Reaction of melanoidins with sulphur dioxide: stoichiometry of the reaction

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Abstract
Summary: Sulphur dioxide, in the form of sulphur(IV) oxoanions(S(IV)), e.g. HSO‐3, SO2‐3, reacts irreversibly with non‐enzymic browning model melanoidins (Mr > 12000, prepared by combination of 1.25 mol glucose with 1 mol glycine (pH 5.5, 90°C, 22 hr)). When the reaction with S(IV) is carried out for > 39 days at 40°C and pH 5.5 with initial concentrations of melanoidin of 5.71 g/l and S(IV) of 0.0371 M (equivalent to c. 2400 ppm SO2), up to one sulphur atom is incorporated for every two molecules of glucose used to form the polymer. This stoichiometry is discussed in relation to the degree of unsaturation of the melanoidin.