Well, fresh is always best as anytime you blend up foods they will begin to oxidize. But if the alternative is not having the smoothies, freezing in an airtight container should be fine for up to a month or so, maybe longer. The key is to reduce as much air exposure as possible. Freezing in a zip-lock bag would work well as it is easy to remove all the air space. The texture may change after thawing.
"Men never commit evil so fully and joyfully as when they do it for religious convictions."