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Modulating state transition and mechanical properties of viscoelastic resins from maize zein through interactions with plasticizers and co-proteins
D. P. ERICKSON (1), S. Renzetti (2), A. Jurgens (2), O. H. Campanella (1), B. R. Hamaker (1). (1) Purdue University, West Lafayette, IN, U.S.A.; (2) TNO Functional Ingredients Expertise Group, Zeist, Netherlands

Viscoelastic properties have been demonstrated in maize zein above its glass transition temperature and the protein has been explored as a possible replacement for wheat gluten in gluten-free dough systems. This functional change is believed to result from the development of fibrous, β-sheet-rich protein networks with different rheological properties. However, current understanding of how these viscoelastic polymers can be further manipulated for food applications is limited. This study serves to present a framework for the manipulation of state transition properties and viscoelastic nature of zein as driven by plasticizers and co-proteins. Using resins formed via precipitation from aqueous ethanolic environments, moisture sorption isotherms and glass transition profiles were constructed for zein, gluten, zein/oleic acid (at 20% and 30% oleic acid), and zein/casein (at 15% and 20% casein). Differences in the viscoelastic and extensional properties of these materials were assessed using small and large deformation rheological techniques. Oleic acid plasticization was shown to reduce water absorption and glass transition temperatures, and created low elasticity/high extensibility resins. Incorporation of casein yielded only slight increases in water absorption and glass transition temperatures, yet imparted a five-fold increase in material strength/elasticity. These findings demonstrate how specific protein-plasticizer and protein-co-protein interactions can impart fundamental differences to the behavior of zein in viscoelastic systems and could serve as a basis for improving the functional properties of this underutilized material. Plasticizers and co-proteins could be further applied to specific food and biomaterial systems for optimal performance with respect to moisture migration and/or mechanical properties.

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