Background Camel milk is valued for its unique nutritional and health benefits, but it is prone to spoilage by psychrotrophic bacteria like Pseudomona s during refrigeration. These bacteria produce heat‐resistant enzymes that survive pasteurisation and cause spoilage. Understanding the diversity and enzymatic activity of Pseudomonas in Chinese camel milk is essential for maintaining product quality and safety. Aim This study aimed to investigate the diversity, proteolytic and lipolytic activities, and biofilm‐forming capacity of Pseudomonas in camel milk of Xinjiang. Methods Camel milk from Xinjiang farms was cultured at 6.5°C to isolate psychrotrophic bacteria, which were then identified by 16S rRNA gene sequencing. Both protease and lipase‐producing isolates were first screened using agar‐based diffusion tests, and their enzyme activities were subsequently quantified via azocasein and p‐nitrophenyl palmitate (p‐NPP) assays. The thermal tolerance of the enzymes was examined by exposing them to high temperatures. The biofilm‐forming capacity of each strain was evaluated by the 96‐well microplate method. Results A total of 214 psychrotrophic bacterial isolates were dominated by Acinetobacter (53.7%) and Pseudomonas (11.2%). Over a third of the isolates produced spoilage enzymes. Pseudomonas species showed the highest protease activity. Pseudomonas bubulae had the highest protease activity (16.26 U/mL), and its protease maintained notable thermal resistance, with 33.33% activity remaining after exposure to 121°C for 10 min. The lipase produced by Chryseobacterium yeoncheonense was the most heat‐resistant, preserving 43.00% activity under the same severe heat treatment. Moreover, 31.0% of the identified psychrotrophic strains demonstrated moderate biofilm‐forming capability with the OD 595 values ranging from 0.365 to 2.012. Conclusion This study identifies the diversity of psychrotrophic bacteria in camel milk and the heat‐stable spoilage enzymes they produce, with Pseudomonas biofilm formation and heat‐resistant proteases being key spoilage factors, providing a basis for improving industry control methods.
Wu et al. (Thu,) studied this question.