36D-34 |
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C. P. PANCHAPAKESAN, H. Dogan, and J. L. Kokini. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Functional properties of thin biofilms are a strong function of their molecular organization. Atomic Force Microscopy (AFM) has been used as an important characterization technique for macromolecules and polymer materials at molecular level. Our objective was to understand and observe the change in nano-level organization and properties of zein as a function of the effect of plasticizer content and compare the findings with results from traditional Differential Scanning Calorimetry (DSC). Zein films were spin-cast onto silicon wafers and analyzed for physicochemical characteristics by using AFM (Nanoscope IIIa, Digital Instruments, CA). Commercial zein was purified into Ą-zein, abundant protein fraction. The purity was evaluated by SDS-PAGE. Both unpurified and purified fractions were evaluated for topographical features at concentrations of 1-40 mg/ml in 70-90% ethanol solutions. Results were compared to Small Angle X-ray Scattering (SAXS). Force measurements were made on 16% w/v solvent-cast films to study the plasticizer effect (Aw: 0.12-0.97) on the molecular mobility of the film at nano-scale. Adhesive force of the films was used as a yardstick for molecular mobility and compared to traditional techniques (DSC). Topographical images of purified and unpurified fractions revealed clearly the presence of ellipsoidal rod like structures on the film surface, thus agreeing with previous studies on zein. Average film roughness ranged between 1-10 nm and thickness ~15nm. The effect of concentration of aqueous ethanol on the properties of the films was also examined. Adhesive force measurements indicated that the molecular mobility of the films at nano-scale levels increased with an increase in plasticizer content which simulated the findings of DSC measurements conducted on zein at macro-levels. The dependence of the nano-forces responsible for surface adhesiveness on the water activity of biopolymer matrix was characterized successfully. Topographical images and SAXS measurements helped in direct visualization and understanding the conformation of zein at nano-levels.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |