Ohmic heating behavior of hydrocolloid solutions

Aqueous solutions of five hydrocolloids (carrageenan, 1-3%; xanthan, 1-3%; pectin, 1-5%; gelatin, 2-4% and starch, 4-6%) were heated in a static ohmic heating cell at a voltage gradient of 7.24 V cm(-1). Time and temperature data, recorded at selected time intervals, were used to study the effect of concentration and temperature on the ohmic heating behavior of hydrocolloi d solutions. Of the test samples examined, carrageenan gave the shortest ti me to raise the temperature from 20 to 100 degrees C: 4200, 1600 and 1100 s at 1, 2 and 3% concentration, respectively. For the same temperature raise , xanthan samples required 5500, 2300 and 1400 s at 1, 2 and 3% concentrati on levels. Pectin and gelatin samples were found to exhibit even lower, but similar heating profiles. At the highest concentration (5%), pectin took 7 300 s to reach 100 from 20 degrees C, and at all other concentrations, the time limit of 10 000 s was exceeded before it reached 100 degrees C. The te mperature of starch solutions never exceeded 62 degrees C within the specif ied time limit. Heating was found to be uniform throughout samples for carr ageenan, pectin (1-3%) and gelatin samples. For xanthan and starch solution s, some nonuniformity in temperature profiles was observed. The observed oh mic heating behavior of hydrocolloid solutions corresponded well with their electrical conductivity values. The homogeneity of heating was related to rheological properties of hydrocolloid solutions and their behavior at high temperatures. (C) 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.