Physical changes induced by the Maillard reaction in a glucose-glycine solution

Some physical changes associated with the development of Maillard reaction in a glucose-glycine aqueous solution were detected by means of thermal and rheological analysis as well as by more conventional determinations. The i ncrease in water content, water activity (A(w)) and enthalpy of ice melting (Delta Hm) during the reaction reflects both the formation of new water mo lecules and the consumption of low molecular weight species. The concomitan t arrangement of more complex molecular structures was indicated by changes in the glass transition temperature of the maximally freeze-concentrated s olution (Tg') and of the freeze-dried solution (Tg((dry))) as well as in th e estimated unfrozen water (UFW). After fractionation of the samples by sol id phase extraction, the nonpolar fractions exhibited much higher Tg((dry)) than the non-fractionated samples. The Tgs((dry)) of samples at increasing heating time were treated with the Gordon-Taylor equation add results were discussed. The expected increase in viscosity due to polymerisation was co mpensated by the formation of water, but it could be detected when viscosit ies were measured on samples equilibrated at a same A(w). (C) 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Lt d. All rights reserved.