Why does the brown part of a banana taste different than the rest?
Bananas break down starches (long chain sugars that we really can’t taste) into shorter chained sugars and flavor compounds as they age. The specific flavor compounds come from the plant’s enzymes and proteins, but is why young bananas, and some other fruits, have little flavor. Brown spots have accelerated the process to some level.
The brown spots you see on a banana are the glucose molecules from the banana condensing into one spot. These parts tend to taste sweeter and mushier than the rest of the yellow banana.