Viscoelastic properties have been observed in maize zein above its glass transition temperature; however, current understanding of how these viscoelastic polymers can be further manipulated for optimal performance is limited. Using resins formed via precipitation from aqueous ethanolic environments, this study presents a framework for understanding how state transition and viscoelastic properties of zein can be controlled through interactions with plasticizers and co-proteins. Resins plasticized with oleic acid exhibited reduced water absorption and glass transition temperatures and formed low elasticity/high extensibility resins. Incorporation of casein increased water absorption and glass transition temperatures and imparted a four-fold increase in material strength/elasticity, as compared to zein alone. Plasticizers and co-proteins influenced zein secondary structure in the resin systems by decreasing and increasing low-frequency β-sheet structures (1640-1615cm-1), respectively. This work demonstrates that specific protein/plasticizer and protein/co-protein interactions are capable of promoting fundamental differences to zein's behavior in viscoelastic systems and could serve as a basis for improving the functional properties of this underutilized material in various food and biomaterial applications.