A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1998

Soy pulp or okara powders were prepared in natural state or by steaming the raw okara at 100 °C for 30 minutes, by dehydrating using a hot-air oven and a drum dryer, and then grinding to powdery form. Hot-air drying was employed at 70, 80, 90 °C by keeping the air flow rate and thickness of okara in the tray to be constant. In drum drying process the variables consisted of initial moisture content of okara, drum surface temperature, drum gap and rotation speed of drum. Performance of drying processes and properties of dried okara were evaluated. The okara powder obtained was then used to replace 10, 20, 30 % of wheat flour in the cookie for evaluation of acceptability. The results showed that drum drying rates of okara were quiet higher than hot-air drying rates. In the present study, drum drying rate of okara varied linearly with initial moisture content of okara, drum surface temperature, rotation speed of drum, and inversely with gap between the drums. Variation of initial okara moisture content, rotation speed of drum, and drum gap respectively showed the most significant effects on the drying rate of okara. The lipid contents, density, and pH of drum dried okara powder did not relatively change due to variations of drum drying process. Conversely the viscosity, water and lipid absorption were slightly disturbed as protein was denatured by different heating effects. The color of drum dried okara powder was brighter than hot-air dried okara powder due to less occurrence of browning. The cookie prepared by using hot-air or drum dried okara powder to replace maximum 20 % wheat flour part were well accepted. It was evident that steaming process of the raw okara prior to drying could increase the acceptability of okara powder to be used as cookie ingredient.