Home » Tech Update: Sterilization - Better processes, healthier foods
When it comes to nonthermal sterilization of food and beverage products, a big, round number applies: zero.
Alternatives to heat and chemicals are available to sterilize food packaging materials. Indeed, the available options continue to grow. But retort and aseptic processes are the only approved methods for sterilizing human consumables, and both rely on heat.
A decade ago, excitement surrounded high-pressure processing (HPP) as a possibility for nonthermal sterilization, but scientific studies soon dispelled that notion. Squeezing the life out of microorganisms is a slam dunk, but there is only one known way to destroy spore formers that lie dormant during processing and spring to life later—notably Clostridium botulinum, the pathogen that thrives in a sealed container—and that is with heat.
Scientists at the National Center for Food Safety and Technology (NCFST) discovered early on in their research on HPP that temperature increases in tandem with pressure. Depending on the product’s density and composition, a temperature increase of 21°-63°C/70°-145°F might occur at a pressure of 700 MegaPascals, or 125,000psi. That is significantly higher pressure than what commercial food presses operate at, which means higher maintenance costs and machine failure rates.
Major funding for NCFST’s research into HPP in the last decade came from the US Department of Defense, since the army is keen to improve the quality and nutritional value of MREs. When pressure is released in an HPP vessel, food quickly returns to room temperature, resulting in less destruction of vitamins and amino acids and improved flavor compared to retort. Goaded by their patrons at the US Army Natick Soldier Research, NCFST successfully petitioned FDA two years ago for approval of pressure-assisted thermal sterilization (PATS), a process combining heat and pressure to render low-acid foods shelf stable.
“It’s still a goal,” Christopher Doona, a Natick scientist who currently chairs the Nonthermal Processing Division of the Institute of Food Technologists, says of PATS, though seal failure and delamination of packaging materials remain major challenges. Research continues at Ohio State University and other food science centers, but in the near term, improvements in MREs likely will be realized by the use of in-container sterilization by microwave (see “Supply chain sweet spot,” Food Engineering, March 2012).
PATS may join retort and aseptic processing for food sterilization in the next decade. In the meantime, HPP is taking hold as a pasteurization technology that enhances food safety and creates new products with superior taste and nutrition. Many of the nation’s largest food manufacturers now utilize HPP, and the technology is enabling entrepreneurs to build successful businesses, some with little or no previous experience in food production. An example is Justin Guilbert, who worked in the cosmetics industry prior to the formation of Harmless Harvest Inc., a New York-based enterprise that began rolling out its 100 percent Raw Coconut Water last September, sold exclusively at Whole Foods stores. The product quickly established itself as the Northeast’s biggest seller in the fastest growing segment of the functional beverages category, according to Guilbert.
Hailed for its health benefits, coconut water is a low-acid and extremely sensitive fluid, making it a prime candidate for aseptic processing and packaging. In fact, Guilbert and partner Douglas Riboud tested aseptic with Tetra Pak after rejecting conventional pasteurization as too destructive to the water’s delicate flavor and volatile compounds. Aseptic was an improvement, says Guilbert, but the entrepreneurs still weren’t satisfied with the results, opting instead to produce a refrigerated drink built around HPP and priced at about a 25 percent premium over aseptic alternatives.
Harmless Harvest sources coconuts and processes them in Thailand, then ships the bottles frozen to the United States prior to pressure treatment. Even refrigerated, raw coconut water would only have a two-day shelf life, explains Guilbert. With HPP, up to 60 days is easily achieved, and all the nutrition is retained. And while there is a learning curve for both consumers and retailers on the benefits of HPP, “pressure is not a word that creates fear,” he adds. “It’s reassuring.”