How do food preservatives work?

Perservatives work in several different ways. One way is to create a chemical environment that is not conducive (is not good) for bacterial growth. Salt asorbs water and creates a high salt concentration. Since cell walls are permiable and there will be a concentration gradient between the inside and outside of the cell, salt will create diffusion across the membrane. Pickling involves creating a basic chemistry, high pH, which influences movement of ions across the cell membrane. Dehydration preserves food because cells loose water thru the wall. Exposure to radiation preserves food because ithe high energy atomic particles destroy the living cells structures. I hope this helps.