Predicting Optimal Cutting Time of Coagulating Milk Using Diffuse Reflectance

Abstract

A method based on changes in diffuse reflectance during milk coagulation was developed for predicting the optimal cutting time of coagulating milk. Time between enzyme addition to milk and occurrence of inflection point on the diffuse reflectance curve was measured at various concentrations of milk fat, protein, calcium, and enzyme at various temperatures and pH levels. Inflection time was compared and found to correlate with measured Formagraph™ cutting time. Using calf rennet and fermentation-derived chymosin enzymes, a cutting time prediction equation was developed by incorporating the inflection time into a multiple linear regression equation with milk protein content. When validated, the prediction equation had a standard error of prediction of .9 and 2.4min for two different validation tests and was sufficiently accurate for commercial application.A cutting time prediction model that used only the magnitude of the change in diffuse reflectance was tested. Changes in diffuse reflectance during coagulation were a function of milk pH, temperature, fat, and protein content. Thus, diffuse reflectance changes can be used to predict optimal cutting time only when these milk property values are known or controlled.