Food Chemistry and Nutrition Basics
Scope of the domain
This domain tests the chemistry behind food behaviour and the nutrition basics a processing operator must control: water, carbohydrates, proteins, fats, vitamins, minerals, pH and water activity.
Core rules and concepts
- Water is the major component. Water activity (aw) measures available water for microbial growth, not total moisture. Most bacteria need aw above about 0.90; moulds can grow at lower aw.
- Carbohydrates include sugars, starch and fibre. Starch gelatinises on heating with water and retrogrades on cooling, causing staling. Reducing sugars react in Maillard browning.
- Proteins contain essential amino acids, denature on heat or acid, and can gel or form emulsions. Denaturation is not the same as digestion.
- Fats may be saturated or unsaturated; oxidation causes rancidity. Emulsifiers stabilise oil-in-water or water-in-oil systems.
- Vitamins: water-soluble vitamins such as vitamin C are heat-, light- and oxygen-sensitive; fat-soluble vitamins A, D, E and K are more stable in fat but can oxidise.
- pH controls enzyme activity, microbial growth and gel formation.
Worked example
A baker brushes milk on a bun before baking and obtains a brown crust. A sugar syrup heated alone also browns. Distinguish the reactions. Reasoning: milk supplies lactose, a reducing sugar, and casein, an amino group; heat produces Maillard browning. Sugar alone lacks amino groups, so heating produces caramelisation. Both need heat, but only Maillard needs protein or free amino acids.
Traps that cost marks
- Equating moisture content with water activity; a dry-looking food can still support mould if aw is high.
- Saying caramelisation needs protein; it does not.
- Treating all vitamin loss as equal; vitamin C loss depends on heat, oxygen, light and leaching.
- Confusing protein denaturation with protein breakdown into amino acids.