Quantification of psychrotrophic bacteria and molecular identification of Pseudomonas fluorescens in refrigerated raw milk

Abstract

In this study, we investigated the contamination of refrigerated raw milk produced in the western region of Paraná, southern Brazil, with psychrotrophic microorganisms, aiming to assay the proteolytic activity of the isolates and to identify Pseudomonas fluorescens, the main proteolytic species associated with the spoilage of milk products. Raw milk samples from 50 dairy farms were submitted to the counting of psychrotrophic microorganisms, being the microbiota characterized by its mesophilic behavior and proteolytic capacity, besides molecular identification of P. fluorescens. Of the samples evaluated, 94% had psychrotrophic counts ranging from 3 to 7.1 log CFU mL-1, and 48.5% of these showed mesophilic behavior. Of the isolates, 48.0% had proteolytic activity in at least one evaluated temperature (21 and 30°C), and 39.3% had proteolytic activity in both temperatures. Among the 61 isolates submitted to molecular identification by polymerase chain reaction (PCR), 86.8% contained the expression of the 16S gene characteristic for P. fluorescens. In this study, we demonstrated that P. fluorescens is the most prevalent psychrotrophic bacteria species in raw refrigerated milk and their proteolytic ability poses high risks to the dairy industry.

Evaluation of the changes in physiochemical properties and fatty acid profile of industrially pasteurized coconut (<em>Cocos nucifera</em>) milk during storage

“…During storage, the micro-biota shifts toward psychrotrophic microorganisms, which can easily reduce the quality of raw milk in low temperatures (Celano et al, 2022). Pseudomonas has been identified as predominant milk-associated psychrotrophic bacteria (Lampugnani et al, 2019). The most commonly identified Pseudomonas species in milk are P. fluorescens, P. gessardii, P. fragi, and P. lundensis (Maier et al, 2021).…”

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

“…Low temperature transportation and storage conditions could not only effectively inhibit the growth of psychrotrophic bacteria, but also inhibit the secretion of extracellular proteases. Therefore, perfecting cold chain transportation technology was essential to ensure the quality of raw milk (Lampugnani et al, 2019). And, the sterilization method at 137°C for 5 s is used in the production of UHT milk.…”

Safranin-O-Mediated Photodynamic Inactivation of Microorganisms Reduces Milk Contaminating Bacteria Count and Prevented New Cases of Mastitis

“…Among the pathogens in milk, Staphylococcus aureus (S. aureus) stands out, a bacterium that spreads through the milking system and is associated with mastitis, which causes a drop in milk production, increased drug costs and even disposal of animals (Ren et al, 2020). As a deteriorating microorganism, Pseudomonas fluorescens (P. fluorescens), considered the biggest obstacle in dairy products, are the main producers of thermo-resistant proteolytic and lipolytic enzymes that change the organoleptic characteristics of milk and reduce the shelf life of dairy products (Lampugnani et al, 2019).…”