Okara is a byproduct from the process of soybean foods, and is rich in proteins, fatty acids and dietary
fibers. Drying of wet okara is essential for long-term storage and its value-added applications. This study
applied response surface methodology and synthetic evaluation method to optimize the drying process
of okara in an air jet impingement drier (AJID). Air temperature (50e70 C), air velocity (1.3e2.3 m/s),
and sample loading density (3e4 kg/m2) were considered as treatment factors in the optimization, while
drying rate, color, trypsin inhibitor activity, soy isoflavone content and antioxidant activity were evaluated
as responding quality parameters. All treatment variables showed significant effects on the drying
rate and soy isoflavone content (P < 0.05). Higher temperature, higher air velocity and lower loading
density contributed to higher drying rate. Temperature and air velocity showed quadratic and interactive
effect on the antioxidant activity of okara. The optimum conditions for AJID of okara were identified as
70 C, 2.3 m/s air velocity, and 3 kg/m2 loading density. This process control study provided baseline data
for developing effective drying of okara using AJID.