Physical Changes
Physical changes alter a nutrient’s form, texture, or structure without changing its chemical composition.
- Texture and form: grinding or chopping increases surface area, which can affect nutrient absorption during digestion. Soluble nutrients, like some vitamins and minerals, can dissolve in water or other liquids.
- Phase changes: heating fats melts them from solid to liquid, and freezing reverses this — these changes don’t alter the chemical makeup of the fat. Boiling can cause water (with dissolved nutrients) to evaporate, concentrating the remaining nutrients.
- Emulsification: mixing oil- and water-based ingredients, such as in making a dressing, affects how nutrients disperse and become available.
Chemical Changes
Chemical changes alter the actual structure of nutrients, which can affect nutritional value, flavour, and safety.
- Nutrient degradation: water-soluble vitamins like Vitamin C and B vitamins can break down from heat, light, and oxygen — boiling vegetables, for example, can cause significant Vitamin C loss.
- Oxidation: fats and some vitamins can oxidize when exposed to air, light, or heat, causing spoilage — unsaturated fats can turn rancid.
- Maillard reaction: a browning reaction between amino acids and sugars during high-heat cooking, responsible for the flavour and colour of roasted meats and baked goods.
- Caramelization: heating sugars changes their flavour and colour, distinct from the Maillard reaction.
- Denaturation: cooking causes proteins to lose their original structure — for example, cooking an egg turns its proteins from liquid to solid, making them more digestible.
- Hydrolysis: breaking complex nutrients into simpler forms using water, such as starches breaking down into simpler sugars during digestion.
- Lipid oxidation: unsaturated fats oxidizing into rancidity, producing off-flavours and reducing nutritional quality.
Why This Matters
Physical changes can make nutrients more accessible for absorption, while chemical changes can enhance or reduce nutrient availability. Prolonged cooking or heat exposure can cause vitamin and mineral loss, while reactions like the Maillard reaction and caramelization develop flavour and texture. Some chemical changes can also affect food safety — for example, overcooking fats can produce harmful compounds, and oxidation can lead to spoilage.
