The internal structure model of casein micelle is based upon the properties of isolated protein components which are involved in the formation of internal structure of the micelle. The patch or reactive site, as illustrated in the image below, that is left on the micelles after enzymatic cleavage is necessary before aggregation of the paracasein micelles can begin. Its biological function is to carry large amounts of highly insoluble CaP to mammalian young in liquid form and to form a clot in the stomach for more efficient nutrition. A casein micelle is composed of several similar proteins, forming a multi- ‐ molecular granular structure. 7: 456-461. The casein micelle system of bovine milk is unique in that protein aggregates of similar spherical shape but extreme variability of size are formed by the self-assembly of three major nonidentical subunits. Walstra, P. 1999. Colloidal calcium phosphate (CCP) acts as a cement between the hundreds or even thousands of submicelles that form the casein micelle. Internat. More recent models suggest a more open structure comprised of aggregates of protein around calcium phosphate nanoclusters. The hairy casein micelle: evolution of the concept and its implication for dairy technology. After weeks to months storage of these products, there is a sudden sharp increase in viscosity accompanied by visible gelation and irreversible aggregation of the micelles into long chains forming a three-dimensional network. During the secondary stage, the micelles aggregate, as illustrated on the right below. how the various components are distributed within the casein micelle, was modeled according to three different models advocated in the literature; i.e. Guelph, Ontario All models agree that the k-casein is mostly present as a stabilizng layer around the exterior of the micelle. 1996. Technol., 2005, 27(1) : 201-212 Milk is a complex biological fluid with high amount of proteins, lipid and minerals. It can be seen from the preceding discussion that it is possible to consider the casein micelle as a sponge-like structure consisting of linked calcium phosphate/casein nanoclusters. Dairy J. The largest structures in the fluid portion of the milk are “casein micelles” which are aggregates of several thousands of protein molecules. If any S-S bonds occur within the micelle, they are not the driving force for stabilization. Casein interactions: casting light on the black boxes, the structure in dairy products. During the primary stage, rennet cleaves the Phe(105)-Met(106) linkage of kappa-casein resulting in the formation of the soluble CMP which diffuses away from the micelle and para-kappa-casein, a distinctly hydrophobic peptide that remains on the micelle. On the structural models of bovine casein micelles - review and possible improvements. Dalgleish, Douglas G. and Milena Corredig. Horne, D. S. 1998. Internat. CASEIN MICELLE: STRUCTURE, PROPERTIES AND ITS IMPORTANCE 8.1 Introduction In order to provide proteins along with a considerable portion of its calcium and phosphate to it’s offspring, the casein in cow milk forms intricate particles which are recognized as casein micelles. A possible structure of the casein micelle based on high-resolution field-emission scanning electron microscopy. It must be remembered that hydrophobic interactions are very temperature sensitive. More recent models suggest a more open structure comprised of aggregates of protein around calcium phosphate nanoclusters. Casein micelle structure: a concise review Chanokphat Phadungath Abstract Phadungath, C. Casein micelle structure: a concise review Songklanakarin J. Sci. Such a model agrees at least in general terms with the physical measurements that can be made by scattering techniques and electron microscopy. Casein interactions: casting light on the black boxes, the structure in dairy products. Holt, C. & D. S. Horne. Submicelles rich in kappa-casein occupy a surface position, whereas those with less are buried in the interior. Besides casein protein, calcium and phosphate, the micelle also contains citrate, minor ions, lipase and plasmin enzymes, and entrapped milk serum. Differences in density indicate the existence of a structure that appears to have string-like connections to the black particles. We were able to confirm the structure of as somewhat high-density, in addition to the black particles, assigned as CCP, in casein micelle. No success in relating these forces to micellular stability. Horne, D. S. 2002. The nanoclusters provide regions of more or less density. Horne, D. S. 1998. Technol. The casein sub-micelle model was prominent for many years, but there is sufficient evidence now to conclude that there is not a defined sub-micellar structure to the micelle at all. The removal of Ca++ leads to reversible dissociation of ß -casein without micellular disintegration. Dairy J. The actual cause and mechanism is not yet clear, however, some theories exist: An excellent source of information on casein micelle stability can be found in Walstra et al., 2006. As the pH approaches its isoelectric point (pH 4.6), the caseins aggregate. Casein sub-micelles: do they exist? Caseins are among the most hydrophobic proteins and there is some evidence to suggest they play a role in the stability of the micelle. Age gelation is an aggregation phenomenon that affects shelf-stable, sterilized dairy products, such as concentrated milk and UHT milk products. Aggregation occurs as a result of entropically driven hydrophobic interactions. At temperatures above the boiling point casein micelles will irreversibly aggregate. Casein micelles disintegrate and casein precipitates. Annual Reviews Food Sci. 2004. The temperature at the time of coagulation is very important to both the primary and secondary stages. Soft Matter. The micelle is considered to be spherical and the diameter is in the micrometer size. 2012. Each of the casein proteins has unique abilitites to either bind with CaP or with other caseins, which gie rise to the aggregates. The structure is sufficiently porous to hold a considrable amount of water, and for the surface, and even part of the interior, to be reactive to other substances. The dynamic aspects ofthe casein micelle are an intrinsic part ofits structure and hence of its biological and food functions. Milk is generally very stable to heat up to 90-95oC. Casein structure, self-assembly and gelation. These micelles are rather porous structures, occupying about 4 mL/g and 6-12% of the total volume fraction of milk. Current Opinion in Colloid and Interface Sci. 50 Stone Road East Proteolytic breakdown of the casein: bacterial or native plasmin enzymes that are resistant to heat treatment may lead to the formation of a slow gel forming over a long period of time. These micelles are rather porous structures, occupying about 4 mL/g and 6-12% of the total volume fraction of milk. Casein micelle image from Dalgleish, D. G., P. Spagnuolo and H. D. Goff. 4. From these experimental data bases have arisen two con icting models for the internal structure of the casein micelle. 7: 2265-2272. Size ranges from 50-250 nm in diameter. Neth. Some occurs between the individual caseins in the micelle but not much because there is no secondary structure in casein proteins. The caseins can be divided in four types: α s1- ‐casein, α s2- ‐casein, α - ‐casein, and α - ‐ casein. International Dairy Journal. Besides casein protein, calcium and phosphate, the micelle also contains citrate, minor ions, lipase and plasmin enzymes, and entrapped milk serum. 50: 85-111. More recent models suggest a more open structure comprised of aggregates of protein around calcium phosphate nanoclusters. The tertiary stage of coagulation involves the rearrangement of micelles after a gel has formed. A definitive structure of the native casein micelle structure continues to elude researchers. 14: 1025-1031. The internal structure of the casein micelles, i.e. Please see any of the following references for great detail about micelle structures and models. The casein micelles also have a strong tendency to aggregate because of hydrophobic interactions. This is due to the loss of steric repulsion of the kappa-casein as well as the loss of electrostatic repulsion due to the decrease in pH. 3:449–67.