15D-30 |
Radio frequency (RF) heating of starch solutions as influenced by system and product parameters at 27.12 MHz |
G. B. AWUAH1, H. S. Ramaswamy1, and P. Piyasena2. (1) Department of Food Science, McGill University, 21111 Lakeshore, Ste Anne-de-Bellevue, Montreal, QC H9X 3V9, Canada, (2) Food Research Centre, Food Research Program, Agriculture and Agric-Food Canada, 93 Stone Road West, Guelph, ON N1G 2W1, Canada Radio frequency heating has the advantage of rapid and uniform heating, high penetration depth and short residence times. These advantages make RF heating a feasible alternative that could be explored to enhance the overall quality of foods economically. Products that could benefit from RF heating include particulate-laden foods. The objective of this study was to evaluate the effect of system parameters (flow rate and RF power) and product parameters (concentration, pH, added salt and sugar) on temperature change (DT) across the applicator tube of a 1.5kW pilot-scale RF unit. Starch solutions (1 to 4% w/w) were used at three different flow rates (0.35, 0.5 and 1 L/min) and five power levels (672, 912, 1152 and 1392 W). The effect of added salt (0 to 0.8 w/w), sugar (0 to 2% ) and pH (3.98 to 8.02) were studied at 0.5 L/min. The heating rate of starch solutions varied from 4 to 15C/min depending on flow rate, concentration and power level. Fluid flow rate and power level had significant impact (p < 0.05) on temperature change (DT). The individual effects of salt and power were not significant (p < 0.01) on DT. Although the combined effect of salt and concentration had an influence (p < 0.05) on DT, observed trends were not clear cut. The individual effects of either pH or sugar was not significant (p > 0.05) on DT due probably to their low conductivities. However, their combined effect on DT was significant. The insignificance of pH was probably due to the relatively weak organic acid used in the present study. A dimensionless correlation was developed to relate DT to the process variables. Developed dimensionless correlation involving the generalized Reynolds, Prandtl, and Grashof numbers, and, a dimensionless power ratio, could be used for estimating the temperature ratio across the RF applicator.
Session 15D, Food Engineering: Processing Technologies
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