Setup of a rapid method to distinguish among dead, alive, and viable but not cultivable cells of Pseudomonas spp. in mozzarella cheese

Abstract

Pseudomonas spp. is the main psychrotrophic genus involved in the spoilage of raw milk and more in general of dairy products, such as mozzarella cheese. The members of this bacterial species are able to produce heat-resistant proteolytic enzymes, determining the casein hydrolysis, and as a consequence, a reduction of the shelf life and sensory quality of the products. Therefore, the spoilage activity could be attributed not only to viable, but also to viable but noncultivable (VBNC) cells. For this reason, the setup of a non-culture-based method is useful for a rapid detection of cells that are still alive, but no longer cultivable, such as VBNC cells. Here we propose a method based on DNA or RNA content (or both) to reveal the presence of dead, alive, and VBNC cells belonging to the genus Pseudomonas. The obtained results clearly indicate the limits of the classical plating count overcome by molecular detection of Pseudomonas spp. through DNA and RNA analysis, enabling us to establish the presence of different states of the cells.

Identification and proteolytic activity quantification of Pseudomonas spp. isolated from different raw milks at storage temperatures

“…Although buffalo milk had the lowest number of strains, more than half of the isolates were proteolytically active at 7°C, 10°C, and 25°C. These results are consistent with the findings of Caldera et al (2015), who reported that comparable levels of blue spoilage in mozzarella cheese were observed after 2 d at 25°C, 7 d at 12°C, and 17 d at 4°C, respectively. However, the association between storage temperature and storage time for other milks, including camel milk, is unclear; in camel milk, a minor fraction of the isolates (≤45% from 2°C to 25°C) exhibited proteolytic activity.…”

Broth depending production of extracellular enzymes by enterobacteria isolated from dairy food (Serbian cheese)

“…Enterobacteriaceae syntheses proteolytic and lipolytic enzymes which are responsible for the deterioration of milk and dairy products (ZAJÁC et al, 2015;MASIELLO et al, 2016). In the production of cheese, these enzymes destabilize casein and may modify or even prevent milk coagulation, which could directly affect the formation of the product (CALDERA et al, 2015). Another major problem is that these bacteria can significantly affect color, odor, taste, and texture (CALDERA et al, 2015;BÖHME et al, 2011).…”

“…In the production of cheese, these enzymes destabilize casein and may modify or even prevent milk coagulation, which could directly affect the formation of the product (CALDERA et al, 2015). Another major problem is that these bacteria can significantly affect color, odor, taste, and texture (CALDERA et al, 2015;BÖHME et al, 2011). Lipolysis may lead to a process called hydrolytic rancidity, where the product develops sour taste and an unpleasant smell (CARPINÉ et al, 2010;KREWINKEL et al, 2016).…”

A Highlight for Non-Escherichia coli and Non-Salmonella sp. Enterobacteriaceae in Dairy Foods Contamination

“…In cheese production, for example, these enzymes destabilize casein micelles and may modify or even prevent the coagulation of milk, what can directly affect the formation of the product (Caldera et al, 2015). Another major problem is that these bacteria can cause off-flavor, i.e., can considerably affect the sensory properties of the foods, such as color, odor, flavor, and texture (Böhme et al, 2013; Caldera et al, 2015).…”

“…Another major problem is that these bacteria can cause off-flavor, i.e., can considerably affect the sensory properties of the foods, such as color, odor, flavor, and texture (Böhme et al, 2013; Caldera et al, 2015). Such changes can directly affect the acceptance or rejection of the product by the consumer.…”