Psychrotrophic bacterial populations in Chinese raw dairy milk

•Sixteen raw milk samples representative of different Chinese farms were evaluated for psychrotrophic bacteria.•480 isolates were clustered into 85 groups based on RAPD profiles.•Pseudomonas was the most dominant genus followed by Acinetobacter and Flavobacterium.•Pseudomonas fluorescens was the most dominant species followed by Pseudomonas fragi and Pseudomonas psychrophila.•26 species belonging to 14 genera proved to be previously unreported psychrotrophic contaminants in raw milk.

Four-hundred and eighty isolates isolated from raw milk samples collected from different farms in China were subjected to random amplified polymorphic DNA analysis and 16S rRNA sequencing for clustering and identification, respectively. All isolates comprised 24 genera and 74 species in total. Pseudomonas was the most prevalent genus, representing 58.8% of all isolates, followed by Acinetobacter (13.3%), Flavobacterium (6.0%) and Sphingobacterium (4.2%). Among the 25 species belonging to Pseudomonas, Pseudomonas fluorescens (15.8%) proved to be the most dominant species, followed by Pseudomonas fragi (7.1%) and Pseudomonas psychrophila (5.4%). Out of these isolates, 12.3% have not been reported in previous studies, highlighting that many psychrotrophic bacteria are rather underexplored in raw milk. In the future, a detailed investigation will be required to characterize these bacterial isolates based on their potential to deteriorate the quality of dairy products.