Stability of Glutamine and Pyroglutamic Acid under Model System Conditions: Influence of Physical and Technological Factors

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Abstract
The 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.