ENZYMATIC-HYDROLYSIS OF SAGO STARCH IN A TWIN-SCREW EXTRUDER

Simultaneous gelatinisation and liquefaction of sago starch with a the rmostable alpha-amylase in a co-rotating twin-screw extruder was inves tigated. Maltodextrins with dextrose equivalent (DE) ranging from 0 to 10 were produced. Response surface methodology was used to study the influence of barrel temperature (70-130 degrees C), screw speed (70-16 0 rpm), enzyme concentration (0-1.0%) and feed moisture content (28.5- 50.5%) on the extrudate properties. Specific mechanical energy (SME) c onsumption was calculated to be in the range of 21-91 Wh/kg for the va rious processing conditions. Structural changes were characterised by measuring DE, wafer solubility index (WSI), water absorption index (WA I), degree of degradation (DGR) and oligosaccharide content. Enzyme co ncentration, barrel temperature and feed moisture were the important v ariables affecting most of the measured physicochemical properties. Hy drolysis of starch granules was the fundamental reaction occurring dur ing extrusion processing with both amylopectin and amylose degraded. H igher breakdown was achieved with lower SME consumption. (C) 1997 Else vier Science Limited.