Changing properties: protein
Denaturation and Coagulation of Protein
Protein-rich foods, such as eggs and meat, undergo significant changes when cooked. Two of these changes are denaturation and coagulation.
Denaturation occurs when the protein’s structure unravels. This action exposes the protein’s peptide chains. Heat, as well as other factors such as acidity or salt, can cause denaturation. Remember that denaturation is a physical change, not a chemical one.
Coagulation follows denaturation. The exposed peptide chains bond together and the liquid protein hardens or sets into a solid mass. Coagulation typically happens between 60°C and 70°C for most animal proteins.
Maillard Reaction and Caramelisation
When cooking proteins at high heat, two other reactions can occur: the Maillard Reaction and Caramelisation.
The Maillard Reaction is a chemical reaction between reducing sugars and protein’s amino acids that gives browned, flavourful foods their distinctive taste. It requires a temperature of 140°C to 165°C. This reaction is responsible for the crust on a loaf of bread, the golden-brown colour of fried onions, and the dark edges of a cooked steak.
Caramelisation is the oxidation of sugar, a process used extensively in cooking for the resulting nutty flavour and brown colour. It occurs at temperatures above 180°C, and is seen in foods like caramel (as the name suggests) and roasted coffee.
Gelatinisation of Protein
-Gelatinisation is simply the process where raw protein transforms into gel, a process we see when cooking egg whites. It shouldn’t be confused with ‘denaturation’, which is a change in the protein’s structure, or ‘coagulation’, which is the setting of proteins to form a network.