Crude Protein Estimation of Feed Stuff in Nutrition Lab

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Crude Protein Estimation of Feed Stuff in Nutrition Lab

Crude Protein Estimation of Feed Stuff is one of very important test performed in nutrition labs of universities and feed mills.

Hello everyone, i am Dr. Kashif Amin and today i will teach you Crude Protein Estimation of Feed Stuff. Crude Protein estimation included in proximate analysis.

What is Crude Protein?

Crude Protein means source of nitrogen is either amino acids or non protein nitrogen like nitrates, nitrites and biurets etc.

What is Difference between  Crude protein and true protein?

In Crude Protein source of nitrogen is either amino acids or non protein nitrogen like nitrates, nitrites and biurets etc while in true Proteins source of nitrogen is amino acids only.

Principle of crude protein estimation:

The basis for the crude protein estimation is the estimation of Nitrogen. For this purpose,  sample is digested using sulfuric acid in the presence of catalyst to convert the nitrogen  present in the sample into ammonium sulphate. Acidic solution is made basic with sodium  hydroxide solution. The ammonia is distilled and trapped in the boric acid solution and titrated  against 0.1N sulfuric acid.

Apparatus:

  • weighing balance
  • Digestion Flask
  • Burner
  • Volumetric flask
  • Kjeldahl apparatus
  • Funnel
  • Beaker
  • Pippeteed Stuff in Nutrition Lab
  • Volumetric Cylinder

Chemicals:

  • Sulfuric acid
  • Digestion Mixture
  • 40% NaOH Solution
  • Distilled water
  • Methyl Red Indicator

Procedure crude protein estimation:

  1. Take 1.000 g Sample (in grinned form)
  2. Take a Digestion flask and add 5 g digestion mixture and 25 ml sulfuric acid in it.
  3. Add sample in it and place it on heater (in fume hood) for about 2 to 2.5 hours (Digestion)
  4. After that allow it to cool about 20 minutes at room temperature.
  5. after 20 minutes add some distilled water in it to enhance the process of cooling.
  6. take a volumetric flask 250ml and transfer the digested sample in volumteric flask and make the dilution 250 ml.
  7. An apparatus known as Kjeldahl apparatus is used to determine the crude protein of sample.
  8. Take 10 ml boric acid in which methyl red indicator is added, place it under Kjeldahl apparatus.
  9. Mix the diluted sample thoroughly and take 10 ml with the help of pippete and pour it in Kjeldahl apparatus.
  10. Add 10 ml of 40% NaOH followed by addition of sample.
  11. Steam coming from distilled water present in flask placed on heater cause release of ammonia gas.
  12. the ammonia gas passes through condenser where cold is running in the surroundings, gas vapors transfer in droplets and added in beaker containig boric acid.
  13. continue collecting ammonia to collect 40-60 ml solution
  14. now titrate it against 0.1N sulfuric acid note the reading of volume used of sulfuric acid.
Crude Protein Estimation of Feed Stuff in Nutrition Lab
Crude Protein Estimation of Feed Stuff in Nutrition Lab

Calculation:

Cp factor = (Volume of sample*N of Sulfuric acid*14*6.25/100*1000)*100

Cp factor = (250*0.1*14*6.25/100000)*100

Cp factor = 21.875 this is for 1 gram of sample.

Performance

Sample weight = 1.02 g

Titration reading = 1.28 ml

Crude protein % = 21.875*1.28/1.02*100

Crude protein % = 27.61 %

Note: Digestion mixture consists of Copper sulphate, ferrous sulphate and Potassium suphate.

Fow to detect Moisture of Feed stuff.

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