open access publication

Article, 2024

Reactivity and mechanism of the reactions of 4-methylbenzoquinone with amino acid residues in S-lactoglobulin: A kinetic and product investigation

FOOD CHEMISTRY, ISSN 0308-8146, 0308-8146, Volume 434, 10.1016/j.foodchem.2023.137473


Liu, Jingyuan 0000-0003-2893-7121 [1] Engholm-Keller, Kasper 0000-0001-5988-2632 [1] Poojary, Mahesha [1] Bevilacqua, Marta 0000-0002-3361-9219 [1] Andersen, Mogens L 0000-0003-4694-486X [1] Lund, Marianne N 0000-0001-8708-2210 (Corresponding author) [1]


  1. [1] Univ Copenhagen, Dept Food Sci, Fac Sci, Rolighedsvej 26, DK-1958 Frederiksberg C, Denmark
  2. [NORA names: KU University of Copenhagen; University; Denmark; Europe, EU; Nordic; OECD]


Quinones, produced by the oxidation of phenolic compounds, covalently bind to nucleophilic groups on amino acids or proteins. In this study, the reactions of 4-methylbenzoquinone (4MBQ) with S-lactoglobulin (S-LG) and amino acids at neutral pH were investigated. LC-MS analysis revealed that Cys121 was likely the most modified residue in S-LG. Identification of reaction products by LC-MS/MS showed that Michael addition occurred in all reactions with amino acids tested. The formation of Schiff base and a di-adduct was found in His and Trp samples. Apparent second-order rate constants (k2) were determined at 25 degrees C and pH 7.0 by stopped-flow spectrophotometry. The rate of reactions decreased in the order: S-LG > His > Trp > Arg > N degrees-acetyl His > N degrees-acetyl Arg > N degrees-acetyl Trp. The rate constants correlated with the pKa values of the amino acids, showing that the amount of unprotonated amine is the major factor determining the reactivity.


4-methylcatechol, Kinetics, Michael addition, Polyphenol-protein binding, Protein modification, S-lactoglobulin

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