Getting Rid of Cat Urine Smell On Hardback Books?

I have over 100 large size hard back cook books that have a cat urine smell to them. The books were in a closed up house on a bookcase and apparently the carpet had been peed on by cats prior to the house being closed up. The books were not peed on. The Cook books just absorbed the smell. It is a collection of books that is worth trying to salvage if at all possible. I don't even know where to start. I have the books boxed up on my carport and open the boxes during the day and try to spread them in the sunlight. That does not help. I would appreciate any help you can give me on this issue.