Improved Utilization of Dairy Proteins: Coextrusion of Casein and Wheat Flour

Coextrudates were produced from mixtures of rennet casein and wheat flour by thermal extrusion using a Creusot-Loire BC 45 twin screw extruder. The influence of casein and moisture in the feed material and processing variables was investigated by response surface methodology. Dependent variables included expansion, Warner-Bratzler shear values, and responses of a trained texture profile panel. All product characteristics investigated, with the exception of flavor, could be predicted from independent variables of the multiple regression equations. Addition of rennet casein did not alter the normally bland flavor of extruded starches. Casein at 10 to 30% of the total solids did not influence significantly any of the extrudate characteristics, which were governed primarily by moisture content. The two major physicochemical reactions thought to be taking place during the extrusion process were starch gelatinization and protein texturization. Although it was not possible to determine directly the degree of each process, an examination of the role of the independent variables, extrudate microstructure and sensory breakdown, suggested that starch gelatinization plays a dominant role in dictating product characteristics. Casein may be used in a protein-fortified, extruded wheat flourbased product at the contents studied without altering the characteristic bland