Two approaches have demonstrated the ability to influence
zein's viscoelastic properties: (i) plasticizers and (ii) co-protein
interactions. Plasticizers are commonly employed to enhance
polymer flexibility by means of reducing its glass transition temperature
such that the polymer exists in its rubbery state at lower
temperatures and/or moisture contents. Oleic acid in particular has
been the subject of several investigations on zein plasticization, due
to its demonstrated strong ability to influence the microstructural
and tensile properties of zein film and resin systems (Lai and Padua,
1997; Budi Santosa and Padua, 1999). To explain the oleic acid's
plasticizing effect on zein, Lai et al. (1999) proposed that oleic acidforms intermittent, liquid-like phases, which surround stacked zein
platelets and improves material flexibility by forming a threedimensional
sponge-like network (Wang et al., 2008). More
recent work on zein film systems alludes to a somewhat more
complicated mechanism of action. Xu et al. (2012) suggested that
the amphiphilic nature of oleic acid changes the supermolecular
structure of zein and allows the fatty acid to serve as an internal (i.e.
molecular) plasticizer for the protein.