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  • Title: Riboflavin photosensitized oxidation of myoglobin.
    Author: Grippa JM, de Zawadzki A, Grossi AB, Skibsted LH, Cardoso DR.
    Journal: J Agric Food Chem; 2014 Feb 05; 62(5):1153-8. PubMed ID: 24456528.
    Abstract:
    The reaction of the fresh meat pigment oxymyoglobin, MbFe(II)O₂, and its oxidized form metmyoglobin, MbFe(III), with triplet-state riboflavin involves the pigment protein, which is oxidatively cleaved or dimerized as shown by SDS-PAGE and Western blotting. The overall rate constant for oxidation of MbFe(II)O₂ by ³Rib is (3.0 ± 0.5) × 10⁹ L·mol⁻¹·s⁻¹ and (3.1 ± 0.4) × 10⁹ L·mol⁻¹·s⁻¹ for MbFe(III) in phosphate buffer of pH 7.4 at 25 °C as determined by laser flash photolysis. The high rates are rationalized by ground state hydrophobic interactions as detected as static quenching of fluorescence from singlet-excited state riboflavin by myoglobins using time-resolved fluorescence spectroscopy and a Stern-Volmer approach. Binding of riboflavin to MbFe(III) has K(a) = (1.2 ± 0.2) × 10⁴ mol·L⁻¹ with ΔH° = -112 ± 22 kJ·mol⁻¹ and ΔS° = -296 ± 75 J·mol⁻¹·K⁻¹. For meat, riboflavin is concluded to be a photosensitizer for protein oxidation but not for discoloration.
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