Aim / question being addressed
To find out about how the amounts of vinegar and other acids will affect the amount of curdling of casein in milk.
Q: How does the acidic liquid make the casein from milk?
A: Casein is a protein in milk which is insoluble, and when the vinegar is poured into the milk and turning it acidic, the casein reacts by precipitating and turning into clumps which can be separated from the rest of the milk.
In milk, casein is not dissolved, just suspended, so it can be filtered out of milk. Heating and boiling milk does not alter its state but dilute acids and rennet cause it to precipitate, stronger ones dissolve it.
Casein is a protein that is commonly found in mammalian milk, making up at least 80% of the proteins in cow’s milk and between 20% to 45% of protein in human milk. Casein has a wide variety of uses, from being component of cheese, to use as a food additive, to a binder for safety matches. As a food source, casein supplies amino acids.
Casein contains a fairly high number of proline residues, which do not interact. It is rather hydrophobic, making it poorly soluble in water. It is found in milk as a suspension of particles called “casein micelles” which show only relatively limited resemblance with other micelles in a sense that the hydrophilic parts reside at the surface and they are spherical.
The isoelectric point of casein is 4.6. Since milk’s pH is 6.6, casein has a negative charge in milk. The purified protein is water-insoluble. While it is also insoluble in neutral salt solutions, it is readily dispersible in dilute alkalis and in salt solutions such as sodium oxalate and sodium acetate.
Casein contains phosphorous and coagulates at pH 4.6.They have a relatively random, open structure.
Casein can also be used and/or found in paint glue, cheese making, plastics and fibre, protein supplements and other medical and dental uses.
There is evidence that it has been used during the middle ages and it has been identified in 18th century ceiling paintings. However, there are problems using casein as paint because it is brittle and can become moldy.