Understanding the Impact of Extrusion Processing on Rheological, Textural and Functional Properties of High-protein, High-fiber Extrudates
Dissertation - Open Access
Doctor of Philosophy (PhD)
Department / School
Agricultural and Biosystems Engineering
apple pomace, chickpea, distiller's dried grains, extrusion, grape pomace, single and twin screw extruder
Extrusion processing is a technology widely used to make ready-to-eat snack and breakfast cereal products. Expanded products mainly consists of high levels of starch resulting in optimal texture and consumer acceptance. However, these products are usually low in nutritional value. One of the many alternatives are to combine legumes and cereals to improve the protein quality of the product. Another possibility is to enhance the nutritional value by incorporating fruits and vegetables. Fruits and vegetables are consistently under-consumed by the American population and incorporation into extruded products may help increase the intake of important nutrients, such as dietary fiber. The study was divided in to three parts. In the first part, a lab-scale single screw extruder was used for processing directly expanded corn based products containing varying proportion of apple pomace and defatted soy flour. Experimental design with apple pomace level (0 to 20%), barrel and die temperature (100 to 140°C), screw speed (100 to 200 rpm), and moisture content of blend (14 to 20% wet basis) as independent variables produced 27 different combinations that were studied using response surface methodology to investigate the effect of these variables on system parameters (apparent viscosity, mass flow rate, torque, die pressure, dough temperature, and SME). As the temperature profile increased, apparent viscosity, die pressure and specific mechanical energy decreased. Increasing AP content in the blends significantly (P0.05) on mass flow rate. SME also increased with increase in the screw speed which could be due to the higher shear rates at higher screw speeds. Screw speed and moisture content had significant negative effect (P< 0.05) on the torque. The apparent viscosity of dough inside the extruder and the system parameters were affected by the processing conditions. FDDG incorporation had a significant effect on the total dietary fiber, color parameters and the functional properties of the extrudate snacks. Desirable expanded extrudates with high level of total dietary fiber were obtained with blends containing 20 % FDDG at 140°C extrusion temperature, 167 rpm screw speed and 19% feed moisture content. In the third part, twin screw extrusion of defatted soy flour and corn grits blends enriched with apple and grape pomace were conducted in two separate studies. Apple pomace-defatted soy flour-corn grits blends were extruded in a conical counter rotating twin-screw extruder. Response surface methodology using a central composite design was used to evaluate the effects of independent variables, namely apple pomace level (0-20%), die and barrel temperature (100-140°C), screw speed (100–200 rpm) and moisture content (14-20 % wb) on the product responses (expansion ratio, bulk density, water absorption index, water solubility index, texture and color). The product responses were most affected by changes in moisture content, pomace level and to a lesser extent by screw speed. Numerical optimization studies resulted in 15% pomace level, 110oC temperature, 175 rpm screw speed and 15.5 % moisture content as optimum variables to produce acceptable extrudates. Structural observation of the extruded snacks was also conducted. Pomace level and processing conditions significantly affected the internal structure of the extrudates. Porous structure exhibited crispness and compact structure indicated dense product. FTIR analysis was carried out to understand the changes in the polysaccharide and amide bonds in the extrudate snacks. Different ratio of grape pomace was mixed with defatted soy flour mixed and corn grits for the development of extrudates using conical twin screw extruder. Response surface methodology was used to investigate the effect of grape pomace level and extrusion processing conditions on the product properties. Five different blends at a level of 0-15 % w/w grape pomace (GP) were extrusion cooked with varied barrel and die temperature (100-160°C), screw speed (100-250 rpm) and feed moisture (15-25 % wet basis). Increasing GP content in the blends significantly (P
Library of Congress Subject Headings
Apple industry -- By-products.
Grape industry -- By-products.
Enriched cereal products.
Snack foods -- Extrusion.
Includes bibliographical references (pages 251-280)
Number of Pages
South Dakota State University
Singha, Poonam, "Understanding the Impact of Extrusion Processing on Rheological, Textural and Functional Properties of High-protein, High-fiber Extrudates" (2017). Electronic Theses and Dissertations. 2144.