Environmental parameters-dependent self-assembling behaviors of α-zein in aqueous ethanol solution studied by atomic force microscopy

Atomic force microscopy was applied to characterize the self-assembling behaviors of alpha-zein molecules in 70% (v/v) aqueous ethanol solution under different parameters including alpha-zein concentration (0.001%-0.1%, w/v), pH (2.0-8.0) and the thermal treatment (90 degrees C, 2-24 h). alpha-Zein (0.1% and 0.01%, w/v) at pH 7.0 formed globules while alpha-zein assemblies (0.001%, w/v) exhibited the co-existence of worm-like strings, bundles of fibers, and rod-like fibers. Heating the aqueous ethanol solutions containing 0.001% (w/v) alpha-zein at 90 degrees C and pH 4.0 converted the irregular aggregates into regular spherical particles (100-120 nm), followed by fibrils (15-50 nm) at a prolonged times (8 h). Besides, fibrils were formed after heating aqueous ethanol solutions containing alpha-zein (0.001%, w/v) at pH 2.0 for 8 h. A two-step mechanism was proposed to explain such findings, which involved the aggregation of alpha-zein molecules to form aggregates, and followed by the rearrangement of alpha-zein molecules to form fibrils.