实验概要
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.
实验原理
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.
主要试剂
1 90% Sulphuric acid
2 100% Amylalcohol
主要设备
1 Good quality balance
2 Special butyrometer
3 Caoutchouc stoppers
4 Pipettes - 1 and 10 ml
5 Centrifuge, - 1200 rpm, equipped with heating element
实验步骤
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:
a: 10 ml of 90% sulphuric acid.
b: 10.75 ml milk (must not be mixed with the acid).
Note: Pipette the required volume of milk
into the butyrometer. Care mustbe taken to avoid charring of the milk,
by ensuring that the milk
flowsgently down the inside of the butyrometer. It then rests on top of the acid.
c: 1 ml amyl alcohol
d: 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.
注意事项
1. Sulphuric acid is toxic, highly corrosive and will cause severe burning if it comes in contact with the skin or eyes.
2. When mixing the butyrometer contents, considerable heat is generated.
3. If the stopper is slightly loose, leakage may occur during mixing, centrifuging or holding in the water bath.