Heat-Stable Proteases from Psychrotrophs in Milk

1980 ◽  
Vol 43 (3) ◽  
pp. 197-200 ◽  
Author(s):  
A. GEBRE-EGZIABHER ◽  
E. S. HUMBERT ◽  
G. BLANKENAGEL
Keyword(s):  
Molecular Weight ◽  
Gel Electrophoresis ◽  
Dairy Products ◽  
Raw Milk ◽  
Gram Negative ◽  
Psychrotrophic Bacteria ◽  
Heat Resistant ◽  
Heat Stable ◽  
Single Enzyme

Twelve gram-negative psychrotrophic bacteria producing heat-resistant proteases that hydrolyzed casein were isolated from refrigerated raw milk. All were pseudomonads and the enzymes of the six most proteolytic cultures were examined further. The proteases were partially purified, and gel electrophoresis indicated that only a single enzyme was present in the preparation. The molecular weight of most of the proteases was approximately 45,000. All six enzymes retained some activity after being heated at 121 C for 10 min and casein was hydrolyzed at pH levels found in normal milk and many cultured dairy products. Although proteolysis was highest at about 40 C, considerable activity was evident at refrigeration temperatures.

Proteolysis in rennet-coagulated Spanish hard cheeses made from milk preserved by refrigeration and addition of carbon dioxide

2003 ◽  
Vol 70 (1) ◽  
pp. 115-122 ◽  
Author(s):  
Patricia Ruas-Madiedo ◽  
Juan Carlos Bada-Gancedo ◽  
Teresa Delgado ◽  
Miguel Gueimonde ◽  
Clara G de los Reyes-Gavilán
Keyword(s):  
Carbon Dioxide ◽  
Growth Rate ◽  
Dairy Products ◽  
Storage Time ◽  
Selective Pressure ◽  
Raw Milk ◽  
Psychrotrophic Bacteria ◽  
Heat Stable ◽  
On Farm

On-farm refrigeration of milk reduces the growth rate of mesophilic bacteria so allowing longer storage time of raw milk before processing. However, refrigeration creates a selective pressure favouring the multiplication of psychrotrophic bacteria present as normal contaminants in raw milk. Psychrotrophs are killed by most of the currently employed pasteurization and sterilization treatments of milk but they can produce extracellular heat-stable proteinases and lipases, which are capable of degrading various milk components, affecting the storage-life of heat-processed milk and the quality of dairy products (Champagne et al. 1994; Shah, 1994).

Rapid Enumeration of Psychrotrophic Bacteria in Raw and Pasteurized Milk

1976 ◽  
Vol 39 (4) ◽  
pp. 269-272 ◽  
Author(s):  
J. S. OLIVERIA ◽  
C. E. PARMELEE
Keyword(s):  
Dairy Products ◽  
Correlation Coefficients ◽  
Raw Milk ◽  
Standard Methods ◽  
Pasteurized Milk ◽  
Psychrotrophic Bacteria ◽  
Count Method ◽  
Plating Method ◽  
Rapid Enumeration ◽  
Good Agreement

A plating method was developed to enumerate psychrotrophic bacteria in raw and pasteurized milk. Standard Methods agar plates were prepared according to Standard Methods for the Examination of Dairy Products, and incubated at 21 C for 25 h (21 C-25 h). Counts obtained by this method were in very good agreement with those obtained by the standard psychrotrophic count. The correlation coefficients between counts obtained by the 21 C-25 h method and by the standard psychrotrophic count method for 132 samples of raw milk and 190 samples of pasteurized milk were 0.992 and 0.996, respectively.

Heat Resistant Psychrotrophic Bacteria in Raw Milk and Their Growth at 7 C

1978 ◽  
Vol 41 (2) ◽  
pp. 93-95 ◽  
Author(s):  
E. M. MIKOLAJCIK ◽  
N. T. SIMON
Keyword(s):  
Heat Treatment ◽  
Raw Milk ◽  
Plate Count ◽  
Psychrotrophic Bacteria ◽  
Standard Plate Count ◽  
Heat Resistant ◽  
Heated Milk ◽  
Standard Plate ◽  
Subsequent Storage ◽  
Microbiological Data

Microbiological data are presented for 109 raw milk samples, and for the same samples after heat treatment at 80 C for 12 min, and upon subsequent storage at 7 C for 7, 14, and 28 days. The Standard Plate Count of the raw milk averaged 110,000/ml with 65% of these organisms being penicillin-resistant. Immediately after heat treatment, 87% of the samples had psychrotrophic spore counts< 10/ml. After 14 and 28 days of storage, 50 and 83% of the samples had psychrotrophic counts ≥ 100,000/ml. It was concluded that growth of heat-resistant psychrotrophic organisms may cause spoilage of heated milk. No relationship could be demonstrated between gram-negative counts of raw milk, or initial mesophilic spore counts of heated milk, and bacterial numbers in heated, stored milk.

Adherence of psychrotrophic bacteria to dairy equipment surfaces

1992 ◽  
Vol 59 (3) ◽  
pp. 381-388 ◽  
Author(s):  
Beatriz Suárez ◽  
Carlos M. Ferreirós ◽  
Maria-Teresa Criado
Keyword(s):  
Raw Milk ◽  
Surface Hydrophobicity ◽  
Bacterial Adherence ◽  
Gram Negative Bacteria ◽  
Relevant Factor ◽  
Gram Negative ◽  
Bacterial Surface ◽  
Psychrotrophic Bacteria ◽  
Gram Positive Bacteria ◽  
Dairy Equipment

SummaryPsychrotrophic bacteria isolated from raw milk were tested for their ability to adhere to steel, two types of rubber, and glass, materials employed in the construction of milking equipment. The adherence assays were carried out by exposure of the materials to radioactively labelled bacteria in both a buffering solution (Ringer's) and milk. The degree of adherence of Gram-positive bacteria was lower (P< 0·001) than that of Gram-negative bacteria. Glass was the material least prone to bacterial adherence (P< 0·001); there were no significant differences between the other three materials. Milk was found to inhibit adhesion significantly (P< 0·05), this inhibition being more evident with the most adherent bacteria. There was no statistically significant correlation between bacterial surface hydrophobicity and adherence. Our results suggest that intrinsic bacterial adherence cannot be considered a relevant factor in the contamination of milking equipment.

Detection of acylated homoserine lactones in gram-negative proteolytic psychrotrophic bacteria isolated from cooled raw milk

Food Control ◽  
2007 ◽  
Vol 18 (10) ◽  
pp. 1322-1327 ◽  
Author(s):  
Uelinton Manoel Pinto ◽  
Eliseth de Souza Viana ◽  
Maurilio Lopes Martins ◽  
Maria Cristina Dantas Vanetti
Keyword(s):  
Raw Milk ◽  
Gram Negative ◽  
Homoserine Lactones ◽  
Psychrotrophic Bacteria ◽  
Acylated Homoserine Lactones

Effect of proteolytic raw milk psychrotrophs on Cheddar cheese-making with stored milk

1979 ◽  
Vol 46 (3) ◽  
pp. 497-509 ◽  
Author(s):  
Barry A. Law ◽  
Anthony T. Andrews ◽  
Allan J. Cliffe ◽  
M. Elisabeth Sharpe ◽  
Helen R. Chapman
Keyword(s):  
Gel Electrophoresis ◽  
Lipolytic Activity ◽  
Polyacrylamide Gel Electrophoresis ◽  
Cheddar Cheese ◽  
Raw Milk ◽  
Water Soluble ◽  
N Losses ◽  
Cheese Making ◽  
Psychrotrophic Bacteria ◽  
Colony Forming Units

SummaryThe effect of proteolytic, psychrotrophic strains of Pseudomonas fluorescens, Ps. putida and Acinetobacter spp. on cheese-making with stored milk has been investigated. Ps. fluorescens and Ps. putida growing for 72 h in raw milk at 7·5 °C to levels of approx. 107 colony-forming units/ml caused a low degree of β- and к-casein breakdown detectable by gel electrophoresis, but this was insufficient to affect N losses in whey or cheese yields. Variations in cheese-making times with pasteurized milks were not attributable to the counts of psychrotrophs in the corresponding raw milks. The water-soluble and TCA-soluble N fractions of maturing cheeses were unaffected by psychrotroph counts in raw milks, but small differences in levels of casein fractions of cheeses made from milks stored for 72 h were detected by quantitative polyacrylamide gel electrophoresis. The incidence of casein breakdown in raw milk and subsequently in cheese were not necessarily related. None of the cheeses developed off flavour related to excessive protein breakdown but many became lipolytically rancid, despite the selection of strains with low lipolytic activity on a diagnostic medium. It is concluded that the numbers of psychrotrophic bacteria likely to occur in stored raw milk under commercial conditions are unlikely to cause significant changes in the yields or quality of Cheddar cheese through their proteolytic activity.

scholarly journals Effect of acidification of raw milk on psychrotrophic microrganims.

2013 ◽  
Vol 2 (2) ◽  
Author(s):  
Marianne Ayumi Shirai ◽  
Maria Lucia Masson
Keyword(s):  
Dairy Products ◽  
Inhibitory Action ◽  
Raw Milk ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
Ph Reduction ◽  
Quality Of Milk ◽  
Micro Organisms ◽  
Milk And Dairy Products

<p>The contamination of raw milk with psychrotrophic micro-organisms has become a concern because they are able to multiply at refrigeration temperatures and produce heat resistant enzymes that affect the quality of milk and dairy products. The objective of this study was to evaluate the effect of acidification with CO<sub>2</sub> and HCl on mesophilic and psychrotrophic bacteria present in raw milk during cold storage. Raw milk samples were acidified with CO<sub>2</sub> and HCl 1N until pH 6,0 and stored at 5 &deg;C for 10 days. The results showed an average reduction of 1 logarithmic cycle in the growth of psychrotrophic and mesophilic microorganisms in samples treated with CO<sub>2</sub>. Acidification with HCl showed no effect, indicating that inhibitory action was due to CO<sub>2</sub> not by pH reduction.</p><p>&nbsp;</p><p>DOI: http://dx.doi.org/10.14685/rebrapa.v2i2.68</p>

scholarly journals Identification of the contaminating psychrotrophic bacteria in refrigerated bulked raw milk and the assessment of their deteriorating potential

2022 ◽  
Vol 43 (2) ◽  
pp. 739-750
Author(s):  
Patricia Rodrigues Condé ◽  
◽  
Cláudia Lúcia de Oliveira Pinto ◽  
Scarlet Ohana Gandra ◽  
Renata Cristina Almeida Bianchini Campos ◽  
...  
Keyword(s):  
Culture Media ◽  
Raw Milk ◽  
Culture Collection ◽  
Economic Losses ◽  
Prevention Measures ◽  
Multivariate Statistical ◽  
Gram Negative ◽  
Psychrotrophic Bacteria ◽  
Components Analysis ◽  
Specific Culture

This work aimed to characterize, identify, and determine the deteriorating potential of the contaminating psychrotrophic bacteria in refrigerated raw milk. Samples were submitted to serial dilutions and plated in specific culture media to form a bacterial culture collection. The isolates were characterized for their morphology and biochemical characteristics. The deteriorating potential of the isolates was determined according to the proteolytic, lipolytic and lecithinase activities at 4.0 ºC, 6.5 ºC, and 25.0 ºC. The results obtained for deterioration potential were assessed by the multivariate statistical method and by the principal components analysis (PCA). A total of 159 isolates were characterized, and of these, 46 strongly proteolytic Gram-negative isolates were selected for identification using the API 20 NE kit. The predominant bacteria were Gram-negative and oxidase and catalase positive, with a predominance of bacteria of the genus Pseudomonas. Using PCA, it was shown that the bacteria with the greatest deterioration potential were lecithinase producers, and that, in the autumn, proteolytic bacteria predominated at 4.0 ºC. Of the 46 isolates identified, more than 80% belonged to the species Pseudomonas fluorescens. Thus, attention should be given to the importance of implementing microbial contamination prevention measures in the bulking process, since, even under refrigeration, psychrotrophic bacteria multiply and produce enzymes that deteriorate lipids and proteins, with consequent quality losses of the milk and its derivatives, yield losses in the production of dairy products, and economic losses.

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