Extrusion Cooking in Enzymatic Liquefaction of Wheat Starch

Wheat starch was treated for gelatinization, partial liquefaction, and subsequent further hydrolysis by extrusion cooking together with a thermostable Bacillus licheniformis α-amylase followed by batch incubation of the extrudates at 80°C. The degree of hydrolysis depended on the extrusion feed moisture content, enzyme concentration, mass temperature during extrusion cooking, and the length of the counter screw elements. The degree of hydrolysis was followed both by dextrose equivalent and by molecular weight distribution pattern as determined by high performance gel permeation chromatography. A reaction velocity model was shown to fit well to the kinetic data obtained. The enzyme was only incompletely inactivated by mercuric chloride suggesting the presence of also other than sulfhydryl dependent amylase.