Good question! You can drink preserved stuff if you choose to, but it's nowhere near as nutritious (or naturally delicious). It's not really recommended, especially if you are using it for cleansing/fasting.
Fresh is best - all canned or bottled food, or drinks in a carton (including coconut water) have been preserved using ULTRA HEAT TREATMENT. This means the product is heated to kill all the living enzymes (and any bacteria present) so that the product doesn't break down. This is a real shame because if you get a fresh juice or food, those enzymes are really good for you. The process also denatures (unravels) the good proteins and breaks hydrogen bonds etc destroying the vitamins and other goodies present in fresh raw food. As far as I am aware, the mineral (electrolyte) content remains unchanged, but I think it's relative to the reactivity of the elements themselves. Feel free to set me straight on this anybody.