Lipids and fats

LIPIDS AND FATS

1. LIPIDS(FATS) Fats-Composition and chemistry,classification , functions,requirements Nutritional disorders-fats deficiency Energy metabolism- digestion,absorption and utilization INTRODUCTION lipids are a group of naturally occuring substances charaterised by their insolubality in water and solubility in some organic solvent. They occur widely in the plant and animal kingdom in the form of oils and fats respectively.The basic structure of lipids is comprised of carbon,hydrogen,oxygen . The lipid fat content of food is the major determinant of the energy density of dites .

2. Classification Lipids are classified as: 1.Simple lipids These are esters of fattyacids and glycerol.Oils are liquid at 200C while fats are solid at 200C 2.Component lipids These lipids contain some other organic compounds,in addition to fatty acids and glycerol they are further characterised as i )phospholipids( Phosphasides )

3. These contain phospheric acid and a nitrogenous base in addition to glycerol and fattyacids.lecithin,cephali,plasmalogns come under this catagory . ii) Sphingolipids T h ese contain the base sphingosine or dihydro sphingosine in addition to glycerol and fattyacids . iii) Glycolipids Complex lipids containing carbohydrates in combination with fatty acids and sphinogosine . iv) Sulpho lipids These contain sulphuric acid in combination with hexose in a cerebroside .

4. 3.Waxes These are ester of fatty acids long-chain aliphatic alcohols. 4.Derivedlipids These includes fatty acids,alohol,sterols Lipids present in Diets The lipids present in foods and also in the animals and human body include: Triglycerids , Phospholipids and other compound lipids,and cholestrol (present only in animals food)

5. Hydrogenation This is a process involving chemically induced hydrogen saturation of the carbon bonds,by which the structure of unsaturated oils is changed . This alters the way the body metabolizes these facts and often changes the physical form . Margine and vanaspathi are hydrogenated facts

6. Functions of Facts Fat has several important functions. It is a concentrated source of energy yielding more than twice the energy supplied by carbohydrate per unit weight. Fats essential for the absorption of vitamins A,D,Eand K and carotenoids . Vegetable fats are good sources of vitamin E and red palm oil is a good source of carotene while some animal facts such as butter and fish liver oils are good sources of vitamin

7. A.Certain vegetable fats are rich sources of the essential fatty acid- lilolein -acid . Fats reduce the bulk of the diet as they provide twice as much calories as carbohydrates per unit weight . Further starchy foods absord lot of water during cooking and increase the bulk of diet Fats improve palatability and give a satiety value ie;a feeling of fullness in the stomach Fats are deposited in adipose tissue acts as an insulting material against cold and physical injury.

8. Properties of fats Solubility Fats are soluble in organic solvents such as ethyer ether, petroleum ether acetone acid Benzine .The quantity of fat present in food materials is usually determined in by extraction with ethyl ether or petroleum ether. Saponification value : THe value is defined as the number of milligrams of potassium hydroxide required to Saponify 1GM of fat or oil. Iodine Value :It is the measure of the extent of unaturated fattyb acids present in fats and oils.It is defined as number of branch of iodine absorbed in 100Grams of fat. Reicheit-Mreissl Value :The is defined as the number of milliliters of 0.1N alkali required to neutralize the steam volatile water soluble fatty acids present in 5Gram sample of fat.that is determine the amount of butyric acid and caproic acid ewhich are readily soluble in water and a part of caprylic acid whicc is slightly soluble in water.

9. Thiocyanogen Value :The Thiocyanogen number is the amount of Thiocyanogen absorbed by 100 g of fat or oil. Rancidity in fats : The development of all flavours in fats is known as rancidity.There are three main types of rancidity, 1.Hydrolytic Rancidity Hydrolysis of fats by lipase need notb always produce off- flaours.In the case of butterfat and coconut oil butyric and other low molicular weight Fatty acids are set free on hydrolysis by lipase.The orders of these acids contribute largely to the smell of rancidbutter.The saturated fatty acids such as palmitic and stearic acidsn have little odour.

10. 2.Oxidative Rancidity This is the common type of rancidity observed in all fats and oils.The oxidation takes place at the unsaturated linkage.Certain metals,such as Copper,Hasten the on set of oxidative rancidity,the addition ofoxygen to the unsaturated linkage results in the formation of a peroxide which, on decomposition,yelds aldehydes and ketones having pronounced off odour .

11. 3.Ketonic rancidity This type is most frequently as a result of action fungi such as aspergilles niger and blue green mould,penicillium glaucum on coconut or oil seeds.The tallow odour developed may be due to aldehydes and ketones formed by the action of the engymes present in the fungi on oil.

12. Effects of the essential fatty acid deficiency in human beings Phrynoderma:Thus is one pf the common diorders of malnutrition observed in adults and children . The condition is characterised by the presence of horny popular eruptions on the posterior and lateral aspects of the limbs,on the back and buttoks . Phrynoderma is cured rapidly by the administration of linseed or safflower seed oil which are rich in essential fatty acids along with B-complex vitamines but not by vitamine -A.

13. Deficiency in infants Hansen and co-workers have reported that infants fed on a EFA deficient diet developed perennial irritation and changes in the skin within a few weeks . The skin changes appears as dryness thickening and desquamation with oozing in the intertriginous folds . Supplimemtation of the diet with linaleic acid restored the skin th normal condition with in 2 weeks.

14. S ources Rich sources of EFA safflower,sunflower,nigerseed,cottonseed,linseed,corn,walnut,sesame and soybean oils are rich in sources of EFA.These oils must form atleast 50% of the fat in the diet. Good source :Egg yolk fat,poultryfat and pig body fat are fair sources of EFA Poor sources :coconut oil,palmkerneloil,vanaspathy and animal fats butter and ghee,beef and mutton fat are poor sources of EFA

15. Fat req ui rements The approximate fat reqiurements of individuals for different age groups are given in table.Atleast 50% of the fat oils rich in EFA . Table:Fat Requirements Group % Adults pregnant and lactating mothers 10 to 20 % of total calories from fat children and adolescents(0 to 18 years) 15 to 20 % of total calories from fat Infants (Birth to 1 year) 25 to 30 % of total calories from fat

16. 1.Triglycerides and fatty acids : Triglycerides comprise about 95% of the food lipids and body lipids . They are the storage form of fat . When we eat a high calorie diet,the calories in excess of our energy needs Triglycerides and srored in the body. All Triglycerides have a similar structure.It is composed of three fatty acids attached to a glycerol molecule . Glycerol is a short-chain carbohyrate molecule that is soluble in water.

17. When Triglycerides are metabolized the glycerol is converted to glucose . Fatty acids may differ in their length and their degree of saturation. They are commonly composed of a series of 16-18 carbon molecules attached to hydrogen molecule . The number of hydrogen molecules determines the saturation of the fat . When each carbon has its maximum number of hydrogens attached the fat is set to be saturated.ie., filled to capacity with hydrogen.

18. Saturated fats Unsaturated fats Essential fattyacids Saturated fatty acids : A fatty acid with no carbon-carbon double bonds. Monounsaturated fatty acid :A fatty acid containing one double bond. Polyunsaturated fatty acid :A fatty acid containing two or more double bond. Essential fattyacids : THese are fatty acids must be present in the diet to maintan health,and include lineleic acid and alpha- lineleic acid.

19. Phospholipids : Phospholipids are important in the structure of all membranes. Their structure is similar to that of triglycerides,but they contain only two poly unsaturated fatty acids . The third molecule attached to the glycerol is a phosphatidylcholine molecule . The most common phospholipid is lacithin.Certain phospholipids also contain inositol and designated as phosphatldyiinositol . Phosphatidylethanolamine is another phosopholipid thatb has several functions, such as being a precursor to choline and acetylcholine . Lecithin is found in highest concentration in soybeans and eggyolk.Recently,egg lecithin has been used in the treatment of accuired immunp deficiency syndrome(AIDS).

20. 3.Sterols/cholesterol cholestrol,is the precursor of the bile acids and the sex harmones.it is manufactured in all tissues of the body except the brain , Cholestrol is present in all cells and its concentration is particularly high in the liver, brain and nervous tissue, and the blood . Cholestrol , like lecithin is also present in foods,eggyolk,meats,and other animal fats, milkproducts .It is not present in vegetable foods.

21. A transport mechhanism of cholestrol called the low density lipoprotein is the likely cause of risk for the cardiovascullar disease called atherosclerosis . In this condition , Cholestrol in the form, of LDL cholestrol accumulates in the living of the arteries these two is the bolld test currently favoured to elevate risk of cardiovascular disease.

22. Factors affecting requirements Food intake in is influenced by several factors,two of the most important being socio-economic status and cultural preferences.Psychological conditions and risk of certain chronic diseases such as heart dusease and diabetes also affect fat requirements. Digestion and absorption of fat Several theories have been proposed for the mechanism of absorption of fats after digestion.The important theories are: Lipolytic hypothesis of varzar , Partilition theory of frazer,and micelie theory of borgstrom .

23. Lipolytic hypothesis of varzar According to this theory,the hydrolysis of fat to fatty acids is complete and the fatty acid and glycerol are absorbed.The fatty acids combined with bilesalts to form loosewater miscible complexes which are absorbed into the intestinal mocosa The triglycerides are passed on into the lactals of the intestinal bile.They then enter the lymphasics and reach the systemic the circulation via thoracduct .

24. Present views on the digestion and absorption of fat Present views on the digestion and absorption of fat are briefly described below. The digestion of the triglyceride proceeds the removal of fatty acid at the 1 position yeilding fatty acid and a diglyceride , The fatty acid in the 3 position is then removed by action of lipase leaving 2-monoglyceride . The removal of fatty acid from the 2-monoglyceride is the slow process.2-monoglyceride will be converted at a slow rate in to 3-monoglyceride by an enzyme called isomerace .

25. The monoglyceride and free fatty acids are converted into micelle in the presence of bile salts and are absorbed into the intestinal wall. The free glycerol also is absorbed.3-monoglyceride is hydrolized in the intestinal wall by the intestinal lipase to fatty acid and glycerol The in testinal wall has enzyme systemd for fat synthesis. The resynthesized fatty acids converted into chylomicrons . The chylomicrons enter the lymphatics through lacteals and are delivered in to the circulation via thoracic duct. The fatty acid composition of chylomicrons of the lymph is different from that of the fat and in the diest as resynthesised in the intestines using fatty acids derived from food fatand fatty acids present in bile