As far as i know based on my knowledge if tokenization means if the convertion from the stock or shares into the token that can represent the ownership of that asset or stock and that just like a convert the conventional shares to the token that can be transfered through the blockchain.
Securitization means a way for a platform or company to get the fresh funds through sell or offer its company shares to the public just like what has already done by whole of icos. They get the fund and they offered the security as an exchange,