Convective Drying Kinetics and Darkening of Okara

Okara pellets were dried in a pneumatic tube from 78% of moisture content (w.b.) to 64% and then in a rotational drum to 3%. Time, temperature, and drum rotation were correlated to the okara darkening. The temperatures used were 130, 150, and 170°C in the pneumatic tube and 50, 60, and 70°C in the rotational dryer. The rotations used for the drum were 27 and 47 rpm. When okara was dried only in the pneumatic tube it became dark; however, when dried in both the tube and the dryer the darkening level decreased significantly. The results showed that the first drying level temperature does not influence the drying time of the combined process.