Ether

Petroleum ether (boiling range 30~60℃)

Applicable to

The processing method depends on the nature of the sample itself. Pre-processing of milk is very simple, whereas processing of plant or animal tissue is more complex.

Crushing: Minimize the physical, chemical and enzymatic degradation of lipids in the sample.

Add sea sand (samples that are prone to caking): Add 4-6 times the sample amount to loosen the sample and expand the contact area with the organic solvent, which is beneficial to extraction:

Add anhydrous sodium sulfate (samples with higher water content): Because the ether can be saturated with 2% water, the ether cannot penetrate into the tissue. The ability to extract fat is reduced, so when some samples have high water content, anhydrous sodium sulfate can be added until the sample is in the form of granules.

Drying: improves fat extraction efficiency. Because when the sample is wet, ether cannot penetrate into the tissue. The appropriate temperature should be chosen.

Acid treatment: hydrolyzes the bound fat and precipitates the fat in a free state.

Some samples contain a large amount of carbohydrates. When measuring fat, the water-soluble carbohydrates should be washed away with water before drying and extraction.

Lipids and fat content in food

The role of lipids

form of existence

Acid value - the mass of potassium hydroxide (mg) required to neutralize the free fatty acids in 1g of oil.

Acid value is the main indicator reflecting the rancidity of oil.

Iodine value (iodine value)--The mass of iodine chloride or iodine bromide absorbed by 100g of grease is converted into the mass of iodine (g).

The iodine value reflects the degree of unsaturation of oil within a certain range.

Peroxide value - (0.002 mol/L) Na, S, 0 required to titrate 1g of grease, volume of standard solution (mL).

The peroxide value reflects the freshness and rancidity of the oil.

Saponification value - the mass of potassium hydroxide (mg) required to neutralize all fatty acids (free bound) in 1g of oil.

Saponification value can identify the type and purity of oils and fats

Principle: After the sample is extracted with a solvent such as anhydrous ether or petroleum ether, the substance obtained by evaporating the solvent is called fat or crude fat in food analysis.

Applicable objects: It is suitable for the determination of samples with high lipid content, low bound lipid content, capable of drying and grinding, and not easy to absorb moisture and agglomerate.

Features: The results are more reliable for most samples, requiring a long cycle and a large amount of solvent.

calculate Fat%=(W1-W2)x100/W

Principle: After the food sample is hydrolyzed with hydrochloric acid, the fat is extracted with ether, then the solvent is recovered and removed in a boiling water bath, and the free and combined fat content is obtained by weighing.

Applicable objects: It is suitable for the determination of lipids in various types of food. It is suitable for solid, semi-solid, viscous liquid or liquid food, especially processed mixed food, which is easy to absorb moisture, agglomerate, and is difficult to dry. The effect is better.

Principle: The ammonia-ethanol solution is used to destroy the colloidal properties and fat globule membrane of the milk, so that the non-fat components are dissolved in the ammonia-ethanol solution, and the fat is freed. Then the fat is extracted with ether-petroleum ether, and the solvent is distilled to remove the residue. The substance is milk fat.

Applicable objects: Suitable for all kinds of liquid milk (raw milk, processed milk, partially skimmed milk, skimmed milk, etc.), various condensed milk, milk powder, cream and ice cream and other dairy products that can be dissolved in alkaline solution. It is also suitable for soy milk or Foods that are milky when added with water.

Principle: Using polar methanol and non-polar chloroform as solvents, it can form a ternary extraction system with the water in the sample to turn the lipids bound in the sample tissue into free fat. It can also extract polar lipids such as phospholipids. (that is, extract all the fat), then evaporate the solvent, and weigh and quantify.

Applicable objects: This method is very thorough for the extraction of lipids and phospholipids contained in sample tissues, and is especially suitable for the extraction of food fats such as fish and poultry. The acid decomposition method can decompose some phospholipids, but this method will not decompose it.

Principle: Concentrated sulfuric acid is used to dissolve non-fat components such as lactose and protein in milk, and the calcium casein salt in milk is converted into soluble casein bisulfate, so that the fat globule membrane is destroyed and the fat is freed, and then heated and centrifuged. The fat is completely and quickly separated, and the value of the fat layer can be directly read to know the fat content of the milk being measured.

Scope of application: These two methods are standard methods for determining milk fat and are suitable for the determination of fat in fresh milk and dairy products. For dairy products containing a lot of sugar (such as sweetened condensed milk, sugar-sweetened milk powder, etc.), the sugar is easy to caramel when using this method, making the result error larger, so it is not suitable.

This method is simple and rapid to operate. The measurement accuracy meets the requirements for most samples, but is not as accurate as the gravimetric method.