Simple and inexpensive tests for rapid qualitative assessment of the microbiological quality of raw milk were described in a recent issue of the Journal of Food Protection. Scientists from the Food Engineering Department at Kasetsart University, Thailand carried out a series of tests including the monitoring of dissolved oxygen levels and changes in the colour 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, the researchers report, 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. They concluded that the results clearly indicated the potential and need for improving such empirical models for grading raw milk with both types of probes. Full findings are published in the November issue of the Journal of Food Protection: Vol. 64, No. 12, pp. 1996-2000.