^^^^I'm pretty sure the skin was gone from where he was actually eating from.
Anyhoo, the oranges sort of took on a life of thier own. They were put places to give some color to the dark cinomatography, and they happened to be mostly in scenes w/ characters who were killed. So in Part 2, the flimmakers dilibrately put them in scenes w/ characters who would die. I base that on the fact that Fredo sits next to an orange basket but does not die in the movie, and FFC doesnt make Part 1 with Part 2 in mind.