Determination of crude fat in food

Determination of crude fat in food

Crude fats include the general term for fat-soluble substances in feed, animal tissues, and animal excreta. The concept is larger than what we usually say. In animals, plants such as soybeans, corn, rice, wheat, etc. all contain a certain amount of fat. Like fat, protein is also one of the essential nutrients. Although medically speaking, we should eat less animal fat instead of vegetable fat. Because vegetable fat is easily digested. Although fat is an essential nutrient for the body, once it is excessive, it will be counterproductive. Excessive consumption of fat, the first obvious characteristic is obesity, followed by a series of chain reactions, such as atherosclerosis, high blood lipids and other diseases, the incidence will be increased accordingly. Therefore, measuring the content of crude fat in the food is called a compulsory course of food science. We often use some instruments to measure crude fat, such as crude fat analyzer, which has a variety of models: SZF-06A crude fat analyzer, SZF -06B Crude Fat Analyzer, SZF-06 Crude Fat Analyzer. Of course, there are other methods for determining the content of crude fats in substances, such as Soxhlet extraction and acid hydrolysis. The most classic method is the Soxhlet extraction method. The principle of Soxhlet extraction is the gravimetric method, which uses fat solvents to lift the 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. That is, weighing before weaving, and then weighing after the extraction, the difference between the two is the data we need to get, and then calculated according to a certain ratio coefficient. Finally, the content of crude fat in the material was obtained.

In this article we focus on how to use Soxhlet extraction for crude fat determination.

Soxhlet extraction:

(I) Instruments: Analytical balance, electric thermostat, CXC-06 crude fiber analyzer, SZF-06B crude fat analyzer, electric constant-temperature water bath, grinder, mortar, color filter silica gel dryer, filter paper cartridge, Soxhlet extractors and jars, skim lines, absorbent cotton, skim fine sand.

(B) Reagents: anhydrous ether

(C) Sample preparation: 1. Grain and beans (excluding peanuts) were taken to remove the net sample of impurities 30 ~ 50g, ground through a 1.0mm diameter round-hole sieve into a wide-mouth bottle for use. 2. The small sample of oil, such as sesame, oil seed, flaxseed, etc., was taken to remove 20 g of the net sample for removing impurities, and placed in a wide-mouth bottle for use. 3. Take 30～50g samples of large-grain oil such as peanut, castor bean, sunflower seeds, and tea seeds. After removing the impurities, peel the shells one by one. The kernels and shells are weighed separately, and the total amount of kernels is calculated, and then Ren cut or sliced ​​into a wide-mouth bottle for use.

(4) Operation method: 1. Sample dressing. From the standby sample, 2-5 g of the sample was weighed with a baking box, baked at a temperature of 105° C. for 30 minutes, poured into the mortar while hot, and grinded with about 2 g of defatted fine sand. After the sample and fine sand were ground into an oily form, they were cleanly transferred into a filter paper tube (a layer of absorbent cotton was inserted at the bottom of the tube and baked at a temperature of 105°C for 30 minutes), and the sample on the mortar was rinsed with a small amount of ethyl ether. And fat, into the filter tube, and then use the absorbent cotton into the upper part, press the sample.

2. Extraction and drying. The extractor is properly installed, then the filter paper tube containing the sample is placed in the extraction tube, and at the same time, the ether is injected to the height of the siphon tube. After the ether is decanted, diethyl ether is added to two-thirds of the height of the siphon tube. A small piece of absorbent cotton was gently inserted into the inlet of the condensing pipe, the inlet pipe of the condensing pipe was opened, and heating extraction was started. The temperature of the heating was 120 to 150 drops of ether refluxed per minute, and refluxed seven times or more per hour. The extraction time depends on the oil content of the sample, generally more than 8 hours, and the ether extracted into the extraction tube is inspected with a glass slide (drip test) without oil traces. After removing the fat, remove the filter paper tube with a long handled tweezers, and then heat the ether to reflux 2 times. Then, recover the ether, remove the condensation tube and extraction tube, and heat to remove residual ether from the extraction bottle. The outer part of the bottle was extracted from the net, and then the extraction bottle was first baked at 105° C. for 90 minutes, then baked for 20 minutes, and then dried until the constant weight was reached. (The weight difference between the front and rear secondary weight is within 0.0002 g, which is regarded as constant weight). The weight added to the extraction bottle is the weight of crude fat.

(E) Calculation of results: The content of crude fat wet basis, dry base content and standard water miscellaneous content are calculated according to equations (1), (2) and (3) respectively:

W1

Crude fat (moisture basis) = —— × 100 --------------- (1)

W

W1

Crude fat (dry basis %) = ————- × 10000 --------------- (2)

W(100-M)

W1 (100-M mark)

Crude fat (standard water miscellaneous, %) = ─────────── × 100 -------------- (3)

W ( 100 - M)

Where: W1 - crude fat weight, g;

W -- sample weight, g;

M -- Percentage of sample moisture, %;

M mark - the standard sample moisture, the sum of standard impurities,%.

The results of the double test allowable difference: grain, oil does not exceed 0.4%, soybean does not exceed 0.2%, for the average, that is, the determination results. The measurement result is the first decimal place.

If the crude fat content of the shelled oil is determined, it must be converted by formula (4) and formula (5) respectively:

N × A

Shelled oil crude fat (wet basis %) = ─────── -------------- (4)

100 N × A

Shelled oil crude fat (dry basis %) = ─────── --------------- (5)

100 - M

Where: N - the percentage of crude fat wet basis content of shell kernels, %;

A -- Percentage of total kernels with shell oil, %;

M -- Moisture percentage of shelled oil, %.

Note: If no filter paper tube is available, filter paper 28cm in length and 17cm in width may be used. Using a test tube with a diameter of 2cm, roll it into a tube along the long direction of the filter paper, and withdraw the test tube to half of the height of the paper tube, flatten the evacuated part and fold it over. Keep it close to the outer layer of the test tube, fasten it with a degreasing line, fold the lower corner upwards, press it into a round bottom, and withdraw the test tube, make it a filter paper tube with a diameter of 2.0cm and a height of about 7.5cm.