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Marcela Alexander - One of the best experts on this subject based on the ideXlab platform.
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addition of sodium Caseinate to skim milk inhibits rennet induced aggregation of Casein micelles
Food Hydrocolloids, 2012Co-Authors: Zafir Gaygadzhiev, Valerie Massel, Marcela Alexander, Milena CorredigAbstract:Abstract The objective of this paper was to observe the rennet-induced aggregation behaviour of Casein micelles in milk in the presence of additional sodium Caseinate. Analysis of the centrifugal supernatants by size exclusion chromatography confirmed an increase in the soluble protein in the milk serum phase after addition of sodium Caseinate. Although the total amount of κ-Casein hydrolyzed over time was not affected, there was a significant effect of soluble Casein on milk gelation, with a dose-dependent decrease of the gelation time as measured by rheology. Light scattering experiments also confirmed that the addition of soluble Caseins inhibited the aggregation of Casein micelles. Addition of 1 mM CaCl 2 prior to renneting increased the extent of rennet aggregation in samples containing additional sodium Caseinate, but the inhibiting effect was still evident. The amount of soluble Casein (as measured by chroma tography) significantly decreased after renneting, suggesting its association with the micellar fraction. Supporting experiments carried out with purified fractions of soluble Caseins demonstrated that both α s -Casein and β-Casein played a role as protective colloids (increasing steric repulsion) during renneting. It was concluded that the inhibiting effect observed during gelation was caused by the adsorption of soluble Casein molecules on the surface of rennet-altered Casein micelles.
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modification to the renneting functionality of Casein micelles caused by nonionic surfactants
Journal of Dairy Science, 2010Co-Authors: Ion G Titapiccolo, Milena Corredig, Marcela AlexanderAbstract:Nonionic emulsifiers of small molecular weight such as polysorbates are widely used in dairy products. Nevertheless, the mechanism of interaction between these surfactants and milk proteins is not yet fully understood. This work investigated the effect of Tween 20 on Casein micelles by studying the renneting behavior of skim milk in the presence of different amounts of surfactant. The presence of Tween accelerated both the first and second phase of renneting in skim milk. The gel obtained showed a higher elastic modulus than that of a skim milk gel, but also showed similar brittleness. By varying the size of the surfactant (Tween 20 or Tween 80) as well as the colloidal state of the proteins in solution, it was possible to demonstrate that the surfactant did not have a direct effect on the activity of the enzyme, but rather had a direct effect on the Casein micelles. The effect of surfactant on the gelation point was reduced by increasing surfactant size. The presence of Tween caused an increase in the size of the micelles without affecting their stability. In addition, Tween did not alter the amount of Caseins free in the serum phase. These findings can contribute to improving our ability to custom design final structures in rennet-induced gels, though further studies are needed to fully understand the mechanism at play when Casein micelles are enzymatically cleaved in the presence of nonionic surfactants of small molecular weight.
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the impact of the concentration of Casein micelles and whey protein stabilized fat globules on the rennet induced gelation of milk
Colloids and Surfaces B: Biointerfaces, 2009Co-Authors: Zafir Gaygadzhiev, Milena Corredig, Marcela AlexanderAbstract:The rennet-induced aggregation of skim milk recombined with whey protein-stabilized emulsion droplets was studied using diffusing wave spectroscopy (DSW) and small deformation rheology. The effect of different volume fractions of Casein micelles and fat globules was investigated by observing changes in turbidity (1/l*), apparent radius, elastic modulus and mean square displacement (MSD), in addition to confocal imaging of the gels. Skim milk containing different concentration of Casein micelles showed comparable light-scattering profiles; a higher volume fraction of Caseins led to the development of more elastic gels. By following the development of 1/l* in recombined milks, it was possible to describe the behaviour of the fat globules during the initial stages of rennet coagulation. Increasing the volume fraction of fat globules showed a significant increase in gel elasticity, caused by flocculation of the oil droplets. The presence of flocculated oil globules within the gel structure was confirmed by confocal microscopy observations. Moreover, a lower degree of κ-Casein hydrolysis was needed to initiate Casein micelles aggregation in milk containing whey protein-stabilized oil droplets compared to skim milk. This study for the first time clearly describes the impact of a mixture of Casein micelles and whey protein-stabilized fat globules on the pre-gelation stages of rennet coagulation, and further highlights the importance of the flocculation state of the emulsion droplets in affecting the structure formation of the gel.
Milena Corredig - One of the best experts on this subject based on the ideXlab platform.
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addition of sodium Caseinate to skim milk inhibits rennet induced aggregation of Casein micelles
Food Hydrocolloids, 2012Co-Authors: Zafir Gaygadzhiev, Valerie Massel, Marcela Alexander, Milena CorredigAbstract:Abstract The objective of this paper was to observe the rennet-induced aggregation behaviour of Casein micelles in milk in the presence of additional sodium Caseinate. Analysis of the centrifugal supernatants by size exclusion chromatography confirmed an increase in the soluble protein in the milk serum phase after addition of sodium Caseinate. Although the total amount of κ-Casein hydrolyzed over time was not affected, there was a significant effect of soluble Casein on milk gelation, with a dose-dependent decrease of the gelation time as measured by rheology. Light scattering experiments also confirmed that the addition of soluble Caseins inhibited the aggregation of Casein micelles. Addition of 1 mM CaCl 2 prior to renneting increased the extent of rennet aggregation in samples containing additional sodium Caseinate, but the inhibiting effect was still evident. The amount of soluble Casein (as measured by chroma tography) significantly decreased after renneting, suggesting its association with the micellar fraction. Supporting experiments carried out with purified fractions of soluble Caseins demonstrated that both α s -Casein and β-Casein played a role as protective colloids (increasing steric repulsion) during renneting. It was concluded that the inhibiting effect observed during gelation was caused by the adsorption of soluble Casein molecules on the surface of rennet-altered Casein micelles.
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modification to the renneting functionality of Casein micelles caused by nonionic surfactants
Journal of Dairy Science, 2010Co-Authors: Ion G Titapiccolo, Milena Corredig, Marcela AlexanderAbstract:Nonionic emulsifiers of small molecular weight such as polysorbates are widely used in dairy products. Nevertheless, the mechanism of interaction between these surfactants and milk proteins is not yet fully understood. This work investigated the effect of Tween 20 on Casein micelles by studying the renneting behavior of skim milk in the presence of different amounts of surfactant. The presence of Tween accelerated both the first and second phase of renneting in skim milk. The gel obtained showed a higher elastic modulus than that of a skim milk gel, but also showed similar brittleness. By varying the size of the surfactant (Tween 20 or Tween 80) as well as the colloidal state of the proteins in solution, it was possible to demonstrate that the surfactant did not have a direct effect on the activity of the enzyme, but rather had a direct effect on the Casein micelles. The effect of surfactant on the gelation point was reduced by increasing surfactant size. The presence of Tween caused an increase in the size of the micelles without affecting their stability. In addition, Tween did not alter the amount of Caseins free in the serum phase. These findings can contribute to improving our ability to custom design final structures in rennet-induced gels, though further studies are needed to fully understand the mechanism at play when Casein micelles are enzymatically cleaved in the presence of nonionic surfactants of small molecular weight.
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the impact of the concentration of Casein micelles and whey protein stabilized fat globules on the rennet induced gelation of milk
Colloids and Surfaces B: Biointerfaces, 2009Co-Authors: Zafir Gaygadzhiev, Milena Corredig, Marcela AlexanderAbstract:The rennet-induced aggregation of skim milk recombined with whey protein-stabilized emulsion droplets was studied using diffusing wave spectroscopy (DSW) and small deformation rheology. The effect of different volume fractions of Casein micelles and fat globules was investigated by observing changes in turbidity (1/l*), apparent radius, elastic modulus and mean square displacement (MSD), in addition to confocal imaging of the gels. Skim milk containing different concentration of Casein micelles showed comparable light-scattering profiles; a higher volume fraction of Caseins led to the development of more elastic gels. By following the development of 1/l* in recombined milks, it was possible to describe the behaviour of the fat globules during the initial stages of rennet coagulation. Increasing the volume fraction of fat globules showed a significant increase in gel elasticity, caused by flocculation of the oil droplets. The presence of flocculated oil globules within the gel structure was confirmed by confocal microscopy observations. Moreover, a lower degree of κ-Casein hydrolysis was needed to initiate Casein micelles aggregation in milk containing whey protein-stabilized oil droplets compared to skim milk. This study for the first time clearly describes the impact of a mixture of Casein micelles and whey protein-stabilized fat globules on the pre-gelation stages of rennet coagulation, and further highlights the importance of the flocculation state of the emulsion droplets in affecting the structure formation of the gel.
Zafir Gaygadzhiev - One of the best experts on this subject based on the ideXlab platform.
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addition of sodium Caseinate to skim milk inhibits rennet induced aggregation of Casein micelles
Food Hydrocolloids, 2012Co-Authors: Zafir Gaygadzhiev, Valerie Massel, Marcela Alexander, Milena CorredigAbstract:Abstract The objective of this paper was to observe the rennet-induced aggregation behaviour of Casein micelles in milk in the presence of additional sodium Caseinate. Analysis of the centrifugal supernatants by size exclusion chromatography confirmed an increase in the soluble protein in the milk serum phase after addition of sodium Caseinate. Although the total amount of κ-Casein hydrolyzed over time was not affected, there was a significant effect of soluble Casein on milk gelation, with a dose-dependent decrease of the gelation time as measured by rheology. Light scattering experiments also confirmed that the addition of soluble Caseins inhibited the aggregation of Casein micelles. Addition of 1 mM CaCl 2 prior to renneting increased the extent of rennet aggregation in samples containing additional sodium Caseinate, but the inhibiting effect was still evident. The amount of soluble Casein (as measured by chroma tography) significantly decreased after renneting, suggesting its association with the micellar fraction. Supporting experiments carried out with purified fractions of soluble Caseins demonstrated that both α s -Casein and β-Casein played a role as protective colloids (increasing steric repulsion) during renneting. It was concluded that the inhibiting effect observed during gelation was caused by the adsorption of soluble Casein molecules on the surface of rennet-altered Casein micelles.
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the impact of the concentration of Casein micelles and whey protein stabilized fat globules on the rennet induced gelation of milk
Colloids and Surfaces B: Biointerfaces, 2009Co-Authors: Zafir Gaygadzhiev, Milena Corredig, Marcela AlexanderAbstract:The rennet-induced aggregation of skim milk recombined with whey protein-stabilized emulsion droplets was studied using diffusing wave spectroscopy (DSW) and small deformation rheology. The effect of different volume fractions of Casein micelles and fat globules was investigated by observing changes in turbidity (1/l*), apparent radius, elastic modulus and mean square displacement (MSD), in addition to confocal imaging of the gels. Skim milk containing different concentration of Casein micelles showed comparable light-scattering profiles; a higher volume fraction of Caseins led to the development of more elastic gels. By following the development of 1/l* in recombined milks, it was possible to describe the behaviour of the fat globules during the initial stages of rennet coagulation. Increasing the volume fraction of fat globules showed a significant increase in gel elasticity, caused by flocculation of the oil droplets. The presence of flocculated oil globules within the gel structure was confirmed by confocal microscopy observations. Moreover, a lower degree of κ-Casein hydrolysis was needed to initiate Casein micelles aggregation in milk containing whey protein-stabilized oil droplets compared to skim milk. This study for the first time clearly describes the impact of a mixture of Casein micelles and whey protein-stabilized fat globules on the pre-gelation stages of rennet coagulation, and further highlights the importance of the flocculation state of the emulsion droplets in affecting the structure formation of the gel.
Donald J Mcmaho - One of the best experts on this subject based on the ideXlab platform.
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investigating rennet coagulation properties of recombined highly concentrated micellar Casein concentrate and cream for use in cheese making
Journal of Dairy Science, 2016Co-Authors: Donald J Mcmaho, Almu H VollmeAbstract:Abstract Highly concentrated micellar Casein concentrate (HC-MCC), a potential ingredient for cheese making, contains ~20% Casein with ~70% of serum proteins removed by microfiltration and diafiltration of skim milk, followed by vacuum evaporation. Our objective was to investigate cold gelation properties of recombined concentrated milk (RCM) by mixing thawed frozen HC-MCC and cream under different Casein levels, pH, and protein-to-fat ratios, and with addition of sodium citrate or calcium. The HC-MCC was recombined with cream using low shear at 50°C for 30 min, and rheological measurements were conducted. Cold-gelling temperature [the temperature at which storage modulus (G′)=loss modulus (G″)] was linearly correlated with Casein levels from 8.6 to 11.5% (R 2 =0.71), pH from 6.6 to 7.0 (R 2 =0.96), and addition of sodium citrate from 0 to 0.36mmol/g of Casein (R 2 =0.80). At pH 7.0, gelation occurred at 12, 26, and 38°C with 9, 10, and 11% Casein, respectively. At pH 6.6, 6.8, and 7.0, RCM with 12% Casein gelled at a mean temperature of 12, 26, and 37°C, respectively. Adding calcium chloride at 0.17mmol/g of Casein significantly increased cold-gelling temperature from 18 to ≥50°C, whereas no significant change was observed at levels up to 0.12mmol/g of Casein. Different protein to fat ratios ranging from 0.8 to 1.2 did not significantly influence gelling temperature. In transmission electron micrographs of RCM with 12% Casein, Casein micelles were nonspherical and partially dissociated into small protein strands. Upon addition of calcium chloride at 0.21mmol/g of Casein, Casein micelles were more spherical and retained colloidal structure with the presence of aggregated Casein micelles. These gelation processes of RCM with or without addition of trisodium citrate were both reversible. We propose that cold gelation of RCM occurs when protein strands that have been partially released from the Casein micelles entangle, restrict their mobility, and form a fine-stranded gel network. Upon addition of high levels of calcium, cold gelation was promoted presumably through direct aggregation of Casein micelles. Understanding cold gelation properties can facilitate potential use of RCM in cheese making.
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supramolecular structure of the Casein micelle
Journal of Dairy Science, 2008Co-Authors: Donald J Mcmaho, S OommeAbstract:The supramolecular structure of colloidal Casein micelles in milk was investigated by using a sample preparation protocol based on adsorption of proteins onto a poly-l-lysine and parlodion-coated copper grid, staining of proteins and calcium phosphate by uranyl oxalate, instantaneous freezing, and drying under a high vacuum. High-resolution transmission electron microscopy stereo-images were obtained showing the interior structure of Casein micelles. On the basis of our interpretation of these images, an interlocked lattice model was developed in which both Casein-calcium phosphate aggregates and Casein polymer chains act together to maintain Casein micelle integrity. The Caseins form linear and branched chains (2 to 5 proteins long) interlocked by the Casein-stabilized calcium phosphate nanoclusters. This model suggests that stabilization of calcium phosphate nanoclusters by phosphoserine domains of alpha(s1)-, alpha(s2)-, or beta-Casein, or their combination, would orient their hydrophobic domains outward, allowing interaction and binding to other Casein molecules. Other interactions between the Caseins, such as calcium bridging, could also occur and further stabilize the supramolecule. The combination of having an interlocked lattice structure and multiple interactions results in an open, sponge-like colloidal supramolecule that is resistant to spatial changes and disintegration. Hydrophobic interactions between Caseins surrounding a calcium phosphate nanocluster would prevent complete dissociation of Casein micelles when the calcium phosphate nanoclusters are solubilized. Likewise, calcium bridging and other electrostatic interactions between Caseins would prevent dissociation of the Casein micelles into Casein-calcium phosphate nanocluster aggregates when milk is cooled or urea is added to milk, and hydrophobic interactions are reduced. The appearance of both polymer chains and small aggregate particles during milk synthesis would also be expected based on this interlocked lattice model of Casein micelles, and its supramolecule structure thus exhibits the principles of self-aggregation, interdependence, and diversity observed in nature.
C G De Kruif - One of the best experts on this subject based on the ideXlab platform.
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Casein micelle structure functions and interactions
2003Co-Authors: C G De Kruif, Carl HoltAbstract:In this chapter, we aim to present a consistent description of the structure and functions of Caseins and the Casein micelle. Function, it must be stressed, is interpreted here to mean both the biological functions of Casein in the mammary gland and milk and the function in dairy foods. Thus, we tread a variation of a well-worn path in biology by exploring a structure-function trichotomy.
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molecular mechanism of the renneting process of Casein micelles in skim milk examined by viscosity and light scattering experiments and simulated by model scf calculations
Langmuir, 1999Co-Authors: M Mellema, F A M Leermakers, C G De KruifAbstract:The properties of the outer hairy layer of Casein micelles have been studied using several methods. Viscosity and light-scattering measurements have been performed on rennet-destabilized skim milk at different concentrations of calcium. We have reproduced the known result that calcium promotes destabilization at relatively high κ-Casein surface coverages (even at only 50% of the κ-Casein molecules cut off). This suggests that calcium bridges contribute to the Casein micelle attraction. The effect may be direct by calcium-mediated bridging of β-Casein or αs1-Casein (phosphate/carboxylate) or κ-Casein (carboxylate) or indirect by altering the interplay between several types of Caseins in the micelle. In the analysis of the experiments, we make use of an adhesive hard sphere approximation. The Casein hairy layer has further been modeled by a self-consistent field (SCF) theory in which coarse-grained molecular details were included. In these calculations the effect of calcium bridges cannot directly be accoun...