Final answer:
Undercooked meringues result in proteins that fail to denature and coagulate properly, thus remaining largely unchanged rather than forming the desired airy and crisp texture of a properly cooked meringue.
Step-by-step explanation:
When meringues are undercooked, the proteins in them do not coagulate properly because they have not been exposed to sufficient heat. Proteins need to be heated to a certain temperature in order to denature, a process where their structure is altered and they can then coagulate into a new, more rigid structure, which is what gives properly cooked meringues their distinctive airy and crisp texture. If meringues are undercooked, the proteins do not fully denature; instead, they may partially denature or remain largely unchanged. They will not break down into amino acids as that requires further degradation. Thus, the correct answer to the question is They remain unchanged which means the proteins do not coagulate properly.