| Abstract: | A systems analytical model for the extrusion of starches and flours was modified to determine the optimal extrusion conditions for the cationization and the carboxymethylation of potato starch and to determine the effect of the extrusion conditions, optimal for the reaction yield (R.E.) and the desired degree of substitution (D.S.), on the rheological properties of the derivatives. In order to improve the describability of the postulated functional relationships between the defined system parameters and the R.E. it was decided to measure the heat flow over the length of the processing part of the extruder in order to enable a more precise measure of the specific thermal energy input (STE). Test run results showed that the STE is highly correlated to the SME. Therefore the initial proposal to substitute the STE for the product temperature in the modified systems analytical model could not be successful. The extension of the working range for these trials to higher SME and mean residence time levels compared to previous studies enabled the production of cationic starch with a maximum R.E.>90% and the production of carboxymethylstarch with a maximum R.E. of about 85%. The modified systems analytical model could not yet be used precisely for the optimization of the R.E. of the derivation of starches. The influence of process parameters and D.S. on rheological properties of the examined derivatives could be described with regression equations. |
