This looks to be a SharedCoin transaction (lots of inputs and outputs, many outputs having similar amounts of BTC). But, in THIS transaction we can find an input that is very large (vs. the others) and an output that is also very large vs. its others:
That's the change. The amount actually mixed is 50 BTC.
(No need for it to be a SharedCoin transaction, it could also by a joinmarket one, which has the features of not having counterparty risk (funds are under your control at all times) and has an incentive mechanism for people to offer themselves for making joins.)
