2000 Volume 47 Issue 1 Pages 13-19
Cornstarch was adjusted to 16% moisture content (dry basis), blended with shellac (natural resin secreted by lac bugs) at 0, 2, 4, 6 and 10% (w/w) and extruded in a twin-screw extruder at a screw speed of 200 rpm and 110, 140 and 170°C barrel temperatures. Expansion ratio, bulk density, mean cell size, water solubility, X-ray diffraction pattern and molecular degradation of the extrudates were measured. Expansion ratio and bulk density were dependent on shellac content, ranging from 1.72 to 14.61 and 62 to 273 kg/m3, respectively. Mean cell size of the extrudates increased with increasing in shellac content up to 6%, but distributions were scattered. Water solubility of ground extrudates decreased with increasing shellac content. V- and E-form X-ray diffraction patterns suggested the formation of cornstarch-shellac complexes, like starch-lipid complexes. Size exclusion chromatography of starch-shellac extrudates showed that shellac suppressed the degradation of starch during extrusion.