The casein is extracted from the milk.

Extract casein from milk(Purposes and Requirements) 1, understanding isoelectrin precipitation method 2, learning how to prepare casein from milk3, deepen understanding of the properties of electric points such as
proteinprotein is a hydrotic collosome, forming a hydrochemical layer on the surface of protein molecules in watersolution. In addition, the protein is a kind of two-sex ion, in a certain pH solution can maintain a stable state.
But when the pH of the protein solution is adjusted to the equal point, the protein becomes unstable due to loss of charge, at which point if dehydrated agent or
heating
is added, the hydration layer is destroyed and the protein molecules condense and predispulate with each other. The isoelectrogen precipitation method mainly uses the principle of the lowest solubility of the electrolyte molecules of both sexes at the isoelectrogen, and a method of separation of various sex electrolytes with different isoelectrogens.protein in cow's milk is casein content of about 35g/L. Casein is a mixture of phosphorus-containing proteins with an isoelectric point of 4.7. When the pH of cow's milk is adjusted to 4.7, casein precipitates. Washing precipitation with ethanol removes lipid impurities and obtains pure casein.But the separate use of isoelectrite precipitation method to separate
biochemic
product effect is not ideal, because even when isoelectrelectrides, some substances of both sexes still have a certain degree of solubility, not all proteins in isoelectrogens can be precipitated down, especially when the same type of two-sex substances are very close. In production,
organic
solvent precipitation method and salt analysis method are used, so that the precipitation effect is better.the purpose of this experiment is to enable students to use isoelectre precipitation legal casein, from which to deepen the understanding of the properties of such as proteins.. Methods and steps are . 1, take pre-positioned refrigerator cooling disinfection milk 6mL, 3,000r/min centrifugation 10min, remove the fat layer of the emulsion placed 50 ml
beaver
, heated to about 40 degrees C, in the stirring slowly added about 10mL preheated sodium acetate buffer, at this time the turbid liquid has a large number of flocs sink. Cold to room temperature, 3,000r/min centrifugation 10min, discard the liquid, casein coarse.2, wash and precipitate with distilled water three times (about 5mL each time), 3,000r/min centrifugation 10min, discard the liquid. 3, the precipitation will be placed in the research, after the study, gradually add 5mL 95% ethanol, sit for a moment, transfer all suspended liquid to the Cloth
funnel
filtration, drained products, with ethanol-ether mixture to wash precipitation twice (5mL each time), and finally with waterless ether washing precipitation twice (5mL each time), drain.4, spread the precipitation on the surface dish, air-dried, casein products (weighing, recording).5, casein solution preparation: called casein 0.1g, placed in a 10 ml beo bowl, plus 5mL 0.2mol/L sodium hydroxide solution, stir well, Insulation heating, dissolved and transferred to 10 ml
capacity bottle
, with a small amount of distilled water to wash the bea cup several times, the lotion into the capacity bottle, and finally add water to the scale, shake well, store in the refrigerator spare.calculated casein content and yield:1, content: casein grams / 100mL milk 2, the theoretical content of 3.5g / 100mL milk
.