100B-26 |
Compression-molded whey protein films:effect of moisture and glycerol content on water vapor permeability, protein solubility and mechanical properties |
R. SOTHORNVIT1, C. W. Olsen2, T. H. McHugh2, and J. M. Krochta3. (1) Dept. of Food Engineering, Faculty of Engineering, Kasetsart University, Kamphaengsaen campus, Nakornprathom, 73140, Thailand, (2) USDA-ARS-Western Regional Research Center, 800 Buchanan St., Albany, CA 94710, (3) Dept. of Biological & Agricultural Engineering, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616-5200 Whey protein isolate (WPI) film formation by compression molding (2-3 min) to time-consuming solvent casting (hours) was studied as an alternative method. Our objective was to determinate the effect of WPI moisture content and glycerol content and molding temperature and pressure on WPI film water vapor permeability (WVP), solubility and mechanical properties. WPI powder and either 30, 40 or 50% (w/w) initial moisture content (M) or glycerol content (Gly) were thoroughly mixed. Films were formed by pressing either a WPI-M or WPI-Gly mixture at a selected temperature in the range 104-140 oC and pressure in the range 0.81-2.25 MPa for 2 min in a Carer Press. The Modified Cup Method, the bicinchoninic acid protein assay and an Instron machine were used to determine film WVP, solubility and mechanical properties, respectively. Films could be formed with WPI at each M or Gly content at temperatures between 104 and 140 oC. Films without Gly were insoluble and had WVP independent of WPI moisture content and molding temperature and pressure (p>0.05). In contrast, films made from WPI-Gly mixtures at 104 oC were soluble and showed hydrogel behavior. WPI-Gly films made at 140 oC were insoluble and had WVP similar to films from solvent casting. Molding temperature and pressure did not significantly affect film elastic modulus (EM), tensile strength (TS) and % elongation (% E) (p>0.05). Increasing the Gly content of compression molded films decreased EM, similar to solvent cast WPI films. Compression molded WPI film TS and % E were greater than values from solvent cast films with same amount of Gly. The compression molding method consumes less time for film formation and produces films with properties similar to solvent cast films. These results indicate the possibility of forming pouches for milk powders and other dry foods and ingredients by the extrusion process.
Session 100B, Food Packaging
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