酪蛋白的制备英文实验报告

Preparation of casein

I.The purpose and requirements

1. Master to use the centrifuge;

2. Master prepared from milk casein in the principles and methods.

II.The experimental principle

Casein is protein phosphorus, but also the heterogeneous mixture, rich in Tyr, Met, Gys, (Gys) 2, pI equal to 4.7 to 4.8, insoluble in ethanol.

The experimental use when in the isoelectric point of the principle of minimum solubility, the milk's pH to 4.7, the casein will precipitate out. Sediment washed with ethanol to remove lipid impurities, you get pure casein

III.E quipment and reagents

1. Equipment

a. Centrifuges

b. Filtration system(Buchner funnel);

c. Constant temperature heating device

2. Reagent

a. pH4.7 acetic acid - sodium acetate buffer (0.2mol/L) 30ml

b. Milk 30ml

c.95% ethanol

IV.Methods of operation

1. The 30ml milk heated to 40℃, stirring slowly add heated to 40 ℃, pH4.7 acetic acid - sodium acetate buffer, 30ml (with a precision pH meter or pH paper and adjusted to pH 4.7).

To have mixed suspension cooled to room temperature, centrifuge (4000 rpm / min) centrifugation for 5 minutes, remove the supernatant, the crude products obtained casein.

2. The precipitate washed once with water, centrifugation for 5 min (4000 r / min), discard the supernatant.

3. Add 30ml of ethanol in the precipitation, stirring a moment, put all the suspension transferred to Buchner funnel filtration.

4. The precipitate on the surface of the dish open, to get pure casein.

5. Accurately weighed to calculate concentration and yield.

V.The experimental results and analysis

1.The experimental results

Data of the measurement is shown in the following table.

The amount

of milk(mL) Casein(g)

Measured

values(g/L)

The theoretical

value(g/L)

Yield（%）

30 2.0 66.7 35 190.5

End of the experiment to be casein yield was 190.5%, far greater than 100%, which is derived from the experimental proof of casein in the more impurities. Impurities which may be: water, ethanol and milk in some of the impurities.

2. The experimental analysis

a. Washed precipitate, when washed only once, did not completely wash out the impurities, so that the product is still more residual impurities, the results of this error is caused by one of the reasons.

b. After the filtration, did not use ethanol - ether mixture washed precipitate, not in the final precipitate washed with ether, resulting in the final product contains fat-soluble substances, alcohol, water and other impurities, which is the result of errors caused by one of the reasons.

c. No air-dried, during the experiment, water and ethanol in the product is not completely evaporate

d.

d. Buchner funnel in the transfer of sediment from the pan to the surface when a small amount of sediment left in the Buchner funnel and filter paper, and a small amount of precipitation is lost, leading to the result of error.