I made some paintings with coffee (as watercolor) now how do I preserve them?

First I made 10 paintings using soluble coffe and I didn't know that they tend to get some mold, also that with time some of the darkest strokes tends to peel away. How can I stop both things? if you could recommend me some chemical please consider the coffee is highly solutable, so the liquid could erase it and that i can't use colored chemicals also.