It will be hard for Ukraine to replace grain exports that went directly to China through Black Sea ports because the countries they will now be exported through, mainly Poland and Romania, don’t have the same approvals from China, whether on hygiene or otherwise, as Kyiv does, according to Sergey Ivashchenko, a director at the Ukrainian Grain Association.
If China can get said grain via Poland and Romania and doesn't want it because it hasn't approved shipments through them, that sounds like a China problem to me. I have a hard time seeing a serious hygiene concern.