Glutamate pyrrolidone carboxylate formation from

IV. Nonenzymic Formation of Pyrrolidone Carboxylic Acid from Glutamic Acid, Glutamine, and Other Compounds... 

Using the data of Wilson and Cannan (18), Cleaves (81) was able to show that the rate of formation of pyrrolidone carboxylic acid from glutamic acid in aqueous solution depends directly on the concentration of the ionic species of glutamic acid in solution. Thus, the reactive species are (I), (II), and (IV), while (III) is relatively unreactive. Protonation of the amino group and dissociation of the y-carboxyl group thus makes these groups less reactive carboxylate ion resonance apparently hinders nucleophilic attack by the amino nitrogen. 

The hydrolysate is subsequently neutralized to pH 5.8 with sodium or calcium carbonate or with sodium hydroxide solution. In this process, the pH range of 2.5-4 must be passed through as quickly as possible to repress the formation of pyrrolidone carboxylic acid from glutamic acid. The hydroysate is filtered and the filtrate (seasoning) stored. The filtration residue is washed with water and refiltered, if necessary. The diluted filtrate is evaporated and added to the seasoning obtained in the first step. 

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