Milk sample conservation methods to determine the total bacteria count by flow cytometry

The objective of this study was to evaluate the effect of storage temperature and sample age on the total bacterial count (TBC) of milk samples preserved with azidiol to verify whether a single sample could be used to perform regulatory milk analysis under the Normative Instruction 51 (IN-51). Three hundred and twenty milk aliquots were used collected from an expansion tank to assess three storage temperatures (0 degrees C - frozen: 7 degrees C - refrigerated, and 24 degrees C - room temperature), three types of conservation (bronopol, azidiol and no preservative) and four sample ages (1, 3, 5, and 7 days). For the total bacteria count, refrigerated control samples, with azidiol and one day old samples, and for composition and somatic cell count (SCC), the controls were defined as one day old refrigerated samples containing bronopol. Samples conserved with bronopol presented lower total bacteria count than the control regardless of storage temperature and sample age. Milk samples conserved with azidiol and stored refrigerated presented lower SCC, regardless of age, compared to refrigerated samples conserved with bronopol. The fat and lactose contents decreased after the fifth day. Two samples had to be collected: one for SCC determination and composition containing bronopol and another for the total bacteria count containing azidiol. Milk samples used for total bacteria count can be tested up to 7 days if they are kept at 7 degrees C with the addition of azidiol.