Psychrotrophs in raw milk: effect on texture, proteolysis index, and sensory evaluation of smoked provolone cheese.

BACKGROUND: Provolone can be fresh or ripened, with its taste varying from sweet to spicy. The high psychrotrophic density of raw milk is associated with thermoresistant enzymes that can change cheese characteristics such as texture, promote sensory defects and decrease industrial yield. Two batches of provolone-type smoked cheese were produced from chilled raw milk with 3 log cfu mL-1 (Treatment 1) and 7 log cfu mL-1 (Treatment 2) of psychrotrophs. The psychrotrophic (21 °C for 25 h) and physical-chemical profile of the raw milk were determined. Cheeses were evaluated by fat level, primary and secondary proteolysis index, yield, protein profile (Urea-polyacrylamide gel electrophoresis), and texture (hardness, cohesiveness, elasticity, and chewiness) at 14, 30, and 60 days of storage time. Sensorially, the cheeses were evaluated (100 tasters/period) using the triangular test. RESULTS: The treatments did not influence proteolysis index, although maturation influenced the proteolytic depth index after 60 days. The psychrotrophic population influenced αs 1- and ß-casein fractions, while maturation time influenced αs 1- and γ-casein fractions. Treatment 2 induced a 3% reduction in cheese yield. Hardness and chewiness showed a linear and positive relationship with the milk's psychrotrophic load. There was a significant difference in the fat content of the cheeses, with Treatment 2 having a lower level. The triangular test showed no difference between the cheeses. CONCLUSION: Although the larger psychrotrophic population in raw milk was associated with superior values of hardness and chewiness, as well as an increase in protein fractions indicating that proteolysis was observed, the tasters did not identify sensorial differences between the cheeses. © 2020 Society of Chemical Industry.

Lipoproteolytic capacity and potential of Pseudomonas spp. isolated from cold raw milk.

The objective of the work described in this research communication was to determine the lipoproteolytic capacity and potential of Pseudomonas spp. from the microbiota of refrigerated raw milk. The influence of temperature and bacterial population on these activities was also evaluated. Pseudomonas spp. (PS) counts (30 °C/48 h) were confirmed by PCR. Proteolytic (10% milk agar) and lipolytic capacities (PLC) (tributyrin agar) were evaluated (21 °C/72 h). Proteolytic (PP) and lipolytic potential (LP) were assessed by measuring the diameter of the halos and were categorized as low or high. A total of 91.3% PS possessed PLC. The PP of 64.16% isolates was high and was frequently observed in PS from milk samples with higher counts and lower temperatures. The LP of 70.52% isolates was low, and higher LP was associated with low microbiological counts and temperatures. Genetic studies evaluating Pseudomonas spp. strains in the milking environment and investigating the origin of these isolates could be useful to improve the quality and shelf life of dairy products.