CHAPTER IV LIPID
I. General introduction to lipids
Lipids or fats are a group of natural organic compounds that are very common in animal and plant cells, with different chemical compositions but the common feature of being insoluble in water but soluble in organic solvents. ether, chloroform,.... Regarding the chemical structure in the lipid molecule, there are polyfunctional alcohol lords and higher fatty acids esters of alcohols and fatty acids. I.1. Biological functions• Provide energy for the body: 1g of protein when burned in the body releases 4.3 kcal of energy. 1 g of glucose burned in the body releases 4.8 kcal, and 1 g of lipid releases 9.8 kcal. • Is a solvent to dissolve vitamins. • A source of vitamins A, D, E, K, F for the body. • Fat forms a natural coat that surrounds and protects the body.• Lipids also participate in cell structure.I.2. Classification of lipids Lipids are simply lipids in which there are only esters of alcohols and fatty acids. In this group, there are glycerides, wax cerides, and sterides. Complex lipids are lipids that, in addition to the above two components, have subgroups. In this group, there are glycerophospholipids, glyceroglucolipids.
II.1. Chemical structure Glycerides are esters of glycerin and fatty acids.
O ||CH2- O – C – R1| O ||CH – O – C – R2| O ||CH2- O – C – R3
II.2. How to name glycerides Introduce some fatty acids:
Although there are many different types of fats in nature, the main difference between them is in the properties of fatty acids. Fatty acids are divided into two categories: noCnH2nO2 and unsaturated. Among the most common saturated fatty acids are palmitic C15H31COOH and stearic C17H35COOH, which give fats a solid structure. Some other less common saturated fatty acids are miristic C14, capric C10, butyric C4. Unsaturated fatty acids are commonly found in vegetable oils, animal oils from fish and marine animals. At room temperature they are liquid. The most common are oleic C17H33COOH, linoleic C17H31COOH, linolenic C17H29COOH and arachidonic C19H31COOH. Three unsaturated fatty acids, arachidonic, linoleic and linolenic, are indispensable components of food because the human body cannot synthesize them. It is considered that the above unsaturated fatty acids have an important role as vitamins, they are called vitamin F. Oleic : CH3- CH2 7- CH = CH -CH2 7-COOH Linoleic :CH3-CH2 4- CH=CH- CH2 2- CH2 6- COOH Linolenic:CH3-CH2- CH=CH-CH2 3- CH2 6- COOH. Arachidonic: CH3-CH2 4- CH=CH-CH2 4- CH2 2- COOH. Glycerides are called by the number of acid radicals involved in forming ester bonds, the name of the acid changes from -ic to di -in. Example: CH2- O – CO – CH2 16- CH3| CH – O – CO – CH2 16- CH3| CH2- O – CO – CH2 16- CH3TristearinCH2- O – CO – CH2 7- CH = CH – CH2 7- CH3| CH – O – CO – CH2 7- CH = CH – CH2 7- CH3| CH2- O - CO - CH2 7- CH = CH - CH2 7- CH3Triolein Fats, animal oils, vegetable oils: It can be said that natural fats and oils are mixed triglycids. For example, the composition of leaf fat in pigs includes: tristearin o, stearodiolein 15, β-palmitodiolein 42-57, β-palmitostearolein 21-36, β-palmitodistearin 2, etc. Animal triglycerides are usually concentrated in cells. of adipose tissue forming a layer of subcutaneous fat, either surrounding some organs or interspersed with other tissues. Aqueous fat can be obtained by melting it at temperatures below 80°C so that the fat is colorless and odorless. The triglycerides of terrestrial animals and birds are solid and are called fats, while those of fish and aquatic animals are not. liquid and is called animal oil. In plants, glycerides are an essential component of seeds. The seeds of some plants containing a lot of glycerides are called oilseeds and are the raw materials for the extraction of oil from peanuts, sunflowers, etc. II.3. Physical properties of glycerides Insoluble in water but soluble in organic solvents. However, under certain conditions, under the action of protein emulsifiers, soaps, sodas, etc., lipids are divided into small particles suspended in solution that, when left to stand, do not separate into two layers, called emulsions. soy sauce. This is because emulsifiers have surfactant properties, which reduce the surface tension of lipid droplets surrounding lipid droplets, preventing them from accumulating together. In humans and animals, lipids are emulsified by bile acids. Solvent for many substances with volatile odors. In cosmetics, people use fat as a solvent to extract oil ethers, for example from roses. Because of this property, when storing fat, it is easy to absorb strange odors. The melting temperature of glyceride depends on the composition of the number of fatty acids. Fats containing a lot of saturated fatty acids have a high melting point, while those containing a lot of unsaturated fatty acids have a lower melting point. As we have seen, all natural oils and greases contain different triglycerides, so there is no obvious melting point but often a melting range. II.4. Chemical properties of glycerid Hydrolysis reaction: glyceride easily participates in hydrolysis reaction under the action of lipase enzyme to produce glycerin and fatty acids.CH2- O – CO – R1CH2OH R1COOH |Lipaza | CH- O – CO – R1CHOH R2COOH |+ H2O | CH2- O - CO - R1CH2OH R3COOHSaponification reaction: Under the action of alkali, the ester linkage in the glyceride molecule is hydrolyzed to form glycerin and salts of fatty acids. These salts are called soap.CH2- O – CO – R1CH2OH R1COONa || CH- O – CO – R1+ 3NaOH CHOH R2COONa || CH2- O - CO - R1CH2OH R3COONa Soap Hydrogenation reaction: It is a reaction to attach hydrogen to the double bonds of unsaturated fatty acids in glycerides.Ni Triolein + 3H2Tristearin to In fact, some vegetable oils are selectively hydrogenated to reducing the linolenic acid content thereby increasing the oil strength eg hydrogenation of soybean oil to reduce the linolenic acid content from 9 to 1 . Sometimes partial or complete hydrogenation is also used for the purpose of creating solid fats as a basis for the production of margarine or for the production of fats for emulsification. II.5. Fat Index Acid Index: The number of mg of KOH used to neutralize the free fatty acids present in 1g of fat. Acidity index is used when assessing the freshness of fats used for food. Acidity index High indicates that the acid is not fresh and has been partially hydrolyzed. Saponification index savon index: is the number of mg of KOH used to saponify 1g of fat and neutralize the free fatty acids present in 1g of this fat. The high savone index indicates that the fat contains many low molecular weight fatty acids and vice versa. Iodine index: Is the number of grams of iodine combined with 100 grams of fat. Iodine is incorporated into the double bonds in the unsaturated fatty acid molecule. Fats contain a lot of unsaturated fatty acids and have a high iodine value. The higher the iodine number of the fat, the lower the melting point. Peroxide index: Oils and fats kept for a long time often have an unpleasant burning smell, called rancidity. The unpleasant burning smell is caused by aldehydes, ketones, low molecular acids, .. formed by the oxidation process. This phenomenon can be caused by many reasons, but the most common type is because oxygen in the air combines with the double bond in an unsaturated fatty acid molecule to form peroxides in the following manner: O – O | |R – C = C – R1+ O2R – C – C – R1| | | | HHH HPeroxide When KI reacts with oxidized fats, it reacts with peroxides, releasing iodine according to the following reaction:O – O | |R – C – C – R1+ 2KI + H2O R – CH – CH – R1+ I2+ 2KOH | |OH Use tiosulphate to titrate the amount of iodine released: 2 Na2S2O3+ I2= Na2S4O6+ 2NaI. The number of grams of iodine released by peroxides in 100 grams of fat is called the peroxide number. The peroxide value is used to assess the degree of oxidation of fats. The fat burning process accelerates under humid, high temperature and light conditions. Some metal ions such as Cu, Pb also catalyze this process. In fact, to prevent fat oxidation, people often add antioxidants such as galatpropil, galatetil ... or find ways to remove oxygen in the storage environment.