The Soxhlet Extractor Method
Fat is widely found in the seeds and fruits of many plants. The determination of fat content can be used as an indicator to identify its quality. There are many methods for determining the fat content, such as extraction, acid hydrolysis, specific gravity, refractive, electrical and nuclear magnetic resonance. The extraction method is widely used at home and abroad, and the Soxhlet extractor method is a well-recognized classical method and the preferred standard method for grain and oil analysis. The Soxhlet extraction method uses a Soxhlet extractor as an extraction apparatus, and is extracted by refluxing with a low-boiling organic solvent (ether or petroleum ether) to remove crude fat in the sample, and the crude fat content is calculated by the difference between the weight of the sample and the residue. Since the extract of the organic solvent contains more or less fats such as free fatty acids, sterols, phospholipids, waxes, and pigments in addition to fat, the result of the extraction method can only be crude fat.
Selection of extraction reagents
Using similar phase-dissolving laws, the polarity of fat in agricultural products is generally small, and petroleum ether or diethyl ether can be used as an extraction reagent. Common laboratory petroleum ethers have low boiling range (30~60 °C) and high and low boiling range (60~90 °C). Generally, low boiling petroleum ether is used as extraction solvent to shorten the extraction time. If diethyl ether is selected as the extraction reagent, careful attention must be paid to the safe use of diethyl ether. It is strictly forbidden to have an open flame in the extraction room or to heat it with an open flame. Do not contain peroxide in the ether, keep the extraction room well ventilated to prevent explosion. The method for checking the peroxide in diethyl ether is as follows: take an appropriate amount of diethyl ether, add potassium iodide solution, shake vigorously, and let it stand for 1 min. If yellow appears, it indicates that peroxide is present and should be used before treatment. The treatment method is as follows: the ether is placed in a separatory funnel, and then washed with a 1/5 diethyl ether solution of dilute KOH for 2 to 3 times to remove the ethanol; then acidified with hydrochloric acid, and a 1/5 ether amount of FeSO4 or Na2SO3 solution is added. After shaking, standing, and layering, the lower aqueous solution is discarded to remove the peroxide; finally, it is washed with water until neutral, dehydrated with anhydrous CaCl2 or anhydrous Na2SO4, and subjected to double distillation.
Sample crushing degree
The thickness of the sample should be appropriate. When the sample powder is too thick, the fat is not easily extracted; if the sample powder is too fine, the pores of the filter paper may be lost with the reflux solvent, which may affect the measurement result.