A novel method was developed for concentrating proteins from sorghum flour utilizing a combination of extrusion and alpha-amylase treatment for starch liquefaction. A central composite design was used to optimize in-barrel moisture content (MC). enzyme concentration during extrusion (E1) and post-extrusion enzyme concentration (E2) in order to produce sorghum protein concentrates with high protein content (PC) and in vitro protein digestibility (D). Extrusion-enzyme liquefaction yielded concentrates with higher protein yield (82 db%) and digestibility (66%) than batch liquefaction alone because extrusion promoted starch and protein degradation. The optimum conditions for developing a sorghum protein concentrate with both high yield and digestibility were 32% MC, no E1, and 2.5% E2. The sorghum protein concentrate developed in this study can augment the nutritional value of gluten-free foods for individuals suffering from celiac disease and other forms of gluten and wheat intolerance. (C) 2011 Elsevier Ltd. All rights reserved.