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Q. WANG and G. W. Padua. Dept. of Food Science & Human Nutrition, Univ. of Illinois, Urbana-Champaign, 382-D AESB, 1304 W. Pennsylvinia Ave., Urbana, IL 61801 Zein, produced from a renewable and sustainable source, has shown potential as food packaging material. Previously, zein was plasticized with oleic acid and formed into sheets and films. Physical properties of those samples are affected by film structure, which is controlled by the interaction between zein and plasticizer. However, the nature of those interactions is still not well understood. The objective of present study was to observe the dynamic adsorption of zein onto chemically different surfaces in order to further understand the mechanisms of film formation. Zein adsorption from isopropanol solutions, 0.05 to 0.5% w/v, onto self assembled monolayers (SAMs) of 11-mercaptoundecanoic acid and 1-octanethiol, on gold-coated glass slides, was monitored by high time resolution surface plasmon resonance (SPR). Surface topography of bare gold, SAMs, and zein deposits was examined by atomic force microscopy (AFM). SPR experiments indicated that zein adsorbed to both hydrophilic and hydrophobic surfaces and maximum surface coverage on both surfaces increased with zein concentration. However, the initial adsorption rate was higher for zein on 11-mercaptoundecanoic acid than on 1-octanethiol. This suggested that different adsorption mechanisms operated in each case. Moreover, zein affinity for hydrophilic SAMs was higher than for hydrophobic SAMs, as evidenced by the different initial slopes of the sorption isotherms. Flushing off loosely adsorbed zein allowed the observation of an apparent monolayer value, which was larger for zein on 11-mercaptoundecanoic acid than for zein on 1-octanethiol. This observation may be explained in terms of footprint size. Zein may have adsorbed to hydrophobic or hydrophilic SAMs utilizing different surfaces of its molecule. Present results support the view that the mechanism of formation of zein-oleate films involves an initial hydrophilic adsorption of fatty acids onto the zein surface followed by hydrophobic oleate-to-oleate and zein-to-zein associations leading to film structure organization.
Session 79, Food Chemistry: Protein and enzyme chemistry
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