Professor, Agricultural and Biological Engineering
Dr. Welt's research focuses on plastics that are used for food packaging. He says that one of the most important issues in using plastics with food is called permeability, which measures the amount of oxygen that can pass through the plastic. Plastics are made of molecules which are long chains of repeating subunits. Electrical and mechanical forces hold the chains together, and that gives plastics their solid but often stretchy nature. There is room between these chains for small molecules to work their way through.
Permeability is not necessarily a bad thing. Welt explains that when broccoli or lettuce are harvested, it is like a cut flower, it is fresh and alive, but the clock is ticking. The goal of the farmer, distributor, and grocer is to get these products to the consumer in the freshest condition possible. Oxygen works both for and against this. Too much oxygen and the products ripen too rapidly and may be in poor condition by the time they get the grocery shelf. Too little oxygen also causes rapid deterioration due to something similar to suffocation. An ideal amount of oxygen leads to the longest preservation of the quality. Researchers in this area of “modified atmosphere packaging” seek first to find the best oxygen level for each specific product, and then they seek package designs that will maintain that optimum level. Research in Welt's laboratory has been aimed at adjusting the properties of common and inexpensive packaging material, polyethylene so that its permeability toward oxygen can be set at just the right level.
Welt has also worked on food irradiation. Food safety is an important issue as the increasing numbers of consumers, products, and outlets meet new packaging materials and new pathogens. Food irradiation is a simple and practical approach that can increase that margin of safety. But there are important questions about how the energy that irradiation uses affect packaging in contact with foods when treated. With a new generation of packaging materials come a host of new questions about this interaction, and Welt is beginning to take on some of these questions.