Potential harmful of extracellular proteases secreted by Pseudomonas fluorescens W3 on milk quality

Pseudomonas fluorescens is one of the main psychrotrophic bacteria that endangers milk quality because they can secret heat-resistant extracellular enzymes. Pseudomonas fluorescens W3 from raw milk was used to analyze its heat resistance and harm on milk. Pseudomonas fluorescens W3 did not have heat resistance, and could be killed effectively by conventional milk sterilization methods. However, the protease secreted by W3 had heat resistance, and could continue to decompose casein after sterilization. The raw milk inoculated with Pseudomonas fluorescens W3 was preserved after UHT treatment, and a visual sediment appeared after 7 days of storage. The increase in free amino acid content also confirmed the breakdown of casein. It was discovered that in addition to the protease AprX, Pseudomonas fluorescens W3 could secrete a variety of other proteases, which could cause potential harm to the quality of dairy products. Novelty impact statement: The protease secreted by Pseudomonas fluorescens W3 strain has a certain degree of heat resistance. We use proteomics technology to find that Pseudomonas fluorescens W3 strain can secrete a variety of proteases and peptidases, which harms the quality of dairy products.