Food Engineering

Tech Update: Antimicrobial Tools

April 1, 2008
Want to get tough on mold and bacteria? An impressive arsenal of microbe killers exists.

Because seafood is regulated by the Department of Commerce, fish processors used ozonated water in direct contact, before other industry segments were permitted to use it. Source: Eco-Safe Systems.

From exotic newcomers like bacteriophage to cheap and effective standbys like chlorine, food and beverage manufacturers have a growing number of arrows in their antimicrobial quivers. Bacteria and mold killers are being swabbed on surfaces, coated inside packages and sprayed on products from the time food enters the supply chain until it’s plucked from a retail shelf. Some recent remedies landed with a thud (activated lactoferrin, for example) or a spectacular flameout (irradiation, for example), but new microbial killers keep coming. Octanoic acid and other found-in-nature solvents are joining biocides and oxidizers as part of manufacturers’ multiple-hurdle mix. Laboratory aids to validate the effectiveness of these interventions are becoming more sophisticated.

Despite the impressive arsenal, unwanted mold and bacteria are dispatched with disinfectants or oxidation. Disinfectants are chemical poisons, which would suggest oxidation is the weapon of choice. Chlorine dioxide, hydrogen peroxide and peroxyacetic acid have oxidative power and are used frequently in food and beverages. But the most powerful oxidant available is ozone, and its use in either a gas or aqueous state remains limited seven years after FDA and USDA approved its direct contact with food and 32 years after the EPA approved it as an antimicrobial. For every ozone generator in a food environment, thousands more are treating municipal water and swimming pools. Three decades of butting her head against industry resistance has left Del Ozone’s Beth Hamil discouraged and a little groggy. “Folks who use ozone rave about it,” says Hamil, vice president of corporate compliance/market development, “but there’s a rough row to hoe to get industry to adopt the technology.”

Fast and accurate detection of food pathogens through polymerase chain reaction is giving leading manufacturers greater confidence in the results of environmental sampling. Source: DuPont Qualicon.

Ozone promoters sometimes boast it kills 3,000 times faster than chlorine, though Hamil dismisses the claim, and she should know: The kill rate is drawn from a swimming pool test she oversaw in the 1980s. More meaningful is a study conducted by Air Liquide, which found one part per million (ppm) of ozone is as effective as 200 ppm of chlorine in killing microbes. Ozone won’t disinfect everything-a system built in the late 1990s to clean poultry chill water was overwhelmed because “it would have been easier to separate the water from the filth than the other way around,” she recalls-but ozone is being used effectively to clean CIP water and as a mold and bacteria arrester in storage bins.

New technology is easier to apply if there isn’t any old technology to replace. That was the situation at Lucky’s Real Tomatoes, a Brooklyn supplier of premium tomatoes. Its Beefsteaks are sliced at the 21 Club, Waldorf Astoria and other exclusive kitchens, though national distribution has been curtailed because of escalating transit costs. Two years ago, the family firm revamped its handling practices, setting up a washing facility in Whittier, NC, where tomatoes are sanitized before heading north. Spray bars, brushes and a dryer clean the tomatoes in a 15-ft. long chamber before they reach an optical color sorter and are repacked

Peroxyacetic acid and other antimicrobial chemicals for fresh-cut salads cost more than chlorine, but they hold up better and deliver more consistent results. Regardless of the treatment, close monitoring is critical if expected performance is to be delivered, argue Ecolab experts. Source: Ecolab Inc.

Chlorine would have been the easy antimicrobial choice. “It’s common, cheap and established,” allows Marc Marcelli, food safety director, “but it’s nasty to handle, it’s not good for the produce because it’s a slow oxidizer,” and based on his research, “it’s not too difficult for the bacteria to develop a resistance.” After considering and rejecting quaternary ammonia, peroxyacidic acid and other disinfectants, Marcelli settled on an ozone system from PurFresh (formerly Novazone) Inc., Livermore, CA. “It was by far the most expensive system we considered,” he admits, “but it also was the most controlled and redundantly safe, and we felt there was a good support system behind the technology.”

Shelf-life extension is a benefit, though not a factor for Lucky’s. Its fruit is hand picked when flavor and ripeness peak. “This is not for ketchup,” Marcelli dryly observes. As with any antimicrobial, hold time and the water’s load must be monitored to ensure adequate bacterial knockdown without damaging the product. That level of sophistication wasn’t available from some vendors a few years ago, after government agencies lifted restrictions against direct contact with food.

Buying a generator and engineering a system never were considered. “It’s not just a spark plug in a box,” Marcelli says. Technical support may be PurFresh’s most important contribution to the ozone equation. Industrial gas companies were the first vendors to introduce food systems, believing ozone generators would expand the market for pressurized oxygen. But modern systems generate their own oxygen, and that torpedoed the vendors’ business model. Likewise, suppliers of chemical sanitizers and antimicrobial oxidizers shy away from ozone because it cannibalizes sales. 

Fish processing and supermarket produce departments have been a major focus for Los Angeles’ Eco-Safe Systems USA, but the ozone supplier is becoming more involved with food processors, reports CEO Michael Elliot. Fresh-cut salad manufacturers want in-plant demonstrations, and ozone gas was applied in a refrigerated area of a Los Angeles poultry processor to eliminate a bacterial problem. “Ultimately, it’s going to replace chlorine,” Elliot predicts.

Technicians prepare bacteriophage cultures in the Netherlands’ lab of EBI Food Safety. The firm is developing phage to attack several types of food pathogens. Source: EBI Food Safety.

Bacterial mutations

Bacterial resistance to antimicrobials is a concern among food scientists, particularly in plants where risk assessment typically isn’t done, and antimicrobials’ role used to be preservation and sanitation, not pathogen control. In a report on antimicrobial resistance by the Institute of Food Technologists, an expert panel noted, “Spraying meat animal carcasses with organic acid solutions may lead to establishment of acid-resistant pathogens.” Stress-resistant pathogens may have contributed to public health problems with traditionally low-risk foods such as fruit juices and dried products, the scientists hypothesized.

The survivability of bacteria in forming biofilms or mutating into disinfectant-resistant strain has been demonstrated in lab tests, though at “levels so low that the results can’t be transferred to the plant,” according to Michael P. Doyle, a food microbiologist and chairman of the IFT panel. Nonetheless, varying the type, intensity and sequencing of antimicrobial interventions is a prudent plant strategy to minimize the likelihood of stress-resistant microbes.

Natural biocidal compounds that don’t have to be declared on food labels are growing in availability, despite the possibility of bacterial mutation. At last fall’s Worldwide Food Expo, Cranford, NJ-based Arnhem Group spotlighted a microbial intervention and shelf-life extender using natural proteins. Sheryl Barringer, a researcher at Ohio State University, presented results on the Listeria monocytogenes-suppression effects of a cocktail of hydrocolloid protein and lactobacillus sprayed on cooked and raw meat, poultry and seafood. A sensory panel could not distinguish beef stored 14 days from fresh product. How the protein protects meat is not fully understood, Barringer noted. And Arnhem leaves it to the end-user to engineer a delivery system.

Octanoic acid is better understood. Ecolab Inc., which also validates acid dispersal and performance in the production environment, is marketing the fatty acid-based antimicrobial. “Just as important as the chemistry is the delivery mechanism,” notes Keith Johnson, director, food & protein marketing. The St. Paul, MN firm in recent years has beefed up its engineering capabilities to deliver turnkey systems.

No instances of microbial resistance to fatty acids have been reported, and regulatory authorities recently approved octanoic acid as a treatment for ready-to-eat (RTE) meat and poultry. In Ecolab’s system, the compound is applied to a package immediately before sealing. The product then passes through a hot water bath, shrinking the package and spreading the compound over the food’s surface.

Another Ecolab tool under development is a poultry chill-water filtration system that adds an antimicrobial to help processors conserve water without compromising food safety.  “The chemical works; the challenge is eliminating the soil,” says Johnson. “That requires an equipment solution.” He declines to identify the chemical, but most certainly it isn’t chlorine: Whether in a gas form or aqueous state, chlorine “gets chewed up in an organic load rapidly,” he points out. “Other chemicals are more expensive, but they are much more resilient and effective.”

The need to balance the bacteria-killing power of an antimicrobial with maintaining the appearance of the food is a practical consideration with any intervention, points out Doyle, a professor at University of Georgia and director of the school’s Center for Food Safety. An organic acid that kills some organisms but not others has value. However, developing a comprehensive strategy involving a number of antimicrobial agents is becoming more difficult because of funding cuts in basic research.

Insufficient research is not retarding commercialization of bacteriophage, the bacteria-specific microorganisms that are harmless to humans but deadly to the pathogens they attack. Regulatory approvals have slowed food deployments, though the market is beginning to heat up.

Wageningen, Netherlands-based EBI Food Safety received GRAS status in June from the FDA for a Listeria-killing phage on the surface of all types of food, according to CEO Mark Offerhaus. That gives EBI a leg up on Intralytix, a 10-year-old Baltimore firm that won FDA approval in 2006 for its Listeria antimicrobial but is still trying to commercialize the product. (See “Bacteria Busters,” Food Engineering, September 2007.)

EBI has an American pedigree. The National Institutes of Health conducted early research before it was divested in a management buyout. Like any antimicrobial treatment, phage “has to make sense financially,” Offerhaus observes, and driving down cost has been an important part of the work. Being able to deliver a turnkey system for food-plant use also is critical, and the company is working with a leading US supplier of spraying systems to ensure the proper flow rates and coverage are delivered.

“Millions of phage are present on food even without our product,” Offerhaus points out, “but without the Listeria phages, they aren’t going to offer any protection.” For the time being, EBI has the food-safety space to itself. “Most phage companies are focused on the sexier products for medical applications,” he says. GangaGen Life Sciences in Ottawa, Canada is developing a phage to attack Campylobacter in poultry, but despite “some promising results,” it is probably two years away from commercialization, the company’s senior research scientist says.

EBI is developing Campylobacter-destroying phage cultures, along with strains to attack Salmonella and pathogenic E. coli. It also is being drawn into the fight against methicillin-resistant Staphylococccus aureus (MRSA), bacteria that are resistant to antibiotics such as penicillin. Two in five swine are infected with MRSA, and half of pig farmers carry the strain, Offerhaus notes. Bacterial mutations like MRSA are chilling examples of antimicrobial resistance. More Americans reportedly succumb to MRSA infections than AIDS.

Lemons and other produce increasingly are being treated with ozone gas in storage to retard spoilage and slow ripening. Source: PurFresh Inc.

Safer contact, quicker tests

Applying antimicrobials in packaging is an appealing option to combat Listeria in RTE meats. With food-safety funding in short supply, validation of effectiveness increasingly falls to developers of the technology, however. “It’s a tough time to be a food researcher,” bemoans Doyle, though his center recently received an ozone system and funding from PurFresh to investigate the efficacy of ozone as a disinfectant for packaging film and containers. “You can optimize the effectiveness of any chemical by controlling pH, temperature and humidity,” explains chemist David Cope, CEO of PurFresh, and determining the best balance with ozone will be the research’s focus.

Vaporized hydrogen peroxide (VHP) may be the newest antimicrobial sterilant for food packaging. Mentor, OH-based Steris Corp. announced in July it was developing a new aseptic filling platform for Tetra Pak. While Steris has deployed 1,500 VHP systems for aseptic medical applications, the joint venture with Tetra Pak is its first foray into the food industry.

Unlike hydrogen peroxide, the only approved antimicrobial for food packaging, VHP is a dry vapor with sporacidal and fungicidal properties. “It’s a broad spectrum sterilizer,” explains Matt Mitchell, director of industrial decontamination. VHP was used in 2001 to kill anthrax spores in large public spaces. DC’s Washington Hospital recently designed new emergency rooms with ports where VHP could be pumped to sterilize the space. While EPA approved VHP, FDA has not approved it for use on food-contact surfaces.

Chlorine dioxide is another antimicrobial trapped in a regulatory netherworld. Farmers can use it when harvesting crops, but processors are forbidden from using it in their plants. Nonetheless, researchers at Purdue University are developing a treatment chamber that could effectively destroy microbes on fresh produce. And unlike hydrogen peroxide, which must be held above its 109°C boiling point to be vaporized, chlorine dioxide is gaseous at a much lower dew point and is less corrosive and more oxidative than peroxide, according to Paul Lorcheim, director of operations at CSI ClorDiSys Solutions Inc., Lebanon, NJ.

Regardless of which antimicrobials a manufacturer deploys, validation of the effectiveness of a treatment is needed. The faster the QA lab can get a reading on swab-test cell counts, the sooner a line can be shut down and remedial action taken if there is a problem. A number of quick assays have been developed for both the food and medical environments. Among them is polymerase chain reaction (PCR), a technique that relies on in vitro enzymatic replication to rapidly amplify the DNA of the target organism. PCR was conceived by a biochemist who attributed the inspiration for his methodology to LSD. 

PCR is the basis of the Bax system from DuPont Qualicon. Microbiologist Siqun Wang, R&D director, says the test has evolved from a lab-based technology unsuited for the food industry to a robust and reliable environmental test that doesn’t require highly trained personnel. Faster results are another evolution: A 48-hour Salmonella test 10 years ago was replaced by a 24-hour Listeria assay last year and, more recently, by an eight-hour test. “We can play as much as we want in the black box, but we have to give a green or red to the user,” and a false red can be an expensive mistake, Wang points out. Precise and accurate results have won users among nine of the 10 largest food companies, he says.

Determining the effective dosage for an antimicrobial intervention can be a laborious, protracted exercise. The spiral gradient endpoint (SGE) assay from Advanced Instruments takes the tedium out of the process, and it’s not just for research wonks: Tyson and other food companies are using SGE to add precision to the process. An antimicrobial compound is placed on an agar plate, which is spun so that smaller concentrations are spread outward from the center. The microbe being targeted is then smeared across the radius of the plate so “you know exactly the amount you need to get the job done,” explains Anthony Pappas, product manager.

SGE appeared in crude form 15 years ago, and while the mechanics of the spinning plate remain the same, the analytical software has advanced significantly. “When it first came out, users had to do a lot of math to figure out the effective concentration,” Pappas says. Now, companies like Ecolab can confirm in three minutes whether the surface treatments they are deploying are sufficient.

Silver ion is a permanent surface treatment that appeared to be going the way of irradiation. AK Steel tried unsuccessfully several years ago to persuade food companies and equipment manufacturers to fabricate food-contact components with silver-based coatings. Some conveyor manufacturers dismissed silver ion as ineffective, despite the vulnerability of conveyor belts to cross-contamination. Milwaukee-based Rexnord Industries began mixing the Microban silver ion compound into some chain polymers to beat back biofilm formations five years ago. So favorable was the reception, the supplier made it standard in all food belts 12 months ago, marketing director Linda Berry says.

Habasit Belting Inc. also reports growing use of its antimicrobial belts, particularly among meat and poultry processors. The actual kill agent remains something of a mystery: It is not silver ion, according to Bill Hornsby, marketing director, and food companies are required to sign a confidentiality agreement before receiving any technical information. The company is restricted from making any claims about the material’s pathogenic effectiveness, though studies by researchers at North Carolina State University and the University of Arkansas’ poultry science center conclude the ingredient does control microorganism growth.

How it works is less important than how well it works with other antimicrobial interventions in a plant. As food safety concerns escalate and failures become make-or-break issues, processors are taking a second look at existing antimicrobial technologies and keeping an eye open for emerging tools.

For more information
Anthony Pappas, Advanced Instruments, 781-320-9000
Sandra Lyna, Arnhem Group, 908- 709-4045, slyna@flavexprotein.com
Paul Lorcheim, CSI ClorDiSys Solutions Inc., 908-236-4100
Beth Hamil, Del Ozone, 805-441-4444, beth@delozone.com
Siqun Wang, DuPont Qualicon, 302-695-5300
Keith Johnson, Ecolab Inc. 651-293-2233
Michael Elliot, Eco-Safe Systems, 818-613-6335, melliot@ecosafesystemsusa.com
Bill Hornsby, Habasit America, 800-458-6431, william.hornsby@us.habasit.com
Colleen Flanagan, Petro Canada, 905-804-3631, flanagan@petro-canada.ca
David Cope, PurFresh Inc., 925-454-0303, dcope@novazone.com
Linda Berry, Rexnord, 262-376-4820
Matt Mitchell, Steris Corp., 440-392-7252

Bugs in the Gearbox

Not too many years ago, most suppliers of food-grade lubricants trumpeted H1 grease and oil with antimicrobial properties. Today, only one vendor can make that claim: Petro-Canada Lubricants.

Lubrication companies stopped beating the antimicrobial drum when the EPA determined those additives were bacteriocides and therefore were subject to toxicological and environmental review. The process is costly and time-consuming, suppliers grouse, and most opted to drop their antimicrobial claims. Petro-Canada, on the other hand, began validation work in late 2003, according to Category Manager Colleen Flanagan, and in January 2007, it secured EPA approval to make bacterial- and mold-resistance claims for the additive Microl. The option is available in three lines of H1 products: grease, gear fluids and hydraulic fluids.

Bacteriocides are required in all metal-working fluids, she notes, but those powerful additives would never pass FDA muster. Petro-Canada researchers tested approximately 300 different agents before finding an antimicrobial agent that satisfied FDA criteria and did not negatively impact performance.

EPA review takes about 18 months, and no additional approvals are imminent. “Right now, we’re not beating that drum,” sniffs a marketer at one lubrication supplier that used to promote its antimicrobial grease. “What does it even mean?” 

Is an antimicrobial lube overkill, or are other vendors suffering from bacteriacide envy? Need is in the eye of the buyer, but for those who put stock in science, Petro-Canada has the data. The firm has funded performance tests in which food-grade grease with and without the agent was inoculated with microbes. “Testing to date has indicated that, when Microl is present, there is no premature breakdown,” says Flanagan. The same was not true of the control lubricant.