Can pH measures be used to estimate bacterial contamination of bovine colostrum?

The primary objective of the current work was to determine whether pH could be used as a proxy measure for bacterial contamination (using reference standard sheep blood agar plates to measure total bacteria counts [TBCs] and MacConkey agar plates to measure total coliform counts [TCCs]) of bovine colostrum (BC). The hypothesis for this work was that bacteria produce acid by-products from their metabolism, thereby more highly contaminated BC is likely to be more acidic, based on lower pH measurement. A secondary objective was to identify optimal thresholds for pH to identify colostrum highly contaminated with total bacteria or coliform species, with industry thresholds for highly contaminated colostrum being TBCs > 100,000 CFU/mL and TCCs > 10,000 CFU/mL. One hundred and one samples were purposively selected from previously frozen BC samples. Sample pH was measured using a pH meter in duplicate, and bacteria counts were measured using the reference tests of 5% sheep blood agar and MacConkey agar plates for TBC and TCC, respectively. Small decreases in pH measurement were associated with increases in bacterial contamination of BC, particularly coliform species, which are those most implicated in the disruption of IgG absorption from colostrum. There was a statistically significant relationship between pH measurements and log-transformed bacterial measurements.