Milesi Flat clear.

Polyurethane does not make hardwood waterproof ( if that's what you're looking for),.It repels water and prevents water absorption, but it never fully blocks it so it will never make it 100% waterproof.

If you're not looking for waterproofing (I assume you are since they are kitchen shelves) Water-based poly will work fine in my opinion because it protects wood from scratches and discoloration. I advise you though to try it out on a sample piece then work on your shelves directly and if you are satisfied with the results then try it on the shelves.

How about Gorilla Waterproof Patch and Seal Clear Spray?