph.D., food safety & technology manager, Air Liquide.

In partnership with the National Center for Food Safety and Technology (NCFST) in Summit-Argo, IL, Air Liquide has worked extensively on this combination technology for two years. Many industry members use NCFST as a research source for novel processes, such as HPP, because the site serves as a liaison between FDA, food industry and academic institutions. Scientists and developers can also use HPP technology in the NCFST pilot plant to test both refrigerated and shelf-stable low- and high-acid foods before investing in the technology for their own plants.

Achieving commercially sterile food products through HPP is an area that academic, industry and government researchers are persistently testing. A number of scientists from all three domains have reported encouraging data on spore inactivation using pressure-combination techniques. Recent reports include commercial sterilization of mac'n'cheese.

"I can say that I believe temperature and pressure -- if you are willing to apply them at the levels needed -- can be used to sterilize a low-acid canned food product. It is logical then to conclude that this high-pressure heating, in conjunction with the right initial temperature, should be able to be used to render a food product commercially sterile," says Larkin. However, he adds that FDA has not at this time received any filings using HPP in compliance with the shelf-stable, low-acid canned food product FDA regulations found in 21 CFR Pt. 101 and Pt. 113.

Pressing ahead As consumer demand for extended quality foods increases, current HPP food manufacturers will be at the forefront to provide prepared foods that still taste fresh. "Avomex is focusing its future on new products that are unique and can really utilize the advantages of HPP to create a safe and value-added product," says Walker.

As HPP becomes more common, it will increase attractiveness to companies that are not currently utilizing the technology. Along those lines, Ting says that Avure plans to continue to increase awareness of HPP, help customers with validation, reduce equipment cost and explore other HPP areas, such as pharmaceuticals.

While HPP has clearly found a niche in the premium refrigerated-foods market, low-acid, shelf-stable foods are still under investigation. "I would expect that within the next 10 years we will see a very mature HPP industry for those areas where it has been a commercial success and a high degree of understanding as to where it will not be a success," says Larkin. The next few years in HPP product development may indeed prove a very interesting time for the food industry as this new technology takes hold. The combined activity among scientists in the regulatory, academic, HPP system-manufacturing and food-industry fields are an excellent indicator that HPP could become widely practiced in the future.

Amy Schauwecker is a senior food scientist focused on global international chain account product development at Unilever Bestfoods Foodsolutions in Lisle, IL. She can be contacted at [email protected].

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