Model optimizes moisture transport.

During moisture transport processes, such as drying and sorption, stress cracks initiate and propagate in biopolymers for a variety of reasons. These include the occurrence of non-uniform shrinkage on the macroscale; certain forces that are exerted by solid materials; vicinal and bulk phases on the micro and mesoscales; and glass transition effects that occur on the microscale level.

The focus of research at the University of Idaho was to use a multiscale model to predict the initiation of cracks during the sorption and drying of pasta. Scientists wanted to be able to predict stress crack initiation in pasta by solving a multiscale fluid transport and normalized stress model. They wanted to determine the viscoelastic properties of pasta and validate the predictions of the mathematical model by performing drying and sorption experiments.

The scientists used the finite element method to predict moisture and stress profiles during the continuous and intermittent sorption and drying of pasta. To determine the viscoelastic properties needed to solve certain equations in the model, experiments were performed using a commercial mechanical analyzer in the temperature range of 250 C to 950 C. Investigators gained information on the impact of glass transition on the Fickian and non-Fickian modes of fluid transport and stress development in foods. (The net diffusion rate of a gas across a fluid membrane is proportional to the difference in partial pressure, proportional to the area of the membrane and inversely proportional to the thickness of the membrane. Combined with the diffusion rate determined from Graham's Law, this Fickian law is a way to calculate exchange rates of gases across membranes.)

To validate the model's predictions, the researchers performed continuous and intermittent sorption and drying experiments in a controlled temperature-humidity chamber. Computer simulations provided information on moisture movement, mechanical properties and crack initiation in foods. The model developed allows researchers to improve moisture transport to obtain materials with a minimum number of stress cracks. Such foods are less prone to microbial damage and are preferred by consumers.

Further information. Pawan Singh, Department of Food Science and Toxicology, University of Idaho, Box 442201, Moscow, ID 83844; phone: [phone]; fax: [phone]; email: [e-mail].