On how κ-casein affects the interactions between the heat-induced whey protein/κ-casein complexes and the casein micelles during the acid gelation of skim milk

Heat (85 °C for 20 min) and pressure (600 MPa for 15 min) treatments were applied to skim milk fortified by addition of whey protein concentrate. Both treatments caused > 90% denaturation of β-lactoglobulin. During heat treatment this denaturation took place in the presence of intact casein micelles; during pressure treatment it occurred while the micelles were in a highly dissociated state. As a result micelle structure and the distribution of β-lactoglobulin were different in the two milks. Electron microscopy and immunolabelling techniques were used to examine the milks after processing and during their transition to yogurt gels. The disruption of micelles by high pressure caused a significant change in the appearance of the milk which was quantified by measurement of the colour values L*, a* and b*. Heat treatment also affected these characteristics. Casein micelles are dynamic structures, influenced by changes to their environment. This was clearly demonstrated by the transition from the clusters of small irregularly shaped micelle fragments present in cold pressure-treated milk to round, separate and compact micelles formed on warming the milk to 43 °C. The effect of this transition was observed as significant changes in the colour indicators. During yogurt gel formation, further changes in micelle structure, occurring in both pressure and heat-treated samples, resulted in a convergence of colour values. However, the microstructure of the gels and their rheological properties were very different. Pressure-treated milk yogurt had a much higher storage modulus but yielded more readily to large deformation than the heated milk yogurt. These changes in micelle structure during processing and yogurt preparation are discussed in terms of a recently published micelle model.

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

Journal of Dairy Research ◽

10.1017/s0022029900024845 ◽

1986 ◽

Vol 53 (2) ◽

pp. 237-248 ◽

Cited By ~ 48

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.

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Interaction between Casein Micelles and Whey Protein/κ-Casein Complexes during Renneting of Heat-Treated Reconstituted Skim Milk Powder and Casein Micelle/Serum Mixtures

Journal of Agricultural and Food Chemistry ◽

10.1021/jf103943e ◽

2011 ◽

Vol 59 (4) ◽

pp. 1442-1448 ◽

Cited By ~ 27

Author(s):

Prashanti Kethireddipalli ◽

Arthur R. Hill ◽

Douglas G. Dalgleish

Keyword(s):

Whey Protein ◽

Milk Powder ◽

Skim Milk ◽

Skim Milk Powder ◽

Casein Micelle ◽

Casein Micelles ◽

Heat Treated

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Changing the isoelectric point of the heat-induced whey protein complexes affects the acid gelation of skim milk

International Dairy Journal ◽

10.1016/j.idairyj.2011.10.006 ◽

2012 ◽

Vol 23 (1) ◽

pp. 9-17 ◽

Cited By ~ 28

Author(s):

Marion Morand ◽

Fanny Guyomarc'h ◽

David Legland ◽

Marie-Hélène Famelart

Keyword(s):

Whey Protein ◽

Isoelectric Point ◽

Protein Complexes ◽

Skim Milk ◽

Acid Gelation

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Acid Gelation Properties of Heated Skim Milk as a Result of Enzymatically Induced Changes in the Micelle/Serum Distribution of the Whey Protein/κ-Casein Aggregates

Journal of Agricultural and Food Chemistry ◽

10.1021/jf0722304 ◽

2007 ◽

Vol 55 (26) ◽

pp. 10986-10993 ◽

Cited By ~ 16

Author(s):

Fanny Guyomarc’h ◽

Marie Renan ◽

Marc Chatriot ◽

Valérie Gamerre ◽

Marie-Hélène Famelart

Keyword(s):

Whey Protein ◽

Skim Milk ◽

Acid Gelation ◽

Induced Changes

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Association of denatured whey proteins with casein micelles in heated reconstituted skim milk and its effect on casein micelle size

Journal of Dairy Research ◽

10.1017/s0022029902005903 ◽

2003 ◽

Vol 70 (1) ◽

pp. 73-83 ◽

Cited By ~ 194

Author(s):

Skelte G Anema ◽

Yuming Li

Keyword(s):

Heat Treatment ◽

Particle Size ◽

Whey Protein ◽

Volume Fraction ◽

Whey Proteins ◽

Skim Milk ◽

Casein Micelle ◽

Casein Micelles ◽

Prolonged Heating ◽

Micelle Size

When skim milk at pH 6·55 was heated (75 to 100 °C for up to 60 min), the casein micelle size, as monitored by photon correlation spectroscopy, was found to increase during the initial stages of heating and tended to plateau on prolonged heating. At any particular temperature, the casein micelle size increased with longer holding times, and, at any particular holding time, the casein micelle size increased with increasing temperature. The maximum increase in casein micelle size was about 30–35 nm. The changes in casein micelle size were poorly correlated with the level of whey protein denaturation. However, the changes in casein micelle size were highly correlated with the levels of denatured whey proteins that were associated with the casein micelles. The rate of association of the denatured whey proteins with the casein micelles was considerably slower than the rate of denaturation of the whey proteins. Removal of the whey proteins from the skim milk resulted in only small changes in casein micelle size during heating. Re-addition of β-lactoglobulin to the whey-protein-depleted milk caused the casein micelle size to increase markedly on heat treatment. The changes in casein micelle size induced by the heat treatment of skim milk may be a consequence of the whey proteins associating with the casein micelles. However, these associated whey proteins would need to occlude a large amount of serum to account for the particle size changes. Separate experiments showed that the viscosity changes of heated milk and the estimated volume fraction changes were consistent with the particle size changes observed. Further studies are needed to determine whether the changes in size are due to the specific association of whey proteins with the micelles or whether a low level of aggregation of the casein micelles accompanies this association behaviour. Preliminary studies indicated lower levels of denatured whey proteins associated with the casein micelles and smaller changes in casein micelle size occurred as the pH of the milk was increased from pH 6·5 to pH 6·7.

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Effect of high hydrostatic pressure and whey proteins on the disruption of casein micelle isolates

Journal of Dairy Research ◽

10.1017/s0022029907002762 ◽

2007 ◽

Vol 74 (4) ◽

pp. 452-458 ◽

Cited By ~ 8

Author(s):

Federico M Harte ◽

Subba Rao Gurram ◽

Lloyd O Luedecke ◽

Barry G Swanson ◽

Gustavo V Barbosa-Cánovas

Keyword(s):

Hydrostatic Pressure ◽

Whey Protein ◽

High Hydrostatic Pressure ◽

Analytical Ultracentrifugation ◽

Whey Proteins ◽

Skim Milk ◽

Casein Micelle ◽

Casein Micelles ◽

Transmission Electron ◽

Thermally Processed

High hydrostatic pressure disruption of casein micelle isolates was studied by analytical ultracentrifugation and transmission electron microscopy. Casein micelles were isolated from skim milk and subjected to combinations of thermal treatment (85°C, 20 min) and high hydrostatic pressure (up to 676 MPa) with and without whey protein added. High hydrostatic pressure promoted extensive disruption of the casein micelles in the 250 to 310 MPa pressure range. At pressures greater than 310 MPa no further disruption was observed. The addition of whey protein to casein micelle isolates protected the micelles from high hydrostatic pressure induced disruption only when the mix was thermally processed before pressure treatment. The more whey protein was added (up to 5 g/l) the more the protection against high hydrostatic pressure induced micelle disruption was observed in thermally treated samples subjected to 310 MPa.

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