Effects of pH on the formation of 4(5)-Methylimidazole in glucose/ammonium sulfate and glucose/ammonium sulfite caramel model reactions.

The objective of the present study was to detail the change of 4(5)-Methylimidazole (4-MI) in sulfite and sulfate reactions with different initial pH values. Glucose/ammonium sulfate and glucose/ammonium sulfite reaction systems with initial pH conditions 4.9, 5.9, 6.9, 8.0 and 8.6, were heated at 100°C for 2h, respectively. Higher concentration of methylglyoxal (MGO) and 4-MI was detected in thermal treated glucose/ammonium sulfite reaction system than that in sulfate system. The SO reacting with MGO and other precursors of 4-MI at higher pH conditions prevented 4-MI formation. However, no inhibition of 4-MI was found at lower pH conditions due to higher reactivity of the nucleophilic NH than SO. The browning intensity of the sulfite system changed scarcely at higher pH values, which was possibly caused by the polyreaction between SO and carbonyl, instead of the intermolecular polymerisation of carbonyl in the advanced stage of the Maillard reaction.