Solandre Perez (above) and Sylvie Assoi of the University of Georgia work with a glove box to produce and package orange juice. To maintain a virtually oxygen-free environment, gas from the nitrogen tank undergoes oxygen scavenging prior to entering the chamber. Source: Louise Wicker, University of Georgia, Athens.
Brewers are the primary users of the Orbisphere 6110, which pierces the tops of beer containers to measure oxygen levels in headspace and extrapolate oxygen and carbon dioxide levels in the liquid. The Orbisphere’s electrochemical sensors are almost as precise as gas chromatography, which is why micro-oxygen researchers at the University of Georgia are using them in their work.
Dissolved and entrained oxygen introduced in production and during filling can add thousands of parts per million (ppm) of oxygen and cause quality degradation that defeats the functionality of air-tight containers, researchers in the University of Georgia’s Department of Food Science and Technology have concluded. Continuous purging with inert gas throughout the production process can lower oxygen to innocuous levels, but achieving that with existing technology is a challenge.
In presenting findings to date at the Institute of Food Technologists’ July annual meeting, Adjunct Professor Aaron Brody cited the success of beer makers in filling plastic bottles with “very, very low levels of oxygen.” To minimize quality deterioration with plastic bottles, brewers focused on micro-oxygen control in processing and filling. Very low oxygen levels have been achieved, but more work remains. By reducing total package oxygen below 50 parts per billion (ppb), says Brody, major breweries can get 100 days’ shelf life from plastic containers at ambient temperatures. At 25 ppb, the bottles have 200 days’ shelf life; at 1 ppb, it stretches to 360 days.
Skunkiness and bitterness are quality issues for beer, but virtually every other food product faces quality degradation because of oxygen, according to Brody, who also is president of Packaging/Brody Inc., Duluth, GA. Commercial retort and aseptic sterilization processes deliver biologically safe foods but leave enough oxygen to permit biochemical reactions. Lipid, protein and flavor oxidation as well as color changes occur over time, resulting in poor-quality foods.
Biochemical reactions help explain why high temperature/short time (HTST) remains a niche application. Fewer nutrients are destroyed than with retort, but the presumed superior quality often is compromised. “There is a lot of praise for aseptic,” Brody allows, “but sterility doesn’t have anything to do with biochemical oxidation. Until you get the oxygen out, food isn’t going to be stable” from a quality standpoint.
In conjunction with NASA’s preparations for a flight to Mars, university researchers became involved in efforts to extend space food shelf life to five years. With oxygen levels of 6 to 7 percent, canned goods would degrade so much, astronauts might opt to jump into a black hole. Consequently, researchers are developing processing and packaging systems that can deliver foods with oxygen levels of 20 ppm-or 0.0002 percent. Conventional instrumentation used in food production cannot measure levels that low, a limitation that drove researchers to Hach Company. The firm’s Orbisphere instruments employ electrochemical sensors that measure oxygen levels down to parts per billion, Brody says. They are used widely in commercial applications such as nuclear power plants, where monitoring of dissolved oxygen in cooling water is done to gauge corrosion potential. Brewers also have used Orbisphere to monitor oxygen and carbon dioxide in both liquid and gas phases of bottled beer.
Creating a virtually oxygen-free environment is a challenge, even in the lab. Brody’s colleagues built an airtight glove box to conduct experiments with high-acid products such as orange juice and applesauce. A nitrogen blanket is introduced while researchers work through the gloves to process and fill products. The purity of food-grade nitrogen is insufficient, however: It contains more than 100 ppm oxygen, he says, and must therefore pass through a robust oxygen-scavenging system prior to entering the chamber. Kevin Sudderth, a Hach application engineer, positioned a membrane-covered oxygen sensor inside the glove box to record actual process-oxygen levels. Because the device also measures partial pressure, the system can apply Henry’s Law to calculate entrained and dissolved air inside the food products that are produced, says Sudderth. The accuracy of the measurements is within 1 ppb, he adds.
Beyond the NASA project, researchers hope to establish the commercial viability of investing in micro-oxygen processing and filling to produce shelf-stable products that retain their quality for years. “Is micro-oxygen the next major food preservation technology?” Brody asks. “We like to think so.”
For more information:
Aaron L. Brody, Packaging/Brody Inc., 770-613-0991, aaronbrody@aol.com
Kevin Sudderth, Hach Company, 770-271-6078, ksuddert@hach.com
