AUTHOR=Meng Lu , Zhang Yangdong , Liu Huimin , Zhao Shengguo , Wang Jiaqi , Zheng Nan 

TITLE=Characterization of Pseudomonas spp. and Associated Proteolytic Properties in Raw Milk Stored at Low Temperatures

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.02158

DOI=10.3389/fmicb.2017.02158

ISSN=1664-302X

ABSTRACT=<p>Milk spoilage is caused by the presence of proteolytic enzymes produced by <italic>Pseudomonas</italic> spp. during storage at low temperatures. The aim of this study was to identify <italic>Pseudomonas</italic> spp. in raw milk and investigate their associated proteolytic properties at low temperatures. Raw milk samples (<italic>n</italic> = 87) were collected from 87 bulk tanks in Shaanxi Province in China. <italic>Pseudomonas</italic> spp. were identified using <italic>Pseudomonas</italic> specific 16S, universal <italic>16S rRNA</italic> sequencing, and <italic>rpo</italic>B gene sequencing. The proteolytic properties of <italic>Pseudomonas</italic> spp. were examined using milk agar, quantitative trinitrobenzenesulfonic acid assay, and by the presence of alkaline metallopeptidase gene (<italic>apr</italic>X). A total 143 isolates from all 87 samples were confirmed as <italic>Pseudomonas</italic>, and were identified as belonging to 14 <italic>Pseudomonas</italic> species. Of these, 40 (28.0%) isolates revealed proteolysis on milk agar at 2°C, 74 (51.8%) at 4°C, 104 (72.7%) at 7°C, and 102 (71.3%) at 10°C. However, proteolytic activity of 45 (31.5%) isolates exceeded 2 μmol of glycine equivalents per mL at 7°C, followed by 43 (30.1%) at 10°C, 18 (12.6%) at 4°C, and 7 (4.9%) at 2°C. The results reveal proteolytic activity of <italic>Pseudomonas</italic> spp. present in milk and their spoilage potential at different temperatures.</p>