The storage of fresh raw milk at low temperature does not prevent proliferation of psychrotrophic bacteria that can produce heat-resistant proteolytic enzymes contributing to the reduced shelf life of dairy products. This study aimed to identify the dominant psychrotrophic proteolytic enzyme-producing population of raw milk from Brazil. Raw milk samples collected in 3 different cooling tanks in Brazil were stored at optimal (45 h at 4 °C followed by 3 h at 7 °C) and suboptimal (45 h at 7 °C followed by 3 h at 10 °C) conditions to simulate farm storage and transportation allowed by Brazilian laws. The highly proteolytic enzyme-producing strains isolated from stored cold raw milk were characterized by repetitive sequence-based Polymerase Chain Reaction (PCR) analysis. This clustering resulted in 8 different clusters and 4 solitary fingerprints. The most proteolytic isolates from each rep-cluster were selected for identification using miniaturized kit, 16S rDNA and rpoB gene sequencing. Serratia liquefaciens (73.9%) and Pseudomonas spp. (26.1%) were identified as the dominant psychrotrophic microorganisms with high spoilage potential. The knowledge of milk spoilage microbiota will contribute to improved quality of milk and dairy products.
Keywords: Rep-PCR; heat-resistant proteolytic enzyme; proteolytic; psychrotrophic; spoilage.
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