Vitamin C Preservation in Food: Cooking & Processing Explained

Question
Hello
My question is, does cooking destroy the vitamin c content of potatoes, greens, canned fruits and vegetables?  All canned, frozen and packaged food items state the vitamin c content, but is that before or after cooking.  I have always thought that heat destroyed vitamin c.  And how about pasturized orange juice?
Any advice you can give me would be helpful
Thank you     Jean

Answer
Yes, cooking does destroy vitamin C.

There's no regulations requiring details of measuring vitamin C content (before or after thermal processing.)

Pasteurization is a better way than boiling since it's being made at lower temperatures. However, many canned foods are processed at boiling water temperature.

Freezing is the best way of keeping vitamins in a food, it's even better than storing it in refrigerator.