Role of κ-Casein in the Association of Denatured Whey Proteins with Casein Micelles in Heated Reconstituted Skim Milk

2007 ◽  
Vol 55 (9) ◽  
pp. 3635-3642 ◽  
Author(s):  
Skelte G. Anema
Keyword(s):  
Whey Proteins ◽  
Skim Milk ◽  
Casein Micelles

Factors affecting the ethanol stability of bovine milk.: I. Effect of serum phase components

1981 ◽  
Vol 48 (2) ◽  
pp. 273-284 ◽  
Author(s):  
David S. Horne ◽  
Thomas G. Parker
Keyword(s):  
Whey Proteins ◽  
Bovine Milk ◽  
Skim Milk ◽  
Casein Micelles ◽  
Ph Profile ◽  
Factors Affecting ◽  
Milk Serum ◽  
Ethanol Stability ◽  
Serum Components

SummaryBy resuspending casein micelles in whey and dialysate it is shown that the role of whey proteins in the ethanol (EtOH)-induced coagulation of skim-milk is minimal. Experiments involving the interchange of milk sera indicated that the position of the EtOH stability/pH profile along the pH axis was governed by the diffusible constituents of the milk serum phase. The identities of those serum components governing the shape and position of the EtOH stability/pH profile were investigated. The addition of Ca2+ caused a shift in the entire profile to higher pH. Reduction of the available Ca2+ by addition of EDTA (up to 5 ran) shifted the profile to lower pH. The addition of phosphate (up to 5 mM) or citrate (up to 1 mM) had no effect on the profile, though higher concentrations of citrate (up to 5 mMi) caused slight shifts to lower pH. When equimolar amounts of Ca and phosphate were added, the system showed a shift in profile approximately equivalent to that of the free Ca introduced. Increasing the ionic strength of a milk by the addition of NaCl did not shift the profile, but decreased the maximum EtOH stability of the high pH arm of the sigmoidal profile. The EtOH stability/pH profile retained the same sigmoidal shape in all cases.

Ethanol stability of casein micelles – a hypothesis concerning the role of calcium phosphate

1987 ◽  
Vol 54 (3) ◽  
pp. 389-395 ◽  
Author(s):  
David S. Horne
Keyword(s):  
Ionic Strength ◽  
Skim Milk ◽  
Buffer System ◽  
Casein Micelles ◽  
Buffer Solutions ◽  
Relative Response ◽  
Using Data ◽  
The Stability ◽  
Ethanol Stability

SummaryThe ethanol (EtOH) stability of skim milk and the stability towards aggregation of casein micelles diluted into ethanolic buffer solutions were compared using data obtained from previously published experiments. Differences in absolute stability and in relative response were observed when Ca2+ level and pH were adjusted, the buffer system results lying below those from skim milk in both cases. Increasing the ionic strength of skim milk adjusted to pH 7·0 lowered its EtOH stability whereas increasing the ionic strength of the diluting buffer increased the stability of the casein micelles. The hypothesis is put forward that the differences are due to the simultaneous precipitation of Ca phosphate when EtOH is added to skim milk. This draws calcium from the caseinate sites of the micelle, counteracting the destabilizing effects of the EtOH towards the micelle. Such removal and the consequent restructuring are kinetically controlled and micellar precipitation in skim milk finally occurs when the micellar coagulation time falls within the time scale of the restructuring reactions.

Gelation of casein-whey mixtures: effects of heating whey proteins alone or in the presence of casein micelles

2001 ◽  
Vol 68 (3) ◽  
pp. 471-481 ◽  
Author(s):  
CATHERINE SCHORSCH ◽  
DEBORAH K. WILKINS ◽  
MALCOLM G. JONES ◽  
IAN T. NORTON
Keyword(s):  
Heat Treatment ◽  
Whey Protein ◽  
Protein Denaturation ◽  
Whey Proteins ◽  
Treatment Sequence ◽  
Gel Properties ◽  
Casein Micelles ◽  
Gelation Kinetics ◽  
Milk Gelation

The aim of the present work was to investigate the role of whey protein denaturation on the acid induced gelation of casein. This was studied by determining the effect of whey protein denaturation both in the presence and absence of casein micelles. The study showed that milk gelation kinetics and gel properties are greatly influenced by the heat treatment sequence. When the whey proteins are denatured separately and subsequently added to casein micelles, acid-induced gelation occurs more rapidly and leads to gels with a more particulated microstructure than gels made from co-heated systems. The gels resulting from heat-treatment of a mixture of pre-denatured whey protein with casein micelles are heterogeneous in nature due to particulates formed from casein micelles which are complexed with denatured whey proteins and also from separate whey protein aggregates. Whey proteins thus offer an opportunity not only to control casein gelation but also to control the level of syneresis, which can occur.

Changes in milk on heating: viscosity measurements

1993 ◽  
Vol 60 (2) ◽  
pp. 139-150 ◽  
Author(s):  
Theo J. M. Jeurnink ◽  
Kees G. De Kruif
Keyword(s):  
Heat Treatment ◽  
Heat Exchangers ◽  
Hard Spheres ◽  
Whey Proteins ◽  
Skim Milk ◽  
Quantitative Model ◽  
Casein Micelles ◽  
Mutual Attraction ◽  
Viscosity Measurements ◽  
Quantitative Basis

SummarySkim milk was heated at 85 °C for different holding times. As a result of such heating, whey proteins, in particular β-lactoglobulin, denatured and associated with casein micelles. This led to an increase in size of the casein micelles but also to a different interaction between them. Both these changes could be described by using a quantitative model which was developed for the viscosity of so-called adhesive hard spheres. We applied the model successfully to skim milk and were able to describe on a quantitative basis the changes due to the heat treatment of milk. It was shown that after heating the casein micelles became larger and acquired a mutual attraction. The unfolding of the whey proteins and their subsequent association with the casein micelles appeared to be responsible for these changes. How this reaction influences the fouling of heat exchangers is discussed.

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.

Improvement of rheological properties of firm acid gels by skim milk heating is conserved after stirring

2003 ◽  
Vol 70 (4) ◽  
pp. 423-431 ◽  
Author(s):  
P Cayot ◽  
J-F Fairise ◽  
B Colas ◽  
D Lorient ◽  
G Brulé
Keyword(s):  
Storage Modulus ◽  
Skim Milk ◽  
Rheological Parameters ◽  
Water Retention Capacity ◽  
Gel Structure ◽  
Casein Micelles ◽  
Retention Capacity ◽  
Β Lactoglobulin

The enhancement of the strength of set acid gels by heating milk was related to rheological parameters (water retention capacity, storage modulus) of corresponding stirred gels. To obtain accurate rheological data from stirred gel it was necessary to maintain a constant granulometry of gel particles and to recognize time after stirring as a contributing factor. Two hours after stirring, the gel exhibited a higher storage modulus when milk was heated above 80 °C. A measurement of viscosity of just-stirred yoghurt was sufficient to predict correctly the quality of a stirred gel analysed by viscoelastic measurements. Increased resstance to syneresis of just-stirred gels was related to higher viscosity. The quantity of β-lactoglobulin (β-lg) bound to casein micelles explains the improvement of these gel qualities. We have considered that the structure of the initial firm gel (mesostructure level) was conserved in fragments within the stirred gel. Consequently, the explanation given by various authors for the effect of heating milk on the properties of set gels can also be applied to stirred gels. The same mechanism, described in literature for structure formation of set gels from acidified milk is purposed to explain the role of heating milk on the recovery of gel structure after stirring. The β-lg association with casein micelles during heating favoured micelle connections during the acidification. It also favoured the association of gel fragments after stirring during the recovery in gel structure.

Effects of heat treatment and acidification on the dissociation of bovine casein micelles

1996 ◽  
Vol 63 (1) ◽  
pp. 35-48 ◽  
Author(s):  
Andrew J. R. Law
Keyword(s):  
Heat Treatment ◽  
Whey Proteins ◽  
Raw Milk ◽  
Serum Concentrations ◽  
Casein Micelles ◽  
Heat Treated ◽  
Decreasing Ph ◽  
The Individual ◽  
Almost All

SummaryThe effects of heat treatment and subsequent acidification of milk on the distribution of proteins, Ca and Pi, between the serum and micellar phases were examined using ultracentrifugation. After heating milk at 85 °C for 10 min, and storing for 22 h at 4, 20 or 30 °C, there was a marked increase in the concentration of κ-casein in the serum. At 4 and 20 °C there was also slightly more β-casein in the serum from heat-treated milk than in that from the corresponding raw milk. The whey proteins were extensively denatured, and were almost equally distributed between the supernatants and micellar pellets. After storage for 22 h the distribution of Ca and Pi between soluble and colloidal phases in heat-treated milk was similar to that in raw milk. After acidifying heat-treated milk by the addition of glucono-δ-lactone and storing for 22 h at 4, 20 or 30 °C there was progressive solubilization of colloidal calcium phosphate with decreasing pH, and at pH 5·0 almost all of the Ca and Pi was present in the serum. At 20 °C, and even more so at 4 °C, serum concentrations of the individual caseins increased considerably with decreasing pH, reaching maximum levels of about 25 and 40% of the total casein at pH 5·7 and 5·5 respectively, and then decreasing rapidly at lower pH. Compared with raw milk, maximum dissociation in heat-treated milks stored at 4 and 20 °C occurred at higher pH, and the overall levels of dissociation of individual caseins from the micelles were lower. At 30 °C, the concentrations of individual caseins in the serum of heat-treated milk decreased steadily as the pH was reduced, and did not show the slight increase found previously for raw milk. The role of the denatured whey proteins in interacting with κ-casein and in promoting aggregation of the micelles on acidification is discussed.

scholarly journals FREE FAT IN MILK AND CHEESE PRODUCTS: INFLUENCE ON QUALITY

Food systems ◽  
2020 ◽  
Vol 3 (2) ◽  
pp. 9-13
Author(s):  
O. V. Lepilkina ◽  
I. V.  Loginova ◽  
O. G. Kashnikova
Keyword(s):  
Whey Proteins ◽  
Skim Milk ◽  
Casein Micelles ◽  
Enzyme Preparations ◽  
Milk Processing ◽  
Fat Globules ◽  
Organoleptic Characteristics ◽  
Oxidative Processes ◽  
Mechanical Factors ◽  
Cheese Products

The theoretical and practical aspects of the formation of free fat in milk, cheese and cheese products with vegetable fats are considered. The amount of free fat in milk depends on the integrity of the fat globules membranes, which are affected by: ineffective emulsification of fat during the synthesis of milk in the cow’s udder (authentic fat) and physic-mechanical factors in the milk processing after milking (destabilized fat). Free fat, primarily subjected to oxidative processes and lipolysis, reduces the quality and ability to store milk. For cheese products, the presence of free fat, available for lipolysis and oxidation, is a prerequisite for obtaining high-quality products. Characteristics of the production of cheese products with vegetable fats, providing for the preliminary emulsification of vegetable fat in skim milk, contribute to the formation of denser membranes on the surface of fat globules, consisting mainly of casein micelles and whey proteins. This is the reason for the formation of a more closed structure of the fat phase with low availability of fat for enzymes and oxidizing agents. The low availability of fat in the structure of cheese products with vegetable fats is one of the factors that worsen their organoleptic characteristics. In order to increase the amount of available fat in the production of cheese products with vegetable fats, it is advisable to use additional enzyme preparations or cultures of microorganisms that activate proteolysis and lipolysis.

Heat stability of milk: further studies on the pH-dependent dissociation of micellar κ-casein

1986 ◽  
Vol 53 (2) ◽  
pp. 237-248 ◽  
Author(s):  
Harjinder Singh ◽  
Patrick F. Fox
Keyword(s):  
Whey Protein ◽  
Cetyltrimethylammonium Bromide ◽  
Opposite Effect ◽  
Whey Proteins ◽  
Sodium Dodecyl ◽  
Skim Milk ◽  
Heat Stability ◽  
Casein Micelles ◽  
Acetylneuraminic Acid ◽  
Ph Dependent

SUMMARYWhey protein complexed and became co-sedimentable with casein micelles after heating milk at ≥ 90°C for 10 min at pH ≤ 6·9 while at higher pH values (7·3) whey proteins and κ-casein-rich protein dissociated from the micelles on heating. κ-Casein-deficient micelles were more sensitive to heat, Ca2+ or ethanol than whey protein-coated or native micelles and were readily coagulable by rennet. Isolated κ-casein added to skim milk before preheating (90°C for 10 min) did not associate with the micelles at pH ≥ 6·9. Sodium dodecyl sulphate increased the level of both non-sedimentable N (NSN) and N-acetylneuraminic acid (NANA) and shifted the NSN-pH and NANA-pH curves to more acidic values while cetyltrimethylammonium bromide had the opposite effect. It is suggested that the pH-dependent dissociation in micellar κ-casein, which appears to be reversible, depends on the surface charge on the micelles; at a certain negative charge, disruption of hydrophobic and electrostatic forces could result in the dissociation of κ-casein from the casein micelles.

Effect of interactions between denatured whey proteins and casein micelles on the formation and rheological properties of acid skim milk gels

1998 ◽  
Vol 65 (4) ◽  
pp. 555-567 ◽  
Author(s):  
JOHN A. LUCEY ◽  
MICHELLE TAMEHANA ◽  
HARJINDER SINGH ◽  
PETER A. MUNRO
Keyword(s):  
Heat Treatment ◽  
Rheological Properties ◽  
Loss Tangent ◽  
Whey Proteins ◽  
Skim Milk ◽  
Casein Micelles ◽  
Heated Milk ◽  
Tan Δ ◽  
Reconstituted Milk ◽  
Acid Milk Gels

The effect of interactions of denatured whey proteins with casein micelles on the rheological properties of acid milk gels was investigated. Gels were made by acidification of skim milk with glucono-δ-lactone at 30°C using reconstituted skim milk powders (SMP; both low- and ultra-low-heat) and fresh skim milk (FSM). The final pH of the gels was ∼4·6. Milks containing associated or ‘bound’ denatured whey proteins (BDWP) with casein micelles were made by resuspending the ultracentrifugal pellet of heated milk in ultrafiltration permeate. Milks containing ‘soluble’ denatured whey protein (SDWP) aggregates were formed by heat treatment of an ultracentrifugal supernatant which was then resuspended with the pellet. Acid gels made from unheated milks had low storage moduli, G′, of <20 Pa. Heating milks at 80°C for 30 min resulted in acid gels with G′ in the range 390–430 Pa. The loss tangent (tan δ) of gels made from heated milk increased after gelation to attain a maximum at pH ∼5·1, but no maximum was observed in gels made from unheated milk. Acid gels made from milks containing BDWP that were made from low-heat SMP, ultra-low-heat SMP and FSM had G′ of about 250, 270 and 310 Pa respectively. Acid gels made from milks containing SDWP that were made from ultra-low-heat SMP or FSM had G′ values in the range 17–30 Pa, but gels made from low-heat SMP had G′ of ∼140 Pa. It was concluded that BDWP were important for the increased G′ of acid gels made from heated milk. Addition of N-ethylmaleimide (NEM) to low-heat reconstituted milk, to block the —SH groups, resulted in a reduction of the G′ of gels formed from heated milk but did not reduce G′ to the value of unheated milk. Addition of 20 mm-NEM to FSM, prior to heat treatment, resulted in gels with a lower G′ value than gels made from reconstituted low-heat SMP. It was suggested that small amounts of denatured whey proteins associated with casein micelles during low-heat SMP manufacture were probably responsible for the higher G′ of gels made from milk containing SDWP and from milk heated in the presence of 20 mm-NEM, compared with gels made from FSM.

Sign in / Sign up

Export Citation Format

Share Document