Culturable Psychrotrophic Bacterial Communities in Raw Milk and Their Proteolytic and Lipolytic Traits

Abstract

During cold storage after milk collection, psychrotrophic bacterial populations dominate the microflora, and their extracellular enzymes, mainly proteases and lipases, contribute to the spoilage of dairy products. The diversity, dynamics, and enzymatic traits of culturable psychrotrophs in raw milk from four farms were investigated over a 10-month period. About 20% of the isolates were found to be novel species, indicating that there is still much to be learned about culturable psychrotrophs in raw milk. The psychrotrophic isolates were identified and classified in seven classes. Three classes were predominant, with high species richness (18 to 21 species per class) in different seasons of the year: Gammaproteobacteria in spring and winter, Bacilli in summer, and Actinobacteria in autumn. The four minor classes were Alphaproteobacteria, Betaproteobacteria, Flavobacteria, and Sphingobacteria. The dominant classes were found in all four dairies, although every dairy had its own unique "bacterial profile." Most but not all bacterial isolates had either lipolytic or both lipolytic and proteolytic activities. Only a few isolates showed proteolytic activity alone. The dominant genera, Pseudomonas and Acinetobacter (Gammaproteobacteria), showed mainly lipolytic activity, Microbacterium (Actinobacteria) was highly lipolytic and proteolytic, and the lactic acid bacteria (Lactococcus and Leuconostoc) displayed very minor enzymatic ability. Hence, the composition of psychrotrophic bacterial flora in raw milk has an important role in the determination of milk quality. Monitoring the dominant psychrotrophic species responsible for the production of heat-stable proteolytic and lipolytic enzymes offers a sensitive and efficient tool for maintaining better milk quality in the milk industry.

Characterization of the bacterial biodiversity in Pico cheese (an artisanal Azorean food)

“…It has recently been described as part of the natural cheese microbiota (Lusk et al, 2012). However, its presence in raw milk is well established (Hantsis-Zacharov and Halpern, 2007), and it has been added to experimental cheeses as part of anti-listerial consortia (Callon et al, 2011). Macrococcus, another member of the Firmicutes that is regarded as an adventitious bacterium in cheese production (Giannino et al, 2009), was part of the predominant microbiota in cheese-maker B and was subdominant in industrial cheese.…”

Pseudomonas helleri sp. nov. and Pseudomonas weihenstephanensis sp. nov., isolated from raw cow's milk

“…Acinetobacter baumannii ATCC 19606 T (JMRY01000009.190604-92490) Several species of Pseudomonas have been reported to be involved in food spoilage (Arslan et al, 2011;Ercolini et al, 2007;Franzetti & Scarpellini, 2007;Tryfinopoulou et al, 2002), and members of the genus are considered to be important milk spoilers due to their psychrotolerant nature and proteolytic activity (Hantsis-Zacharov & Halpern, 2007;Marchand et al, 2009b;Martins et al, 2006).…”

Spoilage potential of Paenibacillussp. in Brazilian raw milk

“…These media were used to verify proteolytic (BEERENS et al, 1990) and lipolytic activities (HANTSIS-ZACHAROV et al, 2007), respectively. DNA was extracted from the colonies that showed spoilage activity following the method of CHENG et al (2006).…”