Lipids are organic compounds formed mainly from alcohol and fatty acids combined together., Schemes and Mind Maps of Food Science and Technology

Download Lipids are organic compounds formed mainly from alcohol and fatty acids combined together. and more Schemes and Mind Maps Food Science and Technology in PDF only on Docsity! Lipids Introduction Chemistry of Lipids Definition: Lipids are organic compounds formed mainly from alcohol and fatty acids combined together by ester linkage. CH 2R Fatty alcohol OH C R Fatty acid HO O + H2O CH 2R O C R O Esterase (lipase) ester (lipid) Cont. 4. Supply the body with fat-soluble vitamins (A, D, E and K). 5. They are important constituents of the nervous system. 6. Tissue fat is an essential constituent of cell membrane and nervous system. It is mainly phospholipids in nature that are not affected by starvation. Cont. 7-Stored lipids “depot fat” is stored in all human cells acts as:  A store of energy.  A pad for the internal organs to protect them from outside shocks.  A subcutaneous thermal insulator against loss of body heat. 8-Lipoproteins, which are complex of lipids and proteins, are important cellular constituents that present both in the cellular and sub-cellular membranes Cont. 9-Cholesterol enters in membrane structure and is used for synthesis of adrenal cortical hormones, vitamin D3 and bile acids. 10- Lipids provide bases for dealing with diseases such as obesity, atherosclerosis, lipid-storage diseases, essential fatty acid deficiency, respiratory distress syndrome, Cont. During the processing, storage, and handling of foods, lipids undergo complex chemical changes and react with other food constituents, producing numerous compounds both desirable and deleterious to food quality. Dietary lipids play an important role in nutrition. They supply calories and essential fatty acids, act as vitamin carriers, and increase the palatability of food, but for decades they have been at the center of controversy with respect to toxicity, obesity, and disease. Classification of Lipids 1. Simple lipids (Fats & Waxes) 2. Compound or conjugated lipids 3. Derived Lipids 4. Lipid-associating substances Major class Simple lipids Compound lipids Denved lipids Subclass Acylglycerols Waxes Phosphoacylglycerols (or glycerophospholipids) Sphingomyelins Cerebrosides Gangliosides Materials that meet the definition ofa lipid but are not simple or compound lipids Description Glycerol + fatty acids Long-chain alcohol + long-chain fatty acid Glycerol + fatty acids + phosphate + another group usually containing nitrogen Sphingosine + fatty acid + phosphate + choline Sphingosine + fatty acid + simple sugar Sphingosine + fatty acid + complex carbohydrate moiety that includes sialic acid Examples: carotenoids, steroids, fat-soluble vitamins Fatty alcohols 1-Glycerol: It is a trihydric alcohol (i.e., containing three OH groups) and has the popular name glycerin. It is synthesized in the body from glucose.  It has the following properties: cont 1. Colorless viscous oily liquid with sweet taste. 2. On heating with sulfuric acid or KHSO4 (dehydration) it gives acrolein that has a bad odor. This reaction is used for detection of free glycerol or any compound containing glycerol. CH 2 OH CH CH 2 OH HO CHO CH CH 2 2 H2O Heating, KHSO4 Glycerol Acrolein Cont. 3. It combines with three molecules of nitric acid to form trinitroglycerin (TNT) that is used as explosive and vasodilator (widening of blood vessels) . 4. On esterification with fatty acids it gives: • Monoglyceride or monoacyl-glycerol: one fatty acid + glycerol. • Diglyceride or diacyl-glycerol: two fatty acids + glycerol. • Triglyceride or triacyl-glycerol: three fatty acids + glycerol. 5. It has a nutritive value by conversion into glucose and enters in structure of phospholipids. Assignment two Describe briefly all types of health problems caused by shortage of essential fatty acids Assignment three Lipoproteins What is lipoproteins Advantage/disadvantage of lipoproteins Quantification of lipoproteins. Cont. 2-Sphingosine: It is the alcohol (monohydric) present in sphingolipids. It is synthesized in the body from serine and palmitic acid. It is not positive with acrolein test. CH CH NH 2 CH 2OH CHCH(CH 2)12CH 3 OH Sphingosine Saturated fatty acids ( no double bond) A-Short chain Saturated F.A. (2-10 carbon). a-Short chain Saturated volatile F.A.(2-6 carbon). b- Short chain Saturated non volatile F.A.(7-10 carbon). B-Long chain Saturated F.A.(more the10 carbon) a-Volatile short-chain fatty acids: They are liquid in nature and contain (2-6) carbon atoms.  water-soluble and volatile at room temperature, e.g., acetic, butyric, and caproic acids. Acetic F.A. (2C ) CH3-COOH. Butyric F.A. (4C ) CH3-(CH2)2-COOH. Caproic F.A. (6C ) CH3-(CH2)4-COOH. b-Non-volatile short-chain fatty acids: They are solids at room temperature and contain 7-10 carbon atoms.  They are water-soluble and non- volatile at room temperature include caprylic and capric F.A. caprylic (8 C ) CH3-(CH2)6-COOH. Capric (10 C ) CH3-(CH2)8-COOH. 1-Monounsaturated fatty acids:  1-Palmitoleic acid :  It is found in all fats.  It is C16:1∆9, i.e., has 16 carbons and one double bond located at carbon number 9 and involving carbon 10. CH3-( CH2 )5CH = CH-(CH2)7 –COOH 2-Oleic acid Is the most common fatty acid in natural fats. It is C18:1∆9, i.e., has 18 carbons and one double bond located at carbon number 9 and involving carbon 10. CH3-(CH2)7- CH=CH – (CH2)7-COOH 3-Nervonic acid (Unsaturated lignoceric acid).  It is found in cerebrosides.  It is C24:115, i.e., has 24 carbons and one double bond located at carbon number 15 and involving carbon 16. CH3 – (CH2)7 CH= CH – (CH2)13- COOH Function of Essential Fatty Acids: 1. They are useful in the treatment of atherosclerosis by help transporting blood cholesterol and lowering it and transporting triglycerides. 2. The hormones(eicosanoid) are synthesized from them. 3. They enter in structure of all cellular and sub-cellular membranes and the transporting plasma phospholipids. Cont. 4. They are essential for skin integrity, normal growth and reproduction. 5. They have an important role in blood clotting (intrinsic factor). 6. Important in preventing and treating fatty liver. 7. Important role in health of the retina and vision. 8. They can be oxidized for energy production. 1-Linoleic:  C18:29, 12.  It is the most important since other essential fatty acids can be synthesized from it in the body. CH3-(CH2)4-CH = CH-CH2-CH=CH-(CH2)7- COOH 1-Simple Lipids (A-Neutral Fats and oils (Triglycerides)  Definition:  They are called neutral because they are uncharged due to absence of ionizable groups in it.  The neutral fats are the most abundant lipids in nature. They constitute about 98% of the lipids of adipose tissue, 30% of plasma or liver lipids, less than 10% of erythrocyte lipids. Cont. They are esters of glycerol with various fatty acids. Since the 3 hydroxyl groups of glycerol are esterified, the neutral fats are also called “Triglycerides”. Esterification of glycerol with one molecule of fatty acid gives monoglyceride, and that with 2 molecules gives diglyceride. H2C O C HO H2C C C O C R1 R3 R2 O O O + 3 H2O CH 2 OH C HHO CH 2 OH HO C R1 O HO C R3 O HO C R2 O Fatty acids Glycerol Triglycerides (Triacylglycerol) Types of triglycerides 1-Simple triglycerides: If the three fatty acids connected to glycerol are of the same type the triglyceride is called simple triglyceride, e.g., tripalmitin. 2-Mixed triglycerides: if they are of different types, it is called mixed triglycerides, e.g., stearo-diolein and palmito-oleo-stearin. • Natural fats are mixtures of mixed triglycerides with a small amount of simple triglycerides. Physical properties of fat and oils: 1. Freshly prepared fats and oils are colorless, odorless and taste less. Any color, or taste is due to association with other foreign substances, e.g., the yellow color of body fat or milk fat is due to carotene pigments(cow milk). Fats of this group are derived from the milk of ruminants, particularly dairy cows. Although the major fatty acids of milk fat are palmitic, oleic, and stearic, this fat is unique among animal fats in that it contains appreciable amounts of the shorter chain acids C4 to C12, small amounts of branched and odd-numbered acids, and trans-double bonds. Cont 2. Fats have specific gravity less than 1 and, therefore, they float on water. 3. Fats are insoluble in water, but soluble in organic solvents as ether and benzene. 4. Melting points of fats are usually low, but higher than the solidification point, Lauric Acids Fats of this group are derived from certain species of palm, such as coconut and babasu.  The fats are characterized by their high content of lauric acid (40–50%), moderate amounts of C6, C8, and C10 fatty acids, low content of unsaturated acids, and low melting points. 3-Halogenation Neutral fats containing unsaturated fatty acids have the ability of adding halogens (e.g., hydrogen or hydrogenation and iodine or iodination) at the double bonds.  It is a very important property to determine the degree of unsaturation of the fat or oil that determines its biological value CH (CH2)7 COO HCHCH2CH Linoleic acid CH(CH 2)4CH3 2 I2 CH (CH 2)7 COO HCHCH2CH Stearate-tetra-iodinate CH(CH2)4CH3 II I I 4-Hydrogenation or hardening of oils  It is a type of addition reactions accepting hydrogen at the double bonds of unsaturated fatty acids. The hydrogenation is done under high pressure of hydrogen and is catalyzed by finely divided nickel or copper and heat.  It is the base of hardening of oils (margarine manufacturing), e.g., change of oleic acid of fats (liquid) into stearic acid (solid).  It is advisable not to saturate all double bonds; otherwise margarine produced will be very hard, of very low biological value and difficult to digest. Advantages for hydrogenated oil or fat are as follows: 1. It is more pleasant as cooking fat. 2. It is digestible and utilizable as normal animal fats and oils. 3. It is less liable to cause gastric or intestinal irritation. 4. It is easily stored and transported and less liable to rancidity. Disadvantages of hydrogenated  fats include lack of fat-soluble vitamins (A, D, E and K) and essential fatty acids Oils (liquid) (with unsaturated fatty acids, e.g., oleic) Hard fat (margarine, solid) (with saturated fatty acids, e.g., stearic) Hydrogen, high pressure, nickel Rancidity Definition: It is a physico-chemical change in the natural properties of the fat leading to the development of unpleasant odor or taste or abnormal color particularly on aging after exposure to atmospheric oxygen, light, moisture, bacterial or fungal contamination and/or heat. Saturated fats resist rancidity more than unsaturated fats that have unsaturated double bonds. Types and causes of Rancidity: 1. Hydrolytic rancidity 2. Oxidative rancidity 3. Ketonic rancidity  1-Hydrolytic rancidity:  It results from slight hydrolysis of the fat by lipase from bacterial contamination leading to the liberation of free fatty acids and glycerol at high temperature and moisture.  The formation of volatile short-chain fatty acids cause unpleasant odor. Cont. CH 2 O C HO CH 2 C C O C R1 R3 R2 O O O 3 H2O H2C OH C HHO H2C OH OHCR1 O OHCR3 O + OHCR2 OLipase Triacylglycerol Glycerol Free fatty acids (volatile, bad odor) Oxydation Primary oxidation product The per-oxydation of unsaturated fatty-acid to hydroperoxide can be caused with a means of autoxydation and lipoxygenase (enzymatic catalyses) The reaction product is primarily Monohydrooperoxide. Monohydroperoxide can react by up grading and degrading it self. While mono-hydroperoxide is sensoric almost indifferent, but their degraded products like (aldehyde, ketone- and carobhydrates) are quality (sensoric) deteriorate groups. Aut-& Foto oxydation Peroxydation is the first phase of a reaction of the alken and polyalkene fatty acids Radical chain mechanism is a chain reaction which produces hydroperoxide. Primary Autoxydations product of the oleic acid. The formation of fatty acid radical (R.) will takes place in the first hand by splitting the hydrogen from - Methylen protons form unsaturated fatty acids. The energy needed to split is depends strongly from the degree of saturations of the fatty acids. Cont. The middle position of the methyl group in the 1, 4- pentadien system e.g linolelic acid) is specially active. There fore, it is very much easy to abstract one hydrogen from this group than the methyl group of the monosaturated fatty acid. During the outoxydation of linoleic acid, the hydro peroxide product on the 8,10,12 and 14 carbon will be together 0.5-1.5%, where as the hydroperoxide product on the 9-and 13-carbon will be about 95%. Cont.  The formation of the first radical and hydroperoxide is not clear until to day. It is supposed to be with thermal activation, and Activation with UV-light as well as activation of sensiblisator (foto oxidation) and enzymatic oxygenation.  Newly, it is assumed that particles in the air, like SO2, NO2, and O3 can cause a chain start, when they react with unsaturated lipids.  by fotooxydation, light activated sensibilisator (sen*) react directly with substrate under radical formation or the activated sensibilisator react with the triplet oxygen of the air. Cont. E.g. Sen (inactivated) +hV  Sen* (activated) Sen*+RH  R. + Sen (typ 1) Sen* + 3O2102 + Sen (typ 2)  The singulett oxygen reacts with unsaturated lipid by the cyclo-addition mechanism to give mono-hydroperoxide.  R-CH=CH-CH2-R + 1O2  R-C (OOH)H-CH=CH-R or R-CH = CH-C(OOH)HR  The above type of hydroperoxide formation with singlet oxygen does not say anything about the radical formation.  Therefore, these processes can not hinder with the common Antioxidant which serves as a radical acceptor. Cont.  The reaction will be inhibited with the so called Quencher.  Some carotenoide and tocopherol deactivate sensibilisatores and oxygen with high state of energy. Therefore they are assumed to be as quencher.  Chlorophyll, phaeophytine, some of protoporphyrine and Riboflavin are typical sensibilisatores for the fotooxydation.  The Hydroperoxide and Radical, produced by foto- oxydation can be used by radical chain mechanisms of the autoxydation. Cont. The main product of oxidation from linoleic acid is the cis, Trans konjugated hydroperoxid. The conjugated hydroperoxide absorbs light by 233 nm-and this specificity is used for the quantitative determination of essential linoleic acid. Lipoxygenases divided in to two categories mainly Type 1 and Type 2.  Type 1 lipoxygenases react with free fatty acids and are emulsified with water higher specificity. Type 2 lipoxygenases oxidized lipoxygenase co- oxidized other substances (e.g. carotenoide) Cont. The effect of lipoxygenases can be inhibited with a means of phenolic antioxdations Lipoxygenase are, like lipases active by low temp. Such characteristic must be considered for foods which stored in deep refrigerator. This problem can be allocated by enzyme inactivation (e.g. by heating). Secondary Oxydation product  The secondary products of the peroxydation from monohydroperoxide belong, like Di-and trihydroperoxide, Hydroperoxi-epidioxide, Endoperoxide, Hydroxiepoxide, Hydroxi-Epoxi-, Oxofatty acids. The most important secondary products are carbonyl compounds. Carbonyl compounds can be obtained with a means of fragmentation from Hydroperoxydations and another oxidation products.  E.g. Aldehyde formed from such fragmentation can change itself with a means of oxidation to the free fatty acids and split with means of oxidation to the double bonds. Cont.  One particular compound, malonaldehyd results from cleavage at both ends of a diene system. It forms a pink color with thiobarbituric acid which forms the basis of a useful method for assessing the deterioration of fats.  Hydroperoxide test can be identified by the reaction with Iodine and characteristic absorbance of conjugated dienes and trienes at 230 and 270 nm. Hydroperoxide test  ROOH + 2KI → ROH + I2 + K2O I2 + 2Na2 S2O3 → Na2S4O6 + 2NaI Cont. The cross linking reactions can be of various types. Free radicals may react directly together. R.+R.R-R R.+ROO.R-O-O-R ROO.+ROO. R-O-O-R+O2 * Or with other alkenic systems:- * R,+R,-CH=CH-R; ———~R,-CH(R,)-C.H(R;3) or remember the Diels -Alder reactions R,-CH=CH-CH=CH-R, . R;-CH=CHR4 CH=CH R, ch HR, .R,HC-CHR, Cont. Termination step R. +A.RA RO.+A. ROA ROO. +A. ROOA  Substances with fotoxydative character form a complex compound with metals are called metal-scavnger e.g. 0- phosphoric acid.  Quenchers are compound which deactivate the exciting sensibilisators- and the excited oxygen, so that the foto- oxygenation inhabited by scavenging oxygen (e.g. Ascorbic acid). The quencher makes a bond with oxygen under oxidation (co-oxidation) so that the lipid oxidation inhibited. Cont. Aut-oxydation processes takes place not only with pure lipids, but also with fat contained foods (e.g. vegetables and fruit juices) can under go lipid change oxidation. The hydroperoxide of lipids can be determined Iodometrically (peroxide number) and carbonyl compounds like aldehyde and ketone can be photometrically by 2, 4-dinitrophenylhydrazine. Transition-metal cations (inevitable trace contaminants of oils processed, stored, or utilized in metal vessels) are important catalysts of hydroperoxide breakdown. Cont. ROOH + M*—— RO. + OH + M*# ROOH + M**— ROO. + H* + MF 2ROOH ——— RO,+ROO. +H20 | Alkoxy radical Hydroperoxy radical Cont.  Lipid can form polymer compounds by thermal as well as by thermal oxidation.  If oxygen participate in the formation of polymerization, then it is a kind of oxypolymerization (oxy polymer).  Other wise it is a simple polymerization (termal polymere).  Depending from type and degree of polymerization of the products, it is calculated the-  increment of boiling points viscosity the change in sensory value biological degrading characteristic. Thermal polymerization  A known polymerization of unsaturated fat takes place first by a temperature above 200ºc (473ºk). The bond formation between two c-c atoms takes place in two ways.  Intra molecular (b/n two fatty acids with in one molecule  Inter molecular (b/n two fatty acids which belongs from two glycerid molecules).  the thermal-polymerizations play a roll by the formation of unpleasant odor from plant fat.  the majority of such a polymerization is dimere compound.  the amount of such a refine fat contained about 0.5% of dimere.  high-molecular weight takes place by inter molecular reaction Cont. The formation of polymers form poly-unsaturated fatty acid take place in the sense of diels-Alder-synthese, where primarily with a means of thermal isomerization the 1,4 –pentadien system changes to1,3- system and then with Dienophil react. Prevention of rancidity is achieved by: 1. Avoidance of the causes (exposure to light, oxygen, moisture, high temperature and bacteria or fungal contamination).  By keeping fats or oils in well-closed containers in cold, dark and dry place (i.e., good storage conditions). 2. Removal of catalysts such as lead and copper that catalyze rancidity. 3. Addition of anti-oxidants prevent peroxidation in fat (i.e., rancidity).  They include phenols, naphthols, tannins and hydroquinones. The most common natural antioxidant is vitamin E that is important in vitro and in vivo. Hazards of Rancid Fats: 1. The products of rancidity are toxic, i.e., causes food poisoning and cancer. 2. Rancidity destroys the fat-soluble vitamins (vitamins A, D, K and E). 3. Rancidity destroys the polyunsaturated essential fatty acids. 4. Rancidity causes economical loss because rancid fat is inedible. Analysis and Identification of fats and oils (Fat Constants)  Fat constants or numbers are tests used for:  Checking the purity of fat for detection of adulteration.  To quantitatively estimate certain properties of fat.  To identify the biological value and natural characteristics of fat.  Detection of fat rancidity and presence of toxic hydroxyfatty acids. 3-Acids Number (or value): Definition: It is the number of milligrams of KOH required to neutralize the free fatty acids present in one gram of fat. Uses: It is used for detection of hydrolytic rancidity because it measures the amount of free fatty acids present. 4-Reichert- Meissl Number (or value): Definition: It is the number of milliliters of 0.1 N KOH required to neutralize the water- soluble fatty acids distilled from 5 grams of fat. Short-chain fatty acid (less than 10 carbons) is distillated by steam. Uses: This studies the natural composition of the fat and is used for detection of fat adulteration.  Butter that has high percentage of short- chain fatty acids has highest Reichert-Meissl number compared to margarine. 5-Acetyl Number (or value): Definition: It is number of milligrams of KOH needed to neutralize the acetic acid liberated from hydrolysis of 1 gram of acetylated fat (hydroxy fat reacted with acetic anhydride). Uses: The natural or rancid fat that contains fatty acids with free hydroxyl groups are converted into acetylated fat by reaction with acetic anhydride.  Thus, acetyl number is a measure of number of hydroxyl groups present.  It is used for studying the natural properties of the fat and to detect adulteration and rancidity.