Variations in Glucosinolate Contents and Quinone Reductase-inducing Activities among Florets, Leaves, and Roots of Broccoli Plants

Glucosinolates are a group of sulfur-containing phytonutrient found in Brassica vegetables known to reduce cancer risk by upregulating Phase II enzymes such as quinone reductase (QR). To investigate organ-dependent variations, five broccoli varieties were cultivated and their florets, leaves, and roots were separately harvested and the glucosinolate contents as well as QR-inducing activities were evaluated. In all, five tested varieties broccoli roots showed higher total glucosinolate contents (37.8 μmol·g^-1) compared to florets (10.4 μmol·g^-1) and leaves (5.4 μmol·g^-1). Each organ exhibited a different composition of glucosinolates in that the major form of glucosinolate was glucoraphanin (31.2%), glucobrassicin (44.3%), and gluconasturtiin (41.9%) in florets, leaves, and roots, respectively. Different broccoli organs showed different QR-inducing effects. Roots exhibited 2.5-fold higher QR-inducing activity compared to control, which was similar to florets (2.5-fold) but significantly higher than leaves (1.7-fold). Variety-dependent difference in QR-inducing effects, however, were not observed. Eleven kinds of quantified glucosinolates glucoraphanin (r = 0.67^**) and total glucosinolate (r = 0.51^**) contents showed higher positive correlationship with QR-inducing activity. These results suggest that different broccoli organs (such as florets, leaves, and roots) may have different profiles of glucosinolates, which may in turn result in different anticancer capability.