Abstract
Mechanisms on formation and disappearance of pungent principles in Daikon (Raphanus sativus L.) Oroshi (grated radish) were investigated. Free isothiocyanates were not detected in nondisintegrated radish root. trans-4-Methylthio-3-butenyl isothiocyanate (TMBI), the main pungent principle, was produced by myrosinase decomposition of a glycosidic precursor in the presence of L-ascorbic acid.
Contents of isothiocyanates were measured by the colorimetric determination. The amounts of isothiocyanates in grated radish decreased rapidly within 60 min. However, the decrease was slightly suppressed by the addition of Sanbai-zu (a seasoning prepared by mixing of soy, sugar and vinegar), especially acetic acid which is a main component of vinegar.
In contrast to the decrease of isothiocyanates, the formation of methyl mercaptan and dimethyldisulfide was confirmed by the analysis of gas chromatography. Formation of methyl mercaptan markedly increased within 60 min, reached a maximum after 90 min and then decreased gradually in course of time. On the other hand, the production of dimethyldisulfide greatly increased with the disappearance of methyl mercaptan.
Furthermore, from the fact that the decrease of isothiocyanates and the production of methyl mercaptan and dimethyldisulfide were also found in the isothiocyanates aqueous solutions which were free of enzymes, it was assumed that the following system (TMBI→methyl mercaptan→dimethyldisulfide) could be proceeded also by non-enzymic action
