I think it was covered by a few people here
https://tropicalfruitforum.com/index.php?topic=46266.0Good hygiene is also important in seed collection, such as picking fruit before it falls to ground,
extracting seed before fruit goes off.
Cleaning seed thoroughly of juice and pulp etc,
using new zip bags for seed,
sterilising tools and strainers with boiling water between seed types/lots.
Working in a clean area, i.e. kitchen when wife not home !!!
Cleaning your hands between seed lots.
Cleaning/sterilizing the the peel of any older, fallen, mouldy fruit etc before getting to the seeds.
I had some mould problems with long term storage, when saving Autumn seed for Spring planting.
This year for Citrus I simply used the gel based hand sanitiser we are all now familiar with. 5 to 10 mins in the gel then rinse thoroughly before storage in bags.
The seed were placed on clean paper kitchen towel. Wetted, then water squeezed out to damp.
The moisture level should be watched in storage. Any excess moisture squeezed out.
Also check the seed bags regularly.
If any mould developed, I repeated the rinsing / gel process, and replaced the zip bag and paper towel.
Often the mould seemed to be on the paper towel, more than the seed.
I haven't had much problem with mould after planting, I delay till soil mix is warmer, use a free draining mix in taller pots.
Techniques that keep the mix moist, but surface drier and reduce watering frequency could help.
I now use a plastic cover on Citrus germination pots, this gives high humidity, but less frequent watering.
Soilless propagation mixes should reduce pathogens, as should heat treating the mix components ( usually not with fertiliser added ).
Heat could be steam, boiling, solarisation.
Probably the first question should be where is the mould coming from ??
On the seed ? From the pot mix ?? (compost organisms ??) From the greenhouse area or general environment ??