Analysis of the Determination of Crude Protein in Feed

1. Determination principle of crude protein:

Kjeldahl method to determine the amount of N in the sample, that is, under the action of the catalyst, the destruction of organic matter with H2SO4, so that the N-containing substances into (NH4) 2SO4, adding strong alkali distillation to make ammonia escape, absorbed with boric acid, and then With acid titration, the N content was determined and the result was multiplied by a conversion factor of 6.25 to calculate the CP content.

2. Determination of Crude Proteins Materials and Appliances:

The instruments used for the determination of crude protein include: H2SO4, mixed catalyst, NaOH, boric acid, mixed indicator, HCl standard solution, sucrose, ammonium sulfate, boric acid absorption solution.

Determination of Crude Protein Equipment: crusher, sample sifter, analytical balance, digester, burette, fully automatic nitrogen determination, conical flask, volumetric flask, digestion tube

3 crude protein determination method steps

1, the digestion of the sample, weighed sample 0.5g, accurate to 0.0202g, add 6.4g mixed catalyst into the digestion tube and the sample mix evenly, and then add 12ml H2SO4 the boiling bottle placed on the electric furnace heating Start a small fire. After the sample is coked and the foam disappears, strengthen the firepower (360-410°C) until the transparent blue-green color. Then continue heating for at least 2 hours.

2. Distillation of NH3

The sample cooking liquid cooling, add 20ml distilled water, transferred to a 100ml volumetric flask, after cooling, dilute to the mark with water, shake, as a sample decomposition solution. The end of the condenser tube of the semi-micro distillation unit was immersed in an Erlenmeyer flask filled with 20 ml boric acid solution and 2 drops of mixing indicator. A few drops of methyl red indicator should be added to the water of the steam generator, and a few drops of sulfuric acid should be kept during the distillation to be orange-red. Otherwise, additional sulfuric acid must be added. Accurately transfer 10-20ml of sample decomposing solution into the reaction chamber of the distillation device, rinse the sample inlet with a small amount of distilled water, stopper the inlet glass stopper, add 10ml of sodium hydroxide solution, carefully lift the glass stopper into the reaction chamber, Plug the glass stopper and seal with water at the entrance to prevent air leakage. Distill 4min lower the conical flask to make the end of the condenser tube away from the absorption liquid surface, and then distill for another 1min. Rinse the end of the condenser tube with distilled water. The washing solution must flow into the conical flask and stop the distillation.

3, titration

The absorbed solution after the distillation was titrated with HCl standard solution, and the solution changed from blue-green to gray-red as the end point.

4, blank measurement

Weigh 0.5g sucrose instead of sample for blank measurement

5. Calculation

CP=

V2: standard solution volume in titration sample ml

V1: When titration blank, the required standard solution volume ml

C: hydrochloric acid standard solution concentration mol/l

M: sample mass g

0.0140: The mass of N in g equivalent to 1 mol of HCl standard solution.

6.25: N is the average coefficient converted from CP.

6, repeatability

A parallel sample of each sample was measured and its arithmetic average was even a result.

When the crude protein is above 25%, the allowable relative deviation is 1%;

When the crude protein is between 10% and 25%, the allowable relative deviation is 2%;

When the crude protein is below 10%, the allowable relative deviation is 3%.

Feed is the source of nutrition for livestock growth. The level of protein in feed directly determines the quality of livestock. Therefore, the determination of protein content in feed is an important step. Protein exists in all animal and plant bodies and is the material basis of all life activities. Livestock ingests protein and its breakdown products from feed to form its own proteins. Therefore, the analysis of protein content in feed has become the main indicator to evaluate the nutritional value of feed.