Pseudomonas spp. and P. fluorescens: population in refrigerated raw milk.Ciência Rural, v.47, n.1, 2017. IntRoDuCtIonGuidelines for cooling milk in dairy farms and its transportation were established in Brazil in 2002 (BRaSIl, 2002 as a response to international regulations and market demands. Since then, changes in milk chain production profile and qualitative advances in the regulation of total bacterial (TBC) and somatic cell (SCC) counts in raw milk have occurred (BRaSIl, 2002), and the guidelines were updated in 2011 (BRaSIl, 2011

BACKGROUNDProvolone 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.RESULTSThe treatments did not influence proteolysis index, although maturation influenced the proteolytic depth index after 60 days. The psychrotrophic population influenced αs1‐ and β‐casein fractions, while maturation time influenced αs1‐ 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.CONCLUSIONAlthough 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

No abstract

Psychrotrophic microorganisms, especially Pseudomonas spp., are present in the microbiota of refrigerated milk as they can grow at refrigeration temperatures irrespective of their optimal growth temperature. Psychrotrophic counts ranging from 105 to 108 CFU/mL in refrigerated raw milk effect cheese quality, since the synthesized thermoresistant enzymes affect the nutritional value, sensory properties, and texture. Cheese is the dairy product with the highest growth rate in the food industry in Brazil in recent years and meets the current consumption trends of nutritious and practical foods. The objective of this review was to address the importance and influence of the psychrotrophic raw milk microbiota on the quality and sensory properties of cheese. The enzymes produced by psychrotrophic microorganisms lead to taste changes, undesirable clotting times, increased concentrations of free fatty acids and free amino acids, and a reduced shelf-life, in addition to negatively affecting cheese yields. Proteases from psychrotrophs are also associated with slicing problems and progressive loss of the elasticity of cheese, a bitter taste, and increased clotting times of cheese produced with pasteurized milk. On the other hand, their lipases increase the clotting time and have a negative effect on the sensory properties by providing a rancid, soap, metallic, or oxidized smell and taste. The control of the psychrotrophic population found in refrigerated raw milk contributes to better cheese production yields and desirable texture and sensory properties, which extends the shelf-life of cheese and improves consumer acceptance.

This work aimed to assess the inhibitory effect of Lactobacillus rhamnosus against different populations of Pseudomonas fluorescens and Pseudomonas putida, isolated from refrigerated raw milk and the compounds responsible for inhibitory effects over storage time. An initial population of 4 log cfu/ml (50 ml) of L. rhamnosus (working culture) was added to 150 ml of reconstituted powder milk (12%) with P. fluorescens and P. putida, with an initial concentration of 2, 4, and 6 log cfu/ml. After activating at 21°C/72 hr, 200 ml of inoculum was stored at 10°C/48 hr. L. rhamnosus inhibited the growth of P. fluorescens and P. putida for all populations analyzed after inoculation (0 hr), 24, and 48 hr. The inhibitory compounds were organic acids. The average diameter measurement of inhibition zones for P. fluorescens was 1.9 cm and for P. putida was 1.6 cm. Practical applications This study demonstrated the antibacterial activity of L. rhamnosus against P. fluorescens and P. putida, both of the species isolated from the milk microbiota found in the environment of milk‐processing facilities. Although these findings need further validation on an industrial scale, it was demonstrated that L. rhamnosus can contribute for the improvement of raw milk quality.

The aim of this study was to evaluate the lipolytic index (LI) of Pseudomonas fluorescens and Pseudomonas putida (2, 5, 6 log CFU/mL) in milk during 96 h by the Lipo R method. The strains were isolated from refrigerated raw milk (30 °C, 48 h), and species were confirmed by PCR, inoculated in reconstituted whole milk, and stored at 2 °C, 4 °C, and 8 °C. The storage time (ST) and temperature were associated with LI of P. putida. The interaction among lipolysis, temperature, and ST occurs even with a low population of P. putida and these variables combined together contributed to about 77% of the free fatty acids (FFA) in milk. The ST, temperature, and population of P. fluorescens showed a significant effect on its LI, and the variables contributed to about 43% of FFA. LI was about 224% higher in milk with P. fluorescens than with P. putida. The reduction in ST and milk temperature resulted in a decrease in lipid lysis and a lower index of FFA by P. putida and P. fluorescens, with P. fluorescens showing a higher lipolytic capacity. RESUMEN:Efecto del almacenamiento en frío, el tiempo y la población de especies de Pseudomonas sobre la lipolisis de la leche. El objetivo fue evaluar el índice lipolítico (LI) (por el método Lipo R) de Pseudomonas fluorescens y Pseudomonas putidas (2, 5, 6 log CFU / mL) en leche durante 96 h. Las cepas se aislaron de leche cruda refrigerada (30 °C, 48 h), las especies se confirmaron por PCR, se inocularon en leche entera reconstituida y se almacenaron a 2, 4 y 8 °C. El tiempo de almacenamiento (ST) y la temperatura se asociaron con LI de P. putida. La interacción entre lipólisis, temperatura y ST ocurre incluso con una población baja de P. putida y estas variables combinadas contribuyeron a aproximadamente el 77% de los ácidos grasos libres (FFA) en la leche. El ST, la temperatura y la población de P. fluorescens mostraron un efecto significativo en su LI, y las variables contribuyeron a aproximadamente el 43% de FFA. LI fue aproximadamente un 224% mayor en leche con P. fluorescens que con P. putida. La reducción de la temperatura de ST y de la leche dio como resultado una disminución en la lisis lipídica y un índice más bajo de FFA por P. putida y P. fluorescens, esta última mostrando una mayor capacidad lipolítica. PALABRAS CLAVE: Actividad enzimática; Lipasa; Lipólisis de la leche; Pseudomonas fluorescens; Pseudomonas putidaORCID ID: Pereira FAB https://orcid.org/0000-0002-8826-1891, Luiz LL https://orcid.org/0000-0002-5364-5131, Bruzaroski SR https://orcid.org/0000-0001-5574-331X, Poli-Frederico RC https://orcid.org/0000-0003-4631-4606, Fagnani R https://orcid.org/0000-0002-7392-2087, Santana EHW https://orcid.org/0000-0002-7789-2575 Citation/Cómo citar este artículo: Pereira FAB, Luiz LL, Bruzaroski SR, Poli-Frederico RC, Fagnani R, Santana EHW. 2019. The effect of cold storage, time and the population of Pseudomonas species on milk lipolysis. Grasas y Aceites 70 (2), e300. https://doi.org/10.3989/gya.0583181

In this research communication the genetic diversity of Pseudomonas fluorescens (n = 67) and Pseudomonas putida (n = 44) isolated from refrigerated raw milk from bulk tank trucks were verified. The relationship between the genetic profile of the isolates and their lipoproteolytic potential was evaluated using skim milk agar and tributyrin agar (21°C/72 h). The lipoproteolytic potential (low or high), evaluated by the diameter of the halos (cm), was correlated with the number of milk producing properties that contributed to each sample (one sample = one bulk tank truck; 8−80 producers/sample) and the distance between the dairy properties and the processing plant (21−370 km). P. fluorescens was confirmed in all samples, while P. putida in 60% samples. For both species, two clusters (I and II) were observed, and the first one showed lower genotypic diversity and the presence of isolates with 100% similarity. P. fluorescens isolates presenting at least 70% similarity were 83.9% in Cluster I (n = 31) and 44.4% in Cluster II. In both clusters (I and II) observed in the P. fluorescens dendrogram, the occurrence of high proteolytic and lipolytic potential were equivalent. The higher the number of farms per milk sample, the greater the lipoproteolytic intensity of P. fluorescens isolates. In relation to P. putida isolates, 74% presented at least 50% similarity in Cluster I (n = 27) and only 35% in Cluster II (n = 17). The occurrence of high proteolysis linked to P. putida was proportional between both Clusters, but the occurrence of high lipolysis was greater in Cluster II. No significant association was detected between P. putida isolates and the variables studied. The results indicate the circulation of P. putida and P. fluorescens with 100% similarity in different milk producing regions. The level of genetic diversity was related only to the lipolytic capacity of P. putida.

No abstract