Hi every one , Beta casein is one type of casiens in milk . this protein is sensitive to calcium at room temperature . low concentration of calcium can precipitate this protein , But at low temperatures ( 5 C) this protein is not precipitated even if we have high concentration of calcium in the solution . Can anyone explain the reason for me ?
Dear Jasim Al-Saadi ,
Your observation is well-described in older literature:
https://www.journalofdairyscience.org/article/S0022-0302(71)85974-X/pdf
It is my educated guess that this has something to do with the fact that at higher temperature water becomes less ‘hydrophobic’ (think about the lower solubility of gases such as oxygen at higher temperature). Consequently at lower temperature water is more hydrophilic and the hydrophobic parts of the protein (or proteins) will be more folded towards the ‘inside’ and consequently less aggregation between proteins can be expected.
For β-casein it has been suggested that the changes upon increasing the temperature can be accounted for not so much because of an increase in α-helix but by an increase in polyProline II structure. In support of this view similar changes in CD spectra were observed when polyProline II model peptides moved from an aqueous to an apolar environment. In other words a more extended structure might be involved more and more.
See for more details and excellent review and with alternative views on this matter:
https://www.researchgate.net/profile/David_Horne6/publication/262910459_Casein_structure_self-assembly_and_gelation/links/5ba10bbf45851574f7d5594f/Casein-structure-self-assembly-and-gelation.pdf
A more than excellent review on what is known about casein gives more ideas:
https://pdfs.semanticscholar.org/4e5f/436c139947487e272745d0b311ba80c027d5.pdf
More recently in a very comprehensive review it is stated clearly that though temperature effects (including low temperature) is studied it is still pretty much unclear why casein is more soluble at lower temperature. The only new insight beside what is stated above might be that at low temperature reversible effects can take place where the protein-protein interactions are less prominent at lower temperature and hence more soluble casein can be found.
Sorry that there seems to be no more of a clear cut answer for your interesting question.
I am sorry to say that but I think your answer is not correct Alaa Kareem Niamah
Associatio and dissociation of beta casein from casein micelle is temperature dependant
Storage of milk at 4 C for 24 h about 50% of beta casein dissiciates from casein micrlle into milk serum. Howover, increasing temperatur to 20 C beta casein return back to the micelles. Morover, heating milk at high temperature (140 C) about 30-40% of beta casein migrate from micrlles into serim
Beta casein is less sensetive for calcium than alpha s1 and alpha s2. However, beta casein do not precipitate at 1 C in the presence of 400mmol calcium. Alpha s2 snd 2 precipitate in the presence of 4 - 5 mmol calcium at 25 C
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