Abstract
Raw milk is susceptible to microbial contamination during transportation and storage. Pseudomonas fluorescens producing heat-resistant enzymes have become the most common and harmful psychrophilic microorganisms in the cold chain logistics of raw milk. To rapidly detect P. fluorescens in raw milk, the protease gene aprX was selected as a detection target to construct a set of primers with strong specificity, and a loop-mediated isothermal amplification (LAMP) assay was established. The detection thresholds of the LAMP assay for pure cultured P. fluorescens and pasteurized milk were 2.57 × 102 and 3 × 102 CFU/mL, respectively. It had the advantages over conventional method of low detection threshold, strong specificity, rapid detection, and simple operation. This LAMP assay can be used for online monitoring and on-site detection of P. fluorescens in raw milk to guarantee the quality and safety of dairy products.
Highlights
Dairy products are rich in all kinds of nutrients necessary for the human body and are easy to be digested and absorbed, so they are increasingly favored by consumers
Milk-derived protease-producing P. fluorescens CICC 23250, CICC 23251, CICC 23253, and PF were the target strains in detection, which were inoculated into Luria–Bertani (LB) broth (QingDao Hope Bio-Technology, Shandong, China) containing 10 g of tryptone, 5 g of yeast extract powder, and 10 g of sodium chloride and were shaking cultured at 150 rpm at 25◦C for 24 h
S. aureus and L. monocytogenes were cultured in brain heart infusion (BHI) medium (Qingdao Hope Bio-Technology, Shandong, China) containing 10 g of peptone, 12.5 g of brain infusion powder, 5 g of heart infusion powder, 5 g of sodium chloride, 2 g of glucose, and 2.5 g of disodium phosphate at 37◦C for 24 h, and the other four strains were cultivated with shaking in LB broth at 37◦C for 24 h
Summary
Dairy products are rich in all kinds of nutrients necessary for the human body and are easy to be digested and absorbed, so they are increasingly favored by consumers. The main material of dairy products, has a direct impact on the quality and safety of products. Pseudomonas fluorescens are types of psychrotrophic bacteria that can grow and reproduce at a low temperature. They exist widely in all links of dairy processing and production, which may cause potential hazards to raw milk (Vithanage et al, 2016). During the later storage of dairy products, the residual enzymes play a role in the hydrolysis of milk protein and fat, resulting in the reduction of nutritional value and adverse sensory changes, which shorten the shelf life (Stoeckel et al, 2016).
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