!! This changed in the release of Alpha 17. This is no longer true. !!
Food does not spoil or deteriorate in a caravan.
I have sent a caravan back and forth in a 3 day journey with meat. Before leaving, every stack of meat were set to spoil in 1 day because they are not refrigerated and had 46/50 hit points since they were left out on the open for a few hours.
After the journey, none of those stats changed, so it is safe to say that nothing will spoil.
However, this could be something that is added in a future update since it looks at like like a missing functionality, which would make sense since this game is still in alpha.
Note: Tested in Alpha 16