Comparison of two methods for crude fat determination

Crude fat refers to the general term for fat-soluble substances in feed, animal tissues, and animal excreta. The concept of crude fat and fat is different. It covers much more than fat. Usually the determination of crude fat, extraction and acid hydrolysis method, of course, there is now a more convenient way, that is, direct use of crude fat analyzer, it has a variety of models, such as SZF-06B crude fat analyzer, SZF-06 Crude Fat Analyzer and SZF-06A Crude Fat Analyzer.

Here we look specifically at the extraction method and acid hydrolysis method to determine the principle of crude fat, reagents and other differences.

principle:

Extraction method: This method is a gravimetric method, which uses fat solvents to lift fat and weigh it. This method is suitable for solid and liquid samples. The sample is usually immersed in a fat solvent, ether or petroleum ether with a boiling point between 30° C. and 60° C., and subjected to cyclic extraction using a Soxhlet extractor. The fat material extracted by this method is a mixture of fat materials, which contain fatty free fatty acids, phospholipid esters, sterols, certain aromatic oil pigments, and organic acids. Therefore, it is called crude fat.

Acid hydrolysis method: The sample was acid-hydrolyzed and extracted with ether. The solvent was removed to obtain the total amount of free and bound fat.

Reagents and instruments:

Extraction method: anhydrous ether, sea sand, Soxhlet extractor, constant temperature water bath, oven, skimmed cotton, degreasing filter paper

Acid Hydrolysis: Hydrochloric acid, 95% Ethanol, Ethyl ether, Petroleum ether, 100 ml stoppered cylinder

Steps:

Extraction method: (a) preparation of samples

Weigh the weight of the sample according to the content of fat in the material, usually the fat content is below 10%, weigh 10-12 grams of the sample; if the fat content is 50-60%, then weigh 2-4 grams, ( Can be used after the determination of moisture).

The sample was dried in an oven at 80-100°C. Generally bake for 4 hours, avoid overheating when drying. After cooling, accurately weigh a certain amount of sample. If necessary, mix and refine the sea sand and remove it in a non-destructive manner in the filter paper tube. Use tight absorbent cotton plugs. Place the filter paper tube in the extraction tube of the Soxhlet extractor. Be careful not to make the filter paper tube. Higher than the siphon part of the extraction tube.

(b) Extraction

The washed extraction bottle was dried in an oven at 1.5°C until constant weight, about 1/2 to 2/3 of the volume of the extracted bottle was added with ether, and then the parts of the extractor were connected according to the figure, taking care not to leak.

Heating extraction should be carried out in a thermostatic water bath (water bath temperature is about 40-50°C). It is also possible to use a water bath heated by a bulb or an electric furnace. It is strictly forbidden to directly heat the Soxhlet extractor with a flame.

During heating, the ether evaporates. The ether vapor rises from the connecting tube to the condenser and condenses into a liquid and drops into the extraction tube. At this time, the fat in the sample is the diethyl ether siphon tube in which the ether liquid level exceeds the height of the siphon tube and the fat flows into the extraction bottle. This cycle extracts, regulates the temperature of the waters, makes the ether circulate 3-5 times per hour, the time is decided according to the nature of the sample, generally takes 6-12 hours, the sample contains fat is extracted completely, you can use the filter paper to roughly judge, from A small amount of ether was drawn from the extraction tube and dropped on a net filter paper. After the ether was dried, the half point of the grease on the filter paper was completely extracted.

After the extraction is complete, ether is again evaporated into the extraction tube and the extraction tube is removed before the liquid level of the ether reaches the highest point of the siphon tube.

(III) Weighing and Calculation

All the ethers in the extraction bottle were evaporated to dryness, the outer wall was washed, dried in an oven at 105° C. to constant weight, and the percent fat-promoting content of the sample was calculated according to the following formula.

Fat () = (W1-W0)/W×100

W1: Accepts bottle and fat weight (grams).

W: sample weight (grams).

W0: Accept the bottle weight (grams).

Acid hydrolysis method: 1, sample processing: (1) solid sample: accurately weighed about 2 grams of water, add weight after mixing. Ml hydrochloric acid. Place in a 50 ml large test tube and add 8 ml; (2) Liquid sample: Weigh 10.0 g, place it in 50 ml large test tube, process 0 ml of hydrochloric acid,

2. Place the test tube in a 70-80°C water bath and stir it with a glass rod every 5-10 minutes until the sample is completely digested, about 40-50 minutes.

3, remove the test tube, add 10 ml of ethanol and mix. After cooling, the mixture was transferred to a 100 ml stoppered measuring cylinder and the tubes were washed with 25 ml of diethyl ether and poured into graduated cylinders. After all the ether was poured into the measuring cylinder, the stopper was shaken for 1 minute, cautiously opened, gas evolved, and then plugged. Let stand for 12 minutes, cautiously unscrew, and use a mixture of petroleum ether and ethyl ether to flush the fat attached to the plug and barrel. Allow to stand for 10-20 minutes until the upper liquid is clear. Aspirate the supernatant in a constant-cone conical flask, add 5 ml of ethyl ether to the stoppered cylinder, and shake it. After standing, the upper layer of ether is still aspirated. Put into the original conical flask. The conical flask was placed on a water bath to dry and placed in a 95-105°C oven for drying for 2 hours. The flask was placed in a desiccator and cooled for 0.5 hour and weighed.

Calculation:

X=(m1-m0)/m2

X: the content of fat in the sample;

M1: Accepts the quality of bottles and fats, g;

M2: Accept the quality of the bottle, g.