Storage and processing conditionsThe stability of glutamine and pyroglutamic acid as regards pH, temperature and oxygen was studied during storage and two thermal processings, the residual products and those which appeared being determined. Contrary to glutamic acid, the two derivatives are labile below pH 2 and above pH 13 and alteration occurs much faster. Temperature increase promotes this phenomenon. Glutamic and pyroglutamic acids convert reversibly into one another, more or less quickly and completely according to the conditions. Glutamine changes during heating in two steps, first into glutamic acid, then into pyroglutamic acid if the pH values are not extreme. The influence of pH conditions on the direction and the rate of the reaction are indicated.The solutions were stored for 15 days at about 20 "C in the dark in sterilized ground-glass stoppered bottles, which were completely filled in order to study storage without atmospheric contact. Each determination of residual glutamine and pyroglutamic acid concentration after a given time necessitated the use of an individual bottle to avoid the entry of air resulting from sampling. The solutions were therefore not entirely oxygen-free, but the influence of air was limited to that of the air dissolved in them. This storage was termed, for convenience sake, "without atmospheric contact."Solutions were boiled under reflux for 60 min and residual and conversion products were determined as soon as the solutions had cooled. In the autoclaving processing, the solutions were heated for 35 min to 135 "C under 2.7 k&m2 pressure in screw-top glass bottles with bakelite caps and Teflon@' seals ("SVL"@, France).
The stability of glutamic acid and monosodium glutamate as regards pH, temperature and oxygen was studied during storage and two thermal processings, the residual products and those which appeared being determined. The initial molecules only change into pyrrolidonecarboxylic acid, never into glutamine nor y-aminobutyric acid. Preservation is good in all cases at pH 0 and pH 14, but glutamic acid is converted to pyrrolidonecarboxylic acid at intermediate pH values. The change is favored by pH values ranging from 2 -3, by temperature increase and by oxygen.
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