Q:

What's the use of onions in teriyaki sauce?

I make my own Teriyaki sauce. Soy sauce, sugar, lemon juice, olive oil and onion. Normally, after marinating, I dry the piece I'm going to sauté and remove the onion.
Does the onion add flavour to the sauce? Does the onion have an effect on the meat that's marinating?
Or can I leave out the onion?

A:

Soy sauce, sake or mirin and sugar are the usual ingredients in a teriyaki sauce. The rice wines in particular are vital for an authentic teriyaki flavour.
So the question is somewhat moot: onions aren't usually found in teriyaki sauce anyway. The onions naturally add flavour to your marinade: if you like it, leave them in, if you don't, take them out. The onions won't have any major chemical effect on the marination process.
Personally I would ditch the olive oil, replace it with toasted sesame oil and add garlic and ginger for a more rounded and authentically flavoured East Asian marinade.

