Thermodynamics of the Dimensional Changes in the Wheat Kernel during Cooking for Bulgur Production

Abstract

Thermodynamics and physical properties of the dimensional changes in the wheat kernel during cooking was carried out for bulgur production at 87, 92 and 97°C for 140min. There were determined changes of the length ( x-dimension), two widths ( y- and z-dimensions), weight, volume and density of the wheat kernel. The length of the wheat kernel during cooking decreased, although crease-side width ( y-dimension) and secondary width ( z-dimension) significantly increased ( p 0.05) at each cooking temperature between 6.95-68.05% and 9.95-69.00%, respectively. The volume of the kernel during cooking also significantly ( p 0.05) increased (27.35-185.20%), and had a greater percentage change value than the weight (19.25-160.70%) due to swelling of the wheat kernel. Therefore, density decreased negatively. Activation energy, enthalpy, entropy and Gibbs free energy were used to describe the changes of physical attributes of the wheat kernel during cooking. Rate constant values for the length and density of the wheat kernel were negative in contrast to positive rate constant values of the widths, weight and volume of the wheat kernel. The influence of cooking temperature on the physical properties of the wheat kernel revealed that the rate of change in the secondary width ( z-dimension), weight and density of the wheat kernel were more sensitive to temperature due to their greater activation energies, 5.95 107, 5.26 107 and 6.11 107 J, respectively. In contrast, the y-dimension of width of the wheat kernel required a lower amount of energy due to crease side. All of the changes in physical properties agreed with the positive values of Gibbs free energy.