HPP: Equipment, Trends and the Science Behind the Technology
With roots in food safety and shelf-life goals, high pressure processing is relatively young but growing in the industry
High pressure processing is growing rapidly as a way to make food safe without heat and keep it tasting and looking its best longer.
According to a MarketsandMarkets report, the HPP equipment market is projected to reach more than half a billion dollars by 2022, growing at a CAGR of more than 11%. The horizontal segment is the fastest growing orientation-type segment in the food and beverage market.
Mark Fleck, HPP technical sales at Universal Pure, a leading HPP services provider in North America, says the key benefits of HPP to processors and consumers include enhanced food safety, cleaner label products, maintaining nutrition and sensory qualities, and a much longer refrigerated shelf life.
In fact, the catalyst for HPP was food safety without the use of heat and preservatives, according to Errol Raghubeer, vice president of food science and microbiology at JBT Avure. “The first commercial products were ready-to-eat meat and guacamole—both of which cannot be thermally processed,” he explains.
Raghubeer says he began to evaluate new food processing technologies in the late 1980s during graduate school and when he was employed at Birds Eye Foods. His earlier research was in partnership with the U.S. Army and universities, mainly about shelf-stable foods. He recognized the commercial advantages of HPP compared to other technologies and joined JBT Avure (formerly Flow Technologies in Seattle) in 1999, focusing mainly on the commercialization for refrigerated food and beverages.
“The main focus of HPP has always been in food safety and shelf-life extension,” he says. By understanding the behavior of food components under pressure, the industry is able to offer foods with better organoleptic properties, he says. For you non-food scientists, those are properties involving the senses. So HPP helps the food look and taste like it should.
“Regulatory is becoming more involved in HPP as it has become a mainstream process,” Raghubeer says. “We have submitted data to the FDA beverage division for consideration of a broad approval of juice beverages that may allow for the production of these without the need for pathogen validation studies. We have also submitted results of studies to the FDA and for publication, which shows that clostridium botulinum is not a hazard in raw refrigerated coconut water. These results are corroborated by other researchers.”
Roberto Peregrina, director at Hiperbaric USA, says, “High pressure processing respects the sensorial and nutritional properties of food because of the absence of heat treatment and maintains its original freshness throughout the shelf life.”
There are not many HPP equipment manufacturers, and the machinery can range in price anywhere from $500,000 to more than $3 million per machine. The two most prominent manufacturers of HPP equipment are JBT Avure and Hiperbaric. The machines are predominately horizontally oriented now, which helps them to accommodate higher volumes than the original vertically oriented models.
The pressure vessels in these machines are built to withstand a certain amount of pressure and temperature, and their size is defined by the volume of fluid that they can hold.
Lisa Wessels, marketing director at JBT Avure, explains that once the packaged product is placed into the basket of the vessel, purified water is pumped into the machine and pressurized to 87,000 psi. “This pressure is equivalent to six times deeper than the deepest part of the ocean,” she says.
Joyce Longfield, vice president of product innovation at Good Foods Group LLC, says the company was built on the premise of the HPP technology. (Click here to read more about the business.) She explains that to accomplish the pressurization, the water fills the machine to atmospheric pressure, and then a pump (or pumps, depending on machine size) forces another 15% more water into the vessel. Pressure is transmitted through the water and through the packaging material to the food itself.
These machines must be able to withstand an incredible amount of pressure, so the companies that want to build them must earn ASME VIII Division 3 Certification, which allows them to manufacture HPP equipment for the North American market.
Because the capital investment for HPP is so high, tolling centers are available through JBT Avure, Hiperbaric, and a range of companies that do their own HPP processing in-house but serve as a source for processors who are not yet ready to commit to such an investment. It’s a solution for manufacturers who want HPP, a clean label, growth into new markets and brand protection but are not ready to purchase their own equipment.
JBT Avure’s tolling centers, for instance, offer the benefits of Avure HPP with no capital or long-term investment needed. Users only pay on a toll basis to use any full-size, highest throughput HPP systems. Also, customers gain access to Avure’s in-house food science lab and microbiology services, where they proof and optimize recipes for flavor, texture and safety, as well as help bring new products to market.
Peregrina says that Hiperbaric’s extensive install base includes customers offering high pressure processing services to other agrifood industries. “This business model makes sense because it allows any food or beverage manufacturer to have access to industrial HPP equipment without the need of directly investing capital in the purchase of Hiperbaric technology.” Instead, customers pay for the use of existing HPP industrial plants offering this service on a toll basis.
“Thus, users of these HPP toll processing services add value to their products through some or all of the various benefits that this technology offers, whether it’s the product shelf-life extension or a constant maintenance of the nutritional and organoleptic quality, or the lethality intervention on possible pathogens present in the product,” he explains.
Because food safety was the impetus for HPP, it is important to understand the science behind the process. Raghubeer explains that in the 1890s it was shown that high pressure could inactivate microorganisms, which was first tested in milk by Bert H. Hite of West Virginia University.
“HPP disrupts several biochemical processes and cell wall osmotic integrity in microbial cells that leads to cell death. In general, gram-negative bacteria, such as E. coli and Salmonella, are more susceptible to the effects of high pressure, possibly due to the complexity of the gram-negative cell wall compared to gram-positive bacteria, such as Listeria monocytogenes,” he says.
Longfield explains the concept in terms of the cell structure. “Cell membranes are like a cheesecloth. Gram-positive bacteria, like Listeria, have a stronger, tighter membrane (using the cheesecloth analogy, a tighter weave) and are more difficult to kill than a gram-negative membrane, such as E. coli or Salmonella, which have a looser ‘weave.’”
Therefore, the type of food or beverage being processed and the kind of bacteria that can grow on it are what determine the hold time, as well as the amount of pressure required during the process. “So, for instance, if I’m a poultry manufacturer and I have to address Salmonella, I might not necessarily need or want as long of a hold time as if I am somebody who has to address Listeria,” she explains.
Some people in the industry mistake HPP as a way to crush the pathogen, but Longfield explains that it is more like imploding it. With HPP, the pressure is 100% uniform. “As an example, if I take a grape and I put it in the HPP machine, the grape will come out like a grape but it’s going to be softer and more malleable to the texture because plants have a protected cell wall. This rigid wall gives them a little bit more integrity and a little bit more protection against pressure but essentially because it’s uniform and not one-directional, the pressure is equal on all sides.”
The pressure is essentially poking holes at the integrity of the membrane, and in doing so the membrane starts to come apart, she says. “With enough pressure for enough time, you can’t fold its membrane together anymore and it just falls apart; it implodes or collapses.” Food is a multicellular structure with cells upon cells upon cells. Bacteria is a vulnerable single-cell organism that with enough pressure will implode, leaving the multicellular food intact.
Raghubeer adds that HPP is very effective at inactivating vegetative pathogens in most foods. Again, the pressure intensity and time of HPP treatment are dependent on intrinsic and extrinsic factors of the food or beverage being processed, he says. These include pH, water activity (BRIX), product ingredients and packaging.
“We have conducted hundreds of validation studies across several product categories to ensure the correct HPP conditions are used, which are generally included in the companies’ HACCP program as the CCP,” he says.
Another bit of science behind HPP is the required water level of the product. “All food, to be successfully HPP processed, has to have a water activity level above 0.8,” Longfield explains. “So if the water activity of water has a value of 1, then anything else is going to start with a water activity less than that. For instance, an avocado’s water activity is 0.98 and peanut butter is typically below 0.6. This is why guacamole is the perfect food for this process, and peanut butter is not.”
She continues, “The efficacy of the technology is that there has to be water in the product to be the conduit which the pressure moves through. Meat is a good example. Deli ham has a high water activity of 0.9 so HPP is great for it. But for dry-cured prosciutto, that can be right on the cusp of 0.8 or a little bit less in water activity. So if you need to get rid of Listeria in a product like that, you typically need a much longer hold time and a higher pressure. So it really challenges the efficacy of the technology as you start to get that water activity too low.”
The Cold Food Chain
Once a food or beverage has undergone the HPP process, it must remain in the cold food chain. “HPP is a pasteurization process that inactivates vegetative foodborne pathogens and spoilage microorganisms,” Raghubeer says. The normal microflora, although significantly reduced in levels after HPP, do survive the process, he explains—particularly certain strains of lactic acid bacteria. The growth of these survivors is controlled by refrigeration, similar to refrigerated pasteurized milk.
“Additionally, and more importantly,” he continues, “the current commercial application of HPP is not effective against bacterial spores, such as Clostridium botulinum. Although most bacterial spores are controlled with refrigeration, the non-proteolytic strains of C. botulinum (Types B, F and the marine strain Type E) can grow at temperatures as low as 38 to 40°F, so intrinsic factors in the foods must be present to prevent the growth and toxin production of these strains. Proteolytic strains of C. botulinum and other spore formers are controlled by refrigeration. The FDA and other regulatory agencies have guidelines for refrigerated food to eliminate the risks of botulinum toxin formation.”
The cold food chain is so important when it comes to HPP that the Cold Pressure Council (CPC) was formed in March 2017 to develop and formalize best practices for cold pressure technology. Good Foods’ Longfield, the CPC chairperson, says that the council’s long-term goal is to become a global organization.
The CPC’s High Pressure Certified logo is designed for members to use on their products once a third-party audit confirms the company’s HACCP plans and verification studies. Companies must also pay a licensing fee. Longfield says that this logo program helps achieve the council’s goal of creating uniformity among the industry through the consistent use of HPP technology and meeting regulatory requirements.
CPC wants to grow consumer awareness of the benefits of products that have been through the HPP process, ultimately creating demand for these foods and beverages, she says. CPC is managed by PMMI, The Association for Packaging and Processing Technologies.
Wessels of JBT Avure adds that the formation of the CPC demonstrates the growth of HPP as a part of food safety and food preservation programs. Fleck at Universal Pure—one of the co-founders of the CPC—agrees and adds that the CPC is actively promoting consumer awareness and user education through webinars, speaking engagements and participation at industry trade shows and events. “The council promotes networking among industry professionals and assists in formalizing industry best practices,” he says.
Using the right type of packaging is imperative for HPP to be successful. “In the earlier days,” Raghubeer says, “there was a significant lack of packaging research compared to food application studies to maximize the antimicrobial effects of HPP. Low oxygen permeability films, such as those with EVOH, proper hermetic seals and correct bottle closures, are necessary to maximize the benefits of HPP.”
He adds, “We are working with a number of companies on HPP indicator inks and labels. Pre-labeled packages are currently done with HPP without compromising readability or layout. Some companies do label after HPP to allow them more flexibility on the final label.”
Peregrina concurs. “Packaging is a key aspect for high pressure processing of food and beverages. It is of utmost importance to protect the product, avoiding any damage or contamination that could affect the brand image or the confidence in the technology.” He says the two main requirements are the water resistance and the flexibility of the packaging materials—characteristics normally accomplished by plastics. “Furthermore, packaging is a relevant issue in marketing, in the consumer acceptance of the HPP technology and in the productivity, since its shape determines the filling ratio of the carriers,” he says.
Although food safety spurred the technology, there are several trends that have kept it going at a record pace. According to Fleck, convenience continues to drive many new food and beverage products.
“Consumers are gravitating toward fresh, clean-label products without chemical preservatives. Reduced sodium products are popular with segments of the aging population. All these innovative products are possible with the help of HPP to address food safety concerns, while at the same time significantly extending shelf life,” he says. “And if you follow the phenomenal growth of ‘clean label’ foods and beverages, HPP is a facilitating technology in that space. A subset of the group are those consumers who are interested in purchasing organic foods and beverages—HPP plays a role there, too.”
Longfield says she sees plant-based foods as a driving force in the HPP market, although she does not see this as a trend or a fad. “I think plant-based foods are here to stay—and not just because more people are becoming vegan or vegetarian. It’s just that people want more plants in their lifestyle—to be healthier.”
Wessels points out that HPP goes right along with the focus on clean label. With HPP, “your product can be completely clean label. You don’t need to add any preservatives because you are ‘pasteurizing’ with pressure. It really fits well with that trend.” More specific trends that she sees include baby food, anything all natural, pet food, juice, soups, salad dressings and dips.
Peregrina agrees. “I see more premium juices, plant-based dips, baby food and pet food being HPP processed.”
Raghubeer says new innovative product categories where nutrition and health are the primary objectives are trending. “These can include non-meat, high-protein meals, functional beverages and foods, easily digestive foods, particularly for the growing elderly population, non-allergenic products, etc.,” he says.
As far as the future of HPP, Fleck says, “Universal Pure anticipates the robust double-digit growth of HPP adoption to continue. Part of this growth is fueled by producers learning about the benefits of HPP and consumers who actively seek cleaner label products.”
And while HPP is currently a batch process that occurs after a product is packaged, there is a patent-pending system that will allow beverages to be HPP processed in bulk, before bottling. “The Hiperbaric Bulk machine is a global innovation for large productions of HPP beverages. The machine delivers up to 4,000 l/h, which is the world’s largest productivity, with the lowest processing cost and minimum energy consumption,” Peregrina says. The machine is designed to fit into any large beverages production line and will allow the use of any kind of packaging after HPP, no matter the material, design or size, he says. “With the new equipment, the process will be simpler, with fewer stages and with a higher productivity. Its design is based on two vessels of a Hiperbaric 525 machine, together with a system of tanks where beverage is stored before and after the HPP process.”
Finally, Raghubeer says, “As the technology grows, it is critical that food safety personnel be effectively trained on the importance of understanding the basic requirements of the food and package and the correct HPP conditions per food category. HPP is very unlike thermal treatment.”
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