33-2 |
Impingement drying applications to foods |
R. G. MOREIRA, Dept. of Agricultural Engineering, Texas A&M Univ., 310 Scoats Hall, College Station, TX 77843-2117 Impingement drying is an old technology that has only recently been used to process food products. The use of impingement drying in processing corn tortillas before frying shows feasibility in production of a lower-fat fried chip. Impingement drying with superheated steam can produce potato chips with less color deterioration and less nutritional losses (Vitamin-C) than drying with hot-air. Tortilla chips and potato chips have been dried by impingement drying using hot air and superheated steam. At higher air temperatures (above 130oC), tortilla chips dry faster when using superheated steam compared to hot air (at the same conditions). Compared to the hot-air drying chips, superheated-steam dried potato chips shrunk more, had higher bulk density, lower porosity, and lighter color when dried under the same operating conditions. To facilitate efficient process design and optimization, a mathematical model was developed to describe the heat and mass transfer mechanisms during impingement drying of corn tortillas. The process was modeled using governing equations for heat and mass transfer during the drying stage. Mass transfer within the product was modeled as diffusion-driven mass flux. Heat transfer was driven according to Fourier's Law of conduction. Boundary conditions for drying in both air and superheated steam were incorporated into the model. Convective heat transfer accounted for heat flow into the product at the surface. When drying in air, convective mass transfer prevailed; in superheated steam, differences in vapor pressure between the drying medium and the product surface accounted for mass transfer. Temperature and moisture content predictions followed the experimental trends with both air and steam drying. Product thickness and the drying medium temperature affect on moisture content and temperature profile over time. The usefulness of the model as a simulation tool encourages future applications of impingement drying to vegetable and fruit-based products.
Session 33, Food processing with air impingement systems: Innovations and opportunities
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