食品分析实验报告 蛋白质

Date: 2011-05-15

Experimental title: Determination of protein content

Purpose or principle:Proteins are nitrogen-containing compounds. Food and concentrated sulfuric acid and digestion catalyst for a common heating, protein degradation, resulting in formation of ammonia and sulfuric acid with ammonium sulfate, stay in the digestive juice, and then distilling the ammonia free alkali, boric acid absorbed, and then hydrochloric acid standard solution titration, according to Multiplied by the consumption of acid in the protein conversion factor, that was protein content.

Because food in addition to protein, also contain other nitrogenous substances, so the protein known as crude protein.

https://www.360docs.net/doc/f71149883.html,anic nitrogen in the intense heat and CuSO4, under the action of concentrated

H2SO4, digestion generated (NH4) 2SO4.

●Reaction equations:

H2SO4==SO2+H2O+[O]

R. CH.COOH+[O]==R.CO.COOH+NH3

R.CO.COOH+[O]==nCO2+mH2O

2NH3+H2SO4==(NH4)2SO4

2.In the Kjeldahl device with the base effect, by distillation to release NH3,

collected in H3BO3 solution.

●Reaction equations:

2NH

4+

+OH

-

==NH

3

+H

2

O

NH3+H3BO3==NH4++H2BO3-

3.Then already know the concentration of HCI standard solution titration,

according to the amount of HCI to calculate the consumption of nitrogen content,

and then multiplied by the appropriate conversion factor to obtain the protein

content.

●Reaction equations:

H2BO3-+H+==H3BO3

Procedure:

?Reagents used in experiments:

1)HCI standard solution (0.1 mol.L-1)

2)H3BO3 solution (3%)

3)H2SO4 (high concentration)

4)Sodium hydroxide solution (40%)

5)Distilled water

A.The digestive juice preparation

1 gram of sample accurately weighed, placed in the flask. and then add 10 ml of sulfuric acid.After the bubble burst samples, which increase the firepower to clarify the solution, and then continue to heat about 1 hour, cooled to room temperature. Adding 30ml bottle wall along the water, dissolved salts, cooling, into 100ml volumetric flask, rinsing the flask several times with water, lotion into the flask, add water to the mark, shake well.

B.Ammonia fixation

Add a few drops to the solution of methyl red indicator, a few drops of H2SO4. Receiver solution was 20ml 2% of H3BO4 solution, which add 2 drops of mixed indicator, the receiving device when the condenser to the exit surface of the immersion fluid absorption Below.

Take 10.0ml sample digestion, the inlet into the reaction chamber, with a small amount of water to wash the inlet, then add 10ml 50% NaOH solution in the reaction chamber, a good glass stopper plug to prevent the escape of ammonia. From beginning to return in mind, the distillation 4min, under the port to move the

condenser surface to leave the reception. Re-distillation, under the port condenser with pure water washing, lotion absorbed into the fluid.

C.Ammonia calibration

By 0.05mol.L-1 HCl standard solution titration to dark red for the end.

D.Calculation of protein content

Protein (%) = N (%) * K (K is conversion factor)

Result:

Experimental and calculated by the protein content of samples was 13.91206%. Discussion:

This method also applies to semi-solid samples and liquid samples testing. Semi-solid samples generally range sampling 2.00g ~ 5.00g; liquid samples sampling 10.0mL ~ 25.0mL (equivalent to approximately N 30mg ~ 40mg). If the test liquid sample, the results represented by g/100mL.

Digestion, if the samples with high sugar or fat content, and more time, pay attention to controlling the heating temperature, so a large number of foam spray Kjeldahl flask, resulting in sample loss. Can be added a small amount of octanol or liquid paraffin, or a defoamer to reduce foam

Kjeldahl digestion flask should pay attention to rotation, will be attached to the carbon washed down the bottle wall, complete digestion of samples. If the sample is not digestible to the clear and transparent, can be cooled solution Kjeldahl flask, add a few drops of hydrogen peroxide, and then continue to heat until completely digested.

Boric acid absorption solution temperature should not exceed 40 ℃, otherwise the ammonia absorption decreased, resulting in lower test results. Cold bath can be placed in the receiving flask.

Obtained under repeatability conditions, the results of two independent determinations shall not exceed the arithmetic mean of absolute difference of 10%. Conclusion:

Protein (protein) is the material basis of life, no life without protein. Therefore, it is with life and activities with various forms of life closely linked to the material. Every cell in the body and have all the important components of the protein involved. Protein accounted for 16.3% of body weight, that is, a 60kg adult weight of the protein the body about 9.8kg. Many types of protein in the human body, nature, different functions, but they are 20 kinds of amino acids by the combination of different proportions and in vivo metabolism and updated constantly. By ingestion of protein in the body after digestion and break down into amino acids, absorbed in the body is mainly used for re-assembled into the body by a certain percentage of protein, and the new protein and the metabolism and break down constantly, always in a dynamic balance. Therefore, food quality and quantity of the protein, the ratio of amino acids is related to the amount of protein synthesis in the human body, especially the young people's growth and development, maternal prenatal and postnatal care, the elderly, health and longevity, with the amount of dietary protein Has a close relationship.

The nutrients the body needs dozens, summed up in six categories: proteins, lipids, carbohydrates, inorganic salts, vitamins and water. Proteins are organic polymer compound, constitutes the basic unit of protein is amino acids. Nitrogen is the most important indigenous body, so that the material basis of life and movement.

Proteins are important components of body tissues, the protein content of the body weight of 16-19% to account for about 3% of daily protein in the body's metabolism. Protein within the body constitutes an important physiological role in a variety of substances, such as: in the metabolic process, with catalytic and regulatory role of enzymes and hormones, hemoglobin oxygen transport and immune function of antibodies, muscle fiber protein, collagen.

Protein to maintain the body's acid-base balance. Proteins involved in energy metabolism in the body, the body part of the daily consumption of energy has come from protein

Because the protein in the human body are so important, so the balance in the measurement of dietary protein content will have a very important significance.