Hydration of casein micelles and caseinates: Implications for casein micelle structure

2017 ◽  
Vol 74 ◽  
pp. 1-11 ◽  
Author(s):  
Thom Huppertz ◽  
Inge Gazi ◽  
Hannemieke Luyten ◽  
Hans Nieuwenhuijse ◽  
Arno Alting ◽  
...  
Keyword(s):  
Casein Micelle ◽  
Casein Micelles ◽  
Micelle Structure

High-pressure treatment of milk: effects on casein micelle structure and on enzymic coagulation

2000 ◽  
Vol 67 (1) ◽  
pp. 31-42 ◽  
Author(s):  
ERIC C. NEEDS ◽  
ROBERT A. STENNING ◽  
ALISON L. GILL ◽  
VICTORIA FERRAGUT ◽  
GILLIAN T. RICH
Keyword(s):  
Whey Proteins ◽  
Skim Milk ◽  
Casein Micelle ◽  
Casein Micelles ◽  
Dense Networks ◽  
Protein Levels ◽  
Micelle Structure ◽  
Milk Casein ◽  
Β Lactoglobulin ◽  
Gel Network

High isostatic pressures up to 600 MPa were applied to samples of skim milk before addition of rennet and preparation of cheese curds. Electron microscopy revealed the structure of rennet gels produced from pressure-treated milks. These contained dense networks of fine strands, which were continuous over much bigger distances than in gels produced from untreated milk, where the strands were coarser with large interstitial spaces. Alterations in gel network structure gave rise to differences in rheology with much higher values for the storage moduli in the pressure-treated milk gels. The rate of gel formation and the water retention within the gel matrix were also affected by the processing of the milk. Casein micelles were disrupted by pressure and disruption appeared to be complete at treatments of 400 MPa and above. Whey proteins, particularly β-lactoglobulin, were progressively denatured as increasing pressure was applied, and the denatured β-lactoglobulin was incorporated into the rennet gels. Pressure-treated micelles were coagulated rapidly by rennet, but the presence of denatured β-lactoglobulin interfered with the secondary aggregation phase and reduced the overall rate of coagulation. Syneresis from the curds was significantly reduced following treatment of the milk at 600 MPa, probably owing to the effects of a finer gel network and increased inclusion of whey protein. Levels of syneresis were more similar to control samples when the milk was treated at 400 MPa or less.

Influence of aggregation on the susceptibility of casein to proteolysis

1970 ◽  
Vol 37 (2) ◽  
pp. 173-180 ◽  
Author(s):  
P. F. Fox
Keyword(s):  
Calcium Phosphate ◽  
Equilibrium Dialysis ◽  
Limited Proteolysis ◽  
Skim Milk ◽  
Sodium Caseinate ◽  
Casein Micelle ◽  
Casein Micelles ◽  
Micelle Structure ◽  
Colloidal Calcium Phosphate

SummaryThe susceptibility of the casein in milk to proteolysis was shown to be greatly influenced by its state of aggregation. In normal milk, where the casein is largely in micellar form, the αs1- and β-caseins are almost inaccessible to proteolysis. On removal of the colloidal phosphate, the casein micelles disintegrate, rendering the components, especially the αs1-casein, accessible to proteolysis. The role of colloidal calcium phosphate in the casein micelle is believed to be that of a non-specific aggregating agent which can be effectively replaced by calcium. Dissolved colloidal phosphate can be effectively reformed by elevation of the pH of colloidal phosphate-free (CPF) milk before equilibrium dialysis. Addition of κ-casein to CPF milk also causes aggregation of the component caseins but the micelles formed are smaller than those of normal milk.The behaviour of micellar β-casein differs considerably from that of micellar αs1-casein. The evidence suggests that part of the β-casein freely dissociates either outside or within the micelle when the temperature is reduced. The temperature dependence of the susceptibility of β-casein to proteolysis was similar in skim-milk and in solutions of sodium caseinate, and increased as the temperature was reduced. αs1-Casein was quite resistant to proteolysis in normal milk but became susceptible when the micelle structure was disrupted on removal of colloidal phosphate.It is concluded that limited proteolysis may prove a valuable technique in the study of casein micelle structure.

Electrophoretic mobility of casein micelles

1979 ◽  
Vol 46 (3) ◽  
pp. 441-451 ◽  
Author(s):  
Donald F. Darling ◽  
John Dickson
Keyword(s):  
Electrophoretic Mobility ◽  
Moving Boundary ◽  
Ionic Composition ◽  
Skim Milk ◽  
Casein Micelle ◽  
Casein Micelles ◽  
Zeta Potentials ◽  
Micelle Structure ◽  
Increase With Increase ◽  
Micelle Size

SummaryA simplified moving boundary electrophoresis technique has been developed for the measurement of the electrophoretic mobility of casein micelles. The zeta potentials of casein micelles from different skim-milk samples were calculated using Henry's equation and shown to decrease with decrease in pH between pH 6.9 and 5.3 and to increase with increase in temperature between 10 and 45 °C. Neither severe heat treatment (up to 135 °C for 51 min) nor centrifugal fractionation of micelles into different micelle size ranges had any significant effect on zeta potential. The ionic composition of the serum phase has been shown to be extremely important in determining the electrophoretic mobility. Casein micelles electrophoresed through milk ultrafiltrate consistently gave a lower mobilities than the same micelles centrifuged through milk centrifugate. The results are discussed in relation to present theories of casein micelle structure; these theories do not accommodate all of the observations.

scholarly journals Association of casein micelle size and enzymatic curd strength and dry matter curd yield

2019 ◽  
Vol 49 (3) ◽  
Author(s):  
Denise Ribeiro de Freitas ◽  
Fernando Nogueira de Souza ◽  
Jamil Silvano de Oliveira ◽  
Diêgo dos Santos Ferreira ◽  
Cristiane Viana Guimarães Ladeira ◽  
...  
Keyword(s):  
Fixed Effects ◽  
Dry Matter ◽  
Linear Models ◽  
Favorable Effect ◽  
Casein Micelle ◽  
Casein Micelles ◽  
Micelle Size ◽  
Milk Protein Content ◽  
Bulk Tank ◽  
Cheese Production

ABSTRACT: The aim of the present study was to explore the association between milk protein content and casein micelle size and to examine the effects of casein micelle size on enzymatic curd strength and dry matter curd yield using reduced laboratory-scale cheese production. In this research, 140 bulk tank milk samples were collected at dairy farms. The traits were analyzed using two linear models, including only fixed effects. Smaller micelles were associated with higher κ-casein and lower αs-casein contents. The casein micellar size (in the absence of the αs-casein and κ-casein effects) did not affect the enzymatic curd strength; however, smaller casein micelles combined with higher fat, lactose, casein and κ-casein contents exhibited a favorable effect on the dry matter curd yield. Overall, results of the present study provide new insights into the importance of casein micelle size for optimizing cheese production.

Influence of calcium chloride on the chymosin-initiated coagulation of casein micelles

1986 ◽  
Vol 53 (3) ◽  
pp. 371-379 ◽  
Author(s):  
Neal A. Bringe ◽  
John E. Kinsella
Keyword(s):  
Calcium Chloride ◽  
Average Rate ◽  
Casein Micelle ◽  
Clotting Time ◽  
Casein Micelles ◽  
Casein Hydrolysis ◽  
Catalysed Reaction ◽  
Low Concentrations ◽  
Hydrolysis Of ◽  
Electrostatic Repulsions

SUMMARYCoagulation of para-casein micelles was monitored using a Platelet Aggregometer at 37·8 °C and pH 6·7. The macropeptide released by chymosin was determined quantitatively with fluorescamine. The aggregatability of para-casein micelles integrated over the complete hydrolysis of κ-casein was calculated from the amount of κ-casein hydrolysed during the clotting time (Tc). Low concentrations of CaCl2 enhanced the rate of κ-casein hydrolysis but increases in CaCl2 concentration above 8 mM caused marked decreases in this rate. Calcium chloride enhanced the ability of para-casein micelles to aggregate. Little aggregation of para-casein micelles occurred at 0·6 mM-CaCl2 even after all of the κ-casein was hydrolysed. As the concentration of CaCl2 was increased from 3 to 60 mM, aggregation of para-casein micelles took place at progressively lower levels of κ-casein hydrolysis and the percentage hydrolysis at the Tc decreased markedly from 71±7% to 26±8%. The combined influence of CaCl2 on the velocity of the chymosin-catalysed reaction and on para-casein micelle aggregatability accounted for its effect on the average rate of coagulation (calculated by the reciprocal of the Tc). Results are consistent with the hypothesis that electrostatic repulsions and ionic bonding are involved in the interaction between chymosin and κ-casein.

A New Preparation Technique for High Resolution Imaging of Protein Structure: Casein Micelles.

1997 ◽  
Vol 3 (S2) ◽  
pp. 353-354
Author(s):  
William R. McManus ◽  
Donald J. McMahon
Keyword(s):  
Electron Microscopy ◽  
Protein Structure ◽  
High Resolution ◽  
Metal Layer ◽  
Casein Micelle ◽  
Preparation Technique ◽  
Electron Microscopic ◽  
Casein Micelles ◽  
Microscopy Method ◽  
Microscopy Techniques

Models for the structure of the bovine casein micelle have been proposed in the past (1,2,3,4). These models are based on the chemical and physical properties of the micelles and fall into two general catagories, framework and submicelle models. Electron Microscopy techniques were one of the tools used in the development of these models. However, no definative model has been established. We have developed a new electron microscopy method and it is being applied to the re-examination of the protein structure of the casein micelle, with the goal of establishing a definative model for the structure of the casein micelle.High resolution scannning electron microscopy has proven unsuccessful in revealing the protein structure in the casein micelle (Fig 1). To create high resolution scanning electron microscopic images, fine metal coatings are required in the 5 to l0nm range. Following the application of these coatings, images of casein micelles resemble a melting lumpy sphere. This is due to the metal layer obscuring the proteins from view.

Heat stability of milk: pH-dependent dissociation of micellar κ-casein on heating milk at ultra high temperatures

1985 ◽  
Vol 52 (4) ◽  
pp. 529-538 ◽  
Author(s):  
Harjinder Singh ◽  
Partick F. Fox
Keyword(s):  
Whey Protein ◽  
Whey Proteins ◽  
Heat Stability ◽  
Casein Micelle ◽  
Casein Micelles ◽  
Ph Profile ◽  
Ph Values ◽  
Maximum Stability ◽  
Β Lactoglobulin ◽  
Maximum Minimum

SUMMARYPreheating milk at 140 °C for 1 min at pH 6·6, 6·8, 7·0 or 7·2 shifted the heat coagulation time (HCT)/pH profile to acidic values without significantly affecting the maximum stability. Whey proteins (both β-lactoglobulin and α-lactalbumin) co-sedimented with the casein micelles after heating milk at pH < 6·9 and the whey protein-coated micelles, dispersed in milk ultrafiltrate, showed characteristic maxima–minima in their HCT/pH profile. Heating milk at higher pH values (> 6·9) resulted in the dissociation of whey proteins and κ-casein-rich protein from the micelles and the residual micelles were unstable, without a maximum–minimum in the HCT/pH profile. Preformed whey protein–casein micelle complexes formed by preheating (140 °C for 1 min) milk at pH 6·7 dissociated from the micelles on reheating (140 °C for 1 min) at pH > 6·9. The dissociation of micellar-κ-casein, perhaps complexed with whey proteins, may reduce the micellar zeta potential at pH ≃ 6·9 sufficiently to cause a minimum in the HCT/pH profile of milk.

Use of Platelet Aggregometer to monitor the chymosin-initiated coagulation of casein micelles

1986 ◽  
Vol 53 (3) ◽  
pp. 359-370 ◽  
Author(s):  
Neal A. Bringe ◽  
John E. Kinsella
Keyword(s):  
Light Transmission ◽  
Average Rate ◽  
Enzyme Concentration ◽  
Casein Micelle ◽  
Clotting Time ◽  
Casein Micelles ◽  
Catalysed Reaction ◽  
High Enzyme ◽  
Lag Period ◽  
Limiting Value

SUMMARYThe chymosin-initiated coagulation of casein micelles was followed by monitoring light transmission using a Platelet Aggregometer. The release of macropeptide by chymosin was monitored using fluorescamine. The lag period in the clotting reaction was proportional to clotting time and the reciprocal of enzyme concentration. The average rate of coagulation, which was approximately equal to the reciprocal of clotting time (Tc), increased in proportion to enzyme concentration at low enzyme concentrations and reached a limiting value at high enzyme concentrations. The percentage hydrolysis at the Tc was 47 ± 5% in the presence of 20 mM-CaCl2 and it was calculated that a 5-fold decrease in the speed of the enzyme-catalysed reaction would decrease this value at the Tc to 43 ± 5%. The possible uses and limitations of the Platelet Aggregometer for determining the influence of the chemical environment on the velocity of the chymosin-catalysed reaction and para-casein micelle aggregatability are discussed.

Influence of homogenization of concentrated milks on the structure and properties of rennet curds

1983 ◽  
Vol 50 (3) ◽  
pp. 341-348 ◽  
Author(s):  
Margaret L. Green ◽  
Richard J. Marshall ◽  
Frank A. Glover
Keyword(s):  
Fatty Acid ◽  
Free Fatty Acid ◽  
Size Distribution ◽  
Casein Micelle ◽  
Structure And Properties ◽  
Moisture Retention ◽  
Casein Micelles ◽  
Micelle Size ◽  
Whole Milk ◽  
Milk Casein

SummaryWhole milk was concentrated by ultrafiltration in a plant causing some homogenization of the fat. Comparisons were made with milk concentrated in a plant causing little homogenization and with milk homogenized conventionally. None of the processes appreciably affected the casein micelle size distribution. On rennet treatment of homogenized milk, casein micelle aggregation occurred more slowly, the protein network in the curd was less coarse and the rate of whey loss was reduced, compared with non-homogenized milk at the same concentration. In using concentrated milks for cheesemaking homogenization improved the composition of Cheddar cheese, because of increased fat and moisture retention, but curd fusion was poorer. Some aspects of the texture of the mature cheeses were improved, but the free fatty acid levels were higher. Values for the firmness of curds, formed from milks processed in different ways, did not relate to the extent of aggregation of the casein micelles. It is suggested that the complete cheesemaking process is driven by the tendency of the casein to aggregate.

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