There are many varieties of perservaties such as...
-Calcium benzoate (Typical products include fruit juice)
-Ethyl para-hydroxybenzoate (Typical products include beer, fruit preserves and juices, sauces, flavouring syrups, fruit deserts, processed fish)
-Sulphur dioxide (Typical products include wine, flour, beer, dough products, fresh fruit, dried fruit, fruit fillings and deserts, etc)
-Potassium metabisulphite (Typical products include wine, frozen vegetables, fruit juice, fruit preserves, pickles, frozen shellfish)
-Hexamethylene tetramine, Hexamine (Typical products include marinated fish)
-Dimethyl dicarbonate/Potassium nitrite (Typical products include processed meats, cured and smoked meat and fish, root vegetables)
And the list goes on...
Unless you grow all your food in your own garden and prepare all your meals from scratch, it's almost impossible to eat food without preservatives added by manufacturers during processing. Without such preservatives, food safety problems would get out of hand, to say nothing of the grocery bills. Bread would get moldy, and salad oil would go rancid before it's used up.
Preservatives serve as either antimicrobials or antioxidants-- or both. As antimicrobials, they prevent the growth of molds, yeasts and bacteria. As antioxidants, they keep foods from becoming rancid, browning, or developing black spots. Rancid foods may not make you sick, but they smell and taste bad. Antioxidants suppress the reaction that occurs when foods combine with oxygen in the presence of light, heat, and some metals. Antioxidants also minimize the damage to some essential amino acids--the building blocks of proteins--and the loss of some vitamins.
Hope this helps mate...cheers