Chapter 6 - Oils, Fats And Detergents

1 6.1. Introduction to fats and oils Fats and oils belong to a group of biological substances called lipids. Lipids are biological chemicals that do not dissolve in water. They serve a variety of functions in organisms, such as regulatory messengers (hormones), structural components of membranes, and as energy storehouses. • Fats and oils are composed of “triglycerides” & The difference is mainly due to the degree of unsaturation and the carbon chain length of the fatty acid in the triglyceride. • Oils from mineral (petroleum) sources are completely different from the oils from vegetable sources. The mineral oils are basically mixture of long chain hydrocarbons and have no triglycerides. 2 Chemical Structure of Fats & Oils • Fats are naturally occurring esters (tri) of the higher alkyl (paraffinic or olefinic) monocarboxylic acids and the trihydric alcohol (i.e. glycerol). However, fats do occur, in sizeable quantities as esters with complex structures involving: a) Alkyl monocarboxylic acid of relatively large alkyl chain and an alcohol with the alkyl chain as big as that of the monocarboxylic acid and b) Alkyl monocarboxylic acid with large alkyl chain and an alcohol of complex structure Since fats are esters, their structure would therefore consist of: (a) An acid: monocarboxylic acids of varying carbon chain lengths and varying degree of unsaturation: in the case of triglycerides there would be three molecules of monocarboxylic acid. (b) An alcohol: glycerol (triglycerides); alcohol with longer alkyl chain and alcohols of complex structure. 3 The general structure of fats and oils Where, ‘R’ is a hydrocarbon chain with varying carbon chain length and degree of saturation. Oils are generally used to indicate a variety of greasy, fluid substances that are: ⸻ Viscous fluids at ordinary temperatures ⸻ Lighter than water ⸻ Insoluble in water but soluble in organic solvents such as aliphatic alcohols, ethers, etc. and ⸻ Flammable 4 Chemical Composition of Fats and Oils • Triglyceride is the major component of most fats and oils especially those of edible grade. • The minor components include mono- and diglycerides, free fatty acids, phosphatides, sterols, fatty alcohols, and fat soluble vitamins. • Many of these minor components have to be removed from the edible grade fats and oils. 5 If the acids are different, it is known as a “Mixed” triglyceride 6 Minor components (i) Mono-glycerides and Diglycerides • Mono-glycerides are those in which only one of the hydroxyl groups of glycerol is combined with one fatty acid where as in diglycerides, two hydroxyl groups combined with two fatty acids. • They do not occur naturally in appreciable quantities except in fats that have undergone partial hydrolysis. • From the point of view of health, the fats and oils must be made free of both these glycerides. However, for certain industrial applications, one may find the mono and diglycerides quite useful as the free hydroxyl groups serve the purpose of the base for producing the derivatives with unique properties. 7 8 Cont’d… (ii) Free Fatty Acids • Free fatty acids are the ones remaining unattached or non- esterified fatty acids present in fats and oils. • The fatty acids that form the triglycerides of naturally occurring oils and fats are predominantly even-numbered, straight chain, aliphatic monocarboxylic acids with chain lengths ranging from C4 to C24. • Most vegetable fats and oils consist predominantly of palmitic, oleic, and linoleic acids as free fatty acids. • The fatty acids from land-animal fats mainly have a chain length of C16 or C18. 9 Cont’d… (iii) Phosphatides • Consist of alcohols (usually glycerol), combined with fatty acids, phosphoric acid, and a nitrogen-containing compound. • For all practical purposes, during the refining of the crude oil the phosphatides from the fat or oil are removed. Lecithin is the common phosphatides generally found in edible fats. (iv) Sterols • Sterols are a class of substances that contain a common steroid nucleus plus 8 to 10 carbon side chain and an alcohol group. • Cholesterol is the popularly known sterol present in the fats and oils derived from animals. The 4 rings makes the molecule rigid & synthesized in the cell membranes to impart rigidity Lecithin 10 The advantages and disadvantages of cholesterol Advantages: ⸻ Cell structure/protective barrier (low level can affect energy production & utilization) ⸻ production of steroid hormones (control weight, sexual functioning, bone health etc.) ⸻ digestion (cholesterol used by liver to create bile acids required for fat digestion) Disadvantages: ⸻ high cholesterol is associated with elevated risk of cardiovascular diseases (coronary heart disease, stroke, high blood pressure and diabetes) The health experts always advice to:  Restrict the consumption of fats that can raise the level of bad (LDL-type) cholesterol in the body and  to consume the fats that help build the levels of good (HDL- type) cholesterol in the body.  Because the vegetable oils do not contain the cholesterol, they are recommended over the animal fat for better health specially the phytosterols in vegetable oils are known for their anti-oxidative and anti-cancerous properties . 11 Cont’d… (v) Fatty alcohols • Alcohols with long carbon chain length called as fatty alcohols • In marine oils, the presence of fatty alcohols can be considerably high and Since the fatty alcohols are non-edible, the fats and oils for edible purposes must be processed to remove the fatty alcohols. • Fatty alcohols find preference in numerous industrial applications. • Various derivatives of fatty alcohols have been in use in different industries for cosmetic and personal care industry. • The bio-degradability of products based on fatty alcohols is the main reason for the rising preference and demands 12 Cont’d… (vi) Fatty esters • Some times, the fats and oils contain small quantity of fatty esters which are nothing but the condensation product of long chain fatty acids with long chain fatty alcohols. • The waxes found present in certain vegetable oils are the example of fatty esters and other unwanted impurities, they must be removed from edible fats and oils. 13 Physical Properties of Fats and Oils • The mpt and fpt of fatty acids increases with increasing degree of saturation as well as with increasing the carbon chain length. As a result, the triglycerides based on fatty acids also follow a similar trend of melting point. • Thermal property: The specific heat of oils and fats increases with the increase in chain length and degree of saturation in the carbon chain of the fatty acid. • Oils and fats are relatively poor thermal conductors. • The density of fatty acids and of the triglycerides decreases with increasing molecular mass and degree of saturation. But Oxidation of the triglycerides generally leads to higher densities. • Then, a high free fatty acid content lowers the density of an oil and hence, density can be a criteria for quality of fats and oils. 14 Cont’d… • Viscosity : Oils tend to have a relatively higher viscosity because of intermolecular hydrophobic attraction between their fatty acid chains. • Generally, viscosity tends to increase slightly with increasing carbon chain length. Fats and Oils on the basis of their chemistry and chemical composition can be Classified as drying, semi-drying and non-drying oils. (a) Drying Oils: The fats having a large proportion of unsaturated acids have the tendency to get solidified on exposure to air. • Oils with high degree of unsaturation slowly develop a hard surface film when in contact with air. 15 Cont’d… It is enhanced by peroxidation at -C=C- bonds and either cleavage of these peroxy linkages to form carbonyls or free radical initiated polymerization of peroxides form gel. The gel formed at the surface extends to the inner layer gradually forms a hard compact surface film. (b) Non-drying Oils: Vegetable oils such as olive, rapeseed, and castor oil and animal oils such as lard oil, do not possess this property of drying oils (c) Semi-drying oils: Those which can neither be termed as completely drying nor as completely non-drying. 16 Classification On the basis of saturation (a) Saturated: A fat or oil is saturated when all available carbon bonds are occupied by hydrogen atom. They are highly stable, and hence they do not normally go rancid. They are straight in form and hence, pack together easily, so that they form solid or semisolid fat at room temperature (eg. Butyric acid). (b) Monounsaturated: Monounsaturated fatty acids have one double bond. The human body can make monounsaturated fatty acids (MUFA) from saturated fatty acids. Such fats have a kink at the position of the double bond so that they do not pack together as easily as saturated fats 17 Cont’d… • Polyunsaturated: Such fats have two or more pairs of double bonds, Such fats have a kink at more positions than in MUFA so that they do not pack together. They are liquid even when refrigerated. • The unpaired electrons at the double bond make these oils highly reactive. They go rancid easily and should not be used for cooking. Polyunsaturated fatty acids are usually found in cis form. 18 Trans fat • Trans fat consists of trans fatty acid which is an unsaturated fatty acid containing trans double bond between carbon atoms. • The trans double bond of fatty acids are less kinked compared to those with cis double bond • A majority of trans fats are formed during the manufacture of processed foods • Trans fat are produced during Partial hydrogenation to increase the shelf life and flavor stability of foods. • Partial hydrogenation also raises the mpt, producing a semi-solid material, which is much more desirable for use in baking than liquid oils. 19 Cont’d… • Saturated and trans fats can be found together in vegetable, shortenings, margarines, crackers, candies, cookies, snack foods, fried foods, baked foods and other processed foods made with partially hydrogenated vegetable oils. • High amounts of saturated fats are found in animal products (such as beef and pork, chicken skin, butter, whole milk and cheese). • Trans fat is an artery clogging fat known to increase levels of LDL (bad cholesterol), while lowering the levels of HDL (good cholesterol) in blood which is responsible for type-2 diabetes and other serious health problems. • Trans fat also increase the risk of heart diseases because the trans fat is not recognized by the body’s metabolism, causing it to deposit in the blood vessels. • Increasing the pressure at which oil is hydrogenated reduces trans fat formation. 20 Chemical Properties of Fats and Oils  Hydrolysis of fats and oils: easily hydrolyzed yielding mono and diglycerides (on partial hydrolysis), glycerol and fatty acid (on complete hydrolysis) and With NaOH, glycerol and Na- salt of fatty acid (soaps) are formed.  Oxidation of fats and oils: Autoxidation: Oxidation at room T0 causes rancidity, occurs only to a limited degree if fats and oils are left for storage. In this process, oxygen reacts with unsaturated fatty acid chains, form peroxides which in turn breakdown the chain of fatty acids into HCs, ketones, aldehydes, and small amounts of epoxides and alcohols, results objectionable flavor and odor that makes it unsuitable for human consumption. 21 Cont’d… Oxidation at higher T0: Differences in the stability of fats and oils when used for frying and baking. The more unsaturated the fat or oil is the greater will be its susceptibility to oxidative rancidity Polymerization of fats and oils: Fats with those high content of polyunsaturated fatty acids tend to form larger molecules when heated under extreme conditions of temperature and for an extended time period. When polymerization takes place, there is a marked increase in viscosity of the oils. In any case, polymer, present in the fat or oil are absorbed poorly by the intestinal tract. 22 Hydrogenation of fats and oils: • Hydrogenation is the single largest chemical reaction in the fatty oil processing industry. • hydrogenation is a means of converting liquid oils to semisolid fats suitable for shortening or margarine manufacture. It also uses for other desirable purposes, including enhancement of the stability and the improvement of the color of the fat. • Oils and fats having unsaturated bonds hydrogenated using nickel, palladium, copper, or platinum and the liquid oil converts into solid form. • Margarine (harden oil that is converted by hydrogenation): prepared by emulsifying about 80% fat & 15% skimmed milk, adding salt, vitamin A&D, preservatives (such as Nabenzoate), a yellow dye and flavoring agents. 23 Essential Fatty Acids • Certain fats are called essential (i.e., for normal cell, tissue, gland, and organ function) because the body cannot synthesize them and must be provided from outside the body through food. • Deficiency of such fats results in the progressive deterioration of the body and ultimately leads to death. There are two essential fatty acids i. Omega 3- alpha linolenic acid ii. Omega 6- linoleic acid 24 Manufacture of vegetable oils • The important oils of this category are: Caster oil, palm oil, hempseed oil, peanut, cotton seed oil, soya bean oil etc. • The two general methods used to manufacture vegetable oils are expression (mechanical extraction method or squeezing) and solvent extraction. The best and widely used method is solvent extraction to get a better oil yield. 25 Manufacture of soyabean oil through solvent extraction 1st → Screening to remove small thin sticks and dirty by blowing in air 2nd → Crushed by feeding through hopper into the crushing chamber 3rd → The oil is conditioned at low T0 in rotary steam heater (heating) for easy flow of oil and coagulation of the impurities and 4th → The crushed material after heating is charged to solvent extractor. Solvents used: n-hexane or benzene Principle: The crushed seeds are placed on the perforated false bottom of the extractor and the benzene or hexane vapour (solvent) is supper-heated to appropriate temperature and passed through the perforated baskets into heated oil material.  The portion of the solvent with oil or fat condenses in the space below the false bottom 26 Cont’d… The uncondensed vapor of the solvent is condensed together with water in the condenser and the solvent is separated from water in a separator and recycled. Degumming prior to refining of the Crude oils (collected at the bottom of the extractor) having high level of phosphatides by addition of water to hydrate the phosphatides and coagulating through centrifugation. 27 Refining of crude vegetable oils • The oil obtained above is refined to remove: i. ii. iii. The Suspended, dispersed & dissolved impurities Colour and odour Saturated glycerides overall processing of crude vegetable oils usually involves alkali refining, water washing and drying, bleaching, hydrogenation and deodourizing. Alkali refining method: the free fatty acids present in the crude vegetable oils are neutralized with NaOH/KOH, forming soaps which are removed by centrifuging. • Bleaching: is a process of removing color-producing substances. It is done by adsorption of the color producing substances on an adsorbent material. The adsorbent materials are silica gel, activated charcoal (has high de-colorization and de-odourization power) or clay either batch wise or continuous process. 28 Deodorization • It is a vacuum steam distillation process for the purpose of removing trace constituents that give rise to undesirable flavors, colors and odors in fats and oils. • Removal of volatile components using steam because there is great differences in volatility between the substances that give flavors, colors and odor to the fats and oils. • It is carried out under vacuum to facilitate the removal of volatile substances to avoid hydrolysis of the fat. • Deodorization does not have any significant effect upon the fatty acid composition of most oil and fats. In the case of vegetable oil, sufficient tocopherols remain in the finished oils after deodorization which provides stability. • The deodorized oil is then cooled, filtered and subjected to winterization. 29 Analysis of Fats and Oils • As stated above, Fats and Oils consist of a major component (triglyceride) and various types of minor components. • For any application (edible or non-edible purpose), not only to process them, it is essential to check their quality through analysis and characterization using simple methods and high-tech instruments (HPLC, GLC, TLC). 30 Saponification value • It is measure of the mean molecular weight of the fatty acid present in the fat. • The process of saponification is hydrolysis of triglycerides into glycerol and Na/K salt of the fatty acid, using an alcoholic solution of KOH. • The amount of alkali required to combine with the fatty acids liberated by the hydrolysis of the fat on saponification gives the equivalent weight as well as molecular weight of the fatty acids. • The saponification value is expressed in milligrams of the KOH required to saponify 1g of fat. 31 Cont’d… Thus, saponification value gives us information whether an oil or fat contains lower or higher proportions of some acids or an oil or fat contains high proportions of lower or higher fatty acids. Eg. butter has a large proportions of lower fatty acids than tallow, has high saponification value. 32 Acid value • It is a measure of the amount of free fatty acid present in fat. • Some of the deterioration that takes place during storage of either the raw material from which the fat is obtained or in the fat itself after isolation results in hydrolysis of triglycerides to yield free fatty acids 33 Peroxide value • Usually used as an indicator of deterioration (rancidity) of fats & oils • As the unsaturated fatty acids are oxidized results peroxides & produce secondary oxidation products (cause rancidity). • The peroxide value can therefore be used to estimate oxidation but as the compound formed is unstable and oxidation proceeds further, it is not a complete measure of oxidation. 34 Iodine value • It is a measure of the degree of unsaturation in the fatty acid chain. Iodine number refers to the number of grams of Iodine absorbed by 100g of the sample (oil or fat). • As the addition of Iodine takes place at the double bond, measurement of the quantity of Iodine absorbed gives the idea about the number of the double bonds present. • For example: Oleic acid ( 1 double bond) absorbs 90% of Iodine  Linoleic acid (2 double bonds) absorbs 181% Iodine  Linolinic acid (3 double bonds) absorbs 274% Iodine 35 6. 3. Soaps and Detergents Soaps and detergents contain surfactants as their active ingredient. Consist of a long, linear & non-polar (hydrophobic)’tail’ with a polar (hydrophilic) ‘head’. The tail is water insoluble and the head is water-soluble. This difference in solubility has two important implications. The surfactant molecule is a wetting agent. The tails migrate to align themselves with the solid-water interface, thus lowering the surface tension at that point so that the surfactant penetrates the fabric better. it allows the oily dirt particles to form an emulsion with the water. The tails of surfactant surround an oily dirt particle, forming a micelle with the oil in the centre and the ionic heads of the surfactant molecules pointing outwards and hence keeping the micelle in the polar solution. 36 Cont’d…. • Animal fats and plant oils contain compounds known as fatty acids. These fatty acids are bound to glycerol to form triglycerides. In the presence of a strong base such as sodium hydroxide, the triglycerides breakdown to form the metal salt of the fatty acid. This reaction is called saponification. • 37 Surfactants are classified by their ionic (electrical charge) properties in water: anionic (negative charge) nonionic (no charge) cationic (positive charge) and amphoteric (either positive or negative charge). • Soaps are anionic detergents because the active portion (RCO2-) is negatively charged. • Na and K soaps are soluble in water but not Ca2+ and Mg 2+ soaps. When these cations are present in water, they displace Na (or K) from the soap and form their own salts which are insoluble in water, hence precipitates. • Examples are scum and linings in bathtubs, decolouration and hardening of fabrics. This precipitate reduces the emulsifying action of soap and more soap is consumed. 38 Cont’d… Soap has retained its dominance as the active surfactant ingredient in toilet soap. The main reasons are: Lower cost of soap in comparison with synthetic detergents.  Difficulties of producing bars of synthetic detergents. Greater degreasing and wetting power of synthetic detergents that can be harmful to the skin. 39 Batch process for soap manufacture Step 1 - Oil preparation • tallow and coconut oil blended & dried in a vacuum chamber. Once the oils are dry, bleaching earth is added to remove any coloured impurities and removal of the bleaching by filtration, the oils are stored ready for saponification. Step 2 - Saponification • The mixture of bleached oils is mixed with recycled spent lye and fresh NaOH solution. The mixture is boiled for several hours after which it settles into two layers with the mixture of soap and unreacted oils at the top. The bottom layer i.e. the lye which contains glycerine is pumped off. Step 3 - Washing • The crude soap is washed with a mixture of fresh caustic solution and nigre lye and sent to the fitting pans. 40 Cont’d…. Step 4 - Fitting  the remaining unwanted glycerine is removed from the soap by reboiling with water, NaCl and a small amount of NaOH solution. The electrolyte concentration in the water is such that the soap and water separates out into two layers. The top layer is ’neat’ wet soap, which is pumped off to be dried left in the pan and is mixed with the next batch of washed soap, while the nigre lye is used to wash the next batch of crude soap. Step 6 - Drying Finally, the water level is reduced down to about 12% by heating the soap to about 125 oC under pressure and then spraying it into a flash tank at vacuum pressure of about 40 mm Hg. The soap chips are scraped off the walls and formed into soap noodles in equipment known as plodder. 41 The base soap is mixed with colour and preservatives and milled. Perfume is then added and the mixture plodded or extruded into a continuous bar. Then, the bar is cut into billets and stamped out into tablets ready for packaging. 42 Toilet soap manufacture Toilet soap is required to have less water and more fatty material than laundry soap. For this reason base soap has extra fatty acids added with the preservatives before it is vacuum dried. These ensure that there is no un-reacted caustic left and make the soap softer. Glycerine makes the soap smoother and softer than pure soap. Perfume, dye and opacifier are added to the dried soap and the mixture milled to ensure mixing.  Then plodded and extruded out as a continuous bar, cut into billets and stamped ready for packaging. 43 Refined glycerine is used in foods, cosmetics, drugs and many other products. Step 1 - Soap removal  excess caustic alkali is removed using HCl HCl + NaOH → NaCl + H2O  FeCl2 is then added to remove the dissolved soap. FeCl2 + 2RCOONa → 2NaCl + (RCOO)2Fe (an insoluble ferrous soap)  This precipitate is filtered out and then excess ferrous chloride removed with caustic: 2NaOH + FeCl2 → Fe(OH)2 (s) + 2NaCl Step 2 - Salt removal  Water is removed from the lye in a vacuum evaporator, causing the salt to crystallize out as the solution becomes supersaturated. Step 3 - Glycerine purification  A small amount of caustic soda is added to the crude glycerine and the solution then distilled under vacuum in a heated still. Two fractions are taken off - one of pure glycerine and one of glycerine and water. The glycerine thus extracted is bleached with carbon black then transferred to drums for sale. 44 Soap forms an insoluble precipitate when hard water is used. This results in soap wastage as well as the soiling of laundry by the sticky precipitate. Soap cannot be used in acidic solutions such as in textile processing. Strong acids will react with soap to precipitate fatty acids which adhere to the fabric and even prevent the application of dyestuffs. 45 Detergents A detergent is a formulated product which is specially designed to promote the cleaning action. Each individual component in the formulation has its own specific functions in the washing process but it can also produce synergistic effect with other components. Some components are added to aid or improve efficiency of the production process while others are added to improve the appearance and odour of the product 46 is a compound with a water-soluble oil-insoluble (hydrophilic) portion on one side and an oil-soluble water-insoluble (hydrophobic) portion on the opposite side. The surfactant exhibits surface activity by lowering the surface tension of liquids.  Specific adsorption 9. Neutral odour  Soil removal 10. Low intrinsic colour  Low sensitivity to water hardness 11.Storage stability  Dispersion properties 12.Favourable handling characteristics  Soil anti-redeposition capability 13. Minimal toxicity to humans  High solubility 14.No adverse environmental impacts  Wetting power  Desirable foam characteristics 15.Good raw material supply 16.Economy 47 A surfactant can be placed in one of four classes: as Anionic, cationic, nonionic & amphoteric. Anionic surfactants  LABS has good foaming ability and foam stability. Its foam can be boosted or controlled by foam inhibitors. But sensitive to water hardness that Its detergency power decreases with increasing water hardness.  Fatty alcohol sulphates (ROSO3H): are the most important class of fat-derived surfactants. They are readily biodegradable & chemically stable on the alkaline side and are easily hydrolysed on the acid side.  Alkyl ether sulphates are highly foaming and have low sensitivity to water hardness. They also have high solubility and good storage stability at low temperatures in liquid formulations. 48 Cont’d… Alkyl polyglycol ethers or nonylphenol polyethylene glycol (recently used): are the most important surfactants because of their improved biodegradability. Most of these nonionics are viscous liquids or soft pastes. Aqueous solutions exhibit an inverse solubility behaviour i.e. the solubility decreases with increasing temperature. Alkylolamides of fatty acids: have the structure RCON(CH2 CHOH)2 (diethanolethamide) and RCONHCH2CHOH (monoethanolamide). Monoethanolamides are usually used in laundry detergents while diethanolamides are used in light duty and dishwashing detergents as well as in shampoos. Their major function is in foam boosting and soil suspension. 49 Cont’d… Cationic surfactants Since the surfactant molecules bears a positive charge, their adsorption reduces the negative zeta-potential of solids present in aqueous solutions. They therefore reduce mutual repulsions including that between soil and fibres. Excess use causes charge reversal with adverse effect. They are not used for the sole purpose of soil removal because charge reversal in the direction of negative zeta-potential occurs during rinsing causing previously remove soil to be attracted to the fibres. Quaternary ammonium compounds are used as cationic detergents. have a single long aliphalic chain & possess bacteriological properties. dialkyldimethyl ammonium chloride possessing two aliphatic chains are used as textile softeners for both household and industrial use. 50 Cont’d…. Amphoterics Possess both anionic and cationic groups in the same molecule. Amphoterics show the properties of anionics at high pH and of cationics at low pH. They are used to overcome problems associated with high electrolyte levels and corrosion. Excellent foaming and lime soap dispersing properties. Antistatic properties Textile softening 51 Cont’d…. Builders • Used to support detergent action and to deal with the problem of water hardness. They include alkalis, complexing agents and ion exchangers. Bleaching agents • Used to increase the reflectance of visible light at the expense of absorption. H2O2 is the main bleaching agent. Sodium perborate NaBO3 is incorporated in detergents as a source of H2O2. 52 Powder Detergent Manufacture by spray drying Step 1 - Slurry making, Step 2 - Spray drying, Step 3 – Post dosing In the spray drying process, dry and liquid ingredients are first combined into a slurry, or thick suspension, in a tank. The slurry is heated and then pumped to the top of a tower where it is sprayed through nozzles under high pressure to produce small droplets. The droplets fall through a current of hot air, forming hollow granules as they dry. The dried granules are collected from the bottom of the spray drier where they are screened to achieve a relatively uniform size. After the granules have been cooled, heat sensitive ingredients such as bleach, enzymes and fragrance that cannot withstand the high temperatures in the spray drier are added. 53 Cont’d…. Detergent manufacture by spray drying 54