My parents once spilled milk in their motorhome fridge.... it took many, many cleanings and lots of Febreeze to get rid of the smell...

One thing, other than baking soda, you can do to help get rid of funk that has permeated the plastic is coffee grounds. There's a little fridge at work that is so nasty that when ever anyone opens it, I want to leave the room..... (no I don't keep any food in there). A half a cup of (new - not used) coffee grounds took care of the nastyness pretty quickly. Coffee is in all the breakrooms, and thus much more accessible at work than baking soda, with the added benefit that it smells nice.