I have heard this is the cat's way of marking their territory, using the oil glands in their paws...similar to when they mark a tree (or my couch) with their scratches! So, they are letting the others know this is their food by scratching around it, as if to cover it up. I don't think it has ANY thing to do with not liking the food...

Mine are more prone to do this when there has been a stressor in their lives, and they feel the need to be territorial (what, like I am going to start eating their food?).

Same thing with the litter box..it is two fold. Yes, they are covering up their gifts, but, they also are marking the area around it to let them and others know it is their gift.