The stomach is very acidic (pH = 2-3). So
all food gets an acid bath. Most of the
breakdown on the molecular level is done by
enzymes. Each type of enzyme has a range of pH
where it works best. For example, saliva contains
an enzyme that breaks starch down into sugar
(salivary amylase). When swallowed, the enzyme is
denatured (destroyed) in the stomach. More amylase
is added in the small intestine to continue the
breakdown of starch.
When food is headed for the stomach, the
stomach increases the acid output. Tasting,
smelling, or even thinking about food gets the
acid production up.
Thanks for asking,