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 2 h, 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 SO32 − 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 NH4+ than SO32 −. The browning intensity of the sulfite system changed scarcely at higher pH values, which was possibly caused by the polyreaction between SO32 − and carbonyl, instead of the intermolecular polymerisation of carbonyl in the advanced stage of the Maillard reaction.