THEORETICAL MODEL OF COLOR CHANGE FOR MILK REDUCTASE SAMPLE WITH RESAZURIN FOR MILK QUALITY CONTROL DURING ITS STORAGE

Subject of Research. The paper deals with theoretical justification of moving from an organoleptic analysis of milk quality in accordance with the requirements of the national standard to objective control based on quantitative assessment by an instrumental method. We propose a theoretical model for changes in color of milk reductase sample depending on its bacterial contamination. Methods. The proposed model was based on the known patterns of the chemical process of resazurin, resofurin and hydroresofurin mutual transformation, as well as the impact of the concentration of coloring matters on the resulting solution color for homogeneous and inhomogeneous media. Real transmission spectra of the mentioned substances were measured for model development. For theoretical model verification, experimental studies of quality changes during the storage of a milk sample, which was delivered to a shop, were carried out by reductase method. The experiment duration was 3 days, until the souring of milk. The milk was stored between the measurements at the temperature of +4 °C. A theoretical dependence of color changes for the reductase sample of milk was built during the experiment taking into account real transmission spectrum of milk. Real transmission spectra of the reductase sample were measured. The chromaticity coordinates (x, y) of the sample were calculated from the transmission spectra obtained through the modeling and measurement. To visualize the color change of the sample, the color coordinates in the sRGB color space were calculated for the case of a D65 light source, which is equivalent to daylight. Main Results. The simulation results are completely consistent with the results of experimental studies. The discrepancy between the results of theoretical modeling and experimental data does not exceed, on the average, 0.01 for the chromaticity coordinates x and y. The proposed model gives the possibility to calculate the concentration of enzymes for reductase sample with resazurin at any time, and, as a result, determine its color coordinates and color in accordance with the standards of the International Commission on Illumination for transparent and translucent media. Practical Relevance. The obtained temporal dependence of the chromaticity coordinates and the color of the reductase sample with resazurin can be used to control milk quality by spectrophotometric method and the method of technical vision.