MSG also forms when glutamic acid meets tablesalt. That's why tomatoes or beef with a tiny bit of salt are so damned tasty, they're full of glutamic acid. Same with cheese (which is usually pre-salted for that lovely MSG-flavour).

Tomatoes and beef already contain MSG naturally, but adding a few grains of salt produces far more.

Edit: This is why walnut oil is amaaaaazing for savory flavours. It's full of glutamate. Just like grape juice, or shi-take. Even potatoes to a lesser extend. And this is why we love combing all those foods for "winter foods" with game and in stews.