Submitted to: International Journal of Food Properties
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 2006
Publication Date: November 1, 2006
Citation: Tunick, M.H., Onwulata, C.I. Rheological properties of extruded milk powders. International Journal of Food Properties. p.835-844. Interpretive Summary: Whey, which is a byproduct of cheesemaking, contains high-quality protein that can improve the nutritional quality of snacks and other foods. Whey protein powder may be altered by processing it with water in an extruder, where it is kneaded and sheared with heat to obtain a product with a different texture. Tests showed that extruded products were liquid, soft, or hard depending on the temperature and amount of water used in the process. These variations were not seen when skim milk powder was extruded. The results show that extrusion changes the structure of whey protein in predictable ways, which could lead to their use in more products and therefore improve the nutrition of consumers.
Technical Abstract: Whey protein concentrate (WPC), whey protein isolate (WPI), and nonfat dry milk (NDM) may be processed through a twin-screw extruder to produce ingredients for protein-fortified food. The products ranged from rigid to flexible to soft, and small amplitude oscillatory shear measurements showed that these properties varied with extrusion temperature and moisture content. The elastic modulus decreased as moisture increased for extrusion temperatures below 100 deg C. The values for loss modulus (an indication of the solid-like nature of the sample) for the whey protein extrudates at 50 and 75 deg C were frequently > 0.5, evidence that these samples were fluid-like. The values for extruded NDM were always in the 0.19-0.32 range, indicating that these samples were quite solid. WPC and WPI showed different effects than NDM due to the type and amount of protein present. The characteristics of extruded milk powders can be manipulated through processing parameters to obtain texturized products with the desired rheological properties.