Glucosinolate-derived amine formation in Brassica oleracea vegetables

Abstract

Glucosinolates are precursors of bioactive and health-promoting isothiocyanates (ITCs). Upon enzymatic hydrolysis, Brassica vegetables, such as cabbage, also often yield nitriles and epithionitriles as main products next to ITCs. Here, we show that amines can be additional main enzymatic hydrolysis products of glucosinolates in Brassica vegetables. We propose that a plant endogenous ITC hydrolase (ITCase) is responsible for the enzymatic-like conversion of ITCs to amines in cabbage samples. This ITCase seems to have high activity towards alkenyl ITCs like allyl ITC and lower activity towards methylthioalkyl ITCs, and not to converting methylsulfinylalkyl ITCs like sulforaphane. In contrast, during heat treatment of homogenized cabbage material, methylsulfinylalkylamine levels increased by 400 % after 2 h of heating, which is likely due to thermal decomposition of ITCs, whereas alkenyl amine levels did not change due to heat treatment. The results show that amines from glucosinolates are part of the human diet.

Keywords: Amine; Brassica; Glucosinolate; Isothiocyanate; Isothiocyanate hydrolase; Raphanusamic acid.