Glucosinolate accumulation and hydrolysis in leafy Brassica vegetables are depending on leaf age

The health-beneficial effects of Brassica vegetables are mainly attributed to their high contents of glucosinolates and the products of their enzymatic hydrolysis, especially isothiocyanates. Distribution of glucosinolates across plant organs can strongly vary. Consequently, the effect of leaf age on glucosinolate accumulation as well as hydrolysis was investigated in two leafy Brassica vegetables, pak choi and giant red mustard. Furthermore, activity of the hydrolyzing enzyme, myrosinase, was evaluated across the leaves. Additionally, a possible glucosinolate transport from older to younger leaves was monitored. Young leaves of both species contained of more glucosinolates than old ones. Accordingly, more isothiocyanates were released upon glucosinolate hydrolysis in young leaves. Myrosinases fully hydrolyzed the whole glucosinolates regardless of the leaf age. It was confirmed that older leaves can supply younger leaves with glucosinolates. The results can help to improve the health-beneficial value of Brassicas in the diet by an increased formation of isothiocyanates.