Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Characteristics of Fats Saponification Number It is defined as the number of milligrams of potassium hydroxide required to saponify one gram of fat. It is an indication of the molecular weight of fat and is inversely proportional to it. Human fat has a saponification number of 194 – 196, butter 210 – 230 and coconut oil 253 – 262. Iodine Number The Iodine number of a fat is defined as the number of grams of iodine taken up by 100 gm of fat. It is an index of unsaturation and is directly proportional to the content of unsaturated fatty acids. Higher the iodine number, the higher is the degree of unsaturation. Different of fats and their iodine numbers are given in Table 3.1. Table 3.1 Fat / Oil Iodine number Human fat 65-69 Butter 26-28 Coconut oil 6-10 Sunflower oil 124- 136 Groundnut oil 84- 100 Palm oil 44-58 100 mg blood contains Triglycerides Phospholipids Cholesterol Nonesterified fatty acids Total 80 - 240 mg 150 – 250 mg 130 – 260 mg 8 – 30 mg 385 – 675 mg PHOSPHOLIPIDS (PHOSPHOGLYCERIDES AND SPINGOMYELINS) Any lipid containing Phosphor is called phospholipid. Phospholipids are good emulsifying agents. They are found in cell membranes and in subcellular structures where lipids and water soluble materials interact. The most common phospholipid is the glycerol phospholipids. They contain glycerol phosphate, two fatty acids and a nitrogen compound that may be choline, ethanol amine, or serine. Lecithins and cephalins are examples of phospholipids. L Y C E R O L Fatty acid Fatty acid P-N O ║ CH2 –O-C-R O ║ CH-O-C-R1 O ║ CH2-O-P-N compound OH Phospholipid or Phosphoglycerides Phosphatidyl Cholines (Lecithins) This is the most common form of phospholipids and has cholin as the nitrogen compound O ║ CH 2O- C – OR1 O ║ CHO- C- OR 2 O ║ CH2 – P-O- CH 2CH 2N+ (CH3)3 OH Choline Phosphoglyceride Free choline is a compound with an alcohol group. Its linkage to the phosphate portion of a lecithin like that of the glycerol to the phosphate is that of a phosphate ester. HO- CH2 – CH2- N+ – (CH3) 2 Choline Lecithins are required for the normal transport and utilization of other lipids especially in the liver. Anything which interferes with the synthesis of choline also will block the synthesis of lecithins and thus interrupt the normal transportation of lipids to and from liver. This usually results in the accumulation of lipid material in the liver giving rise to a condition called fatty liver Cephalin O ║ CH 2O – C- OR1 O ║ CHO – C- OR2 O ║ CH 2O –P- O- CH2-CH2 – NH2 OH Cephalin (Ethanolamine Phosphoglyceride) Cephalin differs from lecithins with respect to base attached to phosphoric acid. If the base is ethanol amine, then it is called phosphatidyl ethanolamine or ethanolamine cephalin. If the base is amino acid serine, then it is called phosphatidyl serine or serine cephalin. Cephalin on hydrolysis yields glycerol, fatty acids, phosphoric acid, ethanol amine or serine. They are found in nerve tissues cephalins are important in the clotting of blood and as sources of phosphoric acid for the formatios of new tissues. Plasmalogens These compounds structurally resemble lecithin and cephalins, with the result that the normal ester is replaced by the ether linkage on the C1 atom. On treatment with acid they give rise to a long chain fatty aldehyde. These compounds constitute as much as 10 % of the phospholipids of the brain and the muscles CH2 – O- CH =CH – R O ║ CH- O- C – R 2 O ║ CH2 –O-P – O – Base OH Sphingomyelins They are found in large quantities in brain and nerve tissue. No glycerol is present. On hydrolysis yield a fatty acid, phosphoric acid, choline and a complex aminoalcohol, sphingosine (in place of glycerol). Sphingosine p Choline Fatty acid Sphingomyelin Cerebrosides (Glycolipids) Glycolipids are carbohydrate – glyceride derivatives containing sugar, sphingosine and a fatty acid. These compounds do not contain phosphoric acid. If the sugar component is galactose, the lipid is termed as galactolipid. The term cerebroside is used because it is found in large quantities in brain tissues particularly in white matter. Sphingosine Fatty acid Cerebroside Galactose Steroids Steroids are non–saponifiales lipids, biological compounds with diverse physiological activities .All steroids are compounds having a cyclopentanoper – hydrophenanthrene ring system. The structures of a number of different types of steroids having greatly varying biological activities. Cholesterol is a light yellow crystalline solid. It is soluble in chloroform and other fat solvents. The - OH group in the 3rd position can be get esterified with fatty acids to form cholesterol esters. This is how cholesterol level in the body is regulated. Cholesterol in the most abundant lipid in the human body. It is synthesized mainly in the liver, adrenal cortex, intestines, testes and skin. Acetyl CoA is the precursor of all the C atoms in cholesterol. The level of cholesterol in body fluids is of primary importance due to its role in the development of atherosclerosis. In addition cholesterol plays an important role as a component of biomembranes and has a modulating effect on the fluid state of the membrane. Poly unsaturated acids (essential fatty acids) tend to lower the plasma cholesterol level. Cholesterol in body fluids can be estimated by colour reactions, e.g. Lebermann Burchard reaction. A solution of chloroform gives a blue or green colour, when acetic anhydride and concentrated sulphuric acid are added. This reaction is the basis of a colorimetric estimation of blood cholesterol. Functions of Cholesterol 1. Cholesterol is an important tissue component. It has a modulating effect on the fluid state of the membrane. 2. Because of its conductivity, cholesterol plays an important role in insulating nerves and brain structure. 3. For the transport of fatty acids in the body through the for – mation of esters of fatty acids. 4.Cholesterol neutralizes the hemolytic action of a number of agents, such as snake venoms, bacterial toxins, etc. 5. Cholesterol gives rise to provitamin D. 6. It is a precursor of cholic acid in the body. 7. It gives rise to sex hormone. LIPOPROTEINS Lipoproteins transport neutral lipids in the blood. These are lipids attached to proteins . These are formed by the combination of proteins with lipids which include the phospholipids lecithin and cephalin, fatty acids, cholesterol, glycerides and fat soluble vitamins. The lipoprotein molecule has lower density than the ordinary protein molecule, due to its combination with lipids. Lipoproteins are widely distributed in body 1. Cell membranes 2. Certain internal structures of cell, such as nucleus, mitochondria and microsome. 3. Thromboplastin which converts prothrombin to thrombin. 4. Egg yolk contains two lipoproteins called α - lipovitellin and lipovitellin. 5. The film that stabilizes the fat droplets in milk contains lipoproteins. 6. Rhodopsin or visual purple is a combination of a protein opsin and retinal aldehyde of vitamin A (fat soluble vitamin). 7. Blood lipoproteins are present in plasma. The lipid fraction consists mainly of cholesterol, phospholipids, neutral fat, traces of fat soluble vitamins and steroid hormone. Lipids such as cholesterol and triglycerides are not soluble in water and are thus need to be complexed to water soluble carrier proteins for transporting them in the blood between different organs. Plasma lipoproteins consist of a neutral lipid core of triglyceride and cholesterol ester that is surrounded and stabilized by free cholesterol protein and phospholipids. The relative proportion of nonpolar lipid, protein and polar lipid, protein and polar lipid determine the density, size and charge of the resulting lipoproteins. The total plasma lipid is 700-1000 mg per dl. Roughly 1/ 3 is cholesterol and rest 1/3 is phospholipids. These are complexed with proteins to form lipoproteins. 1. Chylomicrons are the lipoprotein particles lowest in density and largest in size and contain the most lipid and smallest percentage of protein. They transport mainly TG and smaller amounts of PL, cholesterol ester and fat soluble vitamins from intestines to liver and adipose tissues. The lipids carried by chloromicrons principally in dietary lipids. The lipids carried by chloromicrons principally in dietary lipids. They are formed in the intestinal mucosa VLDLs are synthesized in the liver and released into blood. They transport triacylglycerides synthesized in the liver and cholesterol esters from liver to peripheral tissues. Fatty liver occurs in conditions in which there is an imbalance between hepatic triacyl glyceride synthesis and the secretion of VLDC. Diseases such as diabetes mellitus and chronic ethanol ingestion can cause fatty liver. As VLDL passes through the circulation their structure is altered to LDL . VLDL are composed mainly of TAG , asset are more enriched in cholesterol esters than are chylomicrons . LDL provides cholesterol for cellular needs . LDL promotes coronary heart disease by first penetrating the coronary artery wall and then depositing cholesterol to form atherosclerosis plaque . Estimation of Plasma Lipids The serum lipids tests commonly done are total cholesterol , HDL cholesterol and triglycerides . Total cholesterol is estimated colorimetrically 1. Serum is used for Lieberman – Buchard reaction . Cholesterol in presence of ion H2SO4 , acetic acid and acetic anhydride is oxidized to cholestrapolyenes to give blue green colour . 2. More modern is the enzymatic oxidase method . Cholesterol is oxidized . The H2O2 Produced in this reaction is split peroxidase to produce nascent oxygen which is used to oxidase a colourless chromogen to a coloured product . The plasma cholesterol is distributed in different proteins fractions . In normal persons , cholesterol level varies from 150 to 220 mg / dl with 70 % being esterified cholesterol and 30 % free . In this average normal adult male , the plasma cholesterol should preferably below 200 mg / dl . The females have a lower because of the high estrogen level which also affords protection against atherosclerosis . Normally almost 60 % of total cholesterol in LDL 22% HDL , 13% VLDL and 5% chylomicrons . HDL and LDL HDL cholesterol is estimated after precipitating LDL and VLDL . The LDL cholesterol can be calculated from total cholesterol , HDL cholesterol and serum triglycerides LDL cholesterol = Total cholesterol – [HDL Chol +TAG /5] 1/5 of the triglyceride value is believed to represent VLDL in fasting plasma . The sample serum should be taken after 14-16 hours of fasting . Elevated LDL levels have been associated with increased of developing coronary artery disease , whereas elevated HDL levels appear to reduce the risk . Women have higher HDL levels than men ( 55 Vs 45 mg / dl ) and this may account for women's lower rate of heart disease . Aerobic exercise increases HDL levels ( more runners average 65mg/ dl) .