Investigation of protein-fatty acid interactions in zein films.

摘要

Zein, the prolamin of corn, has shown potential as industrial biopolymer for packaging and agricultural uses. Previous researchers plasticized zein with oleic acid and extruded it into sheets and films. Such products showed reasonable tensile and water barrier properties. However, those properties were affected by film structure, which is believed controlled by the interaction between zein and plasticizer. The nature of those interactions is still not well understood.; Protein-fatty acid interactions in zein resin films were investigated by surface plasmon resonance and atomic force microscopy in this work. Preliminary research was conducted to establish the effect of solvent systems on the plasticization of zein by oleic acid. Although slight differences were observed, it was concluded that the use of 75% ethanol or 75% 2-propanol produced similar results.; Surface plasmon resonance was employed to investigate zein static and dynamic adsorption on surfaces of hydrophilic and hydrophobic self-assembled monolayers (SAMs) generated by 11-mercaptoundecanoic acid or 1-octanethiol, respectively, and representing the two end groups of oleic acid. Results indicated that zein was adsorbed to both surfaces but showed higher affinity for hydrophilic groups. The corresponding thickness of zein specific binding layer on hydrophilic and hydrophobic SAMs was around 4.7 nm and 4.6 nm. Zein exhibited higher affinity for hydrophilic than for hydrophobic SAMs evidenced from the higher initial adsorption rate and ultimate surface coverage at all zein concentrations. Flushing surface with buffer would leave an apparent monolayer of zein, which is 5 times higher for hydrophilic than hydrophobic SAMs. This observation suggested that zein may use different sides of its molecule to interact with hydrophobic or hydrophilic groups. The surface topography of zein deposits on both SAMs was examined by atomic force microscopy. It was found that zein formed distinct ring-shaped structures with height of ∼35 nm on hydrophilic SAMs when exposed to water.; Results suggested that formation of zein-oleate films may involve an initial hydrophilic adsorption of oleic acid onto zein followed by development of hydrophobic associations leading to film structural organization. Results from this study provide new insight on the mechanism for zein-oleic acid resin formation.