Is there any way to keep fresh-squeezed fruit juice (especially apple or orange) for at least one week without losing taste and vitamins in it? Would a jar with a tight lid be useful?
Some quick research indicates there are enzymes in freshly-squeezed juice that will degrade it fairly rapidly, and that they can be deactivated by heat. Of course, that also changes the flavor (especially since you're not going to be able to quickly heat and cool it, as it apparently only takes 30 seconds, but any method doable in a home kitchen will keep it hot much longer than that). So heat-deactivation is out.
Even commercially-produced (that is, both pasteurized and enzyme-deactivated) juice is only supposed to keep 6 days in the fridge, so that's out.
Your best bet, then, is to freeze it. According to the University of California's Division of Agriculture and Natural Resources Publication 8199, you can freeze in clean glass jars or rigid plastic freeze containers. They also note that navel oranges (and their juice) do not freeze well—they will become bitter.
Well, either that, or store the fruit instead, and only juice it as needed.
I have an orange tree and when fruit grows, I hate to see it hit the ground and go to waste. With a funnel, juice reamer, and empty soda bottles, I'm able to stock up on orange juice for weeks.
I know freshly squeezed is the best, but is it really worth the work every time you're thirsty?
If your going to freeze it in a container, make sure to keep the lid or cap open before the freezing process. The pressure will explode if sealed.