Soxhlet extractor consists of reflux condenser tube, fat extraction tube and fat extraction flask. All parts should be washed and dried before fat is extracted. The fat extraction bottle needs to be dried and weighed to a constant amount. (4) Put the filter paper tube into Soxhlet extractor, connect the fat receiving bottle that has been dried to constant weight, add anhydrous ether or petroleum ether from the upper end of the condensing tube to 2/3 of the volume of the receiving bottle, and heat in water bath to make the ether or petroleum ether continuously reflux, generally extracting 6 ~ pieces. Control about 80 drops of ether per minute (about 65 drops in summer and 80 drops in winter); ⑤ Weigh and remove the receiving bottle, and recover ether or petroleum ether. When 65,438+0 ~ 2ml of ether remains in the receiving bottle, it is evaporated in a water bath, then dried at 65,438+000℃ 5℃ for 2h, taken out, cooled in a dryer for 30min, weighed and repeatedly operated to a constant weight. 2 briefly describe the problems that should be paid attention to in Soxhlet extraction method? Briefly describe the problems that should be paid attention to in Soxhlet extraction? Answer: 1) The sample should be dried and ground. The moisture in the sample will affect the solvent extraction effect, and the solvent will absorb the moisture in the sample, resulting in the dissolution of non-fat components. The filter paper tube for loading the sample must be tight, so as not to leak the sample, nor to wrap it too well to affect the solvent penetration. The height of the filter paper tube should not exceed the reflux elbow, otherwise the fat in the sample exceeding the elbow cannot be extracted, resulting in errors. 2) For the sample containing a lot of sugar and dextrin, the sugar and dextrin should be dissolved in cold water first, filtered and removed, and the residue should be dried together with the filter paper, and then put into the extraction tube together. 3) The ether or petroleum ether used for extraction should be anhydrous, alcohol-free and peroxide-free, with low volatile residue content. Because water and alcohol can lead to the dissolution of water-soluble substances, such as water-soluble salts and sugars, the determination results are on the high side. Peroxide can cause fat oxidation, and there is also a danger of explosion when it is dry. 4) When extracting, the water bath temperature should not be too high, and it is advisable to drop about 80 drops per minute in the condenser tube and reflux 6- 12 times per hour. Pay attention to fire prevention when extracting. 5) When extracting, it is best to connect a calcium chloride drying tube at the upper end of the condensing tube to prevent moisture in the air from entering and ether from volatilizing in the air. If there is no such device, a dry absorbent cotton ball can be stuffed. 6) Whether the extraction is complete can be checked by experience or filter paper or ground glass. The ether dripped from the lower mouth of the extraction tube dripped on the filter paper or ground glass, and no oil stain was left after volatilization, indicating that the extraction was completed. 7) When evaporating ether or petroleum ether, do not use direct fire for heating, but use electric heating sleeve and electric water bath. Before drying, all the residual ether should be removed, because there is a slight ether residue, which is in danger of explosion when it is put into the oven. 8) Repeated heating will increase weight due to lipid oxidation. When gaining weight, the weight before gaining weight is the constant weight. 9) Because ether is an anesthetic, attention should be paid to indoor ventilation. How to judge the dry constant weight of extract by Soxhlet extraction method? How to judge the dry constant weight of extract by Soxhlet extraction method? Constant weight means that the difference between the two weights before and after weighing is below 0.3mg, and it usually needs to be baked in the oven for about 30min. Repeated heating will increase weight due to fat oxidation. When the weight increases, the increased weight is regarded as a constant weight. What are the definitions of acid value, base value, peroxide value and carbonyl value of edible oil? What are the definitions of acid value, base value, peroxide value and carbonyl value of edible oil? Answer: Acid value refers to the number of milligrams of potassium hydroxide consumed per gram of oil, indicating the content of free fatty acids in oil or the rancidity degree of oil. Peroxide value: the amount of substance that oxidizes potassium iodide, expressed in millimoles (or milliequivalents) per kilogram of active oxygen, indicating the content of peroxide in oil and the degree of oxidation of oil. The peroxide generated by the oxidation of carbonyl-valent lipids is further decomposed into carbonyl-containing compounds, and the amount or equivalent value of the generated compounds is carbonyl valence, which represents the degree of oxidative deterioration of oils and fats. Chapter 9 Determination of protein 1 Please briefly describe the operation steps in the digestion process of Kjeldahl method? Please briefly describe the operation steps in the digestion process of kjeldahl method.

Accurately weigh a certain amount of samples, add 0.5g of copper sulfate, 10g of potassium sulfate, 20mL of concentrated sulfuric acid, and several pieces of glass beads → carefully move them into a dry and clean 500ml Kjeldahl flask (solid or powder is put into a paper tube with a paper roll), gently shake them, and use 45? Brace the asbestos mesh with small holes → heat it with an electric stove (or use a flask first

Keep it away from the electric furnace), after all the contents are carbonized and the foam stops, increase the firepower (or put the flask on the electric furnace), keep the liquid in the bottle slightly boiling, continue to slightly heat for 30min→, turn off the electric furnace after the liquid becomes blue-green transparent, take out the flask, cool it, transfer it to a 100ml volumetric flask, and add water to constant volume.

2 briefly describe the basic principle of kjeldahl nitrogen determination method? Briefly describe the basic principle of kjeldahl nitrogen determination method? The sample was digested by concentrated sulfuric acid and catalyst, and protein was decomposed. The carbon and hydrogen in the sample were oxidized into carbon dioxide and water to escape, while the organic nitrogen in the sample was converted into ammonia, which combined with sulfuric acid to produce ammonium sulfate. Then all the digestive juice is distilled with alkali to evaporate ammonia, absorbed with boric acid, and titrated with standard hydrochloric acid or sulfuric acid solution. According to the standard acid consumption, the content of protein can be calculated. What problems should be paid attention to in the operation of kjeldahl nitrogen determination method? What problems should be paid attention to in the operation of kjeldahl nitrogen determination method? Answer: (1) The reagent solution should be prepared with ammonia-free distilled water. (2) Don't use strong fire when digesting, and keep moderate boiling. In the process of digestion, the Kjeldahl flask is rotated from time to time to make the acid condense and wash off the solid residue attached to the bottle wall, so as to promote its complete digestion. (3) In order to accelerate digestion, potassium sulfate is often added to raise the temperature of the solution in the digestive system. Copper sulfate catalyst and end point of digestion. See also.