Pseudomonas spp. and P. fluorescens: population in refrigerated raw milk

Raw milk samples were collected from cooling tanks (after they cooled for 48 h) in five dairy farms and the corresponding bulk tank (bulk milk transportation, BMT) when they arrived to the industry. Routine physical chemical analyzes and quantification of psychrotrophic (Pseudomonas spp. and P. fluorescens) and aerobic mesophilic (AM) populations were performed. Only relative density and titratable acidity values for samples of milk from three farms were in agreement to the quality parameters required by law. In the BMT, only the protein content has not reached the minimum value established by law, and counting was performed for AM ( > 10(5) colony forming units (CFU) mL-1) and psychrotrophic bacteria (2.8x106CFU mL(-1)). Pseudomonas spp. counting corresponded to 17.9% of the psychrotrophic population, and P. fluorescens was 3.4% of Pseudomonas spp. count. In milk samples from dairy farms, counts were variable for AM (3.4x10(5) to 3.7 x10(7)CFU mL(-1)), psychrotrophic (4.0x10(4) to 3.1x10(6)CFU mL(-1)), Pseudomonas spp. (2.3x10(4) to 1.8x10(5)CFU mL(-1)), and P. fluorescens (62 to 8.4x10(3)CFU mL(-1)). For the populations studied, no statistical difference (P > 0.05) was observed between counts reported in milk samples collected in dairy farms (cooling tanks) and BMT. Therefore, the genera Pseudomonas spp. and P. fluorescens were not the most frequent psychrotrophic bacteria in this studied milk transportation line.