An evaluation of the Methylene Blue Reduction Method Used for Raw Milk Quality Control in Swaziland

Abstract

The accuracy of the methylene blue reduction test to grade the bacteriological quality of raw milk in Swaziland was evaluated. Milk samples 9130) taken from raw milk received at Swaziland Dairy Board processing plant were analyzed for dye reduction and plate counts. Samples were highest in Psychotrophic counts (10 cfu/ml) and lowest in thermoduric counts (10 cfu/ml). Regression relationship between log plate counts and dye reduction times were poor. The regression relationship between these two tests was not consistent to support continual use of the methylene blue test as an estimate of bacterial counts. Correlation coefficient values were also low (r=0.44 to 0.69). Standard errors of estimates were very high (0.40 to 1.91). This supported the conclusion that the methylene blue test did not accurately estimate the bacterial load of the raw milk in Swaziland.

UNISWA Research Journal of Agriculture, Science and Technology Vol 3 (1) 1999: pp 74-79