ISO recent link regarding preservatives in frozen seafood
If you want to know how a scallop *should* look/taste, buy a live-in-shell one, or some from Island Scallops (from Qualicum, but available in plenty of markets), and you can be sure you'll be getting a so-called "dry" (as in, un-soaked) one. In my experience, it's a bit of a toss-up as to whether ones from the East Coast will have STP or not. As one fish-store owner apologetically told me, they are not *supposed* to have any, the clear implication being that it's not a sure thing.
The mods deleted it, because it mentioned the name of a corporation. Fair enough.
The chemical is STPP / STP, sodium tripolyphosphate. It is used as a water retention agent in frozen (and sometimes fresh) seafood to prevent drip loss. In Canada it is allowed to be used in shrimp/prawns up to a total phosphate content of around 2%. It is not supposed to be in scallops at all, but it can be added by unscrupulous processors anywhere in the supply chain, even on the boats themselves simply by soaking them in a solution.
If over-used it increases the water content of seafood (ie more $ for the seller), gives shrimp a weird soapy texture, and makes seafood (especially scallops) tasteless, bitter or metallic, turns them a lighter color and makes them impossible to sear. So if your scallops are tasteless/bitter and watery, STPP is likely to blame. Scallops shouldn't be white; they should be fairly off-white or even pink/orange. If you goodgle STP and scallops lots of info will pop up.
I'm pretty fed up at how often I buy scallops in Canada that clearly have STP in them even though they are not supposed to. I've got a query in to CFIA about it.