Shrinkage prediction during pasta dehydration
Shrinkage models from different fields of study were reviewed. Pasta was used as a model to further develop the hypothesis of predicting shrinkage in terms of the rate of relaxation and the rate of moisture loss. An extended literature review of pasta properties, such as isotherms, diffusivity, glass transition, rheological properties, and shrinkage was conducted. Isotherm and glass transition models were developed from the literature data acquired. Creep was tested with a 25 mm-diameter flat plate at 20 to 40°C at varying moisture content. Viscoelastic properties for the Burgers model for creep were determined, where higher moisture content samples resulted in higher creep values. A super-sensitive balance with controlled temperature and relative humidity environment was used to obtain drying curves of extruded semolina at 60°C. Samples of different thicknesses were submitted to relative humidity steps from 80% to 0%. The drying kinetics show similar behavior throughout all thicknesses, and discrepancies between curves suggest shrinkage is occurring. The diffusivity constant was shown to increase with decreasing moisture content, while diffusivity has been shown to decrease, which suggests that shrinkage has a significant effect on the drying curves. Diffusivity values obtained based on constant initial length are comparable to literature data obtained. The values were between 1.18×10-12 and 2.84×10 -11 m2/s. Shrinkage curves obtained suggests that shrinkage during pasta dehydration is not linear, which is contrary to the typical linear-shrinkage assumption. Although it was hypothesized that the Berens and Hopfenberg model was applicable for this study, diffusivity and relaxation occur simultaneously and not separable from the data obtained. Further research with longer test times, as well as the application of creep data, and other mathematical models, could help further develop the concept.
Okos, Purdue University.
Food Science|Agricultural engineering
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