Monosodium Glutamate, Purine 5-Ribonucleotides, and Related Substances

2 Monosodium Glutamate, Purine 5 -Ribonucleotides, and Related Substances 

Cooks around the world have known how to prepare good soup using vegetables and meat or bones from time immemorial. Traditionally, the Japanese culture has used 

the most commonly used umami substances are monosodium glutamate, disodium 5 -inosinate, and disodium 5 -guanylate. They are commercially available world-wide. 

Monosodium glutamate (MSG) is the monosodium salt of L-(-H)-glutamic acid (Fig. 3.53). Only the completely dissociated form of L-(-H)-glutamic acid exhibits the umami effect (D-(-H)-glutamic acid has no flavour improving properties). At pH 4.0, only 36.0 % of the acid are dissociated. The percentages of dissociation at pH 5.0,6.0, 7.0, and 8.0 are 84.9, 98.2, 99.8, and 96.9, respectively. This means that only at pH 5.0 to 8.0 glutamic acid shows its optimal effect. 

In practise, MSG (which corresponds to the completely dissociated form of the acid) is used almost exclusively to improve the flavour of foods. It is permitted world-wide, although in some countries and some types of foods maximum concentration limits apply. Other salts of glutamic acid that are occasionally used are potassium, calcium, and ammonium glutamates. These are not permitted world-wide. 

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