Estimation of Fat in Milk Samples

Introduction

Milk fat measurement is a common task in the dairy industry, because milk fat content is one factor that determines milk price and is necessary to know for casein/fat ratio normalization. It is also important for the dairyman to know milk fat content exactly: discrepancies in the results of milk fat tests (usually performed in the dairy industrial plant) have economic relevance. In addition, a low milk fat content could indicate the existence of animal health deficiencies.

Principle

The fat can be separated from fat-containing milk/milk powder through the addition of sulphuric acid. The separation is made by using amyl alcohol and centrifugation. The fat content is read directly on a special calibrated butyrometer after centrifugation.
 

Apparatus

1. Good quality balance
2. Special butyrometer
3. Caoutchouc stoppers
4. Pipettes - 1 and 10 ml
5. Centrifuge, - 1200 rpm, equipped with heating element

Reagents

1. 90% Sulphuric acid
2. 100% Amylalcohol

Procedure

1. Mix the milk sample (temperature about 20°C) thoroughly, taking care to minimize incorporation of air. Allow the sample to stand for a few minutes to discharge any air bubbles. Mix gently again before pipetting.
2. Pipette sequentially into the butyrometer:
   1. 10 ml of 90% sulphuric acid.
   2. 10.75 ml milk (must not be mixed with the acid).
      Note: Pipette the required volume of milk into the butyrometer. Care must
      be taken to avoid charring of the milk, by ensuring that the milk flows
      gently down the inside of the butyrometer. It then rests on top of the acid.
   3. 1 ml amyl alcohol
   4. some drops of distilled water
3. Clean the neck of the butyrometer with a tissue or dry cloth.
4. Close butyrometer with caoutchouc stopper and shak until the milk was dissolved. The butyrometer was turned upside-down 5 or more times.
5. Spin in the Gerber centrifuge for 15 minutes.
6. The fat column was adjusted by using the stopper, so that it will be in the graduated part of the butyrometer. The fat percentage was read directly.
7. Note: Measurements should be carried out in duplicate.
    

Hazards

Sulphuric acid is toxic, highly corrosive and will cause severe burning if it comes in contact with the skin or eyes.
When mixing the butyrometer contents, considerable heat is generated.

If the stopper is slightly loose, leakage may occur during mixing, centrifuging or holding in the water bath.

Precautions

Wear protective eye goggles
Avoid all spillage and dropping of sulphuric acid from acid dispensers.
When mixing, hold the butyrometer stopper firmly to ensure that it cannot slip. Use a cloth or glove to protect the hands when mixing.
Do not point the butyrometer at anyone when mixing.
 

Authors*
* Sanjeev Sharma1, BR Yadav1, Aarti Bhardwaj2, Shalini Jain3 and Hariom Yadav3
1Livestock Genome Analysis Lab, 3Animal Biochemistry Division, National Dairy Research Institute, Karnal-
132001, India
2Meerut Institute of Engeenering and Technology, Meerut, U.P., India