A study on advanced Maillard reaction in heated casein/sugar solutions: Fluorescence accumulation

The advanced Maillard reaction of lactose/caseinate or glucose/caseinate solutions, heated between 110 and 150 degrees C for 0-30 min, was characterized via fluorescence. Fluorescent components were preponderately protein-bound with 'free' fluorescence making only 1% of protein-bound fluorescence. 'Free' fluorescence spectra changed with heating, whereas protein-bound fluorescence increased only in intensity with heating without spectral changes. Glucose/casein and lactose/casein behaved similarly. The fluorescence spectra corresponded to the typical fluorescence of AGEs (advanced glycosylation end products) that arise in proteins under physiological conditions (maximum excitation and emission wavelength of 347 and 415 nm, respectively). Kinetics of fluorescence evolution was characterized by a reaction order of 0.5. The apparent activation energy was about 160 kJ mol(-1) for 'free' fluorescence and about 135 kJ mol(-1) for protein-bound fluorescence (the activation energy of the early Maillard reaction is about 100 kJ mol(-1)). Fluorescence evolution was due to many reaction products, as illustrated by HPLC analysis. Peak areas were related to heat intensity. (C) 1998 Elsevier Science Ltd. All rights reserved.