[Burningkrome]

How is glutamic acid stabilized in pill or powdered form, without using its salt (as in monosodium glutamate)? Is it a glutamic acid dimer?

Is the powdered form of glutamic acid ALSO a food flavor enhancer, or only the salt-of? If only the salt-of, why is it only the salt (biochemically/molecular biologically)?

[chenbeier]

Why it should be stabilized. One is the acid, one the sodium salt. The difference is the taste. Sodium glutamate enhance the food. The acid tastes sour and is not good to use.

[Burningkrome]

@chenbeier

Thanks for the reply.

"Why it should be stabilized."
Well, it's been a while since my last organic class, but don't most acids have to be stabilized in order to remain in solid form. Either by making the salt, adding HCL, forming dimers, or some other method.

"One is the acid, one the sodium salt. The difference is the taste."
Well, and thats really the conundrum for me.

The sodium salt of glutamic acid, as soon as it hits water (like saliva on the tongue), separates into a sodium ion, and then the carboxylic acid forms Rcoo-

In theory, glutamic acid (Rcooh) should ALSO hydrolyze into Rcoo- upon hitting water ... unless it is prevented from doing so by some form of stabilization (like forming a dimer between the Rcoo- ends of two molecules...which I believe it can do).

Ultimately, then, this begs the question of why does sodium-glutamate enhance the flavor of food - and glutamic acid does not.

If Sodium-glutamate's flavor enhancing capability comes from the sodium, there should be no difference to flavor enhancement than using NaCl...but there appears to be a difference.

This means its the Rcoo- of the (now separated from Na) glutamate that is the enhancer. If THIS is the case, then why DOESN'T Glutamic acid in water (which should otherwise form Rcoo-) act as a flavor enhancer.

Does that question make sense?

[Arkcon]

@chenbeier

Thanks for the reply.

"Why it should be stabilized."
Well, it's been a while since my last organic class, but don't most acids have to be stabilized in order to remain in solid form. Either by making the salt, adding HCL, forming dimers, or some other method.

That simply isn't true.  Citric acid, as an example, is a crystalline solid.  Of the top of my head, I can't think of a dimer acid that is a solid.  Liquid or gaseous acid, that dimerizes to a solid, is more likely an anecdote, not a chemistry concept.  Can you give several examples to support what you've said?

"One is the acid, one the sodium salt. The difference is the taste."
Well, and thats really the conundrum for me.

The sodium salt of glutamic acid, as soon as it hits water (like saliva on the tongue), separates into a sodium ion, and then the carboxylic acid forms Rcoo-

In theory, glutamic acid (Rcooh) should ALSO hydrolyze into Rcoo- upon hitting water ... unless it is prevented from doing so by some form of stabilization (like forming a dimer between the Rcoo- ends of two molecules...which I believe it can do).

Ultimately, then, this begs the question of why does sodium-glutamate enhance the flavor of food - and glutamic acid does not.

If Sodium-glutamate's flavor enhancing capability comes from the sodium, there should be no difference to flavor enhancement than using NaCl...but there appears to be a difference.

This means its the Rcoo- of the (now separated from Na) glutamate that is the enhancer. If THIS is the case, then why DOESN'T Glutamic acid in water (which should otherwise form Rcoo-) act as a flavor enhancer.

Does that question make sense?

OK.  Often some really new to science asks a question:

Which is responsible for the health effects of salt (sodium chloride) the alkali metal (sodium in elemental form), or the choking gas (free chlorine)?  The answer is neither, the compound has effects.  Sometimes a new person wants to know, "How can I get the one functional group tacked on to get my medicine or drug effect?"

Such questions are a waste of time, because chemistry doesn't work that way.

On this planet, a number of animals, evolved to detect certain chemicals as umami -- https://en.wikipedia.org/wiki/Umami.  And that's why adding more makes food tastier.

[Burningkrome]

Thanks again for the response. I'm not "super" new to science, and have done my organic- and biochemistry courses as part of a Molecular Biology degree. But that was a while ago, and for the last 10 years I've working bioinformatics...so I'm rusty.

Thats what brought up the question.

The tongue has separate receptors for Na+ and Cl-...as well as for the other common ions (Li+, K+ and Ca2+). the last time I studied this (in college) there was no indication that the Na+ receptor was ALSO dependent on stimulation of the Cl- receptor to induce the "saltiness" effect.

Of course, at that time - the term Umami had not even yet been coined.

If possible, can you direct me to any articles / papers / textbooks that described the inter-dependency between the Na+, Cl- receptors to trigger a saltiness effect. I assume this would also apply to an interdependence between any "Umami receptors" - if they exist - and the Na+ receptors to induce an Umami sensation.

I've Googled but come up short.

[Arkcon]

Start with the basics on the Wikipedia page I linked.  Consider using the references on that page for scholarly sources of further information.  They should lead you to more taste references.

[Yggdrasil]

The sodium salt of glutamic acid, as soon as it hits water (like saliva on the tongue), separates into a sodium ion, and then the carboxylic acid forms Rcoo-

In theory, glutamic acid (Rcooh) should ALSO hydrolyze into Rcoo- upon hitting water ... unless it is prevented from doing so by some form of stabilization (like forming a dimer between the Rcoo- ends of two molecules...which I believe it can do).

Ultimately, then, this begs the question of why does sodium-glutamate enhance the flavor of food - and glutamic acid does not.

If Sodium-glutamate's flavor enhancing capability comes from the sodium, there should be no difference to flavor enhancement than using NaCl...but there appears to be a difference.

Are you sue there is a difference?  Chemistry suggests the two should taste similar (aside from perhaps some added sourness from the glutamic acid) for the reasons you suggest above.  Here's what wikipedia has to say on the subject:

When glutamic acid or any of its salts is dissolved in water, it immediately forms a solution of separate negative ions called glutamates, and positive ions like H3O+ or Na+. There is actually a chemical equilibrium among several ionized forms, including zwitterions, that depends on the acidity (pH) of the solution. At the pH ranges normally occurring in foods, the prevailing ion can be described as −OOC-C(NH+3)-(CH2)2-COO−, with a net −1 electric charge.

Only the glutamate ion is responsible for the umami taste, so the effect does not depend significantly on the starting compound. However, some crystalline salts such as monosodium glutamate dissolve much better and faster than crystalline glutamic acid, a property important for use as a flavor enhancer.

https://en.wikipedia.org/wiki/Glutamate_flavoring#Glutamic_acid_versus_glutamates

So the difference in taste might just be an effect of how fast each substance dissolves (which is a property that dose differ depending on the counter ion used to formulate the salt).

[wildfyr]

Seems like the glutamate taste is going to depend on pH. In a highly acidic medium (like a tomato based food) a greater percentage of the carboxylic acids should be protonated and the umami taste will be suppressed.

Whenever glutamic acid or glutamate hits aqueous solution, its going to sort itself out based on the pH of the medium, not so much on what form it was in when placed into the mouth.

[Burningkrome]

Hi @Yggdrasil

Are you sue there is a difference?  Chemistry suggests the two should taste similar (aside from perhaps some added sourness from the glutamic acid) for the reasons you suggest above.  Here's what wikipedia has to say on the subject:

I'm not sure there's a difference. In my OP, I was speculating there should NOT be a difference. But was convinced by  @Arkcon that they probably were not the same. From a chemical standpoint, glutamic acid in water and sodium glutamate in water should both dissociate to free glutamate.

What is less clear is whether the "umami" taste requires multiple cellular receptor activation (I.e. Na+ AND Umami receptors simultaneously). Unfortunately, there's little research into this. I found a few papers investigating whether Na+ and Cl- receptors needed to be activated simultaneously - with the conclusion the (probably) do not.

I did also find some info on the mGluRx series of receptors as the umami receptors on the tongue, but no research into their simultaneous activation with others (such as Na+).

I have not yet tried a simple taste test between pure (powdered/dissolved) MonosodiumGlutamate and glutamic acid. Maybe that's the next step.

I am also very curious (and will investigate your leads) into whether the pH of the food itself is critical for glutamate umami.