Farm milk storage system's influence on the raw milk microbiological quality

Abstract

Raw milk on-farm refrigeration aims to increase the storage period, decreasing the costs of transport and acidification loses caused by mesophilic microorganisms, however it can allow the development of heat-resistant enzymes producers psychrotrophic microorganisms that cause several defects on dairy products. The present study goals to evaluate the effect on raw milk quality after storage in expansion or immersion tanks regarding to mesophilic, psychrotrophic and proteolytic psychrotrophic microorganisms. Were evaluated ten dairy farms, five of them with immersion system and other five with expansion system. The average of mesophilic in immersion tanks (6.04±0.71 log UFC/ml) were significantly higher comparing to expansion tanks (4.97±0.77 log UFC/ml), indicating that the immersion refrigeration didn't appear been efficient on those microorganism control. 60% of samples were in disagree to the IN51 standards, been 80% of them from farms with immersion tanks and 40% from expansion tanks. No significant difference between the systems were shown for psychrotrophic and proteolytic psychrotrophic. Samples of both systems presented high percentage (77.2 to 96.9%) of psychrotrophic colonies with proteolytic activity. The milk refrigeration in expansion tanks showed to be more efficient in controlling mesophilic microorganisms than samples cooled in immersion tanks, whereas the same result couldn't be statistically proved on psychrotrophic microorganisms.