REDUCING SUGARS EFFECT ON AVAILABLE LYSINE LOSS OF CASEIN BY MODERATEHEAT-TREATMENT

In order to investigate the effect of various reducing sugars on the a vailable lysine loss by Maillard reaction, four model systems were pre pared by mixing casein with glucose, fructose, lactose or maltose, fol lowed by storage at 37 degrees C, 50 degrees C and 60 degrees C. The a vailable lysine contents were monitored periodically. Highest and lowe st reaction rates were observed in the model systems containing glucos e and fructose, respectively, at the three temperatures. The two disac charides behaved very similarly, with reaction rates between those of the monosaccharides studied. The activation energies of glucose, lacto se and maltose systems were similar (116-132 kJ mol(-1)), while that o f fructose was somewhat higher (166 kJ mol(-1)). This difference was s upposed to be in part due to the different mechanism of tautomerizatio n of fructose, highly dependent on temperature. Therefore, though the potential nutritional damage at moderate temperatures is lower when fr uctose is used instead of other reducing sugars, its higher activation energy can reverse the effect at higher temperatures. (C) 1998 Elsevi er Science Ltd. All rights reserved.