![]() ![]() As the pH falls the charge on casein falls and it precipitates. If an acid is added to milk, or if acid-producing bacteria are allowed to grow in milk, the pH falls. This pH is called the isoelectric point of the protein (pH 4.6 for casein). At the pH at which the positive charge on a protein equals exactly the negative charge, the net total charge of the protein is zero. When the pH of milk is changed, the acidic or basic groups of the proteins will be neutralised. The structure of the micelles is not fully understood. Caseins are hydrophobic but Κ-casein contains a hydrophilic portion known as the glycomacropeptide and it is this that stabilises the micelles. The micelles are stabilised by the Κ-casein. Casein can also be recovered from skim milk as a separate product.Ĭasein is dispersed in milk in the form of micelles. In cheesemaking most of the casein is recovered with the milk fat. Casein is easily separated from milk, either by acid precipitation or by adding rennin. Normal bovine milk contains about 3.5% protein, ok which casein constitutes about 80%. The casein is a group name for the dominant class of protein in milk. Milk fat acts as a solvent for the fat-soluble vitamins A, D, E and K and also supplies essential fatty acids (linoleic, linolenic and arachidonic). carotene, which gives butter its yellow colour), and waxes. The fat is present as an oil-in-water emulsion: this emulsion can be broken by mechanical action such as shaking.Ībout 98% of milk fat is a mixture of triacylglycerols, with much smaller amounts of free fatty acids, mono-and diacylglycerols, phospholipids, sterols, and hydrocarbons. The membrane protects the fat against enzymes and prevents the globules coalescing into butter grains. Each sphere is surrounded by a thin skin (the fat globule membrane) which acts as the emulsifying agent for the fat suspended in milk. ![]() Under the microscope cream can be seen to consist of a large number of spheres of varying sizes floating in the milk. The cream differs considerably in appearance from the lower layer of skim milk. If milk is left to stand, a layer of cream forms on the surface. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |