Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 18, 2002
Publication Date: March 18, 2002
Interpretive Summary: Zeins, the maize storage proteins, are the most abundant proteins in the corn endosperm and account for more than half the total mass of the seed protein. The film-forming properties of zein have long been recognized. However pure protein films prepared from commercial zein are generally too brittle and exhibit tensile strength too low for most applications. Mechanical properties of zein films improve significantly when synthetic plasticizers or fatty acids are added. In this study, the effect of endogenous free fatty acids on the mechanical properties of films prepared from zein isolated from dry-milled, bulk yellow dent and ground hybrid corn was investigated. Results from this study indicate that zein isolates are an inexpensive and viable replacement for commercial zein. The blend of lipids in the isolate permit casting of clear zein films and the presence of endogenous free fatty acids obviate the need for added synthetic plasticizer. Scientists in government, academia, and industry involved in developing new packaging materials, should benefit from this research.
Technical Abstract: Dry-milled yellow corn and freshly-ground food and nonfood grade yellow and white hybrid corn kernels were pre-treated in a solution of lactic acid and sodium metabisulfite followed by extraction with 70% ethanol. Zein was precipitated from the extract by reducing the ethanol content of the extract to 40%. Lipid associated with the zein isolates was between 15 and 20% and contained mostly endogenous free fatty acids. The effect of the endogenous free fatty acids on zein isolate films, with and without free fatty acids, was determined by measuring various film properties. Stress- strain measurements indicated 40-200% more elongation for zein films containing endogenous free fatty acids. Films prepared from zein isolated from pre-ground corn stored for approximately 4 months (27 C, RH=17%) were greater than 3 times more elastic than zein films prepared from fresh- ground corn.