Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences


Marie K. Walsh


Different fiber types were incorporated in an extruded expanded high-protein snack food. Three dietary fibers (powdered cellulose, wheat fiber, and oat fiber) were selected based on ease of extrusion, percent total dietary fiber, visible expansion, and commercial availability. A high-fiber, high-protein snack food containing whey protein, normal cornstarch, and pregelatinized waxy cornstarch was extruded using the three selected fibers. The fibers replaced the normal cornstarch at 30, 60, and 80% yielding extrudates with three fiber levels (18, 36, and 48%). Each treatment or combination of fiber type and extrudate fiber level was extruded in triplicate. A control with no fiber added was also extruded in triplicate.

Extrudate characteristics were evaluated on physical (expansion ratio, air cell size, density, and breaking force) and chemical (moisture content, water absorption index, water solubility index, water and total soluble protein , and water soluble carbohydrate) parameters. The physical and chemical characteristics of the extrudates were found to be greatly affected by combined interaction of the fiber type and level of fiber in the extrudate. As the amount of fiber in the extrudate increased, moisture content increased (p < 0.0001) associated with a decrease in expansion ratio (p < 0.0001), air cell size (p < 0.0001), and water solubility index (p = 0.0013) and increased extrudate density (p < 0.0001), breaking force (p < 0.0001), and water absorption index (p < 0.0001). Dependent extrusion parameters (pressure, motor torque, barrel and die temperature of the mix, barrel and die temperatures, residence time, and product flow rate) were recorded and analyzed. All dependent extrusion parameters were influenced by the level of fiber incorporation in the extrudates (p < 0.0001). The temperature at the die was also significantly influenced by the type of fiber used, and the level of fiber and fiber type interaction (p< 0.0001). Differences were deemed statistically significant at p < 0.05. The possibility exists to incorporate dietary fiber at levels > 30% in extruded whey and cornstarch products.