HPP: Culinary Meets Tech
What research chefs need to know about high pressure processing
Nowhere is the technological culinary revolution more evident than in methods such as sous-vide and High Pressure Processing (HPP)—sometimes referred to as High Pressure Pasteurization. HPP is a cold-pasteurization method that allows manufacturers to create cleaner labels by eliminating or reducing the usage of artificial or other preservatives, thus helping companies market products for the growing natural and organic food movements.
HPP involves pressure treatment between 100-800 MPa (14,500-116,000 psi), in the form of water flooding over flexible packaging in a pressurized chamber. This process is variable, depending on the end product, and can be performed for a wide range of water temperatures and durations of time, depending on the specific needs of the processor and food product developer.
Typical HPP processes result in lethality for pathogens, bacteria, yeasts, and molds, as is similar to thermal pasteurizations. However, without the additional use of heat, it does not inactivate spores or enzyme activity. HPP is instantaneously effective—independent of size, shape, or composition of the food product in question.
Errol Raghubeer, PhD, vice-president of microbiology and technology at Avure Technologies Inc., and an expert on HPP, points out the emerging paradigm bridging HPP and the product development side.
“Shelflife and food safety are the major drivers,” he acknowledges, “but what is of great importance is that the nutritional profile of the food remains intact after processing. The reason is that HPP has no effect on covalent bonds within the food. So flavors, vitamins, and any other bioactive components remain intact.”
Raghubeer goes on to explain how HPP can provide an advantage in creating new products or tweaking existing formulations to create better control of the properties of the food, especially in post-processing.
“Pressurization results in a high lethality rate of unwanted microbial contamination, while maintaining desirable color, texture, flavor, and nutrients that could be damaged through thermal pasteurization,” Raghubeer says. “This technology has gained traction with the consumer shift towards clean label and the desire to enjoy better-for-you products.”
Integration of HPP as a mainstream method of processing has touched on many of the most lucrative industries in food manufacturing, including as it applies to perishable ingredients, such as animal proteins, fruits, and vegetables. While fairly new in regards to everyday applications, the process had a slow emergence over a period of decades. It gained the most attention in the mainstream only a few years ago, when it exploded on the scene with fresh, pressed juice products.
Even with today’s HPP spotlight focusing on juice, alternate applications in food remain vast. Kelley Battles, a long-time user of HPP, including more than a decade owning an HPP processing facility in Dallas, indicates that the procedure is more versatile than most food developers realize.
“In the early 2000s, the ‘all-natural’ trend was really starting to take off, and organic was finally coming into its own,” Battles says. “This was just the evolution we wanted to incorporate into value-added products. We investigated removing nitrates, nitriles, and other ingredients that make a label long and unappealing.
When you take out preservatives, especially in meat products, the reduction in shelflife is profound, Battles stresses. He observes how, in today’s market, a short shelflife will prevent a product from gaining space in any major marketplace.
“With a seven- to 10-day shelflife, how could a product move through a distribution center into food service, a steakhouse, and finally onto a consumer’s plate?” he asks rhetorically.
In his own work, Battles identified this niche. He also recognized that, by bringing in HPP products that could displace a preservative-laden product with short shelflife, one could not only improve product quality, but also the bottom line.
The HPP Advantage
The driving force of HPP over the years has been—and still continues to be—fully cooked meat products. Any fully cooked meat (think, turkey, ham, sliced deli meat, brisket, hot dogs, sausages) is well-suited for processing with HPP. In some formulations, it can be possible to remove chemical preservatives altogether.
Today, HPP has become increasingly popular for items ranging from dips, hummus, guacamole, and salsa to chili, smoothies, coconut water, and those now-ubiquitous fruit and vegetable juices. That latter category is where the greatest growth recently has taken place.
An example of how HPP can impact a juice brand: One couple who developed a pressed-juice brand in early 2013 for sale at a local market initially was producing 100-150 bottles each weekend in a commercial kitchen. By Monday, all unsold $9-retail bottles of product had to be discarded. Then, they applied HPP, taking the three-day shelflife to 60 days. Within 20 months, the company attained an annual value of $15 million dollars and still is growing tremendously.
New HPP products are being launched all the time, including beer, pet foods, fresh soups, and baby food, as well as expansion of existing categories with value-added products, capitalizing on brand equity in the market place.
For a food and beverage manufacturer, HPP brings tremendous benefits to the final product, in regards to both safety and quality. The incorporation of this technology in food processing has allowed for the sale of fresh salsas, fruits and vegetable juices, and guacamole with shelflives that have been extended in some cases to more than 10-100 times their natural shelflives.
For food and beverage creators, the fresh flavor retention from using HPP is a major leg-up, allowing for subtleties of tastes once lost on the long road from test kitchen to the consumer’s table. The ability to bring nuance back to the seasoning process means the final product can have a flavor profile much closer to what the culinologist envisioned from the outset.
HPP products can have a superior nutritional profile, as well, when compared to their thermally processed counterparts. Though it is not legal to claim “fresh” status, according to recent cases in the US courts, HPP-treated juices bring all of the benefits of a freshly picked fruit to the table. Heat-sensitive, water-soluble, and other nutrients—such as vitamin C and folic acid in orange juice—are not deactivated by the high pressure processing system.
Research group Mintel confirms the allure of this aspect in its “2016 Juice and Juice Drinks Market Global Annual Review,” declaring, “In more developed markets, a bright spot for the (juice) category can be found in the growth of cold-pressed juices. While cold-pressed brands are quite niche and have yet to make a dent in overall volumes, they have brought positive attention back to the category.”
Battles notes that, in a cooked product, HPP benefits can include an actual increase in flavor. For example, a jalapeño inclusion will have a bolder, more intense flavor.
“In other applications, such as a ‘wet’ salad, it’s possible to achieve color enhancement of particulates, such as carrot pieces and green pepper,” he adds. “The orange is more vibrant, and the green stands out.”
A Question of Balance
Another HPP benefit, from the culinary creation standpoint, is the technology’s allowance for control of the properties of the food, post-processing. Avure’s Raghubeer describes: “HPP impacts hydrocolloids used in food systems beneficially by enhancing their hydration properties and, therefore, water absorption. When looking at starches, they will absorb 100% of the water they are capable of binding.”
Detailing the chemistry, Raghubeer clarifies that starch molecules unfold when subjected to the pressure of HPP, thus exposing all available linkages and maximizing hydration. This allows for increased creaminess, superior mouthfeel, and increased viscosity of the products, compared to similar thermally processed items. As a bonus, more effective moisture absorption also can reduce the total requirement for hydrocolloids in finished products, creating a cost savings during development and full-scale production.
Of note for developers hoping to incorporate HPP technology in their process, Raghubeer indicates that, though it would seem counterintuitive, cold emulsions including mayonnaises and salad dressings, enjoy these advantages as well. Such formulations, often fragile throughout processing, are actually enhanced by HPP. Emulsions can become stronger and often thicker than they were prior to pressurization treatment.
Developers will need to adjust for this in formulation. This is because the mechanism by which the emulsions are formed is different from homogenization. A reduction in thickeners or functional ingredients would be required, in order to compensate.
The same benefits of increased hydration also can be seen in proteins. For example, lobsters treated with HPP can have a final pickup of as much as 4.5-7% more moisture. This improves tenderness and palatability of the product, as well as producing a higher total yield. It is becoming increasingly popular for restaurant chefs to incorporate such food science-based technologies into their kitchens.
Battles concurs, pointing out that certain unique advantages to HPP remain highly product-dependent. Additional beneficial functional aspects and altered cooking properties can result from HPP in different meat products.
“The benefits for raw meat products include better moisture characteristic of the meat; less purge in the final application; and the meat retains more moisture, leading to a juicier final product,” says Battles.
Life in a Vacuum
Discoveries of new technologies are opening the door to the possible functional partnerships HPP can have with the food industry, especially with restaurant chefs (a group notoriously reticent to move away from classic cooking styles). A notable exception has been the seemingly sudden widespread acceptance of sous-vide cooking. A good candidate for “25-year overnight sensation” status (although the method goes back more than 200 years), the low-temperature, water-bath cooking of foods in vacuum-sealed containers gained popularity in French cooking and recently has become prevalent in fine-dining venues.
A Shellfish Approach
In an example of product development specifically designed around the benefits of HPP, Raghubeer worked closely with a chef to bring it to the food service industry. Lobsters—a finicky protein to work with and prone to overcooking—stood as the primary subject for the project.
Multiple cook cycles or overcooking result in a tough and undesirable texture in lobster. Testing the HPP-treated lobsters, the chef found them to require a reduced recook time, in comparison to fresh. This ensured that the meat had a superior, tender texture.
Raghubeer hypothesized the reason for the reduced cook time was due to the added water absorbed by the protein during HPP. This effect might have resulted in more even cooking, compared with conventional cooking, which occurs from the outside in.
In seafood such as lobster, HPP also makes removal of the hard shell much easier, ensuring complete efficiency and less waste in this expensive ingredient. The method works for oysters, as well, and from pressure levels in the lower half of the HPP range (specifically, 40,000 psi). “A lot of food makers are subjecting oysters to HPP,” says Jaime Nicolas-Correa, director of Hyperbaric USA Inc.
Nicolas-Correa cites two main reasons HPP is particularly good for shellfish: “First, HPP kills the extremely virulent Vibrio vulnificus and other deadly bacteria. Vibriosis is a potentially life-threatening disease, so the process makes oysters safer for consumption. The high pressure also opens the shell, yet without denaturing the delicate protein inside, since this application sits at the lower pressure of 40,000 psi.”
The Down Side
HPP is not without its challenges. Economic restrictions are a major hurdle, as the capital investment can be substantial. Full equipment and setup can run in excess of $4 million. Moreover, the large capacities of the systems, ranging up to 60,000lb of product annually, can be challenging.
For many companies, the desire to reap the benefits of HPP leads to co-packers as the solution. However, the sum of freight, service costs, and time can quickly add up. Inherent cost impact also arises from the batching process of HPP. And, even though HPP is highly efficient at what it does, it cannot keep up with a continuous process in terms of throughput. An operator is needed to load and unload the machinery, adding labor costs.
Nicolas-Correa agrees that the inability to make the HPP process continuous limits the technology. “To achieve the pressure, you need to close the vessel to ensure a closed environment,” he says.
Technologists currently are working on speeding up the cycle and making compression faster to increase throughput. Costs for equipment and limited output mean the cost of the end product can be comparably higher. However processors are hopeful this won’t last as the technology evolves. As with any new tech, challenges arise and are overcome with increased usage.
High-pressure treatment, as it is conventionally done, does not result in the inactivation of spores. This can result in food safety and quality concerns, as end products are not typically rendered shelf-stable. Bacterial spores germinate at ambient temperatures and render the refrigerated products’ storage conditions imperative.
Battles sums up that, in a product with a 21-day shelflife, combined with reduced product shrinkage, fewer markdowns on post-dated products, and a highly desirable clean label, savings can be astronomical, impacting the margin by 40% or more. Retailers and consumers need clear direction and education to enforce proper storage at the termination of the carefully controlled supply chain. A visual cue, such as thermally sensitive ink, labels, or packaging materials—technologies that already exist—could be the answer to this uncertainty.
Research is ongoing to create a shelf-stable HPP product, but the quality is just not there yet.
“In combining high pressure and high temperatures, you can achieve a shelf-stable product, as the spores are inactivated,” says Nicolas-Correa, “but most users want a high-quality product with no denaturation from heat, so I am not sure such application of the technology will be advantageous for most HPP products.”
Another issue with HPP is that there is little to no permanent effect on enzyme activity. For chefs, this can be a boon in some formulations, because the enzymes that break down color and flavor in the presence of oxygen will be suspended in the absence of this ubiquitous gas.
“Enzymes are not completely de-activated with high pressure, so we must prevent them from getting in contact with oxygen,” says Raghubeer. “This is why we typically remove the oxygen with nitrogen flushing in a vacuum environment, and use high barrier film to ensure a low-oxygen transfer rate through the package. This delays the activity of certain enzymes, such as polyphenol oxidase (PPO), which causes browning of fresh produce and spreads, such as apples and guacamole.”
One of the early vanguards of the recent HPP surge, guacamole remains vibrant for several weeks while in the package. Still, once opened and exposed to oxygen, the PPO will react and cause a rapid color change. Enzyme activity of pectin methylesterase (PME) also is responsible for pulp settling and flocculation in fruit-containing beverages. (Interestingly, this is perceived by today’s consumers as a more natural appearance and many are accustomed to shaking such a beverage before drinking.)
Raghubeer assures that, although enzyme activity cannot be halted by HPP, the trickle-down benefits of a lower microbial load result in lower enzymatic activity throughout the shelflife of a product.
However, this still raises development challenges for products prone to change once opened, as the enzymatic processes must be combated by label-friendly means to remain inside the clean label halo. The experts prescribe a synergistic incorporation of selective heating for tolerant products. These include proteins; natural antimicrobial agents, such as rosemary extracts; or, in appropriate products, spice extracts and pH control to achieve longer shelflives than possible with HPP alone.
HPP has virtually no impact on foods with a low water activity (0.85aW and below). Such foods do not demonstrate any added microbiological protection, according to Raghubeer. “There must be free water available to inactivate microorganisms,” he says. “The mechanism of HPP in reducing microbial load is the use of extreme pressure; if water is not available, the pressure cannot affect the biochemistry of the microorganisms being targeted.”
Intense pressure also can result in malformation of products with high air content or weak structure. For example, fresh produce such as apples can exhibit high instance of air purge, resulting in a translucent and barely recognizable product. This has been addressed during development in numerous ways. One method uses the vulnerable material as an inclusion rather than a stand-alone product.
“An apple in a matrix, such as apple purée, will receive a 5 log reduction; have an extended shelflife; and the color change will not be noticeable,” Raghubeer explains. Moreover, air caught in the package can cause as much of a headache as the air inside the food product itself. Nicolas-Correa recommends avoiding air in the package as much as possible.
HPP, sous-vide, and other high-tech developments have gained strong footholds in North American and European markets, thanks to a new generation of research chefs approaching the technology with an eye on how it can help rather than hinder creativity. With the social aspects of food now an important instrument in the product development toolbox, some believe the future of these processes, especially HPP, is in aiding developing nations. HPP technology has the potential to help increase food security and diminish food waste in every market.
This opens a wide door for culinary experts to create the kinds of attractive, healthful food and beverage products that serve these demographics. Adding the component of creative culinology to a high-tech system designed to preserve and protect, while slashing waste, turns it into a game-changer. While these technologies have seen dramatic growth in food and beverage product creation and manufacturing, experts predict it will only get bigger.
Kirsten Benneter, Liz Chan, and John Shackelford (MSc) head up the R&D, Processes Improvement, and Culinary factions at private label custom manufacturer Giraffe Foods Inc. Their shared love of cuisine and innovation helps propel Giraffe to new heights, with food safety and customer satisfaction being their top priority. The authors are graduates, respectively, from McGill, Guelph and Louisiana State University. They can be contacted at giraffefoods.com or 905-678-2783.
Originally appeared in the November, 2016 issue of Prepared Foods as HPP: Culinary Meets Tech.