Carbohydrates — AQA GCSE Food Preparation and Nutrition

Carbohydrates are essential macronutrients divided into sugars, complex starches, and dietary fibre, providing the body with its main source of energy yielding 4 kcal per gram. Government dietary guidelines advise that 50% of daily food energy should come from carbohydrates, with free sugars restricted to a maximum of 5% to reduce risks of obesity, type 2 diabetes, and tooth decay.

Carbohydrates are one of the three primary macronutrients required by the human body, providing 4 kcal (17 kJ) of energy per gram. In the AQA Food Preparation and Nutrition specification, this topic explores the nutritional classification into simple sugars, complex starches, and non-starch polysaccharides (dietary fibre), as well as the physiological impacts of deficiency and excess.

Beyond human nutrition, studying carbohydrates is fundamental to understanding practical food science. Students investigate critical culinary working characteristics including gelatinisation in sauces, dextrinisation in baked goods, and caramelisation in confectionery, linking chemical structures to the sensory and structural qualities of prepared dishes.

• →Classification: Monosaccharides (glucose, fructose, galactose), disaccharides (sucrose, lactose, maltose), and polysaccharides (starch, glycogen, cellulose/dietary fibre, pectin).
• →Energy value and dietary targets: Provides 4 kcal/g; government guidelines state 50% of daily dietary energy should be derived from total carbohydrates, with a maximum of 5% from free sugars.
• →Dietary fibre (NSP): Recommended intake of 30g daily for adults to stimulate peristalsis, prevent diverticular disease, lower blood cholesterol, and aid gut satiety.
• →Functional properties of starch: Gelatinisation occurs in moist heat (swelling at 60°C, bursting at 80°C, complete thickening at 100°C); dextrinisation occurs under dry heat via starch breakdown into shorter dextrin molecules.
• →Functional properties of sugar: Caramelisation occurs when pure sugar is heated above its melting point (around 160-180°C), causing oxidation, browning, and nutty flavour development.

• 💡Always state exact temperatures when explaining starch gelatinisation: 60°C (swelling), 80°C (granules burst/rupture), and 100°C (boiling point/complete thickening).
• 💡Use accurate terminology such as 'intrinsic sugars' and 'free sugars' instead of colloquial terms like 'good sugars' and 'bad sugars'.
• 💡When explaining dietary excess, always link excess carbohydrate intake to energy balance: unutilised glucose is converted into glycogen and then stored as adipose tissue, leading to weight gain and obesity.

• Believing dietary fibre provides substantial energy: Dietary fibre cannot be digested by human digestive enzymes in the small intestine, meaning it contributes minimal usable energy (approx. 2 kcal/g via colonic fermentation) and functions primarily for gastrointestinal motility.
• Confusing caramelisation with the Maillard reaction: Caramelisation involves the thermal decomposition of sugars alone under high heat, whereas the Maillard reaction is a chemical reaction between reducing sugars and amino acids in proteins.
• Assuming all sugars must be avoided: Intrinsic sugars within intact cellular structures of whole fruits and vegetables are packaged with micronutrients and fibre, meaning they are healthy components of the diet unlike free sugars.

1. 1Week 1, Days 1-2: Master the classification of carbohydrates by drawing branching diagrams separating monosaccharides, disaccharides, and polysaccharides with food sources.
2. 2Week 1, Days 3-4: Learn dietary recommendations (50% total carbohydrate, max 5% free sugars, 30g fibre) and write practice paragraphs linking dietary excess to obesity, dental caries, and type 2 diabetes.
3. 3Week 1, Days 5-7: Practice food science definitions and mechanisms: write step-by-step flashcards for gelatinisation, dextrinisation, and caramelisation.
4. 4Week 2, Days 1-3: Complete past paper calculation questions using the 4 kcal/g energy conversion factor alongside percentage daily energy calculations.
5. 5Week 2, Days 4-7: Tackle 6-mark and 8-mark extended response questions comparing starch performance in sweet and savoury cooking, checking against official AQA mark schemes.

• 📋Multiple choice / short recall questions: Testing chemical names of mono-, di-, and polysaccharides, daily fibre targets (30g), or energy values (4 kcal/g).
• 📋Data analysis and energy calculations: Calculating the percentage of total energy supplied by carbohydrate in a meal, or determining whether free sugar intake exceeds 5%.
• 📋Food science explanations (4-6 marks): Step-by-step descriptions of culinary processes such as starch gelatinisation in sauces or caramelisation in desserts.
• 📋Dietary evaluation extended response (6-8 marks): Assessing the suitability of a menu for individuals with specific health conditions such as type 2 diabetes, obesity, or constipation.