Question: During prayers, is it permissible to eat and drink or to swallow the crumbs left in the mouth?

Answer: Eating and drinking while praying invalidates it, whether it is a little or a lot, but swallowing the food particles that remain in a corner of the mouth or sucking on a little bit of sugar or cube sugar that exists in the mouth does not invalidates it.
Also, if he eats or drinks something inadvertently or out of forgetfulness, provided that it does not disturb his state as a praying person, the prayer will not be void.