Water and calcium uptake by corn kernel during alkaline treatment with different temperature profiles

In the present work we investigated the joint kinetics of the overall water and calcium uptake in Yellow Dent corn during the alkaline treatment process with three different temperature profiles. The behavior of the difference of moisture gain and calcium gain in the whole grain and the behavior of calcium gain in the pericarp and in the internal part of the grain suggest that the water and calcium uptake in alkaline solution is a complex process governed by a series of kinetic stages of diffusion and reaction with loss of material. Results show that even though the diffusion pathways for the water and calcium uptake during alkaline treatment are the same, the rates of diffusion and reaction with loss of material of water and calcium in different component parts of the grain are different and greatly influence by temperature. Comparing the three kinetic stages observed during soaking at room temperature (24 °C) the effect of soaking at an initial boiling temperature value of 98 °C was found to accelerate the three kinetic stages by 1080 min and to observe an additional fourth kinetic stage during the last minutes of the soaking period. The results also show that the alkaline cooking at 98 °C of the corn kernel during 15 min greatly accelerates the calcium reaction with pericarp material that results in the loss of most of the pericarp structure during the first 30 min of the steeping stage. Comparing the four kinetic stages observed during soaking at an initial boiling temperature value the effect of the cooking period was found to accelerate the four kinetic stages by 1155 min and to observe an additional fifth kinetic stage during the last minutes of the steeping stage.