Fats and Oils 3.pdf

FATS  FATS  Like other organic compounds, all lipids are composed of a carbon skeleton with hydrogen and oxygen substitutions.  Nitrogen,sulfur and phosphorus are also present in some lipids.  Water insolubility is a characteristic for most of them.  Solubility i...

FATS  FATS  Like other organic compounds, all lipids are composed of a carbon skeleton with hydrogen and oxygen substitutions.  Nitrogen,sulfur and phosphorus are also present in some lipids.  Water insolubility is a characteristic for most of them.  Solubility in a “lipid solvent” such as ether,chloreoform,..is common.  TRIACYLGLYCEROL (TAG)  It is the main form of dietary fat  Three fatty acids are bound to a molecule of glycerol  It is in this form that fat is stored, predominantly in adipose tissue  FATTY ACID  Fatty acids consist of hydrocarbon chain with a carboxylic acid group at the head CH3-R-COOH  Typically a fatty acid has between 12 and 22 carbon atoms. If it:  doesn't contain any double bond – (Saturated fatty acid)  contains one double bond – (monounsaturated fatty acid)  More than one double bond – (polyunsaturated fatty acid)  FATTY ACID  The hydrogen atoms at the carbon-carbon double bond may be  on the same side of the double bond (cis)  on opposite sides (trans) Trans fatty acids are absent from plant lipids but may be found in some animals fats such as milk. They also may be formed during processing of some fats for incorporation into foods. (partial hydrogenation) High intakes of them Increased risk of c-v disease-HDL ,LDL  NOMENCCLATURE OF FATTY ACIDS C18 : 1, Number of double bonds n - 9 Position of the first double bond from the methyl terminal CH3 Number of carbons Also omega-9 Oleic acid  PHOSPHOLIPIDS  Similar in structure to Triacylglycerol (TAG).  They have a phosphate group in place of one of the fatty acids  Major constituents of cell membranes  STEROLS  The main sterol of importance in human nutrition is cholesterol.  Sterols have a common cyclopentanoperhydrophenanthrene skeleton with different substitutions giving rise to the multiple sterols and steroids.  FUNCTIONS of lipids  Source of energy for immediate utilization :9 Kcal/g  Vehicle for the absorption of fat-soluble vitamins  Phospholipids and cholesterol are components of cell membranes  Energy storage  Using cholesterol as the starting material, the cells of the adrenal cortex secrete a variety of steroid hormones.  glucocorticoids (e.g., cortisol)  mineralocorticoids (e.g., aldosterone)  androgens (e.g., testosterone)  Subcutaneous adipose tissue is important for the maintenance of body temperature  Internal fat (visceral fat) protects the vital organs such as the kidney and spleen  Long chain PUFA are the precursors of prostaglandins and other eicosanoids.  Fats and oils  FATS that are liquid at room temperature are called OILS.  OILS contain a low proportion of saturated (straight chain) and higher proportion of unsaturated (bent chain) fatty acids.  Unsaturated fatty acids usually have a lower melting point : this facilitates liquefaction of the fats of which they area component.  TAGS of animal origin ---FATS  TAGS from fish or plant--OILS  ω3 Flaxseed= linseed  Metabolism of lipids  Linoleic and α-linolenic acid are precursors of long chain PUFAS (poliunsaturated fatty acids) including eicosapentanoic acid (EPA) and arachidonic acid (AA)  This two PUFAS are precursors of a group of hormon-like compounds called eicosanoids including prostaglandins, thromboxanes and leucotrienes.  Eicosanoids are important for a wide range of processes including inflammatory responses, blood clotting and smooth muscle contraction.  Metabolism of lipids The majority of fat is stored as TAG in adipose tissue cells. Following a meal, ingested fat which is not required by the body tissues for immediate use is transported in lipoproteins. Adipocytes acquire fat from lipoproteins. In fasting state , the fat in adipose tissue is mobilized and fatty acids are released into circulation, bound to serum albumin. These fatty acids enter other tissues and are oxidized for energy production. Insulin regulates this process  Metabolism of lipids  Some fatty acid are converted in the liver in Ketone bodies.  These compounds are important because they can be used as an alternative to glucose by other tissues (but not the liver)  The brain can not use fatty acids but can oxidize Ketone bodies  FAT TRANSPORT: lipoproteins  Lipoproteins are a family of spherical macromolecular complexes of lipid and protein.  They contain specific proteins, apoproteins.  Apoproteins recognize and interact with specific receptors on the cell surface and the receptor- lipoprotein complex is taken into the cell.  FAT TRANSPORT: lipoproteins Lipoproteins are particles which transport lipids between tissues.  Transport exogenous lipids (synthesized in the gut from dietary fat)  Transport endogenous lipids (synthesized in the liver) From these sites of production and absorption to  peripheral sites of utilization : eg. oxidation in muscle,incorporation to membranes, or as precursors of biologically active metabolites  storage : eg adipose tissue  Lipoprotein classes  According to the density 1. Chylomicrons (formed in the gut) 2. Very low-density lipoproteins (VLDL)-(formed in the liver) 3. Low density lipoproteins (LDL) (from the metabolism of VLDL) 4. High density lipoproteins (HDL)(formed in gut and liver)  Lipoprotein classes ► Low density lipoproteins (LDL) ► High density lipoproteins (HDL) transport of cholesterol to and from the cells HDL -is responsible for the removal of excess cholesterol from peripheral tissues and its return to the liver- REVERSE CHOLESTEROL TRANSPORT  Atherosclerosis Atherosclerosis is a cardiovascular disease in which lipids and inflammatory cells accumulate in plaques within the walls of blood vessels. As a result, vessel walls are narrowed and clots may form, impeding blood flow and oxygen delivery and causing tissue injury. Heart disease occurs because the coronary arteries supplying the heart are a major site of atherosclerotic plaque formation.