When a piece of bread is chewed it tastes sweet because

Sea water tastes saltish because

Why does a piece of bread start tasting sweeter after chewed for some time?

Why does a piece of bead start tasting sweeter after chewed for some time?

Many carbohydrates are sweet because

Tilak left a piece of bread on the table. Next day it becomes black. The reason 1) fungal growth appears 2) Rhizopus appeas on the bread 3) Bacterial growth apperas 4) Virus affects the bread