If you give someone an orange to eat and he chooses to keep the orange who is the legal owner of the orange?

The person who you give the orange to would own it - as you have willingly given it to him. If he was to "dishonestly appropriate" it i.e. take the orange, knowing that it was yours and you did not intend to give it away, then you would own the orange, and techinally it would be theft.