KINETICS OF HYDRATION OF RAW AND ROASTED CORN SEMOLINA

Hydration of raw and roasted corn semolina at 30, 50 and 70 degrees C shows that raw semolina absorbs more water, has higher equilibrium moisture content and hydration rate constant values than roasted semolina. The rate of hydration is linearly related to average moisture content. Hydration rate index (HRI), defined as the change of hydration rate constant per unit change in hydration temperature (Delta k/Delta T), is determined for raw and roasted semolina. The activation energies for raw and roasted semolina are 10.6 and 7.7 kJ mole(-1), respectively. Studies on the volume increase and leaching loss of semolina at 30-100 degrees C show that hydration temperatures above 70 degrees C markedly increase the per cent volume increase and the leaching loss. These two values are higher for raw semolina than roasted samples.