Foaming Kinetics Study of Molten Potato Starch Using a Cambridge Multi-Pass Rheometer (MPR)

This paper provides an overview of recent experiments and modelling carried out in relation to the foaming kinetics of molten potato starch containing an adjusted water content of 30 wt%. The paper describes the experimental protocol necessary to form a clear, optically transparent starch melt held within a confined volume between two hydraulically-driven pistons of the Cambridge Multi-Pass Rheometer (MPR). Isothermal pressure release experiments were conducted using the MPR and the kinetics of water vapour bubble growth was followed optically by capturing pictures using a CCD camera during the depressurization process of starch melt, which was maintained at elevated temperature and pressure. It was found that a higher pressure release rate, achieved by increasing the rate at which the pistons of the MPR were drawn apart, produced a larger population of smaller water vapour bubbles at a faster bubble growth rate. A summary of a matching single-bubble growth model is also described. Both the experimental and modelling results provide an insight into the way foaming occurs within starch melts containing water.