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.

Milk Films Exposed to High Humidity: Studies with Electron Microscopy and Electrophoresis1,2

1980 ◽  
Vol 43 (1) ◽  
pp. 29-35 ◽  
Author(s):  
R. C. MABESA ◽  
R. T. MARSHALL ◽  
M. E. ANDERSON
Keyword(s):  
Electron Microscopy ◽  
Relative Humidity ◽  
Gel Electrophoresis ◽  
Polyacrylamide Gel Electrophoresis ◽  
Raw Milk ◽  
Steel Plates ◽  
High Humidity ◽  
Residual Film ◽  
Contact Surfaces ◽  
Scanning Electron

Stainless steel plates, which are similar to milk contact surfaces, were dipped in fresh raw milk. The residual film was dried (37 C and 10% to 20% relative humidity) for 30 min. Treated plates were then exposed to 100% relative humidity for 30 min at 37 C. Scanning electron microscopy revealed splotches of fat on surfaces of dried films and the humidified films had a more aggregated and porous appearance than films that were dried only. The incidence of granulated lactose was greater among humidified samples than among nonhumidified samples. Discontinuous polyacrylamide gel electrophoresis revealed that α- and β-caseins resisted rinsing from plates on which dried films were exposed to 100% relative humidity but not from plates on which films had been dried only.

Lactobacilli in Cheddar cheese

1959 ◽  
Vol 26 (2) ◽  
pp. 157-161 ◽  
Author(s):  
C. K. Johns ◽  
Shirley E. Cole
Keyword(s):  
Cheddar Cheese ◽  
Raw Milk ◽  
Cheese Making

The numbers of lactobacilli present in milk for cheese-making and in the cheese at various stages of ripening, have been determined for 38 Cheddar cheeses made during studies on flavour enhancement. These organisms multiplied rapidly even during the first few days of curing. Maximum levels were attained at 3–6 months; at 1 year counts had declined appreciably.Flavour intensity in the experimental cheese appeared to be correlated with the level of lactobacilli present in (a) milk at the start of cheese-making and (b) at subsequent stages of ripening. These two count levels were usually closely correlated. Factory raw milk had the highest counts and gave the highest degree of flavour, followed by similar milk pasteurized and inoculated with selected strains of lactobacilli.

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.

The effect of lipolytic Gram-negative psychrotrophs in stored milk on the development of rancidity in Cheddar cheese

1976 ◽  
Vol 43 (3) ◽  
pp. 459-468 ◽  
Author(s):  
B. A. Law ◽  
M. Elisabeth Sharpe ◽  
Helen R. Chapman
Keyword(s):  
Heat Treatment ◽  
Fatty Acid ◽  
Free Fatty Acid ◽  
Pseudomonas Fluorescens ◽  
Culture Supernatant ◽  
Lipolytic Activity ◽  
Cheddar Cheese ◽  
Single Strain ◽  
Gram Negative ◽  
Colony Forming Units

SummaryThe highest incidence of lipolytic activity among the psychrotrophic Gram-negative flora of commercial raw milks was found in strains ofPseudomonas fluorescensandPs. fragi.The lipases of all of the lipolytic strains remained wholly or partly active after heat treatment at 63°C for 30 min. Two of the strains tested further had lipases which retained 20–25% of their activity even when heated at 100 °C for 10 min. Cheeses made from milks in which strains or a single strain of lipolytic Gram-negative rods (GNR) had been allowed to multiply to > 107colony forming units/ml became rancid after 4 months even though the GNR had been killed by pasteurization. The rancidity was characterized by a soapy off-flavour in cheeses containing free fatty acid concentrations from 3 to 10 times higher than those in control cheeses made from stored milks with low counts of GNR. Strong rancidity could be reproduced by adding the culture supernatant of a pre-grown lipolytic strain, but not the washed cells, to milk and pasteurizing it immediately before cheese-making, demonstrating the extracellular nature of the rancidity-inducing lipases.

scholarly journals Pseudomonas spp. and P. fluorescens: population in refrigerated raw milk

2017 ◽  
Vol 47 (1) ◽  
Author(s):  
Kelly Molin de Almeida ◽  
Samera Rafaela Bruzaroski ◽  
Daniel Zanol ◽  
Marcela de Melo ◽  
Joice Sifuentes dos Santos ◽  
...  
Keyword(s):  
Titratable Acidity ◽  
Dairy Farms ◽  
Raw Milk ◽  
Quality Parameters ◽  
Pseudomonas Spp ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
Bulk Milk ◽  
Colony Forming Units ◽  
Bulk Tank

ABSTRACT: Raw milk samples were collected from cooling tanks (after they cooled for 48 h) in five dairy farms and the corresponding bulk tank (bulk milk transportation, BMT) when they arrived to the industry. Routine physical chemical analyzes and quantification of psychrotrophic ( Pseudomonas spp. and P. fluorescens ) and aerobic mesophilic (AM) populations were performed. Only relative density and titratable acidity values for samples of milk from three farms were in agreement to the quality parameters required by law. In the BMT, only the protein content has not reached the minimum value established by law, and counting was performed for AM (>105 colony forming units (CFU) mL-1) and psychrotrophic bacteria (2.8x106CFU mL-1). Pseudomonas spp. counting corresponded to 17.9% of the psychrotrophic population, and P. fluorescens was 3.4% of Pseudomonas spp . count. In milk samples from dairy farms, counts were variable for AM (3.4x105 to 3.7 x107CFU mL-1), psychrotrophic (4.0x104 to 3.1x106CFU mL-1), Pseudomonas spp. (2.3x104 to 1.8x105CFU mL-1), and P. fluorescens (62 to 8.4x103CFU mL-1). For the populations studied, no statistical difference (P>0.05) was observed between counts reported in milk samples collected in dairy farms (cooling tanks) and BMT. Therefore, the genera Pseudomonas spp. and P. fluorescens were not the most frequent psychrotrophic bacteria in this studied milk transportation line.

Ultrastructural localization of specific nucleoprotein fractions

1978 ◽  
Vol 36 (2) ◽  
pp. 204-205
Author(s):  
G. L. Brown
Keyword(s):  
Gel Electrophoresis ◽  
Mouse Liver ◽  
Polyacrylamide Gel Electrophoresis ◽  
Ultrastructural Localization ◽  
Polyacrylamide Gel ◽  
Acid Extraction ◽  
Acid Solutions ◽  
Low Salt ◽  
Liver Nuclei ◽  
Phosphate Groups

Bismuth (Bi) stains nucleoproteins (NPs) by interacting with available amino and primary phosphate groups. These two staining mechanisms are distinguishable by glutaraldehyde crosslinking (Fig. 1,2).Isolated mouse liver nuclei, extracted with salt and acid solutions, fixed in either formaldehyde (form.) or gl utaraldehyde (glut.) and stained with Bi, were viewed to determine the effect of the extractions on Bi stainina. Solubilized NPs were analyzed by SDS-polyacrylamide gel electrophoresis.Extraction with 0.14 M salt does not change the Bi staining characteristics (Fig. 3). 0.34 M salt reduces nucleolar (Nu) staining but has no effect on interchromatinic (IC) staining (Fig. 4). Proteins responsible for Nu and glut.- insensitive IC staining are removed when nuclei are extracted with 0.6 M salt (Fig. 5, 6). Low salt and acid extraction prevents Bi-Nu staining but has no effect on IC staining (Fig. 7). When nuclei are extracted with 0.6 M salt followed by low salt and acid, all Bi-staining components are removed (Fig. 8).

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