The acid in the lime juice denatures the protein in the fish, causing it to appear cooked. Denaturation is a process in which the structure of proteins is altered, leading to a change in their physical properties. In this case, when the fish is marinated in lime juice, the acid alters the protein structure in a way that gives the appearance and texture of cooked fish, even though it was never exposed to heat.
Denaturation occurs due to the disruption of hydrogen bonds and other non-covalent interactions within the protein molecules. This change in structure affects the way the proteins interact with water molecules, leading to a firmer texture similar to that of cooked fish.
Therefore, the correct answer to the question is: the acid in the lime juice denatured the protein in the fish causing it to appear cooked.
