I have used IBM Blockchain before to build this app:
It works quite well and has a very nice API, which makes it easy to interact with.
I haven't checked out the other solutions. I know some of our team are looking into blockchain technology and building some connectors, but i don't know their progress yet.
The core value of a blockchain technology is that it enables a database to be directly shared without a central administrator. Rather than having some centralized application logic, blockchain transactions have their own proof of validity and authorization to enforce the constraints. Hence, with the blockchain acting as a consensus mechanism to ensure the nodes stay in sync, transactions can be verified and processed independently.
To me nor IBM Blockchain, nor Mendix could be a real Blockchain solution, simply because it is not a full open source technology without any lock in power.
Not sure if you are still looking into the ethereum block chain. A while back I was researching the same thing and I found this java library that looked promising. I haven't had time to test it out but this should be everything you need.
Hope this helps!