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. Objective To learnprinciples and methods of preparing casein from cow's milk., the main
protein in cow'
milk
is casein, the content is about 35g/L. Casein is a mixture of phosphorus-containing proteins with an isoelectric point of 4.7. Using the principle of the lowest degree of solubility at isoelectrins, the enzyme protein precipitates when the pH of cow's milk is adjusted to 4.7. Wash the sediment with ethanol and remove the lipid impurities to get pure casein. , equipment,
1. Milk
2.
centrifuges . 3. The filtration device
4. Precision pH
test paper
or acidity meter
5. Electric furnace
6.
Beech
7.
thermometer . Fourth,
reagents1. 95% ethanol
2. Aqueous ether
3. 0.2MpH4.7 sodium acetate-sodium acetate buffer
A solution: 0.2M sodium acetate solution
B solution: 0.2M acetic acid solution
organic pure vinegar Acids (content greater than 99.8%) 12.0g, fixed capacity to 1000ml
4. deA liquid 1770ml, B liquid 1230ml mixed, i.e. pH4.7 sodium acetate buffer.
5. Ethanol ether mixture solution: Ethanol: Ether: 1:1 (V/V) . V. Operation1. Heat 100 milk
to
to 4 degrees C. Slowly add a buffer that warms up to 40 degrees C while stirring, adjust the pH and cool to room temperature. Centrifuge 10min at 3000r/min. Discard the liquid and get casein coarse products.
2. Wash three times with water, 3000r/min centrifugation, discard the liquid.
3. Add ethanol to the precipitation, stir for a moment, and transfer all the suspended liquid to the Breits funnel for filtration. The ethanol-ether mixture is precipitated twice, and finally the ether is precipitated twice and dried.
. Spread the precipitation over the surface dish and
dry
the casein pure.
5. Accurate weighing, the content is calculated and the actual yield is calculated compared with the theoretical content (3.5g/100ml). Casein content g/100ml: cow's milk (g%) .