Sodium benzoate (Molecule of the Month for September 2007)
Sodium benzoate is used as a preservative. It is not bactericidal, only bacteriostatic. It has fungistatic activity. It is effective only in acidic conditions (pH less than 3.6) making its use most prevalent in foods such as preserves, salad dressings (vinegar), carbonated drinks (carbonic acid), jams (citric acid), fruit juices (citric acid), pickles (vinegar), and Chinese food sauces (soy, mustard, and duck). It is also found in alcohol-based mouthwash and silver polish. Sodium benzoate is used in many soft drinks. It is found naturally in cranberries, prunes, greengage plums, cinnamon, ripe cloves, and apples. Concentration as a preservative is limited by the FDA in the U.S. to 0.1% by weight though organically-grown cranberries and prunes can conceivably contain levels exceeding this limit.
It is also used in fireworks as a fuel in whistle mix, a powder which imparts a whistling noise when compressed into a tube and ignited.
A study commissioned by the UK's Food Standards Agency found that when used in a mixture of other preservatives and colourants, increased levels of hyperactivity in children were observed.
Update by Karl Harrison
(Molecule of the Month for September 2007 )