Effects of pH and Ferrous Ion on the Degradation of Glucosinolates by Myrosinase

Abstract

During the enzymatic degradation of sinigrin, the release of glucose and the formation of allyl isothiocyanate via subsequent cleavage of the aglucon were studied in the presence or absence of ferrous ion over a pH range of 3.5 ~ 7.5. The liberation of glucose increased linearly with the time of enzymatic cleavage of sinigrin for the first 20 min at the pHs used, and no inhibition of glucose liberation was caused by ferrous ion at the concentration tried. On the other hand, the effects of ferrous ion on the formation of isothiocyanate changed greatly with changes of pH of the reaction medium. At pH 4.5 and 5.5, formation of isothiocyanate was strongly inhibited by ferrous ion, while such an effect of ferrous ion was notably depressed at pH 6.5 and disappeared at pH 7.5. These results were also confirmed by gas chromatographic analysis of the volatile cleavage products of the glucosinolates prepared from the seed meal of hakuran (an artificial variety of Brassica napus). From these results, it was suggested that ferrous ion is not involved in the enzymatic liberation of glucose from glucosinolate but in the subsequent degradation of the aglucon. © 1986, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.