Extrusion of cross-linked hydroxypropylated corn starches - I. Pasting properties

A series of cross-linked (0, 0.014, 0.018, 0.024, and 0.028% POCl3, dry sta rch basis) hydroxypropylated (8%) corn starches were extruded using a Leist ritz micro-18 co-rotating extruder. Process variables included moisture, ba rrel temperature. and screw design. Differential scanning calorimetry and X -ray diffraction studies showed the level of starch crystallinity decreased with increasing severity of extrusion conditions. Pasting properties of th e extruded starches were examined using a Rapid Visco Analyser. Pasting pro files of starches extruded at different conditions displayed different hot paste viscosity and final viscosity. Increasing starch moisture content dur ing extrusion and level of cross-linking increased starch viscosity (P < 0. 0001), whereas increasing extrusion temperature and shear decreased starch viscosity (P < 0.0001). Interactions were found between level of cross-link ing and screw design and between extrusion temperature and starch moisture content (P < 0.0001).