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Characterstics of fats and oil & processing


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Characterstics of fats and oil & processing

  1. 1. 1
  2. 2. Presenter : Jaspreet Kaur 3rd sem Dept. of Food Science and Nutrition 2 Fats and Oils
  3. 3. Content 3 Introduction Types Properties Processing Use
  4. 4. Introduction 4 Fats and oils  Fats and oils comprise one of the three major classes of foods, the others being carbohydrates and proteins.  Chemically they may be defined as esters of the three carbon trihydroxy alcohol, glycerol and various monocarboxylic acids known as fatty acids.  All fats and oils are a mixture of saturated fatty acids and unsaturated fatty acids.
  5. 5. Conti.... 5  Solid fats contain more saturated fats and than oils.  Oils contain more monounsaturated (MUFA) and polyunsaturated (PUFA) fats.  Saturated fats, trans fats, and cholesterol tend to raise “bad” (LDL) cholesterol levels in the blood, which in turn increases the risk for heart disease.  To lower risk for heart disease, cut back on foods containing saturated fats, trans fats, and cholesterol.
  6. 6. Difference between fat & oil Fat Oil 6 1. Remains solid at room temperature 2. Relatively more saturated 3.Relatively higher melting point 4. More stable 1. Remains liquid at room temperature 2.Relatively more unsaturated 3. Low melting point 4. Less stable
  7. 7. Corn oil contains 86% polyunsaturated fatty acids Therefore is a liquid at room temperature. Olive oil contains monounsaturated fatty acids. Therefore is a liquid at room temperature, likely to solidify when refrigerated. Saturated fatty acids (animal fats) are solids, or nearly solids at room temperature. 7
  8. 8. CHEMICAL STRUCTURE 8 Fats are esters of fatty acids and glycerol. Most fats occur in the form of triglycerides, in which three fatty acids are attached to the glycerol. Fatty acids contain the carboxyl group (COOH) and an aliphatic carbon chain of variable length
  9. 9. Conti..... 9 Ester-The chemical linkage that holds an alcohol group (OH) and an acid group (such as COOH) together. An ester bond is the connection between a fatty acid and glycerol in glycerides. Glycerol-A three-carbon chain, with each carbon containing an alcohol group. One, two, or three fatty acids may be attached to glycerol to give a mono-, di-, or triglyceride. Triglyceride-Three fatty acids attached to a glycerol molecule. If the three fatty acids are the same, it is a simple triglyceride; if they are different from each other, it is a mixed triglyceride. Mixed triglycerides are the most common chemical components in fats and oils.
  10. 10. Conti... 10  Fatty acids- A group of chemical compounds characterized by a chain made up of carbon and hydrogen atoms and having a carboxylic acid (COOH) group on one end of the molecule. They differ from each other in the number of carbon atoms and the number and location of double bonds in the chain. When they exist unattached to other compounds, they are called free fatty acids.
  11. 11. Types 11  The oil and fat products used for edible purposes can be divided into two distinct classes:  Liquid oils, such as olive oil, peanut oil, soybean oil, or sunflower oil; and  Plastic fats, such as lard, butter and margarine.
  12. 12. Properties of fats and oils 12  Physical  Chemical  Nutritional  Functional
  13. 13. Physical Properties 13 Crystal Formation  When liquid fat is cooled, the molecular movement slows down as energy is removed and the molecules are attracted to each other by Van Der Waals forces.  Symmetrical molecules and molecules with fatty acids that are similar in chain length align most easily to form crystals.  Fats containing asymmetrical molecules and molecules containing links due to double bonds align less easily, because they cannot pack together closely in space.
  14. 14. Conti.... 14  Molecules that align easily need less energy to be removed before they will crystallize, and so they have high melting points.  They also tend to form large crystals.
  15. 15. Polymorphism 15  Fats can exist in different crystalline forms, and this phenomenon is known as polymorphism.  A fat may crystallize in one of four different crystal forms:  Alpha crystals: The smallest and least stable crystals are called alpha crystals. These are formed if fats are chilled rapidly.  Beta prime crystals: The alpha crystals of most fats are unstable, and change readily to beta prime crystals. These are small needle like crystals, approximately 1 µm long.
  16. 16. Conti..... 16  Intermediate crystal: Fats that can form stable β crystals change to the intermediate crystal form, about 3-5 µm in size.  Coarse beta crystal: Finally convert to coarse beta crystal, which can range from 25 to 100µm in length.  Beta crystals have the highest melting point.  Formation of small crystals is favored by rapid cooling with agitation. Growth of large crystals occurs if cooling is slow.
  17. 17. Melting Point 17 Melting point: The melting point of a solid is the temperature at which it changes state from solid to liquid. For example in animal fat Back Fat: 30-40 degrees, Leaf Fat: 43-48 degrees, Mixed fat: 36-45 degree.  The melting point is an index of the force of attraction between molecules.  The greater the attractive forces between molecules, the more easily they will associate to form a solid.  A lot of energy in the form of heat must be put in to convert a solid to a liquid; thus, the melting point will be high.
  18. 18. Conti... 18  A fat or oil, which is a mixture of several triglycerides, and therefore, do not have a sharp melting point, but melt over a range of temperature, depends on the composition of the fat.  The melting points of individual fatty acids depend on such factors as chain length , number of double bonds and isomeric configuration.
  19. 19. Smoke Point 19  The smoke point is the temperature at which a fat or oil gives off a thin bluish smoke.  Fats and oils with low molecular weight fatty acids have low smoke point.  Normally, oils that are selected for deep fat frying are those, which have a high smoke point.  If oils with low smoke points are used for deep fat frying, then the foodstuff is fried at a lower temperature and thus will take a longer time to acquire the stage of doneness.  In this case, the exposure of the foodstuff to the oil
  20. 20. Plastic Fats 20  Fats may either be liquid, plastic, or solid at room temperature.  A plastic fat is moldable because it contains both liquid oil and solid crystals of triglycerides.  Its consistency depends on the ratio of solid to liquid triglycerides; the more liquid triglycerides, the softer the fat will be, and the more solid triglycerides, the harder it will be.  A plastic fat is two-way system, containing solid fat crystals surrounded by liquid oil.
  21. 21. Conti... 21  The liquid phase acts as a lubricant, enabling the solid crystals to slide past one another, and thus conferring moldability to the fat.  A fat that contains only solid triglycerides is hard and brittle and cannot be molded.  Refractive index: It indicates the purity and identity of fat.
  22. 22. Emulsification 22  The specific gravity of oils and fats is about 0.9, which indicates that they are lighter than water.  Though insoluble in water, they can form an emulsion with water when beaten up with it to form tiny globules in the presence of suitable emulsifying agent.
  23. 23. Conti.... 23  The presence of minute amounts of milk protein helps to stabilize these emulsions. Lecithin, a phospholipid from egg yolk helps to stabilize mayonnaise.  Emulsification of fats is a necessary step in a number of products such as cakes, ice cream and other frozen desserts.
  24. 24. Creaming of Fats 24 Creaming is a process that achieves temporary emulsion status.  Stabilizers may be added to an emulsion to decrease the tendency of the emulsion to separate, which creates a viscosity similar to soft yogurt; this is referred to as a semi-permanent emulsion.  Permanent emulsions are very viscous and stable, to the point that they do not separate.  Solid fats like butter and margarine can be creamed or made soft and fluffy by the incorporation of air.  Fat and sugar are usually creamed together in the preparation of cakes.
  25. 25. Chemical Properties of Oils & Fats 25  Iodine value – express the degree of unsaturation of the FAs in the fat (the amount of iodine absorbed by a fat/100 g basis). The higher iodine value indicates the greater the degree of unsaturation.  Ester cleavage- The ester bonds in fat can undergo a variety of splitting reactions. Some of these are important in food applications, while others have other industrial significance
  26. 26. Conti... 26 Hydrolysis- (breaks down into simpler forms ) A chemical reaction in which a molecule splits into two parts. A molecule of water also splits into H and OH, which are added to the places where the original bond was broken. A fatty acid is removed from a glyceride by hydrolysis of the ester bond. Saponification Number – saponification : A chemical reaction caused by addition of alkali in which the fatty acids attached to a glycerol are cleaved off to produce soap (fatty acid salts) and a glycerol molecule. Is may defined as the number of mg of potassium hydroxide needed to sponify 1 g of fat or oil.
  27. 27. Conti... 27  Glycerolysis- A chemical reaction in which glycerol is combined with one or more fatty acids to form a glyceride.  Alcoholysis- A chemical reaction in which fatty acids react with alcohol to form an ester. The reaction of fat with alcohol is usually catalyzed with an acid such as HCI or a sulfonic acid resin. For example, reaction of fat with methanol yields the methyl esters of the fatty acids, which are used to analyze the composition of the fat by gas-phase chromatography.
  28. 28. Interesterification- 28  Changing the positions of the fatty acids on triglycerides. A free fatty acid can displace another fatty acid from an ester, leaving a glyceride with somewhat changed properties because its fatty acid structure has changed. This reaction is used to change fat properties.
  29. 29. Oxidation- ( exposure to Oxygen) 29  Chemical reaction in which the double bond on a lipid molecule reacts with oxygen to produce a variety of chemical products. The consequences of this reaction are loss of nutritional value and formation of the off- flavors associated with rancidity.
  30. 30. Reduction 30  Reduction- Changing an acid group on a fatty acid to an alcohol group. This is done with metal reducing agents to create fatty alcohols .
  31. 31. Nutritional Properties 31  The quota for polyunsaturated fatty acids. In particular, the ratio of omega-6 to omega-3 acids should be between 5 and 10 to 1 (or less). Since the presence of α-linolenic acid leads to oxidative instability and reduced shelf life.  Fats and oils have a high caloric value, 2.25 times more energy than carbohydrates or proteins.  Each gram of fat contains 9 kcal of energy.  Fats and oils carry the fat soluble vitamins.
  32. 32. Functional Properties 32  Textural qualities (body and mouth feel)  Emulsions  Shortening or tenderizers  Medium for transferring heat  Aeration and leavening  Spray oils  Producing satiety (fullness after eating)  Adding flavor  Decreasing temperature shock in frozen desserts  Foaming  Solubilising flavours and colours
  33. 33. 33 Processing
  34. 34. 34
  35. 35. Extraction/ Rendering Refining (Neutralization or Degumming) Bleaching Deodorization In general, fat and oil undergo four processing steps: 35
  36. 36. Extraction 36  Fats and oils are extracted from either plants or animals. Extraction methods vary. For example, the adipose tissue of the pig is heated, melts the fat and it is further processed. Butter is made by reversing the oil in water emulsion of cream into a water in oil emulsion. Plant extraction procedures involve a variety of different extraction methods.
  37. 37. Types of extraction 37  Rendering  Mechanical pressing  Solvent extraction
  38. 38. RENDERING 38 The melted fat is then separated by skimming or centrifugation. The melted fat then rises, water and remaining tissue settle below. Meat scraps are heated in steam or water to cause the fat to melt
  39. 39. Conti... 39  The fat can be obtained from any of the following three methods: a. Dry rendering b. Wet rendering c. Low-temperature wet rendering
  40. 40. Mechanical pressing 40  Pressing: Used for removing oil from oilseeds or fruit rich oils.. The oil bearing tissues are rolled , crushed or ground into flakes, and then heated by steam at 70 deg. C.
  41. 41. PRESSING OR EXPELLING 41 Various types of mechanical presses and expellers are used to squeeze oil from oilseeds. Seeds are usually first cooked slightly to partially break down the cell structure and to melt the fat for easier release of oil. The heat from cooking or grinding should not be excessive or it may darken the color of the oil With some seeds (e.g. corn) only the germ portion of the seed is pressed to obtain oil, whereas with seed residues by being pumped through multiple filter cloths or by centrifugal clarification.
  42. 42. SOLVENT EXTRACTION 42 It is common in large scale operations to remove the oil from cracked seeds at low temperatures with a nontoxic fat solvent such as hexane. The solvent is percolated through the seeds, and after the oil is extracted, the solvent is distilled from the oil and recovered for reuse. Combined processes employ pressing to remove most of the oil followed by solvent extraction to recover final traces. The oil-free residual seed meal is then ground for animal feed.
  43. 43. Refining of Crude Oil 43 Crude oils as received from the extraction plant contain several non-triglyceride components which must be removed. Refining consists of several processes which accomplish this aim.
  44. 44. Conti... 44  A refining process is carried out extraction of crude edible oils by means of screw presses and/or solvent extraction.  In refining, physical and chemical processes are combined to remove undesirable natural as well as environmental-related components from the crude oil.  These components comprise for example phosphatides, free fatty acids, pigments (such as chlorophyll), odors and flavors (including aliphatic aldehyde and ketone), waxes as well as heavy metals, pesticides etc.
  45. 45. Depending on the requirements, the following basic processes are implemented: 45  Degumming for removal of phosphatides,  Neutralization for removal of free fatty acids,  Bleaching for removal of color,  Deodorization to distill odors and flavors as well as free fatty acids and  Winterization for separation of waxes.
  46. 46. Degumming 46  The first step in the refining process of many oils is degumming. Oils are mixed with water to hydrate phosphatides, which are removed by centrifuging. Phosphoric or citric acid or silica gel are added to enhance the process.  Degumming removes valuable emulsifiers such as lecithin.  Cottonseed oils are not degummed, but degumming is necessary for such oils as soybean and canola.
  47. 47. Degumming 47 The aim of degumming operation;  The emulsifying action of phospholipids increases oil losses during alkali refining.  Gums lead brown discoloration of oil after heating during deodorization.  Salts may be formed with cooper, magnesium,calcium and iron, accelerating oxidative degredation of oil.
  48. 48. 48 Different degumming processes are carried out to remove phosphatides. For efficient and economic application of this procedure appropriate machines and equipments are used. 1. Water degumming 2. Acid degumming 3. Enzymatic degumming
  49. 49. Water degumming 49  A large part of the phosphatides (gums) can be hydrated quickly and easily. If the pressed or extracted oil contains a considerable quantity of gums the oil is subjected to the water degumming process immediately following extraction.  In this process, water is added to the oil. After a certain reaction period the hydrated phosphatides can be separated either by decantation (settling) or continuously by means of centrifuges.  In this process step a large part of hydratable and even a small proportion of the non-hydratable phophatides are removed. The extracted gums can be processed into lecithin for food, feed or for technical purposes.
  50. 50. Water Degumming Process Steps 50 • Heat oil to 60 -70 °C • Water addition and mixing • Hydration mixing 30 minutes • Centrifugal separation of hydrated gums • Vacuum drying of degummed oil • Gums -dried for edible lecithin or recombined in meal
  51. 51. 51 water heater steam reactor seperator mixer gums vacuum Vacuum dryer to storage Water Degumming Phosphorous in degummed oil -50 to 200 ppm max Moisture in dried and degummed oil -< 0.1%.
  52. 52. Acid degumming 52 Dry acid degumming: Dry acid degumming is particularly suitable for processing oils with low gum contents such as palm oil, coconut oil, palm kernel oil or animal fats. Intensive mixing is implemented following addition of acid to the pre- heated crude oil. The benefits of the dry acid degumming process are:  long service life (the components are acid proof),  low investment costs,  environmental-friendly as no wastewater or soap stock occur.
  53. 53. Wet acid degumming 53 Initially oils with higher gum contents (e.g. corn oil) are similarly processed as in dry acid degumming. However, to achieve gum hydration water is added following acid apportioning. The gums are removed by a separator prior to bleaching. This process is beneficial as  centrifuges enable easy separation of gums in oil types with higher non-hydratable gums contents (e.g. rape oil and soybean oil),
  54. 54. Acid Degumming Process Steps 54 • Heat oil to 60 -70 °C • Acid addition and mixing • Hydration mixing 30 minutes • Centrifugal separation of hydrated gums • Vacuum drying of degummed oil • Gums -recombined in meal
  55. 55. Acid Degumming 55 Crude oil heater acid mixer water reactor mixer To drying / storage gums Phosphorous in degummed oil -20 to 50 ppm max. Moisture in dried and degummed oil -< 0.1%
  56. 56. Enzymatic degumming 56 Enzymatic degumming was first introduced by the German Lurgi Company as the “Enzy Max process” . The EnzyMax process can be divided into four different steps: (i) the adjustment of the optimal conditions for the enzyme reaction, i.e. optimal pH with a citrate buffer and the optimal temperature; (ii) the addition of the enzyme solution; (iii) the enzyme reaction; (iv) the separation of lysophosphatide from the oil at about 75°C.
  57. 57. 57 Enzymes for enzymatic degumming;  Lecitase 10L (pancreatic phospholipase A2)  Lecitase Novo (microbial lipase)  Lecitase Ultra (microbial lipase)
  58. 58. 58 Enzymatic degumming
  59. 59. NEUTRALISATION 59 Objective:Removal of free fatty acids Neutralisation of vegetable oils is essential to ensure removal of gums, waxes, phosphatides and free fatty acid (F. F.A.) from the oil; to impart uniform colour by removal of colouring pigments and to get rid of unpleasant smell from the oil by removal of odiferous matter.
  60. 60. Conti.... 60 Two different Neutralising principles: 1.Chemical Neutralisation:Removal by a chemical reaction with alkali(caustic soda) 2. Physical Neutralisation :Removal by distillation at higher temperature and low vacuum
  61. 61. 61
  62. 62. Bleaching 62  Trace metals, colour bodies such as chlorophyll, soaps and oxidation products are removed using bleaching clays which adsorb the impurities. Bleached oils are nearly colourless and have a peroxide value of near zero. Depending on the desired finished product, oils are then subjected to one or more processes of the following processes..
  63. 63. Deordorization 63  Deordization is a steam distillation process carried out in a vacuum, removing volatile compounds from the oil. This may be a batch or continuous process. The end product is a bland oil with a low level of free fatty acids and a zero peroxide value. This step also removes any residual pesticides or metabolites that might be present. Some manufacturers favour the use of cottonseed oil because it can be deodorized at lower temperatures, which results in more tocopherols (natural antioxidants) being retained. Deordization produces some of the purest food
  64. 64. Winterization (Fractionation) 64  Oils such as salad oils, or oils that are to be stored in cool places undergo a process called winterization so that they will not become cloudy when chilled. The refined, deodorized oils are chilled with gentle agitation, which causes higher melting fractions to precipitate. The fraction which settles out is called stearin. Soybean oil does not require winterization, but canola, corn, cottonseed, sunflower, safflower and peanut oils do.
  65. 65. Hydrogenization 65  Treatment of fats and oils with hydrogen gas in the presence of a catalyst results in the addition of hydrogen to carbon-carbon double bond. Hydrogenation produces oil with mouth feel, stability, melting point and lubricating qualities necessary to meet the needs of many manufacturers. It is important to note that hydrogenation is a selective process that can be controlled to produce various levels of hardening.
  66. 66. Sun flower oil Trans fats are made through the chemical process called hydrogenation of vegetable oils. Hydrogenation solidifies liquid oils and increases the shelf life and the flavour stability of oils and foods that contain them. Margarine Margarine from Oil 66
  67. 67. Reversion flavour 67  Mild off flavour developed by a refined oil when exposed to oxygen. Reversion occurs rather easily, and the off- flavour, while undesirable, is not as objectionable as rancidity caused by oxidation.
  68. 68. 68
  69. 69. Effect of heat on fats 69  There is increase in free fatty acids  Smoke point is lowered  Iodine number decreases  Melting point falls  Fat turns darker in colour  Fat gets polymerised  Refractive index increases  POLYMERISATION: This occurs when fats are subjected to intense heat. Free fatty acids are released, colour darkens and gum is formed at the edge of the vessel.
  70. 70. Use of fats and oils 70 AS A MEDIUM OF COOKING  Fat is used in shallow and deep fat frying.  Cooking oil is a better heat transfer medium than air or water in that it heats up very quickly because of its greater specific heat, and its operating temperature of about 200°C is considerably higher than that of water.  Pan frying is used to cook dosas, cutlets and omelettes.
  71. 71. Conti... 71  In basting, foods to be grilled like meat, poultry or vegetables are applied with fat to prevent the surfaces drying.  Deep fat frying method is used in preparing pooris, bajia etc. In deep fat frying, water is lost from the exterior surface of the food as it is converted to steam.  The steam carries off energy from the surface of the food and prevents charring or burning.  Water then migrates from the central portion of the food outward to the edges to replace that loss by evaporation. Finally the interior of the food is
  72. 72. Conti.... 72 FOR IMPROVES THE TEXTURE OF FOODS: FAT AS A SHORTENING AGENT  In many preparations, such as cakes, biscuits etc, fats are added to improve the texture.  The fat covers the surface of the flour particles and prevents the sticking of particles together.  Many factors such as the nature of the fat, the amount added, the temperature, presence of other ingredients, manipulation and the extent of mixing, affect the shortening power.
  73. 73. Conti..... 73 FAT AS A LEAVENING AGENT:  In making cake, leavening occurs by incorporating air into the fat during the leavening process. When the butter is heated in the oven, the small air bubbles expand and fill with steam.  The greater percentage of leavening in cake comes from the steam that collects in the tiny air bubbles rather than from the air itself.  Gluten in the flour forms the walls around each little bubble and during baking they act to a fairly rigid structure.  When the cake is removed from the oven and is
  74. 74. Conti.... 74 FAT FOR SMOOTHNESS  Fats have textural effects in ice creams and frozen desserts. They limit the size of water crystals and help in maintaining smooth texture. AS A SEASONING  Fats and oils are used to season most food preparations in sweet preparations, fats, such butter, ghee, vanaspati are used, as they have mild flavor, which blends with the sweet preparation.
  75. 75. References 75  W. Heimann (1980) Fundamentals of Food Chemistry.AVI Publishing Company .  B. Srilakshmi, (2007), Food Science, New Age International Publishers, New Delhi. Pp. 227-243  A.Karleskind (1996)Oils & Fats Manual . Published by Mauel des crops gras. Vol.I  A.Karleskind (1996)Oils & Fats Manual . Published by Mauel des crops gras. Vol.II  Caisimir C.Akoh and David B.Min (2002) Food Lipid. Printed by The united State of America.  BE7E-4C12-ADD2- DC2C3E4D53CD/0/degumming.swf
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