Food safe fix for broken plastic valve
You already tagged the answer.  Epoxy is fine for food content. 

Food feedstock tanks are painted with epoxy paint, that's what you use for that. (We're talking genuine 2-part epoxy paint, not hardware store 1-part paint that has chunks of already-cured epoxy in it for marketing purposes.  No one will sell consumers uncured epoxy if there's a remote chance you might spray it.) 

Steel cans are lined with epoxy (if you recall the fuss about BPAs, BPA is a common curing agent in epoxy; it should be fully consumed in the curing process unless the mixing is botched.)

Getting the epoxy to adhere to the broken parts is a real problem.  Even if it adheres, it may be stronger than the native material, which if deteriorated, would simply break again at the boundary layer or someplace else.  I would say "sand it flat" but then you'll lose the thread sync. 

You may be wasting your time if the material is deteriorated.  

At that kind of price you ought to be able to consult the factory? They may have deprecated the whole assembly and have a replacement.   Or they may simply say "tough beans, this is a top end product like Beats headphones, not made to be repaired."   In that case they must have prototyped it from something; I would search Grainger, McMaster-Carr etc. for similar components in metal and food-grade.