THE ROLE OF GLUTAMIC-ACID GLUTAMINE AND LYSINE DURING NONENZYMATIC BROWNING IN HEATED GLUTEN

During dry heat processing of a crude gluten preparation (c. 75% prote in) at 160 degrees C for 30 min, about 25% of the available lysine and 10% of the glutamine residues are lost with the evolution of water (a n increase of about 10%). This represents the loss of 6-7 moles of glu tamine for each mole of lysine. In the presence of a low concentration (1-5%) of fructose, glucose and maltose, the amount of lysine made un available increases to a maximum of about 45% of the total while the g lutamine content further decreases by amounts dependent on the sugar a nd its concentration. The number of moles of glutamine lost per mole o f lysine is in the range 5-15. On a weight basis, fructose is the most reactive sugar and maltose the least, but the amount of water generat ed in the systems for each reacted amino group varies. The molar ratio s of additional glutamine lost in the presence of sugar to additional water produced are 4.2, 16 and 21 for glucose, fructose and maltose, r espectively. The possible relevance of these reactions to the quality of extruded foods is discussed.