CHEMICALS THAT MAKE UP FATS AND ITSFUNCTIONS Carbon Hydrogen OxygenFunctions Energy – 1g of pure fat provides 37KJ (9kcal) Formation of Adipose tissue – used as an Energy reserve, Insulates and Protection Source of essential fatty acids Fat soluble vitamins: A,D,E,K
SOURCES OF FAT Meat and Fish Confectionary Processed Foods Butter, Margarine, Lard Egg Yolk (Contains Cholesterol)Uses of Food Production Creaming and Aerating Frying Shortening
CHEMICAL STRUCTURE Fat belongs to a group of substances called Esters. Formed by the reaction between an alcohol and organic acid – known as fatty acids Glycerol is a complex alcohol because it has 3 hydroxyl groups therefore known as a Trihydric Alcohol.
CHEMICAL STRUCTURE CONT. Ester formed is a triglyceride. If all 3 fatty acids are the same, then Simple Triglyceride is formed. If fatty acids are different then they are called Mixed Triglyceride. Fatty acid Formula = R- COOH (‘R’ represents any acid).
CIS AND TRANS FATTY ACIDSCIS 2 hydrogen atoms on the same side of a double bond.Trans Hydrogen atoms on geometrically opposite sides of the double bond.
SATURATED FATS Occur when each carbon atom is attached to the surrounding atoms by a single bond. The carbon atoms are completely saturated with hydrogen atoms. Saturated fats have a melting point at about room temperature and are therefore usually hard – Could lead to heart disease and high cholesterol.
SATURATED FAT STRUCTURE Hydrogen Atom Carbon Atom
UNSATURATED FATS Occur when some of the carbon atoms are joined to the surrounding hydrogen atoms by a double bond. Monounsaturated fats have one double bond. Polyunsaturated fats have more than one double bond. Unsaturated fats are mainly oils and have a melting point at below room temperature.Saturated Fatty Acid Monounsaturated Polyunsaturated Fatty Acid Fatty AcidPalmatic Acid Oleic Acid Linoleic AcidStearic Acid Linolenic Acid
PROPERTIES OF FATS AND OILS SolubilityFats and oils are insoluble in water.However, in the presence of a suitable substance known as an emulsifying agent, it’s possible to form a stable mixture of fat and water Emulsion.The Emulsion may be a Fat – in – Water emulsion e.g. MilkOr a Water – in – Fat emulsion e.g. ButterFats and oils are soluble in organic solvents such as petrol and carbon tetrachloride.Solvents of this type can be used to remove grease and stains from clothing.
PROPERTIES OF FATS AND OILS PlasticityFats do not melt at fixed temperatures, but over a range of temperatures.This is because fats are mixtures of triglycerides (contain 3 different fatty acids), all with different melting points.Some of the fatty acids forming the triglyceride will stay solid for longer than others.This feature gives fat its plasticity that makes some fats spreadable.E.g. Margarine – Has a wide range of plasticity and will spread from the fridge whereas most animal fat will have narrow plasticity and will not spread easily.
PROPERTIES OF FATS AND OILS Effect of HeatOils and fats transfer heat well to foods being cooked but will eventually breakdown.Heating causes the triglycerides to decompose. Melting PointFats melt when heated. Since fats are mixtures of triglycerides they do not have a distinct melting point but melt over a range of temperatures.Temperature when melting occurs is known as the Slip Point.Most fats melt at temperatures of 30 /40 CMelting point for oil is below normal air temperature – The more double bonds, the lower the air temperature.
PROPERTIES OF FATS AND OILS Smoke PointWhen a fat or oil is heated to a certain temperature it starts to decompose, producing a blue haze or smoke.Most fats and oils start to smoke at 200 CSmoke Point for lard = 185 CCorn Oil = 232 CIn general, vegetable oils have a higher temperature than animal fats.Smoke is useful to measure when assessing the suitability of a fat or oil for frying purposes.Repeated heating of a fat or oil will reduce the smoke point.
PROPERTIES OF FATS AND OILS SaponificationSome triglycerides react with alkalis to form soap and a glycerol. HydrogenationSome oils are so unsaturated in the natural state that they need to be treated to make them useful in food.Hydrogenation is used to add hydrogen to the oil to break the double bonds. This makes the resulting fat more saturated and harder.It is achieved by heating the oil in a large sealed vessel under pressure.Hydrogenated fat makes TRANS fats which increases likelihood of cancer and free radicals in the body.
RANCIDITY Used to describe the spoilage of fats and oils. Fat which is rancid will have an unpleasant smell and flavour. Oxidative RancidityReaction between unsaturated triglycerides and oxygen from the air.Oxygen molecules join across the double bond of the triglyceride molecule and a variety of compounds are formed e.g. Aldehydes and Ketones – gives the unpleasant rancid taste.Reaction is accelerated by heat, light and traces of metals e.g. copper/ iron.
RANCIDITY CONT…Hydrolytic RancidityEnzymes known as lipase hydrolyse fats, breaking them down into glycerol and fatty acids.EquationFat + Water Glycerol + Fatty AcidsShort Chains = More rancid
HOW TO STOP RANCIDITY Keep fats free from oxygen and air. Keep metals and light away from fats. Do not store oil in iron containers use glass! Salt speeds up rancidity. Sugar slows down rancidity. Anti-oxidants can be used to slow rancidity.
USES IN FOOD PREPARATION FryingFast cooking method – bad for health as it increases fat content, but tastes good.Frying occurs at 180 C ShorteningIt’s an effect that fat has on a product – increases the crumbly texture of foods.Stops the formation of effects of gluten.Fat coats the flour preventing water making the flour stretchy. Creaming and AeratingAdding air bubblesLighter colourIncreases volume – it rises due to trapped air.
PRODUCTION OF FATS AND OILS Vegetable Oils70% of all oils in the world are vegetable oilsIt increases polyunsaturated fatty acids (PUFA). MargarineAn emulsion of water and fat.The vegetable fat being used is first hydrogenated to give it some hardness (plasticity), and is then blended with skimmed sour milk, salt, colouring and Vitamins A and D (added by law).Hard margarines are more hydrogenated then soft ones.
PRODUCTION OF FATS AND OILS Spreads and Low Fat SpreadsLess then 80% fatIncrease water content – not suitable for cooking. Cooking fats and ShorteningFirst produced in USA as a substitute for lard and are pure fat products rather than emulsions.Blended with fish oils, animal fats and are hydrogenated.These fats are called High Ratio Fats and are designed for recipes e.g. Muffins
PROPERTIES OF FATS AND OILS CONT… LardExtracted from pigs via heating OR ‘rendering’.Almost 100% fat ButterChurning of pasteurised cream, this causes the cream to become more viscous forming a solid butter.Colour and salt is added to butter and is mixed for desired consistency. SuetFat from around the kidneys of animals.Sold in the form of shredded suet and used in Christmas puddings and Suet puddings.
CHOLESTEROLA waxy white substance found in fats, particularly hard animal fats which can block arteries and be one of the causes of heart disease.Cholesterol is carried around the body by specific proteins which come together to form a lipid – protein complexes called Lipoproteins.High-density Lipoproteins (HDL) is beneficial because it transports cholesterol from places where there is too much, to the liver where it is disposed of.Low-density Lipoproteins (LDL) can lead to deposits in the arteries (plaque) which causes narrowing.
ESSENTIAL FATTY ACIDSEssential means that these substances cannot be made in the body so must be gained from food sources. Two main types of essential fatty acids (EFA) are:Polyunsaturated Fatty Acids (PUFA) – Linolenic and Linoleic acid.Longer chain fatty acids: Arachidonic acid, EPA and DHA (these can be made in the body to a limited extent by linoleic acid and alpha linolenic acid) EFAs are needed for:The maintenance of cell membranes.Hormone like substances called Eicosanoids (prostaglandins etc) which are involved in clotting blood.