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Extruder Operation Effect on Whey Protein Tensile and
Moisture-Barrier Properties
By
Daniel Rauch, Kathryn L. McCarthy and John M. Krochta
University of California, Davis, CA
2008
Poster Presentation (PDF)
Edible films sealed into pouches have potential for increasing shelf life and decreasing conventional packaging for foods. While solution-cast edible films are important for determining properties of films formed as coatings on foods, a more efficient way of producing stand-alone films for pouches is needed. Extrusion is a method for producing edible films that is comparable to production of synthetic film packaging. The objective of this research was to determine how processing conditions, including extruder screw speed and input feed rate, affect the properties of the films being formed. This information is essential for maximizing desirable film characteristics while minimizing undesirable traits. Whey protein isolate (WPI), glycerin (GLY), and water were fed to a twin-screw co-rotating extruder (APV, Staffordshire, England) and edible films were produced. The films were made in a 1:1 ratio (WPI:GLY) on a dry basis (DB). The screw speeds and feed rates were varied independently from 100 to 150 rpm and 15 to 25 g/min, respectively. Experimental responses were analyzed using ANOVA and response surfaces. Extruder torque, die pressure and mean residence time (MRT) were determined, and film water vapor permeability (WVP), tensile properties and color were measured. ANOVA showed that increasing the extruder feed rate increased extruder torque and die pressure and film Young’s Modulus, but decreased extruder MRT and film a* and b* color values (p < .05). Additionally, increasing screw speed decreased extruder torque and pressure, as well as film tensile strength and Young’s Modulus (p < .05). Ability to extrude WPI films extends their usefulness in food packaging. This research shows that extruder operating conditions have considerable effects on production of films, allowing optimization of film properties.