Stop trying to feed him other foods for one. If he reacts that way, just stop.
As for punishment, obviously something is wrong with him trying new foods and such, and its not his fault. But if he EVER bites you, GRAB HIS SCRUFF.
Hold it for 5 seconds, on the ground kind of sway him lightly back and forth while holding his scruff. Dont hurt him though. This is the way some frerrets tell eachother 'No no!'.
If a ferret show posseiveness, getting anothe ferret is not a good idea.
I would put it off.