Chapter 3 :- Fat and Oils

 Introduction:-

             The basic use of fats and oils in cookery is to add richness and flavour to food and as a cooking medium to fry or cook food. They improve the texture of various preparations such as cakes, pastries, and biscuits. 
              Fats and oils are organic compounds composed of carbon, hydrogen, and oxygen. They are collectively known as lipids. Unlike carbohydrates, lipids contain a smaller proportion of oxygen and a larger proportion of hydrogen and carbon. This is why lipids provides more energy per gram than carbohydrates. 

	Fats and oils
Description	Fats are the fatty acid esters of glycerol and are the primary energy depots of animals.	Oils act to search artery-clogging cholesterol from the bloodstream, carrying it to the liver for processing.
Origin of the word	Middle English, from Old English, past participle of to cram; akin to Old High German  fat	Middle English oil, from Anglo-French, from Latin oleum olive oil, from Greek elaion, from elaia olive
Derived in	12th Century	13th Century
Room temperature	Solid	Liquid
Derived from	Animals	Plants
Types	Trans fat Unsaturated fat Saturated fat Total fat	Monounsaturated fat Polyunsaturated fat
Functions	Degree of saturation Length of fatty acid structure Cis-trans configuration Crystalline structure	Energy reserve Protect vital organs and thermal insulation Transport medium for oil-soluble vitamins Hunger suppressor
	Animal fats – Butter Cream Lard Meats	Vegetable fats – Olive oil Peanut oil Seed oil Corn oil

Leavening and shortening agent:-

Leavening Agent: Substance causing expansion of doughs and batters by the release of gases within such mixtures, producing baked products with porous structure. Such agents include air, steam, yeast, baking powder, and baking soda.

Shortening is any fat that is a solid at room temperature and used to make crumbly pastry and other food products. Although butter is solid at room temperature and is frequently used in making pastry, the term “shortening” seldom refers to butter, but is more closely related to margarine.

(A.) Classification (based on the origin and degree of saturation):- 

(B.) Autoxidation (factors and prevention measures):-

The spontaneous uptake of oxygen by the unsaturated oils exposed to air is known as oxidative rancidity. It is the most common and important type of rancidity which results in the production of rancid or tallowy flavours. It is caused by the reaction of unsaturated oils with oxygen. Moisture and impurities do not have any effect on oxidative rancidity. Pure and refined oils can turn rancid on exposure to oxygen. Oxidative rancidity is a complex process in the form of a chain reaction. Once the reaction begins, it is a continuous process. 

Factors:-

1. Temperature:- High storage temperatures accelerate the development of off-flavours and odours in fats and oils.
2. Moisture:- Low moisture content in cereals, specially breakfast cereals, to keep them crisp, accelerates their deterioration due to rancidity. Presence of moisture in butter and oils brings about hydrolytic rancidity. In butter, the enzyme lipase hydrolyses butter fat to butyric acid, which gives stale butter a rancid smell.
3. Air:- The amount of air in contact with the fat or oil is an important factor in determining shelf life. Auto-oxidation or oxidative rancidity occurs when fats are exposed to oxygen. Potato chips and salted nuts ,because of their large surface area, turn rancid at a faster rate. 
4. Light:- Light accelerates the development of both rancidity and reversion. 
5. Metals:- The presence of metals in traces accelerates the development of both rancidity and reversion as they are active pro-oxidants. Metal contamination can occur from equipment used for extraction and refining of oils. Rust from steel equipment, traces of copper, lead,zinc,and tin can accelerate the onset of rancidity. 
6. Degree of Unsaturation:- This is an important criteria for oxidative rancidity and reversion. Oils containing high proportions of unsaturated fatty acids and shortenings made from such oils show flavour reversion. Oils with high proportions of linolenic and linoleic acids revert. Oils with unsaturated fatty acids turn rancid. 
7. Absence of Antioxidants:- The natural presence or addition of antioxidants to oils prevents rancidity. Vitamin E or tocopherol is naturally present in vegetable oils and acts as an antioxidant preventing auto-oxidation of oil. The antioxidant takes up oxygen and gets oxidized, thereby preventing rancidity. 

Prevention measures:-

• Store fat at low temperatures in a cool, dark place. 
• Use airtight containers. Keep minimum headspace.
• Do not keep strong smelling foods in the vicinity of fats and oils as they absorb foreign odours and get tainted. 
• Copper containers and rusted iron accelerate rancidity. Only steel or aluminium should be used. 
• Avoid undue exposure to light and air. Expose minimum surface area. 
• If antioxidants are added to fats rich in unsaturated fatty acids, oxidative rancidity can be significantly delayed. Tocopherol (Vitamin E) and lecithin are antioxidants naturally present in some oils. 
• If fats and oils have to be stored for sometime, they should be hydrogenated and stored. Hydrogenation increases the shelf life of fats and prevents rancidity. 

(C.) Flavour Reversion:-

                Many fats and oils undergo a change in flavour before becoming rancid. This change in flavour which is very different from the rancid flavour is called reversion. In rancidity the change in flavour is the same for all fats. But in reversion the flavour may be buttery, beany, grassy, painty, and fishy. Reversion is seen in fish oils, linseed, and soya been oil. Very small amounts of oxygen are required as compared to oxidative rancidity. 

(D.) Refining, Hydrogenation & Winterization:-

Refining:- The oil extracted by rendering, pressing, or solvent extraction is called crude oil. It may contain undesirable constituents such as gums, free fatty acids, pigments, cellular material, and odorous compounds such as aldehydes, ketones, and essential oils. 

Crude oil needs several types of treatment to extend its shelf life and make it suitable and pure for use.

Steps in refining oil are as follows:

1. Settling-- The cell debris is allowed to settle down and is removed by filtration. 
2. Degumming and neutralization-- The gum and free fatty acids present are removed by steam distillation. Steam is passed through hot oil under pressure. Water-soluble low-molecular-weight fatty acids which are volatile are removed.                          Hot oil is treated with sodium hydroxide or sodium carbonate. The free fatty acids saponify and soap is separated out. This step is called alkali refining. 
3. Bleaching-- This step removes undesirable colouring and flavouring contaminants. Pigments are removed by filtering the oil through activated charcoal till it is light in colour.
4. Steam deodourization-- Steam is injected into the hot fat under pressure. Low molecular weight aldehydes, ketones, peroxides,and free fatty acids are removed. The oil is cooled rapidly. 

Hydrogenation of oils:- Liquid oils can be converted to solid fats by a process known as hydrogenation. In this process, hydrogen is added to unsaturated fatty acids. Some unsaturated fatty acids become saturated and the melting point of the fat increases.

         The hot oil and finely divided nickel catalyst is stirred together under an atmosphere of hydrogen. Hydrogen is introduced under pressure so that maximum is dissolved in oil. The oil and catalyst are heated under vaccum. The reaction is continued till the desired consistency of fat is obtained. The oil is cooled, filtered to remove the catalyst, and chilled rapidly. By chilling, small crystals are formed and the fat gets a grainy texture. 

Hydrogenation is utilized in the manufacture of a wide variety of fats such as vanaspati and margarine. These can replace costly animal fats such as butter and clarified butter. The hardness of a fat depends on the degree of hydrogenation. Sometimes additives, such as antioxidants, monoglyceride, and vitamin A and vitamin D, are added to the fat. Air may be whipped in to impart a snow white colour. 

            Palm oil, palmolein, rice bran, cotton seed, sunflower, maize, soya bean, groundnut, and sesame oil are generally hydrogenated. 

Winterization:- After steam deodourization, the oils are chilled rapidly without stirring so that large filterable crystals are formed. These crystals are composed of high molecular weight triglycerides which have a high melting point. They are separated out by filtration and the cold viscous oil obtained is said to be winterized.

                 Winterized oil does not turn cloudy or solidify in the refrigerator. It is suitable to be used in foods which require refrigeration, e.g.,salad dressings and mayonnaise which can be poured even when chilled. It is an important step in refining oil. Olive oil is not winterized or deodourized as desirable flavour is lost in these processes. 

(E.) Effect of heating on fats & oils with respect to smoke point:-

During cooking or prolonged heating of fats and oils certain changes are seen:

1. There is an increase in the free fatty acid content 
2. Smoke point is lowered 
3. Iodine number decreases
4. Melting point falls
5. Fat turns darker in colour 
6. Fat gets polymerized
7. Refractive index increases.

All these changes influence the overall quality of food. These changes are faster when the cooking temperature is increased. 

(F.) Commercial uses of fats (with emphasis on shortening value of different fats):-

Fats and oils are used in the food industry because of their ability to

1. Increase tenderness and make the product short 
2. Form emulsions
3. Spread and be plastic 
4. Fry or cook food 
5. Get creamed and form foams
6. Impart flavour, aroma,and colour to food.

Fats available in the market are specially manufactured for a variety of applications. Separate hydrogenated fats are available for each of the following:

1. Crispness of biscuits 
2. Puff pastry and kharis for excellent layer separation, i.e.,highly plastic variety available as vanaspati or as margarine 
3. Soft and tender cakes with high volume 
4. Softer bread with easy dough handling 
5. Cream filling for cakes and biscuits 
6. Crunchy cookies and biscuits 
7. Easy release of baked products from the baking pan.

Shortening Power:-

                  Superglycerinated or high ratio shortenings are specially manufactured to achieve a desired consistency by hydrogenation of oil. Mono and diglycerides are added to improve the emulsification ability of the shortening in batters and doughs. The amount of water and sugar used in a recipe can be increased and these are used to produce high ratio cakes of sufficient strength. The usual sugar:flour ratio is 1:1, but with high ratio shortenings it is possible to prepare cake with a 1:4:1 ratio. Antioxidants are generally added to prevent the development of rancidity. 

                  These shortenings are not suitable for deep fat frying as they have a lower smoke point. Mono and diglycerides added are glyceryl monostearate (GMS) and glyceryl monooleate (GMO) which help in softening the crumb, reduce spattering in margarine when it is heated, and are good emulsifying and stabilizing agents. 

Key Terms:-

• Antioxidant:- A compound that is oxidized very readily. Thus, preventing unsaturated fatty acids from getting oxidized quickly. 
• Auto-oxidation:- Oxidation reaction which is auto-catalytic and continuous easily once it begins with little added energy. 
• Bleaching:- A step in refining oil in which oil is filtered through charcoal to remove colouring and flavouring matter.
• Hydrogenation:- Addition of hydrogen to an unsaturated fatty acid in the presence of a catalyst to increase saturation and melting point. 
• Neutralization :- A step in refining to remove free fatty acids from oils.
• Polyunsaturated fatty acids:- Fatty acids containing two or more double bonds between the carbon atoms in the carbon chain. 
• Rancidity:- Development of off-flavours and odours in fats because of oxygen, lipases, heat,etc.
• Rendering:- Process by which fat is extracted from animal tissues using dry or moist heat.
• Triglycerides:- Esters of glycerol with three fatty acids to form a simple fat.
• Unsaturated fatty acid:- Fatty acids having one or more double bonds in the carbon chain. 
• Winterization:- Removal of high molecular weight triglycerides with high melting points by chilling the oil, so that oil remains clear and pourable at refrigeration temperature.