To increase the purity and yield of mung bean protein concentrates obtained by dry separation, the state of the powder was optimized from the milling to air classification processes. Relatively coarse milling (rotator frequency 40 Hz) by a full-scale airflow impact mill generated sufficient detached protein bodies while not overly damaging the starch granules. Subsequently, a higher classifier wheel frequency (50-70 Hz), an induced-draft fan frequency (50-70 Hz), and a lower feed rate (1.0-6.0 kg/h) reduced the cut point and fish-hook effect, thereby contributing to the improvement of protein separation efficiency. Under optimal conditions designed by response surface methodology (RSM), the protein concentrates with separation efficiency 84.0 +/- 4.4% and superior free radical scavenging capacity when compared with original flour and protein isolate (wet) was obtained. These results provide insight into the critical parameters affecting powder state, thus facilitating the development of a dry separation method to fractionate mung bean protein. (C) 2020 Published by Elsevier B.V.