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.
North America's High Pressure Processing Tolling Services
More than 200 HPP machines are in service in North America, most owned by food companies that primarily use them for their own products. A growing number are owned by tollers who accept packaged food and beverage products in fee-for-service arrangements. Download a list of those firms.
Just as cholesterol in mammals is converted to vitamin D-3 when exposed to sunlight, ergosterol in fungi is converted to vitamin D-2 when exposed to ultraviolet. Research by Robert Beelman at Penn State University demonstrated that a single UV pulse at a three-pulse per second rate was sufficient to trigger enough vitamin D production in mushrooms to exceed recommended daily intake in a 3 oz. serving.
His research led to a patented process that accounts for a significant portion of university royalties, according to Beelman, who retired from the faculty in 2010 but remains active at the university’s Center for Plant and Mushroom Foods for Health.
Giorgio Foods Inc. in Temple, Pa., licensed the PUV technology several years ago. Sold under the D’Lightful label, the enhanced portabella mushrooms account for about 3 percent of production, or about 50,000 lbs. a week. “It’s a niche market, for sure,” allows David Carroll, president, though he’s hopeful greater attention to the need for increased vitamin D intake by Americans and Europeans might spur increased mushroom consumption.
The simplest way to raise mushrooms’ vitamin D level is to convey a single layer of them under PUV lamps, an extra step that only commands a small premium in price. “The process needs to be controlled, but it’s not difficult,” says Carroll.
The health benefits of vitamins and amino acids in foods is a contentious area, and a lively debate of the bioavailability of D-2 vs. D-3 is ongoing. D-3 typically is derived from the lanolin in sheep wool, “and most of it is produced in China” in pill form, Beelman points out. Before products like D’Lightful can make much headway, public awareness of vitamin D deficiency must be raised, he believes.
Beelman lobbied Penn State’s athletic department to evaluate football players’ vitamin D levels and found nine of 10 had deficiencies or insufficient levels. The Pittsburgh Steelers took notice and incorporated more vitamin D in players’ diets, Beelman says.
UV without a pulse is technology that doesn’t need to be sold to industry or the public. Consequently, its use in pasteurizing process water is further along than PUV. More relaxed standards for potable water entering a plant are prompting many processors to treat municipal water used in applications that don’t necessarily require treatment.
Pasteurization of push water used to evacuate product in filling lines between production runs long has been required by the Pasteurized Milk Ordinance (PMO), but relaxed city-water standards have prompted many dairy processors and carbonated soft drink manufacturers to also treat CIP water used in final rinses and water used to clean membranes in ultrafiltration and reverse-osmosis systems, according to Craig Nelson, principal of Food Automation LLC, a Mission Viejo, Calif., consulting and engineering service. “Proactive processors want to err on the side of caution,” notes Nelson, who has drafted many of the PMO’s technical sections on behalf of FDA.
UV pasteurization has received an additional push from the Food Safety Modernization Act, Nelson adds. Given the increased risk posed by potable water, the onus is on manufacturers to explain how, for example, they maintain pasteurization when membranes are flushed between runs without a complete line shutdown.
Conventional water pasteurization requires more floor space, tanks, an operator and a lot of energy for boiling. All told, operating costs typically exceed $300,000, three times the cost of an in-line UV pasteurizer. “The capital cost (for thermal treatment) is much higher,” Nelson adds, “and UV pasteurizers have proven to be very effective.”
A number of antioxidants used for cleaning and sanitizing food contact surfaces are being evaluated as antimicrobials on the food itself. Generally speaking, regulators are giving the go-ahead to use these chemicals in dosages up to 50 parts per million. The questions then become, are they effective at that concentration, and is there any adverse impact on the food?
Processors of fresh produce are among the food segments evaluating electrolyzed oxidative water (EOW), an alternative to chlorinated water in flumes, rinses and baths to knock out bacteria. Another segment is poultry, where EOW has enjoyed isolated use for several years.
Most EOW systems utilize a reactor chamber with a membrane to create an oxidizer and an alkaline chemical, usually sodium hydroxide or sodium chloride for cleaning. Hypochlorous acid is the oxidizer, and while it is more stable than ozonated water, it requires separate storage from the cleaner. However, a single-cell technology developed by Samsung can create 90 percent hypochlorous solution, reducing storage needs.
Operating under the name Ecolox, American investors took an ownership stake in the factory where the single-cell units are manufactured. Miami-based Ecolox had its earliest success in South America, where a Nicaragua poultry plant now owned by Cargill Meats Central America installed 16 of the generators in 2014. Now, Ecolox is testing the waters in North America and Europe.
“Everybody’s interested in a disinfectant applied directly to the food,” reports Scott Hartnett, Electrolox’s chief medical officer. “We have the silver bullet.”
Extensive scientific research confirms the effectiveness of hypochlorous acid in combating pathogenic bacteria, including spore formers, with 5-log reductions within 30 seconds at 50 ppm across the board. The timeline stretches to 5 minutes to achieve a 3-log reduction in norovirus. “It’s what people are looking for,” says Hartnett, “but they have to be educated.”
A plug-and-play version of the reactor is finding fertile ground in foodservice, particularly at organic restaurants. An industrial-scale unit barely measure 1.5 cubic ft., though it does require external tanks. The unit can generate hypochlorous acid at concentrations up to 400 ppm, which then can be diluted to supply up to 2,500 gallons of aqueous solution an hour, Hartnett says.
Heat treatment will play an integral role in food processing for the foreseeable future. Nonetheless, a number of more benign replacements or aids to thermal treatment are available or under development, raising the likelihood of food products that are both safe and healthier.