Adding oxygen to a fat molecule makes the fat rancid. The presence of natural antioxidants in wine and chocolate (the latter having a lot of fat) prevents them from going off, and in particular, allows chocolate to remain fresh for years without refrigeration or special storage.
Where are antioxidants found?
Antioxidants are found naturally in red wine, chocolate, tea (particularly green tea), fruit (eg. apples, blackcurrants), soybeans and vegetables (eg. onions). Vitamins C and E are antioxidants, and so foods high in these vitamins have a significant antioxidant effect.
Function of antioxidants
The presence of antioxidants in red wine is said to explain the so called French paradox, in which the French have a low incidence of heart disease despite a high fat diet, because of their regular consumption of red wine with meals from an early age. Similarly, the Japanese have a low rate of heart disease and the longest average life span in the world with their consumption of green tea, but the Japanese also have a low fat diet, and consume more than an average amount of seafood.