The Effect of Heating Rate by Ohmic Heating on Rheological Property of Corn Starch Suspension

摘要

Granule swelling is essential phenomenon of starch gelatinization in excess water, and characteristic of heated starch dispersion depends largely on size and distribution of swelled starch granule. Although swelling characteristic of starch granules depends on type of starch, heating rate, and moisture content, influence of heating rate on swelling phenomenon of starch granule has not been fully discussed, because constant heating rate of starch dispersion cannot be obtained by conventional heating method. Ohmic heating, electric-resistant heat generation method, applies alternative current to food materials, through which heating rate can be easily controlled precisely and conveniently at wide range of constant heating rates. Starch dispersion heated at low heating rates below 7.5°C/min showed Newtonian fluid behavior, whereas showed pseudoplastic behavior at heating rates above 16.4°C/min. Apparent viscosity of starch dispersion increased linearly with increasing heating rate, and yield stresswas dramatically increased at heating rates above 16.4°C/min. Average diameter of corn starch granules during ohmic heating was dramatically increased from 30.97 to 37.88 mu m by increasing hearing rate from 0.6 to 16.4°C/min (raw corn starch: 13.7 mum). Hardness of starch gel prepared with 15% corn starch dispersion after heating to 90°C at different heating rates decreased gradually with increasing heating rate, then showed nearly constant value from 9.4 to 23.2°C/min. Hardness increased with increase of heating rate higher than 23.2°C/min.