Processed foods wouldn’t exist without thermal processes, often the only way to preserve raw food and make them safe. But heat also alters organoleptic properties and destroys nutrients, leaving processors with limited options in delivering the healthiest products possible.
Fortunately, the list of cold or lukewarm process options is growing. Topping the list is high-pressure processing (HPP), this century’s most commercially successful nonthermal pasteurization process. Some elevation of temperature occurs, though not enough to destroy spore-formers, which is why HPP isn’t used to process shelf-stable foods. Increasing temperature and hold time to kill spore formers would also destroy nutrients, defeating one of the technology’s primary benefits.
HPP has been a game-changer for scores of processors. Old Neighborhood Foods, a 102-year-old meat company in Lynn, Mass., installed a Hiperbaric 420-liter press in a shuttered seafood plant in nearby Danvers two years ago, paving its entry into the fast growing healthier-for-you segment of processed meats. The technology has been instrumental in a 38 percent sales spurt in five years.
The reliability and throughput of HPP systems continues to improve, and capital cost, while still in the millions of dollars, is more favorable than at any previous time. Hiperbaric’s 525-liter press, for example, only costs 10 percent more than the 420-L, previously the largest capacity machine.
But throughput is 50 percent higher (up to 7,000 lbs. an hour), notes Jaime Nicolás-Correa, director of Hiperbaric USA in Miami, and when capital costs are inflation-adjusted, the price differential is negligible. Cycle times also are contracting as engineers leverage better intensifier pumps to reach each batch’s pressure setpoint faster.
The potential for near-continuous HPP processing exists, suggests Cem Yildirim, HPP sales manager at Multivac Inc. The Kansas City vacuum packaging OEM is a partner with Uhde High Pressure Technologies in delivering end-to-end HPP systems. “We could cycle three presses to eliminate dwell time when the pumps aren’t working and pretty much have continuous flow,” according to Yildirim.
Variable frequency drives that eliminated starts and stops by the pumps would reduce maintenance, he adds. Even with a trio of presses, a bottleneck would exist where packaged goods are loaded into carriers that convey food into the pressure chamber. Automating that process step with a pick-and-place machine that ties a thermoformer to carrier staging will have a big impact on higher throughput, he predicts.
A hiccup in HPP processing surfaced recently. Coconut water supplier Harmless Harvest abandoned HPP pasteurization, which it had used since its product launch four years ago, in favor of a multi-step microfiltration process. Finite filtration may be the ultimate in cold pasteurization, although validating a 5-log bacterial reduction is a challenge. The company dropped HPP and improved a filtration process it had been using after FDA issued a warning letter in November, citing the firm’s inability to validate a 5-log reduction in Clostridium botulinum for its low-acid juice.
Combining pressure with dense-phase carbon dioxide can enable continuous processing of low-acid juice. Researchers at the University of Florida developed just such a system, which was commercialized in 2003 by Praxair under the name Better Than Fresh. The system, which operated at pressures below 10,000 psi (85,000 psi is typical in HPP processing), was validated the prior year to produce a 5-log pathogen reduction at a juice manufacturer’s plant.
Unfortunately, the system enjoyed “very limited commercial success,” according to a Praxair official, and the company halted commercialization efforts after a licensing agreement with the university lapsed. Continuous processing of 40 gallons a minute was not an issue, but residual CO2 in the product resulted in “fizzy juice,” a university researcher familiar with the technology’s development explains.
More promising is dynamic high-pressure processing or Pascalization. Using a continuous HPP homogenizer from Stansted Fluid Power Ltd., a U.K. equipment supplier, George Cavender began researching the system’s effectiveness as a replacement for thermal pasteurization while a doctoral candidate at the University of Georgia. Making modifications to the Stansted machine, he has minimized temperature increases caused by shear when fluid passes through a pressure-release valve and assessed the effectiveness of microfluidization on product quality and microbial inactivation.
“There’s a reasonable amount of heat because of the (relief valve) friction, but you can alleviate that,” Cavender explains. “Near linear pressure” of 350 megapascals, or about 51,000 psi, is delivered by the machine’s dual-action intensifiers, contributing to creamy texture and other positive attributes in ice cream mix.
In one study, he demonstrated improved sensory properties in ice cream mix using locust bean gum instead of more expensive guar gum. Less protein denaturization and greater water retention also was shown.
Milk and mushrooms
Chemicals and relatively benign wave lengths in the electromagnetic spectrum sometimes can be considered nonthermal processing aids. One of the more intriguing involves pulsed ultraviolet light (PUV) and its interaction with mushrooms.