Enzymatic hydrolysis of sago starch in a twin-screw extruder

Simultaneous gelatinisation and liquefaction of sago starch with a thermostable alpha-amylase in a co-rotating twin-screw extruder was investigated. 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 (70-160 rpm), enzyme concentration (0-1.0%) and feed moisture content (28.5-50.5%) on the extrudate properties. Specific mechanical energy (SME) consumption was calculated to be in the range of 21-91 Wh/kg for the various processing conditions. Structural changes were characterised by measuring DE, wafer solubility index (WSI), water absorption index (WAI), degree of degradation (DGR) and oligosaccharide content. Enzyme concentration, barrel temperature and feed moisture were the important variables affecting most of the measured physicochemical properties. Hydrolysis of starch granules was the fundamental reaction occurring during extrusion processing with both amylopectin and amylose degraded. Higher breakdown was achieved with lower SME consumption. (C) 1997 Elsevier Science Limited.