Is Pascal the New Pasteur? High Pressure Food Processing

06 May 2016

During his brief 39 years, Blaise Pascal built up a colossal treasure trove of discoveries across mathematics, physics, and philosophy. While Pascal is best known for his breakthroughs in geometry and probability theory, his work on fluid dynamics also made him an important, albeit unlikely, trailblazer in food preparation. 

His namesake law in fluid mechanics postulated that an increase in pressure on any part of a confined fluid is transmitted equally across a fluid, such that there is an equal increase at every other point of the container. More than 200 years after Pascal’s death, a chemist at the West Virginia Agricultural Experimental Station began studying the potential applications of this law to the preservation of meats, juices, and milk.

And he found something exciting: exposing foods to high pressure can actually inactivate microorganisms. And unlike other preservation methods, this pressure-based process, known as pascalization, can inactivate pathogens without considerably affecting taste or nutritional content. 

Still, the ease and low cost of preserving via pasteurization or by adding preservatives   discouraged additional research into the potential of pascalization until the late 20th century. As with many developments in the food industry, it took a confluence of societal forces and indirect scientific breakthroughs to encourage the exploration of the potential of High Pressure Processing (HPP). 

What if nutrition and food preservation weren’t mortal enemies?

Because nature starts to take its toll on food as soon as it is harvested, civilizations since the beginning of time have faced the same conundrum of how to ensure sufficient food supply between growing seasons. Even in ancient times sun drying, freezing, fermenting, pickling, and curing were used to preserve food after harvest.

With the advent of modern transportation, however, societies were suddenly able to access foods that were previously unavailable, out of season, or scarce, and consumers’ tastes broadened accordingly. This evolution, in turn, encouraged the development of global supply chains—comprised of grain storage facilities, cold storage units, and logistics networks—along with advancements in food preservation methods.

But consumers’ preferences for variety had unintended consequences. During most of the 20th century, the drive for improved food safety and increased food security, combined with Cold War politics, encouraged an emphasis of cost and efficiency over taste, quality, and nutrition. These food attributes weren’t completely overlooked, but they required substantial efforts from international advocates to be brought to the forefront. 

While the slow food, farm-to-table, and “locavore” movements have been successful in encouraging conversations about how food should be grown, delivered, and prepared, the reality is that food and beverages in many cases still have to be delivered across an extended supply chain and therefore require some form of preservation. This is where treatment methods like pasteurization (using heat) and pascalization (using pressure) come in. 

Pressure treatment versus heat treatment

The practical application of Pascal’s work on fluid mechanics for food preservation was not apparent until scientists discovered that uniform pressure between 300-600 MPa could inactivate or suspend the growth of yeasts, molds, and most vegetative bacteria. Because water is used to distribute pressure across the enclosed container in a HPP module, the technique is sometimes also referred to as high hydrostatic pressure processing. Various academic studies have concluded that high pressure processing has a minimal effect on low-molecular-weight food components such as flavoring agents, pigments, and vitamins.

Specifically, with pascalization, listeria, salmonella, vibrio, norovirus and other bacteria are silenced while shelf life is extended and flavor compounds and nutrients remain intact. High pressure processing (HPP) has been shown to maintain the antimutagenic and antioxidant components of fruits and vegetables even as shelf life in days is extended by a factor of two to ten (compared to untreated fresh products). 

Over the past 25 years, processors have succeeded in developing the equipment and packaging technology that made HPP commercially viable.

On the other hand, thermal heat treatment, the go-to food preservation method for much of the 20th century, can be more destructive. Conventional or ultra-pasteurization (UHT-ultra high temperature) methods are more likely to not only affect the nutritional makeup of food, but they can also require the use of food additives (i.e. epicatechin, a flavoring compound) to add back taste. Heat treatments such as pasteurization, by inducing changes to sulfhydryl and disulfide content of protein fractions, can lend unsavory, cooked flavors to foods. 

HPP may not offer a one-size-fits-all solution for the food industry, but it is showing promise as an alternative to conventional pasteurization for many foods. One of the first commercial applications of HPP was the preparation of guacamole by Mexican food processors in the late ‘90s, but it is also now being used in preparing juices, jams, smoothies, wet salads, some meat cuts (cured and sliced ham, turkey, and chicken), seafood, and some dairy products.

Of course, canning, dry freezing, dehydrating, and freeze concentrating are still feasible ways to preserve food and beverages, but these methods aren’t necessarily always viable options for food companies. With consumers increasingly demanding fresh and natural options, high pressure processing is offering food companies the ability to cut the use of preservatives (i.e. chemicals and salt) even while respecting sensorial and nutritional properties. 

HPP rides the juice wave

The first evidence of humans “juicing” for health benefits is documented in the Dead Sea Scrolls (circa 150 B.C-70 A.D). According to the scrolls, “A pounded mash of pomegranate and fig” resulted in “profound strength and subtle form.” Several examples exist of cultures that have incorporated juicing into their daily diets or healing rituals since then, but juicing as a health movement didn’t gain significant traction in Western culture until the first half of the 20th century when German scientist Max Gerson developed a (now controversial) therapy combining a vegetarian diet and raw juices. Although the popularity of juicing waxed and waned in the subsequent years, the health-conscious movement of the 1970s and the widespread introduction of juice bars in the 1990s were pivotal milestones in the development of a global industry.

As consumers have increasingly gravitated towards clean label (i.e., little-to-no preservatives) foods, fresh juice has been at the forefront of the trend. At the same time as retail juice chains—including Pressed Juicery, Juice Press, and Juice Generation in the US—have become popular for their fresh-pressed products, national HPP juice brands are also gaining traction, owing to their lower price point and greater distribution reach. In fact, New York-based Organic Avenue, a pioneer of cold-pressed juices, filed for bankruptcy last fall. The fact that national HPP brands have launched juice beverages at price points as low as $4—a third of the price of many of Organic Avenue’s products—didn’t help matters for the floundering operation.  

Suja, Blueprint Juices, and Evolution Fresh have led the pack in establishing national HPP brands within the $13.4 billion US juice production industry. However, it didn’t take long for established consumer food and beverage companies to take notice. In 2011, Starbucks scooped up Evolution Fresh for $30 million, and Hain Celestial followed suit in 2012 with its acquisition of Blueprint. Suja remains independently run, although the company recently sold a 30% stake to Coca-Cola for $90 million.

Beyond juice

Markets and Markets, a market intelligence group, estimated that global sales of HPP products would reach $12 billion by 2018, up from roughly $5 billion in 2013 (to put this into context, USDA’s Economic Research Services places global retail food sales at roughly $4 trillion). And according to Euromonitor International, the global market for organic, functional allergen-free and healthy foods will reach a record $1 trillion in 2017. Scoping the potential size of the HPP food segment is difficult at this point, as food science will ultimately dictate its potential as much as consumer demand (for example, HPP can result in the denaturation of proteins responsible for color and texture in some red meat cuts). Still, it is safe to say that global food and beverage companies such as Hormel, Perdue, and Starbucks wouldn’t be embracing this technology if there wasn’t significant growth potential.

The “organic raw” label:  Next best thing to “fresh” or a brewing legal maelstrom?

HPP foods and juices are succeeding in capturing some health-conscious consumers, and many have done so in part by labeling their products as “organic raw.” But there is still significant debate over what that term actually means. 

The murkiness stems from the fact that while the USDA and FDA provide clear rules for whether products can be labeled as organic-certified and fresh, they do not provide regulations that spell out whether a product can be labeled as “organic raw” or “natural.” The FDA has ruled out cold-pressed and HPP products from being labeled as fresh, so producers initially adapted by calling their products “organic raw & cold pressed” to emphasize that they had not been subject to heat treatment. However, there are no clear boundaries for what can be considered as “organic raw” aside from the requirements under the USDA’s organic certification program.

This branding sleight of hand has spilled over into the courts with plaintiffs arguing that the “organic raw” label is misleading while companies have argued that the cold pressure process have few nutritional or sensory effects. One notable example of this type of lawsuit was Samuel F. Alamilla and Colleen King vs. Hain Celestial in 2014, in which the plaintiffs argued that Hain Celestial’s sale of HPP juices meant that its products were misleadingly nutrient-stripped. 

Hain Celestial won (at least, the first round) of the labeling controversy, as the judge dismissed the case due to lack of evidence: “The [scientific] articles the plaintiffs cite … contradict the allegation upon which their entire complaint hinges—namely, that pressure treatment deprives juice of nutritional value to a similar degree as pasteurization.” Nevertheless, the threat of future lawsuits has led some companies to pare down their labeling to just “organic and cold pressed” or “natural-no artificial preservatives/additives added.”

Despite the legal win, HPP technology still faces criticism and limitations

Scientific research suggests that HPP is less destructive than thermal processing to key food quality components such as pigmentation, vitamins and flavor content. Nevertheless, additional desired food and beverage composition qualities, such as PH levels, texture, and sensory attributes must also be considered when HPP is applied to a particular product. And sometimes pascalization can fall short.

For example, most food products can be processed by HPP in an ambient temperature range, but the National Food Labs has found that HPP increases the temperature of more compressible food ingredients (fats) by over 3°C per 100 MPa (commercial applications of HPP are generally conducted within a range of 300–600 MPa). As such, the benefits of HPP for some foods such as butter and cream may be limited without further thermal application. 

Several types of bacteria, such as Staphylococcus areus, are capable of forming resilient outer walls, or spores, when in unfavorable conditions. Some of these bacteria, specifically gram-positive varieties, can be more resistant to HPP than gram-negative ones when in their spore form. A combination of pressure and heat, or some other antibacterial intervention, is often required to reduce bacterial spores in foods. In fact, an FDA study concluded “inherent high resistances of bacterial endospores and food enzymes are the major challenges to the broad application of HPP.” There is still, therefore, some hesitation over HPP on the grounds that pasteurization may still be more effective in immobilizing harmful bacteria, particularly in dairy products.  Japan, for example, an early explorer of the technology, has yet to officially approve HPP as a substitute for pasteurization, despite its approval in other markets, such as the EU, North  American countries and several other Asian countries.

The use of HPP also faces criticism from some consumer groups. Purists argue that because HPP may make some enzymes inactive, it could potentially immobilize enzymes that are found naturally in fruits and vegetable and are critical for digestion. Additionally, the capital investment required for HPP processing equipment is still expensive, even after a threefold decline in the price per processing output between 2005 and 2011. Equipment prices still range from $650,000 to $2.6 million (FDA), and food manufacturers must be convinced that they can either recoup the investment through higher prices or reduced spoilage. 

Conclusion

HPP is gaining popularity with food processors in North America, Asia, and Europe looking for an alternative to conventional thermal processing methods. According to Avure Technologies, a leading producer of HPP equipment, the HPP market has experienced annual average growth of 15 percent from 2003 to 2014. Driving this shift are consumers who are not only demanding products that are extremely safe, convenient, but also fresh, nutritious, and clean-label. 

Nevertheless, a potential technological shift rarely arrives without facing initial skepticism from the business status quo, lingering technical challenges, and resistance from purists. HPP is no exception. HPP as a food processing technology still has its limitations and is not always optimal. However, the method appears preferable for a growing number of food and beverage products when considering the current alternatives of thermal heating and chemical food preservatives.  Taking the long view, HPP is, at least, enabling food processors to move in the right direction while giving consumers more nutritional options in a sea of artificial food additives. 

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