Which of the following processes results in both solidification and texture change in proteins?

Coagulation is the process that leads to both solidification and a change in texture in proteins. When proteins are subjected to heat or acid, their structures unfold and then bond together, resulting in solidification. This change in the protein's structure alters its texture, typically making it firmer. This is particularly evident in cooking processes, such as when eggs are heated; they transform from a liquid to a solid state, demonstrating both a physical change in texture and the formation of a firmer structure through coagulation.

In contrast, emulsification primarily involves the mixing of two immiscible liquids (like oil and water) and does not directly deal with protein structure or texture changes. Bulking refers to adding ingredients to increase the volume or mass of food, often without changing the properties of protein. Colouring entails the addition of substances to enhance the appearance of food, which is not related to the structural changes of proteins. Therefore, coagulation is unique in its ability to affect both the solidification and textural changes of proteins.