iGCSE Food Technology: The Functions and Properties of Food: Starch and Sugars Starch There are two types of carbohydrates: ● Starch – found in bread, flour, potatoes, rice ● Sugars – found in fruits, drinks, honey Types of starches: ● Wheat flour ● Corn flour ● Arrowroot Functions of Starches: ● Bulking agent: flour is often the main ingredient in many food products and is called the bulk ingredient. The starch forms the main structure of the food product (e.g flour is added in a cake to thicken the wet ingredients so it can be baked.) ● Gelling agent: After full gelatinization, the liquid sets and forms a gel. When reheated the gel reverts back to its liquid state. (e.g custard) ● Thickening agent: Raw starch tastes floury and needs to be cooked. When starches are heated in a liquid, they expand and absorb the liquid. The starch granules swell and burst. This is called gelatinization: ○ Starch particles do not dissolve in liquid – instead they form a suspension ○ When heated in a liquid, at 60°c the starch granules begin to absorb the liquid ○ At 80°c the starch would have absorbed about 5 times their volume in water until they burst and thicken the liquid. The mixture becomes viscous. ○ Gelatinization is complete when the liquid reaches its boiling point. ○ As the mixture cools, it thickens further – forming a gel. Examples of gelatinization: ● Flour is added to butter to make a roux for a white sauce ● Arrowroot is added to fruit juice for a glaze ● Corn flour is used for many dishes such as sweet and sour pork Modified Starches (Smart Starches): are starches that have been modified to perform other functions. ● Used to thicken foods when boiling water is poured over (e.g cup-a-soup) ● Pre-modified starches do not need heat to thicken (e.g instant desserts – jellies, custard, instant whip) Sugars Sugars come from sugar beet (grows in cool countries such as the UK) and sugar cane (which grows in hot climates such as the West Indies) Types of sugars: Type of sugar Description Uses Granulated Most commonly used. White medium sized Sweetening drinks.
crystals. Caster Small white crystals that dissolve quickly. Baking. Icing Fine white powder that dissolves almost instantly. Cake decorating and icings. Confectionary. Demerara Large, light brown crystals. Toppings on puddings (e.g crumbles) Muscovado Dark brown, soft, stickycrystals with a strong, slightly smoky flavor. Gingerbread, fruit cake, puddings. Functions of sugar: ● Sweetens ● Preserves food: large quantities make an unsuitable environment for bacterial growth. Also used in jams and chutneys as it contain pectin. ● Bulking agent: gives a characteristic texture to food ● Aerates: traps air when beaten with butter or eggs to give food a light texture ● Keeps food moist ● Stabilizes: strengthens whisked mixtures (e.g meringues) ● Color: when sugar is heated it turns brown – caramelisation Sugar Substitutes: In response to healthy eating habits, a demand for low calories sugar substitutes have risen. These include: ● Honey ● Artificial sweeteners (e.g Stevia, Splenda) ● Agave nectar