Modeling extrusion process and reaction kinetics in a twin-screw extrusion system

Extrusion process is an important food manufacturing method with variable thermal and mechanical energy inputs. Although the effect of extrusion conditions on the properties of extruded starch based foods has been previously studied, using one-variable-at-a-time approaches or response surface methodology, data on the effect of extrusion cooking conditions on the color of the product are scarce and the reaction kinetics of starch extrusion are still not fully understood. Research is necessary to construct the mathematical modeling or reaction kinetics modeling about the effect of interactions of process variables on the property attributes (especially color development and starch transformation) of starch based foods during extrusion. The objective of this research is to understand the operating characteristics of the extrusion process with mathematical modeling and to provide engineering understanding of the interactions between extruder designs, material characteristics, and the operating conditions of the extruder to gain an insight into the operating characteristics of this thermal and mechanical extrusion process. Detailed research was conducted on property changes during extrusion', extrusion process modeling, residence time, extrusion color development, and reaction kinetics modeling of starch transformation, all of which will help improve understanding of the extrusion process. Mathematical models for predicting die pressure, product temperature, shaft torque, specific mechanical energy input, and mean residence time based on rice flour extrusion using a twin-screw extruder were proposed. The validity of the developed models was extensively evaluated, tested, and verified using different screw geometries, and other processing variables with reasonable accuracy. A computer vision method was developed to determine the color change of a rice-glucose-lysine blend during extrusion. The browning properties of extrudates were modeled, tested, and verified at various screw configurations and extrusion conditions with reasonable accuracy. Starch gelatinization was also modeled as a function of extrusion system and process parameters. Reaction kinetics models were developed to predict water solubility index during extrusion. The applicable modeling methods can be used to simulate different extrusion conditions for process control, process optimization, and product design.