Canned food, particularly acidic food, can often suffer from problems where chemical reactions
occur between the food and the can. This at best may cause discolouration of the food and at worst may raise the level of metal oxides
in the food to unacceptable levels.
For this reason many cans use an interior coating of enamel
to prevent contact between the food and the metal. Coatings used may include oleoresins
It should be noted however that a recent WWF
Toxics Programme Report (http://www.panda.org/toxics/downloads/bisphenol.pdf) raised the spectre of Bisphenol A
a known endocrine
disruptor leeching into food from some of these coatings.
I dont know they they are white - aesthetics? or perhaps they are just white