Sources of psychrotrophic contamination and proteolysis indices in raw milk

Storage of raw milk under refrigeration makes it possible to reduce operating costs for production and prevents losses of this raw material by the acidifying activity of mesophilic bacteria. Meantime, storage for prolonged periods may result in decreased quality of dairy products, due to the growth and enzymatic activity of psychrotrophic bacteria. Thus, in this study, we evaluated the presence of psychrotrophic microorganisms, Pseudomonas spp. and Pseudomonasaeruginosa tracing sources of microbiological contamination in the milking process as well as the level of proteolysis of the milk in the expansion tank. The highest contamination (P <0.05) occurred with the psychrotrophic count, with maximum values of 5.11 log CFU•mL-1a value that has hydrolytic potential for K-casein. Some dairy farms were found to have a maximum caseinomacropeptide value of 142.93 mg•L-1, representing loss of quality for the industry and a raw material that is not suitable for human consumption. The points of greatest contamination were udder surface, insufflator, milking bucket and colling system. According to principal component analysis, the values obtained for the microbiological counts were not determinants of the release of caseinomacropeptide.