scholarly journals Characterisation of the thermostable protease AprX in strains of Pseudomonas fluorescens and impact on the shelf-life of dairy products: preliminary results

2016 ◽  
Vol 5 (4) ◽  
Author(s):  
Nadia Andrea Andreani ◽  
Lisa Carraro ◽  
Luca Fasolato ◽  
Stefania Balzan ◽  
Rosaria Lucchini ◽  
...  
Keyword(s):  
Shelf Life ◽  
Pseudomonas Fluorescens ◽  
Proteolytic Activity ◽  
Dairy Products ◽  
Trinitrobenzenesulfonic Acid ◽  
Predominant Role ◽  
Typing Method ◽  
Milk Samples ◽  
Different Strains ◽  
Reference Strains

Bacterial proteases are involved in food spoilage and shelf-life reduction. Among the bacterial proteases, a predominant role in spoilage of dairy products seems to be played by the thermostable metallo-protease AprX, which is produced by various strains of <em>Pseudomonas fluorescens</em>. Differences in AprX enzyme activity among different strains were highlighted, but the most proteolytic strains were not identified. In this study, the presence of the aprX gene was evaluated in 69 strains isolated from food matrices and 18 reference strains belonging to the P. fluorescens group, which had been previously typed by the multi locus sequence typing method. Subsequently, a subset of reference strains was inoculated in ultra-high temperature milk, and the expression of the <em>aprX</em> gene was evaluated at 22 and 6°C. On the same milk samples, the proteolytic activity was then evaluated through Azocasein and trinitrobenzenesulfonic acid solution assays. Finally, to assess the applicability of the former assay directly on dairy products the proteolityc activity was tested on industrial <em>ricotta</em> samples using the Azocasein assay. These results demonstrate the spread of <em>aprX</em> gene in most strains tested and the applicability of Azocasein assay to monitor the proteolytic activity in dairy products.

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

2019 ◽  
Vol 86 (4) ◽  
pp. 467-469
Author(s):  
Bruna de Moura Aguiar ◽  
Rosana de Longhi ◽  
Regina Celia Poli-Frederico ◽  
Rafael Fagnani ◽  
Elsa H W de Santana
Keyword(s):  
Shelf Life ◽  
Dairy Products ◽  
Bacterial Population ◽  
Raw Milk ◽  
Genetic Studies ◽  
Influence Of Temperature ◽  
Pseudomonas Spp ◽  
Research Communication ◽  
Milk Samples ◽  
Quality And Shelf Life

AbstractThe 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.

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

2019 ◽  
Vol 86 ◽  
Author(s):  
Camila Lampugnani ◽  
Mykaella Zanatta Was ◽  
Maike Taís Maziero Montanhini ◽  
Luis Augusto Nero ◽  
Luciano dos Santos Bersot
Keyword(s):  
Pseudomonas Fluorescens ◽  
Proteolytic Activity ◽  
Molecular Identification ◽  
Raw Milk ◽  
Chain Reaction ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
16S Gene ◽  
Polymerase Chain ◽  
Proteolytic Capacity

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.

Detection of proteolysis in raw milk stored at low temperature by an inhibition ELISA

1994 ◽  
Vol 61 (3) ◽  
pp. 395-404 ◽  
Author(s):  
Catherine Picard ◽  
Isabelle Plard ◽  
Dominique Rongdaux-Gaida ◽  
Jean-Claude Collin
Keyword(s):  
Proteolytic Activity ◽  
Limit Of Detection ◽  
Bacterial Count ◽  
Raw Milk ◽  
Enzyme Linked Immunosorbent Assay ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
Inhibition Elisa ◽  
Different Strains

SummaryAn inhibition ELISA (enzyme-linked immunosorbent assay) was developed for the determination of caseinomacropeptide (CMP) in order to estimate the proteolysis of κ-casein due to the enzymes of psychrotrophic bacteria in bulk raw milk. The CMP present in milk was quantified specifically by an antibody. The limit of detection was ∽ 0·1 μg/ml and the CV was < 10%. This method was used to study the proteolytic activity of three strains of psychrotrophic Pseudomonas fluorescens in raw milk and to analyse different raw milk samples supplied by four dairy plants. The proteolytic activity for different strains of psychrotrophs and for different milk samples varied considerably, but no correlation was established between the level of microbial flora and κ-casein proteolysis. It is thus not possible to determine the extent of proteolysis from the bacterial count alone. However, by CMP determination in bulk raw milk samples after 6 d storage at 4°C, the mean κ-casein proteolysis was ∽ 4%. Among the milk samples analysed that contained < 107 cfu psychrotrophs/ml, 30% exhibited a proteolysis of κ-casein < 0·5%, i.e. < 5μg CMP/ml.

Heat-Resistant Psychrotrophic Bacteria Isolated from Pasteurized Milk1

1977 ◽  
Vol 40 (2) ◽  
pp. 101-108 ◽  
Author(s):  
C. J. WASHAM ◽  
H. C. OLSON ◽  
E. R. VEDAMUTHU
Keyword(s):  
Thermal Resistance ◽  
Shelf Life ◽  
Detailed Examination ◽  
Genus Bacillus ◽  
Pasteurized Milk ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
Heat Resistant ◽  
Different Types

Psychrotrophic bacteria were isolated from 227 pasteurized milk samples which had a shelf life in excess of 20 days at 7.2 C. Of 700 cultures isolated, 135 were resistant to heating at 72 C for 16 sec and were able to re-establish growth at 7.2 C. Thirty-five cultures, representing 15 different types were subjected to detailed examination to determine their actions on refrigerated milk, growth temperatures, thermal resistance at various temperatures, and their identities. The spore-forming genus Bacillus occured most frequently. The non-sporing types were assigned to the genera Arthrobacter, Microbacterium, Streptococcus, and Corynebacterium.

scholarly journals Manufacturing of Fermented dairy products by using Lactobacillus casei which had the ability to lower cholesterol

2010 ◽  
Vol 4 (1) ◽  
pp. 72-81
Author(s):  
Abdul Wahed Baker ◽  
Zaid A. A. ◽  
Amer A. A.
Keyword(s):  
Shelf Life ◽  
Dairy Products ◽  
Lactobacillus Casei ◽  
Storage Period ◽  
Bacterial Cells ◽  
Manufactured Products ◽  
Fermented Dairy Products ◽  
Therapeutic Properties ◽  
Fermented Dairy ◽  
Number Of Bacteria

The study included manufacturing of fermented dairy products by using full cream milk of four kinds of mammalian: (Buffalos, Cows, Sheep's and Goats); with the use of Lactobacillus casei as a starter for the production of fermented dairy products which had the ability to lower cholesterol percentage in the above mentioned products by (71.4, 70, 74.8 and 67.7)% respectively. The viability of Lb. casei had not been affected significantly during storage shelf life of 21days " The product shelf life " , keeping their therapeutic properties unaltered with high viable number of bacteria at time of consumption. The viable counts of the bacteria after storage period for manufactured products were (1.06× 109, 8.1× 108, 7.5× 108and 8× 108) CFU/ml respectively. These numbers represent a decrease equal to one logarithmic cycle for each of manufactured products of Cows, Sheep's and Goats milk, and the decrease of bacteria's viability of manufactured products of Buffalos milk was less than one logarithmic cycle. Results of statistical analysis showed that there was highly significant differences (P<0.05) in the viable bacterial cells counts between manufactured products. By sensory comparison of the manufactured fermented products together, the results shows that the manufactured products from Buffalos milk was the best then the manufactured products of Cows milk then Sheep's milk then goats milk

scholarly journals The Occurrence of Aflatoxin M1 in Milk, soft cheese and yoghurt in Baghdad Province by Using ELISA Test

2014 ◽  
Vol 38 (2) ◽  
pp. 9-16
Author(s):  
Najim Hadi Najim
Keyword(s):  
Dairy Products ◽  
Raw Milk ◽  
Elisa Test ◽  
Mean Value ◽  
Aflatoxin M1 ◽  
Contamination Level ◽  
Milk Samples ◽  
White Cheese ◽  
The Mean ◽  
Milk And Dairy Products

     Milk and dairy products are fundamental components in the human diet and may be the principle way for entrance of Aflatoxin M1 (AFM1) in to the human body. All milk and dairy products samples were tested for the occurrence of AFM1 by the competitive ELISA technique. Out of 32 bovine raw milk samples that were collected from eight villages around Baghdad province, 32 samples (100 %) were contaminated with AFM1 ranging from 0.15 to 86.96ng/kg with mean value of 42.37±26.07 ng/kg, of which 17 samples were contaminated with concentrations < 50 ng/kg and 15 samples exceeded the maximum acceptable level of AFM1 in milk (50 ng/kg) imposed by the European legislation. The raw milk samples belonged to animals fed with composite and stored fodder as in Althahab Alabiadh, Radhwaniya and Fadhaliya villages had higher significantly AFM1 concentrations over all the other five villages (Grazing feed). All 32 (100%) locally produced soft white cheese samples analyzed were contaminated with AFM1 ranging from 31.84 to 89.44 ng/kg with the mean value of 59.92±17.03 ng/kg. Out of 32 locally produced yoghurt samples analyzed, 32 samples (100%) were contaminated with AFM1 ranging from 0.16 to 42.74 ng/kg with the mean value of 16.92±11.55 ng/kg. Thirty samples (100%) of the examined 30 imported UHT milk samples that were collected from different commercial companies in the province of Baghdad presented significantly  high contamination level with AFM1 that were found to range from 0.18 to 85.66 ng/kg.

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