Submitted to: Journal of Cereal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/16/2007
Publication Date: 1/7/2008
Citation: Kim, S., Xu, J. 2008. Aggregate formation of zein and its structural inversion in aqueous ethanol. Journal of Cereal Science. 47(1):1-5. Interpretive Summary: Recently, a new methodology for the production of biodegradable polymer composites that will potentially replace existing petroleum-based polymers was introduced at NCAUR. Unlike conventional techniques that produce polymer composites by mixing the component materials in the extruder at high temperature, the newly developed particle-bonding technique requires neither extrusion nor processing at high temperatures. Instead, micrometer-scale raw materials are coated with a corn protein, zein, and compressed to form a rigid material. The most important step of this procedure is coating the raw materials with zein. This research offers both theoretical and experimental explanations on how micrometer-scale raw materials are coated with zein. This research offers a theoretical background on the behavior of zein whereby we can understand how the new process for the production of degradable biopolymer composites works. Scientists and manufacturers in industry and academia developing new biodegradable polymer materials would benefit from this work.
Technical Abstract: 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 that 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 a micelle-like structure formation 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.