In-line colour and composition monitoring in the extrusion cooking process

This paper demonstrates the feasibility of using a fiber-optic equipped visible-near-infra-red (Vis-NIR) spectrometer to monitor both colour and composition in an extruder during the extrusion of yellow corn flour. A first series of experiments was conducted without adding any colouring in order to study the changes in colour and composition during the extrusion process. Screw speeds of 40, 50 and 60 rpm and temperatures of 130, 150 and 170 degrees C were used in a 3x3 factorial design to examine the effect of screw speed and temperature. The main effects of these factors and their interaction effect was shown to be highly significant to the L*a*b* colour co-ordinates obtained from the reflectance spectra of the reacting corn hour. The near-infra-red (NIR) spectra were also greatly affected. A second series of experiments involved adding a food colouring (FD&C red 40) to the flour prior to extrusion at different levels. The results showed that difference in food dye concentrations can be detected in-line. Correlation of the colour values obtained in the extruder with chemical composition and with colour of the cooled product as well as development of calibration methods for quantitative interpretation of the composition from the NIR spectra are in progress. (C) 2000 Elsevier Science Ltd. All rights reserved.