Microbiological quality of refrigerated raw milk in the dairy farm and after transport to the processing dairy plant

Abstract

ABSTRACT: Transport of cooled raw milk in bulk has greatly improved the quality of the raw material collected by dairy plants as it reduces the proliferation of mesophilic microorganisms that cause milk acidity and hinder its processing. However, refrigeration has favored the growth of psychrotrophic microorganisms which are able to grow at low temperatures (below 10ºC) and that produce heat resistant enzymes which degrade some milk components, reducing milk shelf life and causing organoleptic changes. The aim of this paper was to evaluate the microbiological quality of raw milk in dairy farms and after its transport to the processing dairy plant, through plate counting of mesophilic and psychrotrophic microorganisms. Fourteen milk samples were collected from tanks of the dairy-farming properties, and one sample was collected from their milk transport tanker at the entrance of the processing plant. Our results showed that the mean number of mesophilic microorganisms was higher in samples collected straight from the dairy farm tanks than in the samples collected from the transportation tankers at the entrance of the plant. Of the 14 sampled tanks, 64.3% were non-compliant with legislation. The sample collected from the milk transportation tanker containing milk from all properties showed a higher mean number of psychrotrophic microorganisms than the dairy farm samples. We conclude that the milk from dairy properties showed a higher amount of mesophilic microorganisms, and after transportation, at the entrance of the processing plant, there is a higher amount of psychrotrophic microorganisms.