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Ohmic heating of viscous liquid foods

The technical feasibility of ohmic heating was evaluated for viscous liquids in static ohmic heating cells in three stages. First, electrical conductivities and time/temperature profiles were measured and compared for selected hydrocolloids (carrageenan, gelatin, pectin, starch and xanthan) in water at various concentrations (1--6%). Of the thickening agents examined, carrageenan gave the highest value for electrical conductivity and the shortest time to raise the temperature from 20 to 100°C. It was followed by xanthan. Pectin and gelatin samples were found to exhibit lower, but similar electrical conductivities and heating profiles. Starch samples had the lowest electrical conductivity and the temperature of starch solutions never exceeded 62°C within the specified time limit of 10000 s. / In the second stage, the effect of salt and acid concentration was evaluated on electrical conductivities and time/temperature profiles of the above selected hydrocolloids in water solutions at a concentration necessary to achieve a similar apparent viscosity of 0.2 Pa.s at 300 s-1 and 20°C (carrageenan 1.7%, pectin 2.5%, starch 4.3% and xanthan 2%). / In the third stage, measurements of electrical conductivities, time/temperature and heating rate profiles were performed applying six voltage gradients (5.26, 7.14, 13.16, 17.86, 21.05 and 25 V/cm), with two electrode cross-sectional surface areas (19.84 and 37.95 cm2) and the electrodes separated at three specific distances (10.05, 14.33 and 20.01 cm) at 150 V. Applied voltage gradients had a major effect on temperature and heating rate profiles but no effect on electrical conductivities. / Rheological properties of carrageenan, pectin, starch and xanthan solutions were investigated at various temperatures (20--80°C) and concentrations (carrageenan 1.5, 1.7 and 1.9%; pectin 2.3, 2.5 and 2.7%; starch 3.8, 4 and 4.2%; xanthan 1.6, 1.8 and 2%) in the presence of 1% salt. Both temperature and concentration influenced the rheological properties of solutions. / Finally, electrical conductivity measurements and rheological properties of starch at 4% and 1% salt were used as input to evaluate a theoretical model for the electrical, thermal and flow behaviour in a continuous ohmic heating unit. (Abstract shortened by UMI.)

Identiferoai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36036
Date January 1999
CreatorsMarcotte, Michèle.
ContributorsRamaswamy, Hoshahalli (advisor)
PublisherMcGill University
Source SetsLibrary and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada
LanguageEnglish
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation
Formatapplication/pdf
CoverageDoctor of Philosophy (Department of Food Science and Agricultural Chemistry.)
RightsAll items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated.
Relationalephsysno: 001687494, proquestno: NQ55357, Theses scanned by UMI/ProQuest.

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