New Pasteurization Processes Give Food Companies Options

Thermal pasteurization systems continue to improve, giving food and beverage processors an expanding universe of alternative treatments that align with changing market demands.

By Kevin T. Higgins, Managing Editor

RFmachineAn unintended consequence of the Food Safety Modernization Act is a small explosion in the number of new pasteurization technologies available to food processors.

As processors undertake their due diligence in evaluating potential safety hazards in their production processes, many are finding that ingredients and raw materials previously considered no-risk actually are potential carriers of microbial or viral hazards. FSMA requires processors to take steps to remove those risks, and that can mean adding a pasteurization step.

In addition, some industrial manufacturers are demanding that their ingredient and raw-material suppliers pasteurize their finished goods prior to shipment. The aforementioned risk assessments have inspired a proactive approach to even low-moisture products that carry a slight probability of microbial contamination. Those ingredients and raw materials usually are subject to a kill step in the manufacturing process, but once inside the four walls of the plant, food pathogens can migrate undetected to any area, including packaging.

“Been there, done that,” is the knowing reaction from growers of almonds, a low-moisture food that was considered exempt from salmonella contamination until outbreaks in 2001 and 2004 proved otherwise. At the growers’ request, USDA in 2007 began requiring that all almonds, whether raw, blanched or roasted, be treated to achieve a 4 log reduction in salmonella. Consequently, equipment manufacturers and technology providers validated their systems and submitted them for review to the Almond Board of California’s Technical Expert Review Panel (TERP). The result is hundreds of validated pasteurization systems, including many alternative and leading-edge technologies.

Even when thermal or chemical treatment is the defense against pathogens, operating systems are subject to continuous improvement. When Deamco Corp. engineered a pasteurization system for Hilltop Ranch in Ballico, Calif., space constraints necessitated the use of a vertical pasteurization chamber and two Kason vibratory fluid bed cooling and drying units, which were selected because of their small footprints. The design resulted in a system half the size of a comparable pasteurizer. Real estate always is in short supply, though higher throughput, not space savings, remains the primary driver in pasteurization system design, notes Deamco’s Armand Guilion.

Throughput may be manufacturers’ priority, but consumers want minimal processing and nutrient retention, particularly with products associated with healthy eating. Nuts, seeds and sprouted grains are among the fastest growing food categories, and a number of TERP-approved processes retain the flavor, mouthfeel and nutrition of raw seeds and grains.

Among them is Log5, a system developed by Duyvis Wiener, a Dutch firm that originally engineered the system to treat cocoa and chocolate. The system mixes humid air with saturated (dry) steam to manipulate water activity and temperature level with moist heat and achieve a 5 log bacterial reduction without adversely impacting product quality. The first North American unit is expected to be commissioned in August at CHS Inc.’s sunflower seed facility in Fargo, N.D.

The continuous process can pasteurize up to 20,000 lbs. an hour, depending on the product, according to Jochem Dekker, vice president at Log5 Corp., (www.log5.com) Phoenix, Md. Because temperatures are above the dew point, moisture pick-up doesn’t occur, and the machine can both pasteurize and roast, says Dekker. The firm has U.S. orders for three more machines.

Saturated steam and vacuum are employed by Napasol North America LLC (www.napasol.com) to pasteurize at a relatively low temperature. The batch process was installed last year at Hazelnut Growers of Oregon’s facility, pasteurizing 15,000 lbs. per hour. Systems capable of processing volumes as high as 30,000 lbs. per hour can be fabricated, according to David Barbera, business development director of the Fargo, N.D., unit of the Swiss firm.

Nuts, seeds and dried fruit can be pasteurized in either static or rotating autoclaves. Product is placed in bins before entering an autoclave, then transferred to a cooling plenum. The batch approach reduces the possibility of cross contamination, Barbera points out.

Electricity generates most of the thermal wallop in Revtech Process Systems’ sterilization and pasteurization technology, with a blast of saturated steam finishing off any surviving microbes. A bigger distinction is the vibratory transport of the product with a technique described as impedance tube transfer by managing director Martin Mitzkat, cofounder of the Loriol-sur-Drome, France-based firm (www.revtech-process-systems.com).

Direct contact with a hot tube is the primary kill mechanism, and manipulation of counterweights to motors at either end of the circular tube creates the vibration. The earliest systems had two-inch diameter tubes; scale up to higher-throughput machines has produced 10-inch versions that can process 10,000 lbs. an hour. The next engineering challenge: a machine capable of 33,000 lbs. of throughput.

Besides validated effectiveness with nuts and other dry products, the system has successfully treated natural gums and corks for wine bottles, Mitzkat reports. The combination of chlorophenols and mold can result in cork taint, a phenomenon that threatened sustained use of natural cork as a closure. Pretreating corks with his system eliminates the problem.

Step in to the light

Light-based technologies have an even more benign image than steam and vacuum. Ultraviolet in combination with other microbial interventions remains experimental as a pasteurization solution, but validated lethality exists from other points on the electromagnetic spectrum. Among them are radio waves and ionizing radiation, both of which are playing a larger role in pasteurization.

Until recent years, radio frequencies were used almost exclusively for drying. The Macrowave system from Radio Frequency Co. (www.radiofrequency.com) has been used for decades in baking as a final moisture-removal step to prevent checking in cookies and crackers. Six years ago, pathogenic E. coli in cookie dough produced in Nestle USA’s Danville, Va., bakery was traced to the product’s flour, opening a new frontier for pasteurization.

“Pasteurization has only gained momentum in the last couple of years because of FSMA,” notes Lisa Mitchell, marketing manager at the Millis, Mass., machine fabricator. Partially cooked products and ingredients destined for manufacturers with zero-tolerance bacteria policies are expanding RF’s use.

Sub-pasteurization to achieve a 2-3 log reduction often is acceptable. Although sterilization is possible, the technology imparts heat, making it unsuitable for delicate products. The system operates at a frequency of 41.6 meghertz (MHz).

Longer wavelengths at a frequency of 27.12 MHz are used in a system from RF Biocidics Inc. (www.rfbiocidics.com), a Sacramento, Calif., start-up that recently received TERP approval. The waves create an electric field that polarizes living cells, altering their metabolism and eliminating them. The technology was developed at the University of California-Davis and is being commercialized by Allied Minds, a funding firm specializing in intellectual property developed at U.S. universities and federal research institutions.

“The molecule that most attracts the radio-frequency energy is water,” aligning it with low-impact drying, says Vincent Chun, vice president at Allied Minds. “The challenge with agricultural product is that you want the product close to its natural state, which requires very tight control of the radio frequency energy.” He pegs treatment cost at about 2 cents per lb., including equipment costs.

Food with relatively high moisture levels can’t be pasteurized with most of these technologies. For fruits and vegetables, an emerging option is electron beam, which operates at much higher frequencies and shorter wavelengths than either radio frequency, microwave, ultraviolet or visible light.

Imported produce in particular is fertile ground for e-beam. Last year saw an almost five-fold increase in application of the technology for fruit, according to the National Center for E-Beam Research at Texas A&M University.

E-beam is close to X-ray and gamma in the electromagnetic spectrum and was tried unsuccessfully 15 years ago for food pasteurization.

Technology providers are steering clear of the term irradiation this time, though food treated with E-beam still must carry the redura symbol. In the past, the redura frightened some members of the general public, who mistakenly believed it signified radioactivity.

Today’s public is better educated, e-beam proponents believe, and the symbol’s graphics are more consumer friendly. “Negative perception can become positive perception when people understand the risk tradeoffs for safe food,” suggests Dolan Falconer, CEO of ScanTech Sciences Inc. (www.scantechsciences.com), Atlanta. “The redura will become a symbol of quality.”

ScanTech is targeting early 2017 for the startup of its e-beam treatment center in McAllen, Texas, the port of entry for the majority of Mexican produce entering the U.S. A Texas pension fund is an investor in the $20 million project. Instead of irradiation, the firm refers to the process as “electronic cold pasteurization.”

Uneven control, which resulted in overdosing, plagued e-beam systems of a decade ago, but that problem has been resolved, says Falconer, and today’s systems are much more precise. His system treats from the top and bottom, with each wave penetrating to a depth of 7 inches. “The Food Safety Modernization Act will have a huge impact on the business,” he adds, “and will strengthen the acceptance of our technology.”

High Pressure Processing

Low temperature also is the new emphasis for high pressure processing (HPP), with processors and equipment suppliers employing terms like “cold-pressed processing” to describe the technology.

The cold emphasis is partly a counterpoint to researchers and regulators focused on high pressure and heat to inactivate Clostridium botulinum in low-acid foods. While HPP destroys bacteria and viruses in food, it does not eliminate spore formers such as C. bot.

The effectiveness of HPP and heat in destroying C. bot is well known: In 2009, FDA accepted a petition for commercial use of such a process involving low-acid food (mashed potatoes) from Illinois Institute of Technology, Avure Technologies Inc. and the forerunner of the Institute for Food Safety and Health (IFSH), which is based in Bedford Park, Ill., in a facility that includes an office of FDA’s Center for Food Safety and Applied Nutrition. However, no food companies were interested in producing such a product, and it’s doubtful that HPP’s strengths—better flavor and higher nutritional value than canned foods—would be retained. In fact, conventional HPP might have a protective effect on spores when combined with processing temperatures of 80°C/176°F. The pressure needed for inactivation would be greater than the upper limits of the approximately 350 HPP presses currently in operation worldwide.

Aside from commercial impracticality, such treatment runs counter to the appeal of cold-pressed juices, which are refrigerated and popular in part because of minimal processing. If the cold chain is broken and product is held for an extended period above 50°F, a C. bot culture can develop—as was the case in 2006 with carrot juice produced by Bolthouse Farms. Several botulism cases tied to the carrot juice were reported.

Consequently, FDA inspectors have demanded that HPP processors either acidify juices above 4.6 pH or prove that a 5 log reduction in C. bot occurs in their process. Addition of citric acid can lower pH, but it isn’t an option with coconut water, which has a mild taste that would be masked by another flavor. FDA fired off a warning letter to Harmless Harvest, a leading coconut water brand, in November, demanding that it validate a 5 log reduction in C. bot. The firm subsequently abandoned HPP in favor of a microfiltration process.

Equipment suppliers are responding with validation research of their own. Hiperbaric is working with process authorities in the Netherlands to demonstrate the efficacy of HPP with low-acid products, and Avure commissioned a study at IFSH that concluded that C. bot cannot germinate and produce toxin in coconut water held at temperatures below 50°F for 45 days. Avure’s resident microbiologist plans to seek publication of the study’s methodology and conclusions in a peer-reviewed journal.

It remains to be seen if FDA accepts those findings or maintains its position that HPP processors must account for cold-chain abuse, even when it is the consumer who fails to properly refrigerate treated products. With almost half of the worldwide network of HPP presses operating in the U.S., FDA’s future direction could either encourage or put a chill on the most promising new pasteurization technology.

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