Food Engineering

Tech Update: Non-Thermal Processing

January 1, 2011
As consumers desire fresher tasting food, the challenge for processors is to produce bacteria-free products while maintaining flavor, color and texture.

Avure’s HPP equipment currently enhances food safety for a vast majority of more than $3 billion of food products sold annually around the globe. Source: Maple Lodge Farms, Ltd.


Did you ever notice that the space allotted to canned foods in your supermarket seems small compared to that of fresh, frozen, shelf-stable and RTE foods? Why? With today’s emphasis on fresh and healthy meals, consumers are purchasing fresh, frozen and RTE foods that maintain vitamins and nutrients and seek lower sodium alternatives.

Adjusting to this changing market requires some rethinking of processes. We all want food that is safe and delicious, so how can food products be kept fresh and free of bacteria? What options are available with non-thermal processing techniques that are both effective and reasonable in cost? Are there other benefits besides killing residual bacteria? Will consumers accept these new techniques?

Not every technology works equally well for each food or beverage, and while some options are more effective than others in killing bacteria, convincing consumers to buy products treated by particular methods may prove to be a challenge. However, there have been some changes in efficacy and consumer acceptance.

This chart shows the reduction of E. coli O157:H7 on lean wafers sprayed with various antimicrobials in a Ross tenderizer with integral intervention. There were 14 antimicrobials tested with varying results-not all are yet approved by regulatory agencies. Source: Oklahoma State University/Ross Industries.

Irradiation thrives

When FE investigated some of the non-thermal options open to processors in 2007, it seemed irradiation had lived its last half-life, especially after a cold storage warehouse in Quakertown, PA lost its battle with the local government to set up an irradiation operation. Now, according to Ron Eustice, Minnesota Beef Council executive director, two operations are up and running around the clock to handle hamburger and other products. Sadex Corp. (Sioux City, IA) offers electron beam technology, and Food Technology Services Inc. (Mulberry, FL) provides gamma radiation-based services; a third company in Hawaii uses X-ray on produce. Because irradiation has a high initial cost and requires specialized equipment and know-how, processors will probably find that irradiation service providers (as the three just named) will be the best solution. With this option, processors send off their pallets, which are irradiated and ready for distribution to retail stores.

Though the market for irradiation is still in a nascent stage, the global market is expected to exceed $145 million by 2015, according to a Global Industry Analysts (GIA) report entitled, Food Irradiation Trends: A Global Strategic Business Report. North America and Europe account for a major share of the revenues in the global irradiation market. Growing concerns over food-borne disease outbreaks caused by pathogenic bacteria such as Campylobacter, Salmonella and Trichinae and the need for complying with international standards of quality in an increasingly globalized world are expected to fuel the adoption of irradiation, says the report. Countries looking for alternatives to fumigation, chemicals and other treatment processes are looking toward irradiation as a solution as well.

“Thanks to Codex Alimentarius Commission of FAO/WHO [CAC], food irradiation has been cleared for use in any foods using any dose of radiation,” says Venkatarao Potty, chairman of Diversified Food Technologies (Mysore, India). More than 40 countries have adopted food irradiation to a varying extent in different foods, though Brazil and Pakistan are the only two countries totally adopting the CAC guidelines, says Potty. Food wastage, especially in poorer countries, will be a major reason for adopting irradiation. “The irradiation process is one of the cleanest with very low recurring cost, but there is still significant consumer resistance because of the inherent fear of radiation and the hazards associated with it.”

While the Center for Food Safety May 2007 Fact Sheet says studies found benzene, toluene and 2-alkylcyclobutanone (2-ACB) in foods after irradiation, there has been confusion about the levels recorded and the validity of the studies. Information from Food Irradiation Processing Alliance (FIPA) says FDA reviewed the data supporting the safety of irradiated foods and concluded there is no adverse effect from eating irradiated foods that may contain 2-ACB in the quantities produced. Likewise, benzene, a known carcinogen, is naturally present in an ordinary egg with levels 1,000 times greater than that in an irradiated hamburger, according to FIPA.

When asked who’s using irradiation and if there have been any negatives, Eustice says, “Omaha Steaks and Schwan’s irradiate 100 percent of their raw ground beef items and have done so since 2000. Both companies have seen sales rise; however, the increase is not necessarily due to irradiation. But one can certainly conclude that the fact they sell irradiated product has not been a negative. Wegmans Food Markets proudly offers irradiated fresh-ground beef in chubs and has done so for many years.”

The naysayers argue that irradiated food products have an off-taste or color. But if that were true, argues Eustice, Schwan’s, Omaha Steaks and Wegmans would not be marketing the millions of pounds of beef they irradiate. “The issue of taste as far as I’m concerned is a red herring,” he states.

On August 22, 2008, FDA published a final rule allowing the use of irradiation to make fresh iceberg lettuce and fresh spinach safer and last longer without spoiling. According to FDA, irradiating these vegetables will help protect consumers from bacteria such as Salmonella and E. coli O157:H7. This final rule came after lettuce and spinach contaminations, largely in San Benito and Monterey Counties in California.

In the article, “Wild Pigs in California: The Issues” (Dec. 2007), Marcia Kreith, program analyst at the University of California Agricultural Issues Center,  cited wild pigs as one possible source for the produce contamination. Helping to confirm this issue as a problem, Peter Muriana, professor/food microbiology at Oklahoma State University (OSU), points out that pigs captured and tested from the affected areas had the same E. coli species in their feces as the nearby cattle, which were also suspected because of runoff from farms. Muriana suggests that even if a field with crops were fenced off from land animals, an airborne assault would still be possible from flies and/or bird droppings.

Other foods approved for decontamination by irradiation in the US include (followed by irradiation level in kGray): pork (1), spices (30), dried vegetable seasonings (30), enzymes (10), herbs (30), fresh or frozen poultry (3), mechanically separated poultry meat (3), fresh (4.5) and frozen (7) red meat, shell eggs (3) and sprouts (8). Fresh vegetables and fruit have also been approved for disinfestations at 1 kGray levels of radiation. The Gray equals the equivalent of 1 joule (1 watt-second) of energy absorbed by 1kg of matter, or 100 rad.

Sandridge Food installed a high-pressure processing system from NC Hyperbaric to pasteurize foods without any noticeable change to its products’ appearance, taste, texture and nutritional value. The system can extend shelf life beyond 60 days for a variety of products. Source: Sandridge Food.

Pulsed electric field

The use of pulsed electric field (PEF) technology has been tried in some juice applications, but was providing inconsistent results. Since then, according to Glenn Hewson, Avure Technologies vice president of global marketing, Genesis Juices has switched from PEF to high-pressure pasteurization because PEF was not providing enough coverage.

According to recent FDA information, application of PEF is restricted to food products that can withstand high electric fields, have low electrical conductivity and do not contain or form bubbles. The particle size of the food in both static and flow treatment modes is a limitation. Also, due to the variations in PEF systems, a method to accurately measure treatment delivery is still needed, according to FDA.

There is still some interest in PEF in food and beverage processing, but it seems to be a technology looking for a large-scale application. Most recently, a paper entitled, “Design of High Voltage Pulse Generator for Pasteurization by Pulse Electric Field (PEF),” published in the International Journal of Computer and Electrical Engineering, describes a PEF system to be applied for the pasteurization of apple juice. The paper found that to achieve an efficient kill rate, the average voltage and current required were 17 kV and 0.48 mA respectively. Power was applied from 10 s to 60 s, and the electric field strength delivered to the chamber was 0.65 kV/cm.1

Originally covered in a lengthy article entitled “Kinetics of Microbial Inactivation for Alternative Food Processing Technologies-Pulsed Electric Fields,” which can be found on FDA’s website, PEF has found new potential in wastewater treatment. However, the authors of a paper given at the Second Euro-Asian Pulsed Power Conference suggest PEF energy requirements are too great and costly to make it a good choice for most food applications, and suggest processors would still find thermal pasteurization less expensive based on energy requirements. Consequently, the authors suggest PEF is a good technology to apply in conjunction with thermal methods in hospital wastewater treatment.2

ListShield is an FDA-cleared and EPA-registered non-chemical antimicrobial preparation for controlling Listeria monocytogenes. The active ingredients are naturally occurring bacteriophages that selectively and specifically kill Listeria bacteria. The product can be used directly in food or on food contact surfaces. Source: Intralytix.

High pressure is on

The reasons for choosing high-pressure pasteurization are many-even though the entry cost can range from $1 to $2 million depending on the capacity of the unit. But processors can opt to choose a service provider if they can’t justify the initial investment. For those processors that actually want to purchase HPP equipment, adjusting the workflow is often necessary, but may at first seem counterintuitive, says Avure’s Hewson. A processor may assume it needs one HPP unit per line. But it makes more sense to stack up finished product from several lines during the course of the day, and then run it through the HPP system, since most of these systems are now designed to operate up to 22 hours a day with some time set aside for cleaning and routine maintenance.

Grid Path Solutions is a system integrator and installer/servicer of NC Hyperbaric Systems (Spain) HPP equipment in Canada and the US. According to Grid Path’s Vice President of Marketing Mike Billig, NC Hyperbaric’s equipment has been built with redundant system components so it can continue to run while being repaired by the maintenance crew.

It’s important to remember that HPP equipment is batch operated, and capacities generally run from 55 l to 420 l. One historical barrier toward a more mainstream implementation of HPP was that batching supported relatively low throughputs, says Francisco Purroy, NC Hyperbaric technical sales manager. But he says this barrier no longer exists with the faster, bigger machines capable of achieving more than 10 cycles per hour and capacities in excess of 2,000kg/hr. (4409 lbs./hr.). NC Hyperbaric also offers a 300 l tandem machine.

Both Avure and NC Hyperbaric offer horizontal-loading machines, which makes them easy to load and unload. Depending on the application, hold times under pressure generally range from three to five minutes, with the longer time being needed for drier products such as salami. HPP at 6,000 bar (87,000psi) reduces Listeria by a log of 3.5 and both E. coli and Salmonella by a log of 5. Listeria, a gram-negative bacterium, is harder to kill because its outer coating is more difficult to penetrate than gram-positive bacteria, says Hewson. But with the pressure, the spoilage mechanism bacteria are also killed.

Why choose HPP? Consumers have been putting the pressure on retailers for fresh products with a minimum of salt and preservatives, says Hewson. So retailers have pressured processors for food that meets these requirements. Besides HPP’s advantage of killing bacteria, consumers enjoy the extended shelf life of fresh product. For example, a 48-oz. jar of Jack’s Special Medium Salsa purchased at Costco on November 15, 2010 has a “best by” date of December 24, 2010. Made with entirely fresh ingredients, a 2-tablespoon serving has only 140mg of sodium.

While extended shelf life is a plus for consumers, processors can take advantage of it as well, says Billig. “This technology allows such a long extension of shelf life that a lot of meat manufacturers don’t give up all that shelf life to the consumer; instead they keep it as internal gains so they can run full shifts, accumulating product, rather than making several short-run changeovers.” This, he says, improves overall efficiency and lowers manufacturing costs.

Three years ago, the average cost of HPP processing was approximately 5-10¢ per pound. Billig says the larger-capacity machines available today can allow processors to get the costs down to about 2-3¢ per pound, which includes the labor to run the equipment, depreciation, utilities and spare parts. Hewson’s estimate is a little more conservative at 2-8¢ per pound, but he reminds processors they can subtract the cost of chemical additives from his estimate.

As both Hewson and Billig suggest, many processors are using HPP for reasons such as: touting products as “all natural” with no preservatives, using shelf life to gain precious time and having an extra measure of quality and assurance that their products are safe.

While HPP can gray the color of hamburger, it does not change its flavor or texture. But HPP, says Billig, can separate the protein that holds lobster meat to its shell, making it easy to extract 100 percent of the raw lobster meat once the lobster has been run through HPP.

Processors that use HPP include Sandridge (bulk deli items), Maple Lodge Farms (High Pressure Protection brand deli meats), Ifantis (Athens, Greece-Freshpress brand deli meats), Ghezzi (Florence, Italy-preserved cod), Fresherized Foods, Calavo, Simplot, Garden Fresh Gourmet and Hormel (Natural Choice meats).

The future may be bright for HPP for yet another reason. Diversified Foods Technologies’ Potty suggests that in many parts of the world the cost of traditional thermal processing may eventually become so high that HPP will make sense, not only for all the reasons already covered, but also because HPP uses less energy and, therefore, will cost less to use.

Bacteriophages spread

EBI Food Safety and Intralytix have developed bacteriophages to combat Listeria, and work is underway to develop phages that can fight E. coli and Salmonella as well. According to Food & Water Watch (FWW), in January 2007, the US Department of Agriculture approved an OmniLytics Company bacteriophage product designed to be sprayed, misted or washed onto cattle hides to reduce the presence of E. coli bacteria.

E. coli presents its own problems when it comes to creating a successful bacteriophage. According to Dirk de Meester, EBI Food Safety director of business development, O157:H7 isn’t the only E. coli serotype that is at issue. There are several other dangerous serotypes (e.g., O26, O103, O111 and O145), and tests are only now becoming available for them. Fighting O157 may take up to 60 different phages, and being successful with O157 doesn’t guarantee success with other serotypes. In addition, since E. coli hasn’t been as much of an issue as Listeria and Salmonella in Europe, research on O157 isn’t as critical. De Meester attributes Europe’s fewer E. coli problems to better animal husbandry in the feedlots and stockyards.

According to Alexander Sulakvelidze, Intralytix chief scientist, his company has an application pending with FDA for the E. coli-targeted phage preparation called EcoShield, to be used for reducing or eliminating E. coli O157:H7 levels in ground beef. This phage is expected to be available this year. In addition, Intralytix has developed a phage preparation targeting major pathogenic serotypes of Salmonella. The phage, SalmoShield, is being submitted for regulatory review early this year.

It’s important to remember that the use of bacteriophages is an additional measure to a processor’s best hygiene methods, says de Meester. EBI’s product, Listex, will get rid of Listeria, but not other bacteria that might be harmful or will decrease shelf life. “It’s not an excuse to go weak on cleaning,” he adds.

How effective is the use of bacteriophages compared to other non-thermal techniques? “Typical reduction of targeted bacterial loads as the result of phage treatment is 95-100 percent,” says Sulakvelidze. “This is comparable to HPP or irradiation. However, there are important differences among these three approaches, including costs.” For example, he says HPP’s use on fresh products (except liquids) can give the appearance of being cooked. Both HPP and irradiation require very large up-front capital expenditures and may cost upwards of 15-30¢ per pound, according to Sulakvelidze. With phage applications, there is no need to purchase equipment, application costs about 2-5¢ per pound, and the treated food’s flavor, appearance and texture are not changed.

FWW raised the concern of bacteria developing resistance to phages in the same way they have to antibiotics. According to Sulakvelidze, the emergence of phage-resistant mutants is likely to occur eventually (as happens with other antimicrobial agents); however, that situation has not been reported to negate the efficacy of phage applications thus far. Furthermore, when such mutants do emerge, the bacteriophage preparations can be easily and rapidly upgraded by substituting new phages that have full potency against the resistant mutants (in clear contrast to antibiotics). Such regulatory practice is somewhat unique to bacteriophage products, but FDA’s clearance of the Intralytix ListShield application, which allows the company to maintain that cocktail’s future efficacy by updating it with new phages if necessary, indicates the approach has merit, says Sulakvelidze.

According to de Meester, bacteriophages do not lead to resistance, but it may be easier for bacteria to learn resistance where a large population of the bacteria exists. For example, you wouldn’t use a phage to treat a reservoir with fish because the probability of a dominant strain developing in such a large environment would be greater than treating the bacteria on the fish after processing.

Surface treatments and other considerations

One application that may have more than one solution is the intervention against E. coli for blade-tenderized beef. Currently, the FSIS does not require mechanically tenderized (non-intact) meat products to be identified. Therefore, consumers and retail outlets, such as restaurants, do not know whether the products they have purchased are intact or mechanically tenderized.

OSU’s Peter Muriana has been working with Brad Morgan, professor/meat science at OSU, and Wayne Spillner, an engineer at Ross Industries, to find an appropriate surface treatment that can be applied to steaks before running them through blade-tenderizing equipment. In one sense, the problem is similar to hamburger: If bacteria are on the surface, grinding and mixing meat together or hammering the surface with knives will drive the bacteria through the meat unless it is treated first. Muriana recalls some recent E. coli outbreaks were attributed to blade tenderization of steak.

Because most people prefer steaks not well done, killing any E. coli before the knife-tenderization process is vital. Muriana and Morgan, working out of the R.M. Kerr Food & Ag Products Center’s 100,000-sq.-ft. research and food processing facility, examined the application of 14 different antimicrobials provided by 10 chemical suppliers for efficacy. Some of the chemicals included HCl and citric acids, copper sulfate pentahydrate, buffered sulfuric acid, lactic acid, hydrobromic acid and several others and combinations. One particular solution provided a 3.61 log reduction in bacteria, although not all chemicals have been approved by FSIS/USDA.

Muriana says the group will also be experimenting with ozonated water and possibly ultraviolet radiation. A problem with ozonated water is its potency can be diminished when using it with organic material. This is also true when using chemical generators to create hypochlorous acid, especially when the legal concentration that can be used is 50ppm. Ultraviolet light is a line-of-sight intervention, and the ability to penetrate nooks, crannies and bottom surfaces is difficult without a method to turn the meat so it is evenly exposed before the tenderizing operation. Liquid antimicrobials may be subsequently used to exacerbate the injury to bacteria caused by UV light.

Muriana has been working with both Unitherm and SanAquel to undertake further testing with hypochlorous acid generators in combination with produce and vegetables, where the legal concentration limit of hypochlorous acid is 200ppm. With less organic content in vegetables and fruits, the E. coli kill rate using hypochlorous is much more effective than with meats. In addition, vegetables with tough skins like tomatoes, peppers and onions are good candidates for this treatment.

Consumers want fresh, tasty and safe products, and non-thermal pasteurization techniques are making it possible to deliver safe food products with longer shelf life that also taste good. Finding the right treatment(s) will take some careful consideration, and chances are more than one treatment may be necessary. Most important, non-thermal pasteurization techniques should be used as part of an all-encompassing food safety quality program-not as an excuse to be sloppy prior to the treatment. In addition, what might seem obvious needs some attention; that is, farms must follow best agricultural practices to help assure their produce and livestock are not delivered to processors laden with excess bacteria that could have been eliminated at the farm.


References:
1Design of High Voltage Pulse Generator for Pasteurization by Pulse Electric Field (PEF),” International Journal of Computer and Electrical Engineering, October 2010; Vol. 2, No.5.
2 “Critical Comparison between the Pulsed Electric Field and Thermal Decontamination Methods of Hospital Wastewater,” Gusbeth, Frey, Schwartz, Rieder; Institute for Pulsed Power and Microwave Technology, Forschungszentrum Karlsruhe, Karlsruhe, Germany. 


For more information:
Francisco Purroy, NC Hyperbaric, 34 947473874, f.purroy@nchyperbaric.es
Brad Morgan, Oklahoma State University, 405-747-2960, brad.morgan@okstate.edu
Dirk de Meester, EBI Food Safety, 31 (0) 317 421 414, d.demeester@ebifoodsafety.com
Peter Muriana, Oklahoma State University, 405-747-0040, peter.muriana@okstate.edu
Wayne Spillner, Ross Industries, 540-439-3271, wspillner@rossindinc.com
Ronald Eustice, Minnesota Beef Council, 952-854-6980, ron@mnbeef.org
Alexander Sulakvelidze, Intralytix, 410-625-2533, asulakvelidze@intralytix.com
Glenn Hewson, Avure, 800-959-1135, glenn.hewson@avure.com
Mike Billig, Grid Path Solutions, 905-643-0955, mbillig@gridpathinc.com
Venkatarao Potty, Diversified Food Technologies, vhpotty@gmail.com