Near Infrared On-Line Measurement of Degree of Cook in Extrusion Processing of Wheat Flour

Product texture in extrusion processing of cereals is controlled by the extent of depolymerisation of the starch, referred to as degree of cook. On-line measurement of degree of cook would enable improved process control. An NIRSystems Process Analytic Analyser with transmittance fibre optic probes has been used to measure the degree of cook on-line during the extrusion processing of wheat flour. The absorbance of the second derivative of the peak minimum in the region 1400–1450 nm in the transmission spectrum of extrudate melts has been shown to follow changes in degree of cook when three process parameters were varied in a factorial design. The r² between on-line minimum absorbance and degree of cook as measured by shear rate of the corresponding dispersed powdered extrudate sample was 0.77.