Chemicals, natural or artificial, that prolong shelf life and improve the palatability of food. They fall into two broad categories: antimicrobials (which thwart the growth of the microorganisms of spoilage) and ANTIOXIDANTS (which prevent oxidation and thus any discoloration or rancidity due to it). Under food-labeling laws, all preservatives (with the exception of SALT, sugar, vinegar and certain spices) must be listed not only by name but also by function. For example: CALCIUM PROPIONATE (to retard mold).