A Comparison of Phosphate Buffered and Distilled Water Dilution Blanks for the Standard Plate Count of Raw-Milk Bacteria1

Abstract

Raw milk samples were diluted with distilled water or distilled water with added phosphate buffer as recommended by Standard Methods for the Examination of Dairy Products. The standard plate counts were higher in diluent without phosphate buffer with both high and low count milk. The higher counts were significant when analyzed by a nonparametric sign test or a t-test of differences but were not significant with an analysis of variance technique. Reproducibility was not statistically different in the two diluents. It is suggested that the use of phosphate buffer for raw milk bacteria counts be discontinued until information showing definite advantages is provided.