Characterisation and modelling of specific enthalpy and heat conductivity of corn grits under consideration of water sorption behaviour

摘要

Extrusion of starch is a common process not only in food industry, but also for technical applications. In this context, a special type of extruder with a very short plastication unit allows the processing of foamed products like loose-fill based on non-modified, starch-containing raw materials. A crop product which has been defined as very suitable for this process is corn grit. In order to describe the process behaviour of an extrusion machine, the knowledge of the relevant material properties is indispensable. This paper provides results from investigations focused on the determination of material data like specific enthalpy (SE) Delta h and heat conductivity (HC) lambda. Both characteristics increase with rising temperature and water content. Based on these experimental results, mathematical models have been formulated in order to calculate the specific enthalpy and heat conductivity in dependence on temperature and moisture content, which in turn depends on air temperature and relative humidity during the storing of the material before processing. Therefore, the water vapour sorption behaviour of this material was also investigated. The GAB model for the mathematical description of sorption behaviour of starch could also be applied to corn grits and integrated into the models for the calculation of Delta h and lambda.