Food Chemistry and Nutrition
This domain tests food composition, chemical changes during processing, and basic nutrition calculations. Expect questions on macronutrients, micronutrients, water activity, browning, lipid oxidation and vitamin losses.
Core rules and concepts
- Energy factors: protein 4 kcal/g, fat 9 kcal/g, carbohydrate 4 kcal/g; alcohol supplies 7 kcal/g.
- Maillard browning occurs between reducing sugars and amino groups under heat; caramelization involves sugars alone.
- Lipid oxidation produces rancidity; light, heat, oxygen and trace metals accelerate it. Antioxidants and low oxygen slow it.
- Protein denaturation changes structure without necessarily changing nutritive value; it affects texture and water holding.
- Water activity (aw) measures available water, not total moisture. It predicts microbial growth better than moisture percentage.
- Vitamins differ in stability: vitamin C and thiamin are heat-labile; riboflavin is light-sensitive; fat-soluble vitamins can oxidize.
Worked example
A 100 g food sample contains 10 g protein, 20 g fat and 60 g carbohydrate. Energy = (10 × 4) + (20 × 9) + (60 × 4) = 40 + 180 + 240 = 460 kcal. The remaining 10 g is water, ash and fibre, which are not counted using these factors unless the label method specifies otherwise.
Traps that cost marks
- Using 4 kcal/g for fat instead of 9.
- Treating moisture percentage as water activity.
- Assuming all browning is Maillard; caramelization is sugar-only.
- Ignoring that frying adds fat and changes the energy calculation.
- Assuming heat always destroys all vitamins equally.