Reaction kinetics for the reactions between four polyphenols (trans-resveratrol, apigenin, kaempferol and fisetin) and methylglyoxal (MGO) were determined at pH 7.4 and 37 °C, and the effect of functional groups of polyphenols on MGO trapping ability was examined. Reaction products of polyphenols with MGO were characterized by HPLC-MS/MS. The apparent second order rate constants for the reaction of MGO with trans-resveratrol, apigenin, kaempferol and fisetin were (2.7 ± 0.2) × 10⁻² M⁻¹ s⁻¹, (4.4 ± 0.4) × 10⁻³ M⁻¹ s⁻¹, (6.3 ± 0.2) × 10⁻² M⁻¹ s⁻¹, and (3.6 ± 0.1) × 10⁻³ M⁻¹ s⁻¹, respectively. The rate constants were used to evaluate the possible competition between MGO with nucleophilic sites on proteins and polyphenols at concentrations relevant to UHT milk. Combining this information with solubility and flavour of the polyphenols, it was concluded that kaempferol could effectively trap MGO and hereby inhibit Maillard reactions in UHT milk.