Aggregate formation of zein and its structural inversion in aqueous ethanol

Zein is a prolamine of maize. Conventionally, 70–90% aqueous ethanol is used to dissolve zein. When the hydrodynamic radii of zein molecules in aqueous ethanol were monitored with a dynamic light scattering instrument, it was found that zein aggregates in the solvent and the degree of aggregation depends on the composition of the solvent mixture. As the ethanol content of solvent increased from 70% to 90%, the aggregation number of zein molecules decreased from 10,000 until it reached a minimum. The aggregation number then increased abruptly to greater than 10,000 as the ethanol content of the solvent mixture increased to 92%. Since zein has amphiphilic characteristics, this behavior was interpreted as the formation of a micelle-like structure in its solution whereby ca. 90% ethanol that showed minimum aggregation number is regarded as a structural inversion point. This point of view was supported by a simple experiment that showed selective interaction of zein molecules with hydrophilic or hydrophobic particles.