FLUORESCENCE ASSOCIATED WITH MAILLARD REACTION IN MILK AND MILK-RESEMBLING SYSTEMS

The progress of the Maillard reaction in milk and milk-resembling syst ems during heating was followed by monitoring free fluorescent interme diary compounds. Fluorescence intensity was examined over a wide tempe rature/time range (90-140 degrees C/0.5-30 min). Different kinetic beh aviours were found in the presence or absence of amino groups in the s ystem. Traces of fluorescence were detected when the lactose system wi thout proteins was heated; the isomerization and degradation reactions of lactose could also generate fluorescent compounds. Fluorescence ac cumulation in the lactose system (without proteins) proceeded accordin g to first-order reaction kinetics, whereas systems with lactose and c asein, lactose and whey protein and milk fitted zero-order reaction ki netics. Apparent activation energies calculated were 61.3, 78.6, 59.6 and 83.9 kJ mol(-1) for lactose system, lactose/casein system, lactose /whey protein system and milk, respectively. Moreover, levels of inter mediary fluorescent compounds in Spanish commercial milk (pasteurized, UHT-treated and in-bottle sterilized milk) have been studied. Copyrig ht (C) 1996 Elsevier Science Ltd