Zein has been commercially available for over 60 years and is currently used as a specialty coating because of its excellent film forming capabilities.
However, the scope of its applications have been limited by its inherent yellow color and off-odor.
That is until now. ARS scientists have been researching ways to efficiently eliminate the yellow color and odor problems which have made that protein difficult for commercial applications such as cosmetic formulations.
Hydrogels and microspheres from purified zein
Research chemist, David Sessa, has been working on this problem at the ARS, National Center for Agricultural Utilization Research, in Peoria, Illinois, USA - work that has culminated in devising a purification method.
With the purified zein, he developed methodologies to produce zein hydrogels and microspheres.
Hydrogel polymers are particularly useful for their water absorbancy properties and are commonly used in diapers and contact lens solutions.
Microsphere polymers are hollow spheres that are frequently used in cosmetic formulations to give a silky feel.
Two important features of zein-based hydrogels and microspheres is that zein is resistant to bacterial growth and it breaks down to harmless amino acid byproducts, the building blocks of protein.
The zein purification process
Sessa examined the removal of yellow color and odor from the ground up by first identifying the causative factors.
He identified the yellow color as xanthophylls and the major contributor of the off-odor as an amine compound that binds tightly to the protein.
He then devised a simple colorimetric assay that could be used to follow their removal.
Activated carbons (AC), which are porous and charcoal-like, will remove the color and odor compounds.
However, ACs not only bind those components, but also, bind considerable amounts of zein protein which cause losses of 37 – 95 percent of the corn protein in the process.
With the aim of developing a more efficient purification process with a better recovery of a purified zein product, Sessa explored a variety of methods.
The most promising is based on the use of zeolites which are porous, clay-based particles that entrap the low molecular weight color and odor causing components.
In a multi-columnar, pilot-scale system that Sessa co-designed, an algorithm can be devised to selectively switch the flow of pumped zein solutions through selective combinations of columns.
This tactic can lead to an efficient purification scheme, which in tur means that the purified zein recoveries are much improved when compared with AC treatments.