Vitamin C and Cooking: Does Heat Destroy It?

Question
Hello
My question is, doesn't cooking or heating destroy vitamin c?  Canned, packaged and frozen food products usually list the vitamin c content, but isn't that before cooking ?  I have always wondered about potatoes, which are rich in vit. c and greens of most kinds.  But once the potatoe or greens are cooked, is the vit. c value the same?  Also wondered about pasturized orange juice.
Any advice you can give me will help
Thank you     Jean

Answer
Yes, vitamins are very heat sensitive and can be destoyed easily through high heat.  That is why it is best to steam vegetables as opposed to boiling them.  The information listed on food labels is AS THE FOOD IS in the package.  Once you get it home and prepare it you can definitely destroy some of the vitamins and the values will not be the same.  Not sure what your question is about orange juice?
Kim Tessmer, RD LD
www.Nutrifocus.net