bleach is possibly your best bet.
bicarbonate of soda is fantastic at getting rid of the black mould in and around fridge door seals,
you could try that, it should work, it's the same
type of mould i guess.
if you have to use silicone sealant !!!!!
beware !!!!
all silicone sealants are not the same, usually the more expensive ones inhibit mould growth
longer, read what it says on the tube. some really are better than others.