Stochastic modeling of expansion of starchy melts during extrusion

Abstract

The objective of this study was to develop a stochastic model for flow behavior of starchy melts inside an extruder barrel and bubble growth dynamics after exiting the extruder and obtain the variability of the end product characteristics, using the variability of operating conditions (screw speed, water injection) and material properties (consistency coefficient). The model was written in Visual Basic and experimentally validated using pilot-scale twin screw extrusion of corn meal based expanded products. Process and product data was measured at different in-barrel moisture contents (19–28 g/100g dry basis) and screw speeds (250–330 rpm). The variability in input parameters was characterized using a Data Acquisition System and Monte Carlo Simulation was used to incorporate this variability into the model. The coefficient of variation (CV) of expansion ratio obtained from the model (0.24–3.11%) compared well with CV of the experimental expansion ratio (2.54–4.89%). This model was also used to conduct sensitivity analysis for understanding which raw material and process characteristics contribute most to product variability. Sensitivity analysis showed that the relative increase in CV of expansion ratio was affected more by the CV of water added in extruder (160.5%) as compared to screw speed (3.25%) and consistency index coefficient (25%).