Humans have salivary amylase in their saliva to break starch into sugars.
Certainly in the deep evolutionary past cats and dogs did not eat starches. Many mammals have salivary amylase but dogs do not and neither do cats, agrees the Waltham Centre for Pet Nutrician in Moscow, Russia. Digestion of starch begins in the mouth for species, like humans, whose saliva contains amylase. Many dogs bolt their food and maybe lack amylase for this reason. Dogs and cats digest starches in the small intestine where they use amylase produced in the pancreas.