Looking for advice on how to clean and prevent mold in grout/caulk of marble shower. Needs to be marble safe and ideally without strong smell/fumes.

We squeegee every day after shower, run fan, etc. The shower looks like new except there are a couple of spots in the corners where the grout/caulk is just beginning to turn a little yellow so I want to get/stay on top of it. For regular cleaning we use Dawn/water but need something a little extra for now and then.

Ideas? Thank you!