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M. J. RESSING and T. D. Durance. Food, Nutrition & Health Program, Univ. of British Columbia, 6650 N.W. Marine Dr., Vancouver, BC V6T 2G9, Canada Microwave heating under vacuum (VM) removes water at reduced temperatures while minimally altering desirable biochemical characteristics compared to traditional methods. Puffing has been observed in VM dried products and reportedly contributes to improved rehydration and eating quality of VM processed foods. However, the mechanisms behind VM puffing are poorly understood. Wheat dough was selected as a model system since its rheology is well researched. The objective was to compare the degree of VM puffing in relation of rheological and dielectric properties of the prepared dough and use this data to develop and validate a numerical model of VM puffing. Doughs prepared with high and low gluten flour (HG, LG) and water, at 0.0 - 1.5% NaCl, were formed into small uniform balls and dehydrated at 700 and 1300 W microwave power and 27 Torr absolute pressure. Volume, weight, moisture and dielectric properties were recorded pre and post drying. For raw dough, elasticity, stress relaxation and biaxial extension were determined. In-process puffing was video-recorded. Internal structure and mechanical hardness of puffed, dried dough balls was also determined. HG balls exhibited volume change, to a maximum 170% and a minimum 80% increase for 0.0 and 1.5% NaCl respectively. LG balls only exhibited limited volume increase without salt, following a similar but less pronounced decrease with added salt. Applied power levels, salt content, flour type and dielectric properties all significantly influenced the density change (P=0.0001). Salt dependent, rheological parameters of raw dough matched the trend in density changes. The results suggest that the decrease in elasticity and increased strain hardening have an influence on the degree of puffing, with rising salt content especially for HG flour. These findings agree with observations in HG dough during baking where steam and gas release are dependents of these rheological properties, suggesting a gluten-salt interaction.
Session 113, Product Development: General
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