Using ultrasound waves to dry high-protein gels is being tested by researchers at the University of Illinois. The gels can be made from peas and lentils, for example, to create dehydrated-food products.
More people are turning to plant-based proteins to promote health and lose weight. High-protein foods such as energy bars and shakes are popular. But the moisture in those ingredients can cause problems for food manufacturers.
Edible gels from plant proteins also are used to produce capsules for medications. But the gels tend to form films around the heat exchangers used for drying them. That reduces heat transfer and increases both energy used and cost of chemicals needed to clean the machines.
The most popular methods of processing the proteins are baking or freeze drying. But baking can destroy or diminish plant nutrients and damage the foods' structural integrity. Freeze drying is time-consuming, requiring as much as a day and one-half to complete, according to the researchers.
The food industry has explored ultrasound-drying methods. In collaboration with Ozan Khahraman, University of Illinois alumnus, we’ve developed and refined a method for it. Ultrasound dehydration can remove water and solvents from protein gels without significantly raising their temperature. It also is gentle enough to use on delicate food products.
In the laboratory we mixed almond-, lentil- and pea-protein powders with water and let them sit for two hours. When ethanol is added to the mix it forms a visco-elastic protein gel. Even when stressed the gel tends to maintain its shape.
The gel is placed in a custom-designed ultrasound transducer box. The device converts electrical energy into sound energy. We make sure the gel is within a few millimeters of the energy source. The box is then submerged in a water jacket to hold the temperature constant at 82.4 degrees Fahrenheit.
The box vibrates at 40 kilohertz – a significantly greater frequency than medical ultrasound. It dehydrates the protein gel as pockets of moisture that are expelled as a room-temperature mist. In less than 10 minutes the gel changes into a thin film that retains a fresh look and feel. It’s water soluble and easily digestible.
The processing method has numerous advantages. First it’s efficient. We can extract moisture from the protein source in minutes rather than the one to two hours needed in baking or 36 hours required for freeze drying. Second because ultrasound drying doesn't significantly increase the temperature of the protein nutrients are preserved. Finally the protein film doesn’t come in contact with any hot surfaces so we don’t need to clean the heat source.
The method for drying plant proteins has generated excitement among people in the biotechnology and food-science industries. We presented our findings at the Center for Advanced Research in Drying, the American Oil Chemical Society and the Institute for Food Technologists.