Final answer:
Umami is an indicator of protein due to the relationship between the umami taste and foods rich in proteins, particularly those containing the amino acid L-glutamate.
Step-by-step explanation:
The taste known as umami is often referred to as the savory taste, which is a result of activating G protein-coupled receptors by the amino acid L-glutamate. This unique taste is significantly associated with foods that are rich in proteins. When answering the question ‘Umami is...’, the correct option is E: Indicator of protein. As for the evolutionary advantage of recognizing the umami taste, the answer is C: Umami identifies foods that might contain essential amino acids. Such a capability likely evolved to help our ancestors identify and select protein-rich foods, which are crucial for body growth, repair, and various bodily functions.