Starch removal treatment, not the specific thermal processing techniques, improved protein digestibility of corn (Zea mays) gluten meal

Abstract

Corn gluten meal (CGM) is a promising alternative protein source for human consumption, yet it remains under utilized due to its low protein digestibility and poor functionality. Thermal processing techniques have been demonstrated to effectively improve digestibility of plant proteins. The presence of other components such as starch also play a vital role in protein digestibility. However, the impact of starch removal and various thermal processing methods (such as microwaving, extrusion, heating, and baking) on the in vitro protein digestibility of CGM, as well as the underlying mechanisms, remains unexplored. This study demonstrated that the applied thermal processing did not significantly enhance CGM protein digestibility, while starch removal using α-amylase significantly improved protein digestibility by 26.3%–37.8% (P < 0.05). The elevated protein digestibility resulting from starch removal could possibly be attributed to the improved water absorption capacity and zeta potential, reduced disulfide bond content and particle size, and changes in secondary structures from ordered β-sheet to disordered random coils. The altered surface morphology with more pores and lower aggregation, as evidenced by SEM and CLSM images, also contributed to the increased digestibility after starch removal. This study presented novel evidence supporting the potential applications of CGM with removed starch as a sustainable protein source with enhanced digestibility and has unraveled its underlying chemistry mechanism.