Bioplastic film making properties of quality protein maize (QPM) zein

Abstract

BACKGROUND AND OBJECTIVE : Quality protein maize (QPM) has abundant γ-zein, which crosslinks itself and other zeins through disulfide bonding. The work aims to develop zein bioplastics with better functionality by using QPM zein. Physical properties of cast QPM zein films from QPM maize were compared with zein films from regular maize types and commercial zein, all without added plasticizers. FINDINGS : QPM zein contained 3.8% cysteine compared with 1.8%–2.7% in regular maize zeins and 1% in commercial zein and the QPM zein had a much higher proportion of γ-zein. QPM zein films cast from glacial acetic acid (GAA) were opaque but absorbed the least liquid (≈16%) and swelled less (≈11%) after buffer immersion than the other zein films and aqueous ethanol-cast films. Notably, the GAA-cast QPM zein films became highly flexible after ambient storage, whereas the other zein films remained brittle. CONCUSIONS : The low buffer uptake and swelling of QPM zein films is attributed to crosslinking involving the cysteine-rich γ-zein polypeptides. Their flexibility is attributed to better solubilization of the zein in GAA and water molecules bound to the γ-zein polypeptides acting as a plasticizer. SIGNIFICANCE AND NOVELTY : QPM zein can enable the formation of flexible zein bioplastics without added plasticizers.