The single screw extruder as a bioreactor for sago starch hydrolysis

Simultaneous pregelatinization and preliquefaction of sago starch with a thermostable α-amylase was carried out in a Brabender single screw extruder. Response surface methodology was employed to study the effects of processing conditions; feed moisture content (21–38%), enzyme concentrations (1.48–6.52%) and mass temperatures in the compression and die zones (70.5–97.5 °C), on the properties of the extrudates. Twenty runs were performed based on a multifactorial composite rotatable design. Changes in the dextrose equivalent (DE), water solubility index (WSI), water absorption index (WAI), degree of gelatinization (DG) and high performance size exclusion chromatography (HPSEC) profiles were assessed. From the HPSEC profiles, the degree of degradation (DGR) and oligosaccharide content were calculated. Feed moisture content and enzyme concentration were found to be the most significant variables affecting most of the measured physicochemical properties. Hydrolysis of starch granules was the fundamental reaction occurring during the extrusion process as indicated by the higher DE, WSI, oligosaccharide content and correspondingly lower WAI, DG and DGR. Product spectra from HPSEC showed that the amylopectin (Ap) was preferentially degraded and amylose (Am) was apparently protected. The predominant oligosaccharide species were G3, G5 and G6.