Food Science Principles: Nutrients, Food Chemistry and Food Properties
Nutrients and their chemical behaviour
A candidate must know the six nutrient classes (carbohydrates, proteins, lipids, vitamins, minerals, water), their energy yields (carbohydrate and protein about 17 kJ/g, fat about 37 kJ/g, alcohol about 29 kJ/g), and how each behaves during preparation. Distinguish macronutrients from micronutrients, and water-soluble vitamins (B group, C) from fat-soluble vitamins (A, D, E, K), because solubility predicts loss: water-soluble vitamins leach into cooking water and are heat-sensitive, while fat-soluble vitamins survive boiling but oxidise with heat, light and oxygen.
Food chemistry in the kitchen
Understand the chemistry behind observable change: gelatinisation of starch (heat plus water causes granules to swell and thicken), dextrinisation (dry heat breaking starch into shorter chains, as in toast), caramelisation (sugar browning without protein), the Maillard reaction (amino acids plus reducing sugars producing brown colour and flavour), denaturation and coagulation of protein (heat, acid or mechanical action), emulsification (lecithin in egg yolk stabilising oil and water), and aeration and foam formation. Gel formation by pectin and acid, and syneresis (weeping) when gels are over-cut or frozen, are common exam targets.
Food properties and sensory science
Know functional properties (solubility, viscosity, gelation, emulsification, water-holding capacity) and sensory properties (appearance, aroma, flavour, texture, sound). Sensory panels may be trained or consumer-based, and testing may be difference, ranking or hedonic. Traps include confusing denaturation (structure unfolds, usually irreversible) with coagulation (unfolded proteins set into a network), and confusing caramelisation with the Maillard reaction.
Rule of thumb
When asked to explain a change, name the molecule, the condition and the observable result: for example, 'heat and water cause starch granules to gelatinise, thickening the sauce'.
Worked example
A question asks why bread crust browns but a boiled dumpling does not. The crust browns through the Maillard reaction between reducing sugars and amino acids at high dry heat; boiling keeps the surface moist and below browning temperature, so the reaction cannot proceed.