15D-31 |
Electrical conductivities and the ohmic heating behavior of two phase food systems |
M. R. ZAREIFARD1, M. Marcotte1, H. S. Ramaswamy2, and M. Trigui1. (1) Food Research & Development Centre, Agriculture & Agri-Food Canada, 3600 Cassavant Blvd. W., Saint-Hyacinthe, QC J2S-3E8, Canada, (2) Dept. of Food Science & Agricultural Chemistry, McGill Univ., Macdonald Campus, 21111 Lakeshore Rd., Sainte-Anne-de-Bellevue, QC H9X 3V9, Canada During ohmic heating of two-phase foods, the overall resistance of food materials controls the heating rate. There are many factors affecting its value and homogeneity: size, concentration and location of particles, fluid and particle electrical conductivities (ECs), specific heat and process temperature. The ohmic heating behavior and the ECs of two-phase food systems were studied. The objectives were (1) to measure temperature profiles as influenced by particle size and concentration (2) to determine the heating behavior as affected by the location of particles in parallel, in series or in well-mixed conditions (3) to evaluate overall ECs as affected by particle size and concentration and process temperature. A 4% w/w starch solution and 0.5% w/w salt was used. Carrot puree and cubes (6 & 13 mm) were prepared. Food systems were selected by combining various percentages (0 to 60 % w/w) of carrot materials in starch solutions. Ohmic heating was applied using a static cylindrical cell (I.D.: 35 mm, L: 20 mm) bounded with two electrodes at a constant voltage gradient of 12.5 V/cm. The heating time to reach 80°C from 20°C increased as particle size and concentration increased. Overall ECs varied from 0.2 to 1.8 S/m increase for the range of temperature. It decreased as particle size or concentration increased. The heating behavior of the liquid and solid phase could be opposite depending on particles location. A slight difference was obtained on overall ECs if liquid and solid phases were separated as compared to well-mixed conditions. ECs were mainly reported for liquid foods containing very fine particles of different concentrations. Very little has been published on the ECs of two-phase food systems containing large solid particles at different concentrations. These data can be used for process design purposes.
Session 15D, Food Engineering: Processing Technologies
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