Can a food contain 'extra' sodium? I have always heard how food companies deliberately add 'extra' sodium to make foodstuffs like fried snacks and instant noodles addictive. But my question is, if I were to make the same food at home, won't I add an equivalent amount of sodium to get that taste? Or is some of the sodium content somehow 'hidden' in the food industries' products?
I get that flavour enhancers like supersalt and MSG have sodium in it. But doesn't the addition of those in packaged foodstuffs compensate for some of the salt that would otherwise be added?
Update: I am talking about extra sodium being added without an effect on taste, or it being added in a way that we get a greater 'kick' from the food, rather than the sodium being hidden in some way.
I think you've misunderstood people talking about sodium; I would expect they are generally just talking about table salt, NaCl.
Addressing your question about quantity, it's very common that when cooking, people judge ingredients by eye and by their expectation of what a normal quantity would be, so use much less salt than a restaurant or commercial preparation. (Something similar is true of butter.) Commercial ice cream, for example, will contain salt, but home ice cream makers are unlikely to include much if any.
If you want to think of that as 'hiding' sodium in products, I suppose that's reasonable, but it's not being done through mystery sodium compounds you're not aware of.