What is an example of a preservative?

A preservative is a substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes.
Some examples are:
Antimicrobials, such as lactic acid, nitrate, nitrite, and hydroxybenzoate.
Oxidation prevention preservative, such as ascorbic acid sodium ascorbate and butylated hydroxytoluene.
Natural (non synthetic) preservatives, such as ascorbic acid, citric acid, salt, and vinegar.

For more information visit http://en.wikipedia.org/wiki/Preservative