If I remember correctly (anyone who has better info please chime in) a componant of citric acid is ascorbic acid - vitamin C.
The problem with all fruit juices is that drinking a glass of juice, for example apple juice, is like eating several apples. You get a lot of sugar, and little of the nutrients found in the pulp and skin. It's almost like drinking soda pop. As a diabetic, I've had to give up fruit juices for that very reason.
However, if you take whole fruit, such as stone fruits (plumbs, peaches, nectarines, etc), strawberries, apples, pears, etc. and combine them with raw veggies such as carrots and such, you can make very tasty and viatmin packed smoothies in your blender or Magic Bullet. They are more filling and contain all of the nutrients and minerals of the whole fruit.
Seeeeeeeya; Goodweed of the North