How do I stop or slow down yellowing?!?

[Takuleechch]

so I recently picked up an item, a pair of white satin shorts, but they are yellowing quite a bit
some of it is sweat stains and use, which I'm fine with, but part of it is yellowing from age.
what can I do to stop it or slow the process down?
I want to frame them but take care of this issue first