Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/5/2004
Publication Date: 9/20/2004
Citation: Lawton Jr, J.W., Sessa, D.J., Selling, G.W., Willett, J.L. 2004. Zein: a new look at an old industrial protein[abstract]. Association American Cereal Chemists. p.53:138.
Technical Abstract: Zein has been examined as a possible raw material for polymer applications since the early part of the 20th Century. Commercial production of zein did not start until the mid 1930's and for the next 20 years it was used in the manufacture of fibers, coatings, films, adhesives, and plastics. Most of the markets that zein once enjoyed were supplanted by petroleum-based materials. Zein is currently having somewhat of a renaissance in its examination and utilization. Of all the research done on zein, surprisingly little is known about its molecular structure and how its structure relates to its properties. Traditionally, zein has been classified as a prolamin (soluble in aqueous ethanol). Now, all proteins which reside in the protein body of corn are classified as zeins. Four types of zein are located in the protein body: alph, beta, gamma, and delta-zein. Only alpha-zein is a traditional prolamin. Commercial zein is mainly alpha-zein. How these other types affect the properties of zein is not really known. There is some speculation that these other zeins are associated with zein gelling. Water also is known to have an effect on zein. Water has long been known to be a plasticizer for zein. It has been demonstrated that zein solutions which contain water will gel and levels of this, should be kept at a minimum. Commercial zein containing water will become turbid over time and will eventually precipitate. Zein solutions in 70% aqueous ethanol become turbid faster than zein in 90% aqueous ethanol. Zein solutions that contain no water, like those prepared in 2-ethoxyethanol or 80% ethanol-20% acetic acid mixtures do not become turbid. Zein prepared in the laboratory contains all four types of zein. Solutions containing lab prepared zein and aqueous ethanol usually gel, but can also aggregate and precipitate. Zein gels put into aqueous ethanol containing guanidine HCI or into 100% glacial acetic acid can break up the gel. Water also affects the melt processing of commercial zein. When zein containing greater than 10% water was processed on a torque rheometer, a network formation occurred and the resulting torque increased exponentially over time. When triethylene glycol (TEG) was used as a replacement for water the ensuing torque increased linearly over time. Upon processing zein-water melts displayed multiple torque rises, that were not seen when TEG was used as a plasticizer for zein.