Q. _Does ascorbic acid help keep fruits and vegetables from darkening?_

A. Yes. The addition of ¼ teaspoon of crystalline ascorbic acid (vitamin

C) to a quart of fruit or vegetable before it is processed retards

oxidation, which is one cause of darkening of canned foods. One teaspoon

of crystalline ascorbic acid weighs about 3 grams (or 3,000 milligrams).