Simple tests for rapid assessment of the quality of raw milk

Simple and inexpensive tests are described for rapid qualitative assessment of the microbiological quality of raw milk. These tests included the monitoring of dissolved oxygen levels and changes in the color of raw milk with time in a slightly modified methylene blue test using 16 ppm of dye concentration. The initial bacterial population in raw milk determined by standard plate count could be estimated with coefficients of determination (r2) of about 0.697 and 0.613 from the respective normalized voltage outputs of the dissolved oxygen probe and light-sensing probes at selected time intervals in less than 1 h. However, a comparison of experimental and estimated initial bacterial populations in raw milk showed correlation coefficients (r) of about 0.754 and 0.616 for the dissolved oxygen probe and light-sensing probe, respectively. These results clearly indicated the potential and need for improving such empirical models for grading raw milk with both types of probes.