kinds of acids, and several different kinds
of alcohol. The acids may be either tart
substances in the cell fluids or vacuole —
acetic acid, cinnamic acid — or fatty-acid
portions of oil molecules and the
molecules that make up cell membranes:
hexanoic acid, butyric acid. The alcohols
are usually by-products of cell metabolism.
Fruits have enzymes that join these basic
cell materials into aromatic esters. A
single fruit will emit many esters, but one
or two account for most of its
characteristic aroma. Some examples:
ethyl alcohol + acetic acid = ethyl acetate,
a characteristic note in apples
hexyl alcohol + acetic acid = hexyl acetate
in pears
ethyl alcohol + butyric acid = ethyl
butyrate in pineapple
isoamyl alcohol + acetic acid = isoamyl
acetate in bananas