Chapter 8. Determination of lipids

1. Chapter 8. Determination of lipids

2. Section 1. General

3. fats lipids Fatlike substances 1. Lipids in foods • Lipids are usually defined as food components that are insoluble in water and that are soluble in organic fat solvents.

4. Lipids amounts in foods • Corn foods • Dairy foods • Plant or animal lipid • Vegetables and fruits • legume • Meat, fish, egg

5. 2. Significance of determining lipids • Lipids have at least three important functions in foods: culinary, physiological, and nutritional. • Carrying odors and flavors and their contribution to the palatability of meats, to the tenderness of baked products, and to the richness and texture of ice cream. • Affording energy. • Providing essential fatty acids, and fat-soluble vitamins.

6. 3. Determination of lipids • Lipids forms in foods: free and componds • Sparing solubility in water and considerable solubility in organic solvents • Organic solvents: • Ethyl ether • petroleum ether • chloroform-methanol

7. Pretreatment of samples • Grinding: The extraction of dry materials depends on particle size. • Drying: Only part of the lipids can be extracted with ether from moist material, as the solvent cannot penetrate the tissues and the extractant becomes saturated with water and inefficient for lipid extraction.

8. Determination methods • Soxhlet extraction method • Chloroform-methanol method • Acid hydrolyzed method • Rose-Gottlieb method, Babcock method, Gerber method

9. Section 2. Determination methods of lipids

10. 1. Soxhlet extraction method • Direct extraction of lipids is often carried out in a Soxhlet. • The sample in an extraction thimble from filter paper), covered with defatted cotton wool to prevent small particles from finding their way into the flask, is placed in the middle part of the apparatus. • The flask is filled with solvent; the condenser attached to a tap; and heating of solvent in the flask started.

11. The condensing vapors fill the middle part containing the sample and carry the dissolved lipid into the flask by siphoning action each time the height of the siphon is attained. • At the end of exhaustive extraction, the apparatus is disconnected, the solvent from the tared flask is evaporated, and the weight increases calculated.

13. 冷凝 管 索氏抽提器 滤纸筒 接收瓶

14. Applying area and specility • The result is crude lipid. • The extractions of ethyl ether and petroleum are free-lipid, not conjoint-lipid.

15. Determining procedures • 1. Preparation of filter paper package. • 2. Treatment of sample. • 3. Extraction • 4. Weigh

16. Notice • No water in sample. • Filter paper package should be no leaking of sample. • Extraction temperature. • Safety.

17. 脂肪自动测定仪 • 原理：样品首先浸泡在沸腾的溶剂中，提取出大部分的脂肪→再把样品提出至溶剂液面上，用溶剂淋洗，提取样品中残余的脂肪→除去溶剂，将抽提杯烘干称重。

18. Auto-analyzer of lipids

19. 该系统由一套浸提单元和一套控制单元组成。样品分析时，将预先称重的样品放入浸提杯中，溶剂随后被加到密闭系统中（浸提杯），通过电子加热板对浸提杯加热。浸提程序包括了浸提、淋洗、溶剂回收及干燥四个步骤。 • HHT-2055主要用于对烟草中石油醚提取物的测定，也可应用于食品、饲料、环境、工业等其它领域，可适用全部用于浸提的溶剂，溶剂的回收率可达90%。本系统同时可适用于GC/HPLC的样品制备。系统精度完全能达到传统的索氏提取装置一样的精度（1%或更高）。

20. 意大利ＶＥＬＰ全自动脂肪测定仪

22. 2. Chloroform-methanol method • Principle: • The sample is homogenized with a mixture of chloroform and methanol in such proportions that a miscible system is formed with the water in the sample. • Dilution with chloroform and water separates the homogenate into two layers, the chloroform layer containing all the lipids and the methanol layer containing all the nonlipids. • A purifeid extract is obtained by isolating the chloroform layer.

23. Applying area:conjoint lipids, especially samples containing much phosphor-lipids, such as animal tissue, fish muscle, poultry, egg, soybean

24. 3. Acid hydrolysis method • Principle: The sample is hydrolyzed using HCl, and lipids in conjoint-compounds or stored in tissues is free. Then free lipids are extracted using ethyl ether or petroleum ether. • Applying: Those samples who can not determined by Soxhlet extraction. Not fit sugar-rich sample. • The results contain lipids of free and conjoint.

25. 4. Determination of lipids in milk • In milk, fat globules are present as an emulsion of oil in water and are surrounded by a thin protein film. • The emulsion must be broken and the protein film removed before the fat can be separated and determined volumetrically.

26. Milk is mixed with sulfuric acid in a special bottle, shaken till apparently homogenous, centrifuge, and submerged into water at 63℃. The rising fat is determined from the height formed in a graduated neck. 4.1 Babcock method

27. 11 ml of milk followed by 1 ml isoamyl alcohol are added to a Gerber glass butyrometer containing 10 ml sulfuric acid. A lock stopper is inserted and the bottle is shaken until the curd disappears and the contents are homogeneous. The butyrometer is centrifuged 4 min, submerged to top of graduate stem in water at 63℃ for 5 min, and the fat content are read off. 4.2 Gerber method

28. The Gerber test is simpler and of wider general application than the Babcock test. • Charring is generally avoided by the ratio of milk to sulfuric acid. • Isoamyl alcohol improves the fat separation and reduces the effects of sulfuric acid.

29. The sample is rendered alkaline with ammonium hydroxide. The digested mixture is extracted repeatedly with ethanol, ehter, and petruleom ether. The combined extracts are dried, purified by extraction with petroleum ether, and weighed. 4.3 Rose-Gottlieb method