Determination of fat in soybeans

There are two national standard methods for the determination of fat in food: Soxhlet extraction method and acid hydrolysis method
.
This training uses the Soxhlet extraction method (according to the first method of GB/T5009.

1.
Purpose requirements

(1) Master the basic principles and methods of fat determination by Soxhlet extraction
.

(2) Master the operation essentials of Soxhlet extraction method to determine fat, and use Soxhlet extractor to determine the fat content in food
.

2.
Principles of training

According to the nature of fat insoluble in water but easily soluble in organic solvents, low-boiling ether (boiling point 35℃) or petroleum ether (boiling point 30-60℃) is selected as the solvent, and the fat in the sample is extracted with a Soxhlet extractor , And then evaporate the solvent and then dry, the residue obtained is fat
.
Since the organic solvent extracted from the sample is not only fat, but also contains other fat-soluble components (such as sterols, organics and pigments, etc.

3.
Training supplies

(1) Soxhlet extractor (see Figure 1-2)
.

(2) Electric heating constant temperature water bath (50～80℃)
.

(3) Oven (80～120℃)
.

(4) Analytical balance: Sensitivity is 0.
1mg
.

(5) Anhydrous ether
.

(6) Refined sea sand
.

4.
Safety reminder

Diethyl ether is narcotic, so please pay attention to indoor ventilation when using it and avoid inhalation
.
When volatilizing ether , do not use direct fire to heat it

5.
Operation steps

(1) Preparation of the filter paper cartridge Take a 15cm×8cm qualitative filter paper, roll it into a cylinder with a diameter of 2cm, tie it with a thin degreasing white thread, fold one end of the filter paper cartridge into the cylinder, press it into the bottom of the cylinder, and take a small amount Put the absorbent cotton into the bottom of the tube, and accurately weigh the filter paper tube
.

(2) Preparation of the sample.
The soybean sample is crushed through a 40-mesh sieve with a crusher, and 2.
000～5.
000g is accurately weighed in the filter paper cylinder.
A layer of absorbent cotton (mixed with sea sand if necessary) is placed on the sample, and the cylinder is Fold the top edge of the paper into the tube to make the entire filter paper tube about 4cm high
.

(3) Extraction Put the filter paper cartridge into the fat lifting tube of the Soxhlet extractor, connect the receiving bottle which has been washed with anhydrous ether and dried and weighed, install the condenser, and put a funnel on the top of the condenser.
Pour the anhydrous ether through the funnel into the extractor to 2/3 of the volume of the receiving bottle
.
Heat on a water bath at about 45°C.

If there is still ether in the receiving bottle, repeat it several times until there is about 2 mL of ether left in the receiving bottle.
Remove the receiving bottle and let the ether evaporate completely on the water bath
.

(4) Drying Dry the water droplets attached to the outer wall of the receiving bottle after evaporation with a dry cloth, dry in an oven at 100-105°C for about 1 hour, cool in a desiccator for 30 minutes, weigh, and repeat drying to constant weight
.
In the repeated operation of drying to constant weight, the weight should be reduced, but because the extracted fat will increase again due to oxidation, the weighing value before the weight increase again can be used as the constant weight value

6.
Result calculation

In the formula-the fat content in the sample,%

m——the mass of the sample (should be based on the mass of the sample before drying), g

m ₁ ——The mass of receiving bottle and fat, g

m ₀ ——The mass of the receiving bottle, g

7.
Tips

(1) Scope of application: The Soxhlet extraction method is suitable for the determination of food samples with high lipid content, mainly containing free lipids but less bound lipid content, capable of drying and grinding, and not easy to absorb moisture and agglomerate
.
The detection fat content meat products, soy products, nut products, grains fried products, in Western->

(2) The sample should be ground after drying, and the sample after measuring the moisture can be used to measure the fat
.
The filter paper tube containing the sample must be tight, and the sample must not leak, otherwise it should be redone

(3) Diethyl ether can saturate about 2% of water, and water-containing diethyl ether will extract non-fat components such as sugar at the same time, so anhydrous diethyl ether must be used
.
Anhydrous ether can be made by the following method: fill 1000mL ether in a narrow-necked bottle , add 50g of anhydrous gypsum, shake for several times, stand for more than 10 hours, distill on a water bath, and collect the distillate below 35°C

Related link: Determination of fat in food