We have a strange smell under kitchen sinks I have replaced the vent valve and checked the garbage desposal seems OK could copper bollttom pans be the cause

If this does not work you may have to try something stronger like disinfectant a bit like what you do to clean a toilet, though some people have said coke cola can clean and get rid of something's.

Usually, smell under the sink is from wet cabinet. Make sure there are no leaks. Also, if there are any holes in the cabinet, like larger penetration holes for plumbing, dishwasher, etc - plug them. They may allow stagnant air into your cabinet. Moreover, check what's stored inside the cabinet and remove what could be the source of foul odor.

Milo

Depending on its it's a rotten cabbage type smell, and you have metal drain pipes... look for a corroded pipe... sewer gas could be leaking from it.

Dampness is a whole different smell and needs dealt with as well.