Asepsis Reconsidered

March 28, 2003
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New technologies and a broader view of objectives could help aseptic processing realize its potential.

Sterilizing food with high pressure using wire-wound presses like this Flow International unit exemplifies the new approaches being taken to aseptic processing.
If you can pump a food, proponents say, you can process it aseptically. But as the 21st century begins, aseptic processing remains the Karl Malone of the food industry: great ability, but where's the championship ring?

With few exceptions, aseptic processing has failed to make inroads in the domestic food industry. The failure is partly food-code related, partly perceptual. There may be no slam-dunk for aseptic in the supermarket aisle, but bits and pieces of the process are being applied.

Aseptic is most closely identified with milk that, by regulatory requirement, has been thermally treated to the point where flavor degradation has occurred. That may be an acceptable trade-off for a military organization concerned with feeding a mobile fighting force, but is it relevant to the American consumer? Extended shelf life is more a benefit to the manufacturer and the retailer, not the consumer, and anemic sales of aseptic products are a consequence.

Commercial sterilization is the goal of aseptic processes, and thermal treatment certainly sterilizes. A 12-D cook, for example, typically eliminates 5 logs of more of Bacillus stearothermophilius spores, and it makes short work of vegetative microorganisms such as Salmonella, Lysteria, E. coli and C. botulinum. Consumers expects safeguards against those pathogens, but they also want foods and beverages that are more flavorful and better quality than retort or frozen processes deliver.

As a result, food scientists are adopting a broader view of aseptic, borrowing elements of the process and applying them to products that are both shelf-stable and refrigerated. If heat treatment is too severe, they try alternative methods. The nation's aseptic think tank reflects this broader view: the Center for Aseptic Processing and Packaging Studies (CAPPS) recently substituted the word Advanced for Aseptic in its name.

By expanding their vision of the benefits and objectives of aseptic, re-searchers hope to push the technology beyond puddings and juices and into wider commercial use, including versions of particulate products that could render the 10-lb. retort can obsolete.

"Industry has not grasped the huge potential for two-phase in processing ingredients," maintains Kenneth R. Swartzel, chairman of the food science and technology department at North Carolina State University and director of CAPPS. "When that occurs, we will see tremendous movement" toward aseptic particulate.

Four years ago, Swartzel helped organize a series of workshops that led to the first FDA-sanctioned protocol for two-phase processing. Aseptic potato soup was produced at Tetra Pak's testing facility in Buffalo Grove, Ill. Verifying that the temperature reached in the center of each particulate was sufficient to achieve asepsis was a difficult and expensive process. For three years, the potato soup protocol has languished in a state short of commercialization.

Better testing methods could help change that. A process involving magnetic thermometry developed by Swartzel and his colleagues at N.C. State was granted a U.S. patent in January. "We now have a process that is very robust, simple, easy to understand and conservative, in the sense that it is nondestructive, noninvasive and cheap," he says.

The technique involves magnetic implants in various food particles and the use of sensors to generate a residence time measurement. When combined with data on the temperature inside the processing system, the kill rate of microbes and their spores can be calculated. Measuring the speed of the fastest moving particle is especially important so that sterility is accomplished without gelatinizing the product. Lack of such a measurement method has stymied development of complicated foods like beef stew.

Thermal evaluation has been one of Swartzel's two principal contributions to the science of food asepsis in the last 20 years. "We have a boneyard of failures" in the field of particulate measurement, he wryly notes, including a thermal memory cell that worked well but was too complicated for industry to grasp and adopt.

I am the egg man

Swartzel's other contribution involves aseptic processing of liquid whole eggs. The ultrapasteurization method he and other N.C. State food scientists developed 11 years ago transformed a product category and a company.

The liquid whole egg process was licensed to Minneapolis-based Michael Foods Inc., a then-$150 million company that rang up sales of $1.2 billion last year, most of it from egg products. Michael was just another player in the foodservice egg sector until it capitalized on aseptic technology to deliver a superior product delivered in 300-gallon aseptic bags with a 16-week refrigerated life to foodservice and industrial accounts. Today, Michael is the largest such supplier in the world

Although pasteurization of shelled eggs is the hottest area in the hen house today, more than 100 patents for pasteurized liquid egg have been issued, and work continues. In February, Mohammad Hossein Hamid-Samimi, a onetime prot? and colleague of Swartzel, secured the latest patent for a lower cost way to produce pasteurized liquid eggs.

One of the biggest hurdles that process engineers have to overcome with liquid eggs is coagulation. Producing salmonella-negative liquid eggs at temperatures that won't cause frequent shutdowns of the processing system or result in an unacceptable product is a challenge. How they accomplish it varies widely, with radio frequency, electroheating and heat exchangers among the methods tried. One approach is to introduce hydrogen peroxide to oxidize bacteria in the first of two heat-and-hold stages at 500 psi, then subject the product to a higher temperature for a shorter duration before pumping it to a refrigerated holding tank. The goal was to produce a viscous product that retained baking functionality.

Improved thermal processes for achieving asepsis are tested at the Louisville, Ky., proving center of Waukesha Cherry-Burrell.

Superior fruit pulp

Killing pathogens while retaining flavor was the objective at Avomex Inc., and it takes extremely high pressure to achieve that. The Keller, Texas, firm processes avocados in a Mexican plant to produce a refrigerated guacamole dip for foodservice and supermarket sales. Avocados are subjected to 87,000 psi of pressure in a batch process using wire-wound presses, inactivating microorganisms and enzymes without degrading taste, color or nutritional value.

Commercial sterility is not the objective at Avomex, though the product has successfully passed botulism challenge tests. Rather than reach asepsis, formulators wanted some bacterial competition to retain guacamole's slightly nutty taste throughout the five-week code period. Pressurized sterilization costs about a nickel per pound of processed food.

The dip, which retails between $4 and $5 for two eight-ounce pouches, is the unquestioned sales leader in its core markets. In Dallas, Avomex guacamole has taken over the market from Calavo, the former guacamole king. Sales of Avomex's dip last year reached $2.6 million, based on supermarket scanner data, compared to $108,000 for Calavo. A similar shift in market dynamics is occurring in San Antonio, where Avomex rang up $2.2 million in sales.

High pressure preserves the product without causing the acidification that occurs with thermal processing. Off-tastes are not masked as they are in traditional processes, so Avomex must use higher quality avocados.

Pressure is effective with high-acid foods and juices, but low-acid foods pose a different challenge. One interesting development in that area is a process developed by Richard S. Meyer that combines pulsed, ultra-high pressure with thermal treatment. The process accomplishes absolute sterility, not simply commercial sterility, without overcooking foods, the Tacoma, Wash., food scientist maintains.

Meyer, who heads Washington Farms Inc., a pie-filling company, began experimenting with high-pressure food processing a decade ago, eventually combining pressure with heat but still not attaining the desired results. "As a last ditch effort, I tried a double pulse to open up the spores, and it worked," he explains. "A two-second pulse is all you need," and absolute sterility can be achieved at 194 degrees F.

"With high pressure, you don't have much effect on flavor, and you don't blow the cell walls and produce a mushy texture," he adds. Pressure of about 120,000 psi is required, considerably higher than what is attainable in commercially available wire-wound tanks but less than what would be needed for low-acid foods using pressure alone. "There may be a point where you get sterility with pressure alone, but it's over 200,000 psi, maybe 300,000," Meyer says.

"High temperature with high pressure is the future," predicts Ed Ting, vice president-technology at Flow International Corp., which is working with Meyer. "It will be the replacement of the metal can, which is incredible."

In the coming months, Meyer's process will be tested at NCFST's lab in suburban Chicago.

Economies favor the process's adoption: its cost is comparable to retort and half that of frozen, Meyer says, because there is no need for elaborate cooling -- products emerge from the pressurized chamber at the same temperature they entered.

Multitube processing systems like this unit designed by JCS Controls have brought the benefits of aseptic processing to juices; now the industry is out to conquer particulates.

Longer green pastures for pulsed electric

Overcoming the cost barrier to commercialization has derailed many promising technologies for asepsis. A recent example is cool pasteurization through pulsed electric field treatment. Though the technology still has many proponents, the company that tried to commercialize it recently abandoned the food business in favor of pharmaceuticals and medical supplies.

The technology and the related broad spectrum pulsed light (BSPL) method grew out of research by Maxwell Technologies Inc. Its potential for preserving perishable fluid foodstuffs led to the formation of PurePulse Technologies Inc., a venture that included Kraft Foods and Tetra Laval Group as equity partners. In 1995 Tetra committed an additional $6.5 million to develop the sterile packaging applications of BSPL.

Last year, Tetra Pak backed away from BSPL as a replacement for peroxide treatment of packaging film. Roy Wallen, PurePulse's marketing manager, says the company now has determined that the operating margins in the food industry are insufficient to bring either BSPL or pulsed electric field technology to commercialization.

Another technology facing an uphill battle to commercialization is electric conductivity, commonly referred to as ohmic heating. Developed in the 1980s, the application hasn't progressed beyond pilot plant status in the U.S., and the owner of that unit is shopping for a buyer.

Electric conductivity heats the center of a particle to precisely the same temperature as the outside, a great advantage in verifying asepsis. But temperature spikes of 150 degrees can occur within seconds, and a scraped surface system used in the cooling stage can degrade the particles.

The outlook is more promising for falling stream heater (FSH) technology developed by den Hollander Engineering of the Netherlands and licensed domestically to Waukesha Cherry-Burrell. An egg processor already is using this infusion system, and two dairy plants with FSH will come on-line in the next few months.

Originally designed for evaporates such as baby formula and ice cream mixes, FSH now is being applied to "fairly viscous, heat-sensitive products," notes Craig Reinhart, senior process engineer at Waukesha Cherry-Burrell's Louisville office. Particles up to an eighth inch might be feasible, though FSH was developed for finer particulate where plate burn-on is an issue and longer run times are desired.

"Compared to existing infusion systems, the benefits are carried to the next level," says Reinhart. He estimates the temperature of the steam is at least 5 degrees cooler than in other infusion systems.

Demonstrably better taste is essential if manufacturers are to switch to new equipment or processes. The need to find processes that yield more flavorful foods is at the heart of nonthermal alternatives for achieving some form of asepsis.

Military-industrial R&D

Nonthermal's focal point is Dual Use Science and Technology (DUST), a cost-sharing initiative for nonthermal research and development. DUST's first project involves building a pulsed electric field system. The U.S. military is chipping in $1 million, with Kraft, ConAgra and other organizations contributing another $2 million.

Pulsed electric field is "still destined for use with pumpable products," believes C. Patrick Dunne, a food scientist at the U.S. Army Natick Soldier Center. "The limitation is the size of the particulates that have to be pumped through a small orifice," and that can be boosted to the 2 to 5 mm range.

"We're creating a database on all these different technologies: RF, ohmic, high pressure, pulsed electric fields, oscillating magnetic and so on," reflects Swartzel, whose CAPPS membership includes many of the same researchers involved in DUST. "Companies want new technologies that will let them produce products that are as safe or more safe than existing products, that are higher quality, and they want to do it more cheaply and have better documentation. Nonthermal systems have that potential, but unlike thermal applications, there is so much critical information we lack. How much pressure is needed to knock out the most resistant toxin, for example? We don't know."

Whether the answer lies in refinements to thermal processes, a new nonthermal approach, or a hybrid approach like Meyer's, food engineers have enough arrows in their quiver to raise expectations for aseptic processing. The question is when, not if, one of them breaks through as a commercial hit.

Sidebar: Consumer-Friendly Packaging for Asepsis

Consumers can't see product quality, but they can see quality packaging. Fortunately for food processors, their packaging partners are developing new options for communicating the quality benefits of their aseptic processes.

The venerable brick- style container has been the aseptic fluids' workhorse for generations, but consumers often complain about the difficulty in opening those packages and their tendency to spill. That has caused some manufacturers to shy away from the brick. One promising solution is Clip-Pak, International Paper's spout system for the Fuji LA-60 aseptic filler.

The low-profile plastic spout offers improved pouring and reclosing. When the plastic tab is lifted, a flange at the opposite end punches a hole in the carton's board. Manufacturers can attach the spout off-line in a single-station applicator that runs at speeds up to 7,200 packages per hour.

Solutions like that should keep the brick around for years to come, but aseptic particulate packaging poses new challenges. Roll-fed technology that pinches the content when sealing isn't going to work with particulates, so the industry is eyeing other options.

"It's one thing to process something aseptically but another to match it up with a package that will keep it aseptic," observes Jeffrey Kellar, marketing manager at Tetra Pak in Vernon Hills, Ill. The firm recently deployed a linear high-density polyethylene plastic filler in Germany for low-acid particulates, and Kellar hopes FDA will approve the system for particulates within a year.

Sidebar: Valve System Relieves Engineers' Asepsis Concerns

Ever since public health inspectors ordered two-stem flow diversion valves downstream of heaters in dairies processing both ESL and pasteurized milk, food engineers have fretted about a potential threat to both plant personnel and aseptic integrity in dairy processing.

The U.S. Food and Drug Administration began requiring those systems in early 1999, raising concerns that the single-seat block-and-bleed systems could lead to product contamination and could pose a danger to workers, should the divert valve lift and flash scalding steam into the room. Fortunately, FDA blessings for a safer, simpler alternative may come in the next couple of months.

Dubbed the JCS Differential Protection Isolation Barrier FDV Replacement, the system uses double-seated valves and steam barriers with differential pressure and thermal protection to provide superior product integrity. If a leak or some other interruption causes pressure to come from the wrong direction, a steam barrier protects the product and pumping activity is shut down.

According to Philip R. Frechette, president of Rochester, N.Y.-based JCS Controls and designer of the system, the diversion device required by FDA does not provide the stringent safeguards from atmospheric conditions required of aseptic processing systems. JCS retrofitted its clients' plants with flow diversion valves, then presented FDA with documentation showing how the double-differential pressure in the JCS system better addresses the agency's concerns.

"This is the bridge that has been missing to solve a problem that existed," Frechette says. The system could be used at U.S. dairy facilities affected by the earlier FDA order, as well as at plants processing high-acid aseptic juices where there is an interest in greater product integrity, he adds.

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