A New Method for Measuring Rheological Changes in Food Processing

Application of Cross-Correlation Function of Electrical Impedance

Abstract

To estimate rheological changes in food processing, a method for measuring the speed of flowing materials was developed. Changes in electrical impedance at two points 2mm apart from each other in the same direction of a flow were continuously measured. A crosscorrelation function was calculated from signal intensities of impedance. The peak of cross correlation indicates the lag time taken by materials to move from one messuring point to the other. The speed of flowing materials can be calculated from the lag time. This speed is considered to reflect rheological properties of the materials, so the relationship between the speed of flow and viscosity was investigated. A commercial amylograph was used as a food processing machine and a measuring instrument of viscosity. Two electrodes to neasure electrical impedance, which simply consisted of two needles, were installed inside a rotating cup of the amylograph. Model samples with three diflerent levels of viscosity were prepared by mixing flour and water. The speed of flow and viscosity were measured at four step rotating speed. As results of these experiments, it became obvious that for the application of this method, an adequate data length for calculation of cross-correlation and a suitable location of measuring points must be chosen according to a flow-speed level of samples.