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FUNTIONS AND PROPERTIES OF FOOD THIS SECTION WILL LOOK AT THE FOLLOWING; • CARBOHYDRATES (STARCH AND SUGARS) • PROTEIN • FATS AND OILS Their functions in food products CARBOHYDRATES Job (function in the body) – Gives the body energy There are 2 types or carbohydrate; • Starches – found in flour, potatoes, pasta, rice and bread • Sugars – found in fruit, drinks and sweet baked goods Starch TYPES • Flour is high in starch • Cornflour and arrowroot are pure starch USES • Bulking agent – flour is often the main ingredient in many food products. The starch forms the main structure of the product e.g. pastry • Thickening agent – raw starch tastes floury and needs to be cooked. When starch is heated in liquid, the walls of the starch become soft and hollow and allow liquid to pass through them. This makes the granules swell until they burst. This process is called gelatinisation (see next slide) • Gelling agent – after gelatinisation the liquid forms a gel. On cooling the gel solidifies. When reheated it goes back to a liquid e.g. custard where cornflour is used STARCH - GELATINISATION Starch granules do not dissolve in liquid. Instead they form a suspension Suspension – a solid held in a liquid When heated at 60◦c, the starch granules begin to absorb the liquid and swell. At 80◦c the particles will have absorbed about 5 times their volume of water until they burst open and release starch, thickening the liquid. Gelatinisation is complete when the liquid reaches boiling point, 100◦c CARBOHYDRATES – FUNCTIONS OF SUGAR Preserves food. It creates unsuitable conditions for bacteria to grow e.g. in Jam Sweetens drinks and food e.g. coffee Flavour. It improves or changes the flavour by removing sour taste e.g. in tomato sauce Bulking agent. Gives the food texture e.g. ice cream and cakes Colour. When sugar is heated it turns golden brown. This is called caramelisation. Aerates. When sugar is beaten with butter or eggs it helps trap air to make cakes light Stabilises whisked mixtures e.g. meringue because it strengthens the foam Keeps food moist and extends shelf life PROTEIN Job (function in the body) – growth and repair in the body Protein foods are made up of amino acids that are linked together like the links in a chain. When protein foods are heated the links in the chain change and this alters the structure of the food. Example – a raw egg can change depending on if it is fried, scrambled or boiled. Bind – bind dry ingredients. When heated the eggs hold the ingredients together e.g. burgers Enrich – in sauces by adding colour and nutritional value USES OF EGGS Coagulation – setting a mixture to hold a frim structure e.g. quiche. Full coagulation happens at 70◦c Aerate – trap air when beaten e.g. cakes, meringue Coat/enrobe – the eggs act like a glue and hold dry coating to a surface e.g breadcrumbs Emulsify – eggs are used to stop oil and water separating; allowing an emulsion to form e.g. mayo Glaze – they add colour and give products a shiny glaze e.g. pastry Thicken – the protein sets when heated e.g. custard FATS AND OILS Job (function in the body) – Protection and insulation and gives some energy Fats are produced from 3 different sources; Animals Fish Vegetables Saturated Fats • Mostly found in solid fats e.g. butter • High in cholesterol compared to other fats Unsaturated Fats • Mostly found in fats that are liquid at room temperature. • Mainly in vegetable oils e.g. cooking oils • Less cholesterol than saturated fats Required to aerate food. When fat is creamed with sugar it helps trap air. Prevents lumps of flour forming in a sauce e.g. white sauce Adds flaky texture to pastry. Fat helps to separate layers by creating steam Shortens pastry to give it a crumbly texture – see Section A Function of Fats and Oils Acts as a cooking medium for roasting foods e.g. chicken Extends shelf life of baked products by keeping the product moist. Adds distinct flavours and odours to food e.g. buttery biscuits Adds colour and shine to food e.g. scones