Heat induced gelation of acid milk: balance between weak and covalent bonds

2003 ◽  
Vol 70 (2) ◽  
pp. 253-256 ◽  
Author(s):  
Olivier Surel ◽  
Marie-Hélène Famelart
Keyword(s):  
Protein Interactions ◽  
Whey Proteins ◽  
High Heat ◽  
Heat Treatments ◽  
Protein Protein Interactions ◽  
Casein Micelles ◽  
Covalent Bonds ◽  
Disulphide Bonds ◽  
Initial Stage ◽  
Β Lactoglobulin

Gelation of acidified milk at pH[ges ]5, after heat treatments is a well known phenomenon, due to the precipitation of whey proteins, and especially β-lactoglobulin onto κ-casein (Sawyer, 1969). High heat treatments cause denaturation of whey proteins which associate with κ-casein through disulphide interchange reactions (Hill, 1989). Since their charge is reduced, the denatured proteins associated with casein micelles become susceptible to aggregation when milk is then acidified, which promotes enhanced protein–protein interactions (Lucey et al. 1997). The gelation phenomenon involves disulphide bonds (Hashizume & Sato, 1988; Goddard, 1996) which are responsible for the gel firmness (Goddard, 1996). However, other interactions between proteins can occur, such as hydrogen and hydrophobic bonds, especially at the initial stage of interactions (Haque et al. 1987; Haque & Kinsella, 1988; Jang & Swaisgood, 1990). It is therefore relevant to investigate a possible contribution of weak linkages to the gel structure and firmness.

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.

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.

scholarly journals The effect of nanoscale surface curvature on the oligomerization of surface-bound proteins

2014 ◽  
Vol 11 (94) ◽  
pp. 20130818 ◽  
Author(s):  
M. Kurylowicz ◽  
H. Paulin ◽  
J. Mogyoros ◽  
M. Giuliani ◽  
J. R. Dutcher
Keyword(s):  
Single Molecule ◽  
Protein Interactions ◽  
Protein Function ◽  
Higher Order ◽  
Surface Curvature ◽  
Protein Protein Interactions ◽  
Single Molecule Force Spectroscopy ◽  
Adsorbed Proteins ◽  
Β Lactoglobulin

The influence of surface topography on protein conformation and association is used routinely in biological cells to orchestrate and coordinate biomolecular events. In the laboratory, controlling the surface curvature at the nanoscale offers new possibilities for manipulating protein–protein interactions and protein function at surfaces. We have studied the effect of surface curvature on the association of two proteins, α-lactalbumin (α-LA) and β-lactoglobulin (β-LG), which perform their function at the oil–water interface in milk emulsions. To control the surface curvature at the nanoscale, we have used a combination of polystyrene (PS) nanoparticles (NPs) and ultrathin PS films to fabricate chemically pure, hydrophobic surfaces that are highly curved and are stable in aqueous buffer. We have used single-molecule force spectroscopy to measure the contour lengths L c for α-LA and β-LG adsorbed on highly curved PS surfaces (NP diameters of 27 and 50 nm, capped with a 10 nm thick PS film), and we have compared these values in situ with those measured for the same proteins adsorbed onto flat PS surfaces in the same samples. The L c distributions for β-LG adsorbed onto a flat PS surface contain monomer and dimer peaks at 60 and 120 nm, respectively, while α-LA contains a large monomer peak near 50 nm and a dimer peak at 100 nm, with a tail extending out to 200 nm, corresponding to higher order oligomers, e.g. trimers and tetramers. When β-LG or α-LA is adsorbed onto the most highly curved surfaces, both monomer peaks are shifted to much smaller values of L c . Furthermore, for β-LG, the dimer peak is strongly suppressed on the highly curved surface, whereas for α-LA the trimer and tetramer tail is suppressed with no significant change in the dimer peak. For both proteins, the number of higher order oligomers is significantly reduced as the curvature of the underlying surface is increased. These results suggest that the surface curvature provides a new method of manipulating protein–protein interactions and controlling the association of adsorbed proteins, with applications to the development of novel biosensors.

High pressure treatment of bovine milk: effects on casein micelles and whey proteins

2004 ◽  
Vol 71 (1) ◽  
pp. 97-106 ◽  
Author(s):  
Thom Huppertz ◽  
Patrick F Fox ◽  
Alan L Kelly
Keyword(s):  
High Pressure ◽  
Treatment Time ◽  
Whey Proteins ◽  
Bovine Milk ◽  
Casein Micelle ◽  
Pressure Treatment ◽  
Casein Micelles ◽  
High Pressure Treatment ◽  
Micelle Size ◽  
Β Lactoglobulin

Effects of high pressure (HP) on average casein micelle size and denaturation of α-lactalbumin (α-la) and β-lactoglobulin (β-lg) in raw skim bovine milk were studied over a range of conditions. Micelle size was not influenced by treatment at pressures <200 MPa, but treatment at 250 MPa increased micelle size by ∼25%, while treatment at [ges ]300 MPa irreversibly reduced it to ∼50% of that in untreated milk. The increase in micelle size after treatment at 250 MPa was greater with increasing treatment time and temperature and milk pH. Treatment times [ges ]2 min at 400 MPa resulted in similar levels of micelle disruption, but increasing milk pH to 7·0 partially stabilised micelles against HP-induced disruption. Denaturation of α-la did not occur [les ]400 MPa, whereas β-lg was denatured at pressures >100 MPa. Denaturation of α-la and β-lg increased with increasing pressure, treatment time and temperature and milk pH. The majority of denatured β-lg was apparently associated with casein micelles. These effects of HP on casein micelles and whey proteins in milk may have significant implications for properties of products made from HP-treated milk.

Disruption and reassociation of casein micelles during high pressure treatment: influence of whey proteins

2007 ◽  
Vol 74 (2) ◽  
pp. 194-197 ◽  
Author(s):  
Thom Huppertz ◽  
Cornelis G de Kruif
Keyword(s):  
High Pressure ◽  
Treatment Time ◽  
Light Transmission ◽  
Whey Proteins ◽  
Casein Micelle ◽  
Casein Micelles ◽  
Β Lactoglobulin ◽  
Steric Stabilisation ◽  
Prolonged Holding

In the study presented in this article, the influence of added α-lactalbumin and β-lactoglobulin on the changes that occur in casein micelles at 250 and 300 MPa were investigated by in-situ measurement of light transmission. Light transmission of a serum protein-free casein micelle suspension initially increased with increasing treatment time, indicating disruption of micelles, but prolonged holding of micelles at high pressure partially reversed HP-induced increases in light transmission, suggesting reformation of micellar particles of colloidal dimensions. The presence of α-la and/or β-lg did not influence the rate and extent of micellar disruption and the rate and extent of reformation of casein particles. These data indicate that reformation of casein particles during prolonged HP treatment occurs as a result of a solvent-mediated association of the micellar fragments. During the final stages of reformation, κ-casein, with or without denatured whey proteins attached, associates on the surface of the reformed particle to provide steric stabilisation.

Catalysis of disulphide bond formation in the endoplasmic reticulum

2004 ◽  
Vol 32 (5) ◽  
pp. 663-667 ◽  
Author(s):  
L. Ellgaard
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Interactions ◽  
Protein Misfolding ◽  
Mammalian Cells ◽  
Specific Protein ◽  
Surface Proteins ◽  
Redox Conditions ◽  
Protein Protein Interactions ◽  
Disulphide Bonds ◽  
Correct Pairing

Disulphide bonds are critical for the maturation and stability of secretory and cell-surface proteins. In eukaryotic cells, disulphide bonds are introduced in the ER (endoplasmic reticulum), where the redox conditions are optimal to support their formation. Yet, the correct pairing of cysteine residues is not simple and often requires the assistance of redox-active proteins. The enzymes of the thiol-disulphide oxidoreductase family catalyse oxidation, reduction and isomerization, and thereby play important roles for the folding of many proteins. To allow all three redox reactions to take place concurrently in the same compartment, specific protein–protein interactions regulate the function of individual enzymes, while a careful balance of the ER redox environment is maintained. At the same time, the system must be capable of responding to changes in the cellular conditions, caused, for instance, by oxidative stress and protein misfolding. This review presents recent progress in understanding how ER redox conditions are regulated and how protein disulphides are formed in the ER of mammalian cells.

EDTA-induced dissociation of casein micelles and its effect on foaming properties of milk

1997 ◽  
Vol 64 (4) ◽  
pp. 495-504 ◽  
Author(s):  
BRENT R. WARD ◽  
SIMON J. GODDARD ◽  
MARY-ANN AUGUSTIN ◽  
IAN R. McKINNON
Keyword(s):  
Heat Treatment ◽  
Foam Stability ◽  
Whey Proteins ◽  
Skim Milk ◽  
High Heat ◽  
Foaming Properties ◽  
Water Interface ◽  
Casein Micelles ◽  
Air Water Interface ◽  
Powder Manufacture

The effects of addition of EDTA on the dissociation of caseins and foaming properties of milks (100 g solids/l) reconstituted from skim milk powders given a low-heat (72°C for 30 s) or high-heat (85°C for 30 min) treatment during powder manufacture were determined. The EDTA-induced dissociation of caseins was independent of heat treatment but in high-heat milk was accompanied by release of denatured whey proteins. EDTA changed the proportions of individual caseins in the supernatant. EDTA addition improved both foam overrun and foam stability of low- and high-heat milks. The increase in serum protein on addition of EDTA contributed to the improvement in foaming properties of milks by increasing the availability of the proteins for formation of the air–water interface.

Kinetics of heat-induced whey protein denaturation and aggregation in skim milks with adjusted whey protein concentration

2005 ◽  
Vol 72 (3) ◽  
pp. 369-378 ◽  
Author(s):  
David J Oldfield ◽  
Harjinder Singh ◽  
Mike W Taylor
Keyword(s):  
Whey Protein ◽  
Protein Concentration ◽  
Protein Denaturation ◽  
Polyacrylamide Gel Electrophoresis ◽  
Whey Proteins ◽  
Pilot Scale ◽  
Casein Micelles ◽  
Reaction Orders ◽  
Β Lactoglobulin ◽  
Kinetics Of

Microfiltration and ultrafiltration were used to manufacture skim milks with an increased or reduced concentration of whey proteins, while keeping the casein and milk salts concentrations constant. The skim milks were heated on a pilot-scale UHT plant at 80, 90 and 120 °C. The heat-induced denaturation and aggregation of β-lactoglobulin (β-lg), α-lactalbumin (α-la) and bovine serum albumin (BSA) were quantified by polyacrylamide gel electrophoresis. Apparent rate constants and reaction orders were calculated for β-lg, α-la and BSA denaturation. Rates of β-lg, α-la and BSA denaturation increased with increasing whey protein concentration. The rate of α-la and BSA denaturation was affected to a greater extent than β-lg by the change in whey protein concentration. After heating at 120 °C for 160 s, the concentration of β-lg and α-la associated with the casein micelles increased as the initial concentration of whey proteins increased.

scholarly journals WHEY PROTEIN ADDITION TO FACILITATE ACCELERATION OF YOGHURT FERMENTATION

2019 ◽  
Vol 57 (3B) ◽  
pp. 69
Author(s):  
Nguyen Chính Nghia ◽  
Vu Thu Trang ◽  
Do Van Duong
Keyword(s):  
Whey Protein ◽  
Protein Interactions ◽  
Water Retention ◽  
Whey Proteins ◽  
Whey Protein Concentrate ◽  
Water Retention Capacity ◽  
Protein Protein Interactions ◽  
Retention Capacity ◽  
Fermentation Time ◽  
Fresh Milk

Whey proteins were present in appropriate proportion in milk, during heat-treatment at pasteurization temperatures; whey proteins and casein have the ability to form firm gel of uniform porosity through heat-induced protein-protein interactions. In this study, the addition of whey proteins in fresh milk were carry out to investigate whether whey protein would accelerate yoghurt fermentation time and facilitate the yoghurt structure. The results indicated that the addition of whey concentrate 80 increased the water retention capacity of the final product. Whey protein concentrate 80 supplement at the content of 0.8% shortened fermentation time for the product 12.5%. The addition of whey protein also improved the properties of water retention until 26%, viscosity and structure of yoghurt products.

Sign in / Sign up

Export Citation Format

Share Document