With government funding drying up and businesses curtailing in-house programs, food technology research often has an entrepreneurial feel in the 21st century.
In a nondescript industrial park surrounded by prairie, independent scientists are engaged in primary research that helps improve food safety and address operational issues in production. Before outsourcing became the norm, major food companies conducted this type of work in house. Today, fundamental R&D is becoming a cottage industry, often carried out by researchers whose 20th century work broke ground for today’s industrially hardened systems.
The scientists in this suburban Chicago lab were first linked together at the National Center for Food Safety and Technology (NCFST), a consortium of academia, FDA and private industry. The lab’s first resident was Chuck Sizer, a former NCFST director and pioneer in aseptic packaging and processes. Before joining Cambrooke Foods, a firm providing foods for people afflicted with phenylketonuria and other metabolic diseases, Sizer patented a container sterilization process that combines hydrogen peroxide treatment with a sodium hydroxide rinse. After a few seconds of rinsing, the container is ready for filling, saving significant time, space and water. The process is oriented toward plastic containers for aseptic filling.
With Sizer now in the Boston area, the lab’s two other scientists have continued to develop his concepts, along with their own projects. One is food chemist George Sadler, chief technical officer of Prove It LLC. The other is microbiologist Joseph Dunn, president and owner of NanoMed Technologies Inc.
Dunn is a graduate of the University of Nebraska-Lincoln and Oregon State University, where he earned a doctorate in microbiology. After directing a lab that performed molecular virology research, he became principal scientist at PurePulse Technologies, a subsidiary of Maxwell Laboratories Inc. PurePulse attempted to transfer Maxwell’s pulsed power technologies for military weaponry to nonthermal pasteurization and sterilization of liquids and food packaging. The research included pulsed electric fields and pulsed light, an intense light and UV treatment that paved the way for a package sterilization system from the French firm Claranor (see “La lumière pulse s’il vous plaît,” Food Engineering, June 2009). Dunn served as NCFST’s director of technology assessment from 2000 to 2003, during which time he investigated the use of high-pressure processing for sterilization of shelf-stable foods.
FE: What sterilization techniques for aseptic packaging are you working on?
Dunn: We are trying to develop several new methods, including a process in which rolls of plastic are irradiated before bag forming. We’re still gaining an appreciation of the challenges of sterilizing plastic packaging for aseptic products. For a long time, dogma was that plastic is sterilized during extrusion in the blow molding process, but now it’s understood that’s not the case. Plastic is not a solid; it is a mesh, with many capillaries linked together. Microbes can take up residence at the base of those capillaries, which is why it takes time and resources to ensure plastic film is sterile.
With bag-in-box packaging for aseptic products, processors must wait one to two weeks for bags to be irradiated and delivered. In our process, rolls of plastic are irradiated and stored until needed. Bags are then formed, and a tiny droplet of a peroxide-based agent is placed inside. Within a couple of days, the bag is rendered sterile and ready for use. Irradiation costs are greatly reduced, as are fulfillment lead times.
Another project concerns high-speed filling lines. Conventional sterilization with hydrogen peroxide or peracetic acid requires large energy or water inputs to get peroxide residuals down to the 0.5 parts per million maximum allowed by FDA. Drying typically is done with sterile air heated to about 85°C [185°F] or with water rinses. The process generally takes more than 15 seconds. At these systems’ flow rates, that requires a lot of space, energy and time.
We have developed a chemical sterilant that is effective in five seconds at room temperature and a second method that is catalytic and will remove residues just as rapidly. This catalytic system rapidly degrades the peroxide and only leaves water and materials generally recognized as safe [GRAS], so only one rinse is needed. Catalytic reactions generally are very fast. In this case, it essentially constitutes an oxidation-reduction reaction which breaks down any chemical residue after sterilization occurs.
FE: How does the process differ from existing peroxide-based sterilization?
Dunn: Peroxides are old chemistry and, in my opinion, under-utilized. They typically work as well as anything else around, and there are a lot of things they can do that have not been optimized or even fully recognized. Development of an alternative sterilization method for bags, bottles and other preformed plastics attempts to address that.
Peroxide is a powerful oxidizer and is pretty stable as generally formulated. It breaks down relatively slowly on its own. Heat or UV light can be added to accelerate the breakdown and release the oxidative potential faster. Peracetic acid is widely used to sterilize food packaging and only requires about a 15-second treatment, but lowering the residuals to an acceptable level takes time. By using peroxide in combination with a chemistry we have identified, and which is GRAS, we can eliminate the residuals almost instantly. The catalyst we’ve identified is the subject of a pending patent application.
FE: How does this chemical method sterilize?
Dunn: When the bond between the two oxygen atoms of the peroxide falls apart, you are left with an OH hydroxyl radical, one of the most active chemistries known. It lasts for a few nanoseconds before doing something, and that usually involves pulling off a hydrogen atom from the nearest molecule. If the hydrogen radical is near a bug, it’s going to do a lot of instantaneous damage to the microbe. That is what white blood cells essentially do when they attack bacteria with hydrogen peroxide or reactive oxygen. Gamma irradiation also produces hydroxyl radicals and results in exactly the same chemistry.
FE: Can you describe the catalyst?
Dunn: Iron is ideal in many ways, but the catalyst doesn’t have to be iron; there is a wide range of transition metals that could be used as well. The nice thing about iron is that it’s GRAS, and only trace amounts are left at the end. Currently we’re investigating several options, determining the optimal concentration and characterizing their performance.
In the presence of hydrogen peroxide, ferrous metal ion—or iron 2+—is converted to the ferric ion—or iron 3+—and at the right pH, this reaction is catalytic. With the Fenton Reaction, under the right conditions, iron 3+ is catalyzed back to iron 2+, and it happens very quickly. A tiny bit of iron will eat up a lot of hydrogen peroxide with this catalytic reaction.
FE: Are you currently collaborating on any technologies with Dr. Sadler?
Dunn: George is just a brilliant chemist. He has developed a polymer that can be used as a coating to create a bactericidal active surface. It has tremendous antimicrobial power. It could be sprayed onto surfaces in hospitals to effectively control the growth of Staphylococcus aureus, a pathogen that kills tens of thousands of patients every year. The same kind of antimicrobial protection could be sprayed onto food processing contact surfaces, such as valves or gaskets.
FE: How does the antimicrobial compare to silver-ion coatings?
Dunn: We’re looking at a range of agents, but I really don’t know how it compares with silver ion. I sure hope it’s going to be more cost effective.
In a recent trial, we combined the agent with an acrylic-urethane coating. A 20 milliliter droplet of staph was placed on glass coated with the active polymer and allowed to dry. The droplets came from a culture containing more than 7 logarithms of colony-forming units, but of course, there’s some die-off in the process of drying. On plates without any coating as well as the ones with the polymer only, about 4.2 logs of colony-forming units were recovered. On the plates coated with the agent mixed with the polymer, no organisms were recovered.
We’re also looking at polymeric systems that might give the agent a volumetric effect with fluids. For example, dispensers or tubing in soda dispensing systems might be coated to assist in sanitation.