Effect of sulphite treatment on allyl isothiocyanate in mustard paste

Allyl isothiocyanate (AITC), the major constituent of black and brown mustard oils, reacts with hydrogensulphite, used as an antioxidant in some types of mustard paste, to afford allylaminothiocarbonylsulphonate (AITC-SO−3). The reaction was studied in a model aqueous system of pH 4 and mustard paste of the Dijon type, respectively. The reaction rate was influenced considerably by temperature, but not by oxygen dissolved in the media. About 10% of total AITC (ctot[AITC] = 1.81gkg−1) in the mustard paste treated with bisulphite (co[K2S2O5] = 1.5 gkg−1) converted to AITC-SO−3 within a period of four weeks regardless of storage temperature used. The primary reaction product, AITC-SO −3, showed good stability both in diluted acidic solutions and mustard paste. A rapid decomposition of this adduct was observed in diluted alkali (pH 9). A method for the simultaneous determination of AITC-SO−3 and AITC in mustard paste was developed and its performance characteristics assessed. Sensory analysis revealed slight fading of characteristic mustard flavour and the appearance of garlic-like flavour in model solutions. In mustard pastes, the original pungent flavour became much milder, but the development of garlic-like notes was not detected.