TOTAL ISOTHIOCYANATE CONTENTS IN COOKED VEGETABLES FREQUENTLY CONSUMED IN SINGAPORE

The degradation products of glucosinolates in cruciferous vegetables, organic isothiocyanates (ITCs), inhibit carcinogenesis in numerous ani mal models including cancers of the lung, esophagus, forestomach, colo n, mammary gland, and pancreas. To assist investigations aimed at unde rstanding the role of dietary ITCs in the protection of human cancers, we examined ITC contents in various cooked vegetables frequently cons umed by Singapore Chinese, whose cancer profile is distinct from that of U.S. whites (e.g., much lower rates of cancers of the breast, colon , rectum, and pancreas). Using an HPLC method to quantify the cyclic p roduct of ITCs and 1,2-benzenedithiol after treatment of vegetable jui ces with myrosinase, we analyzed a total of 102 vegetable specimens. T he results show considerable variation in ITC contents in the nine typ es of cruciferous vegetables analyzed, ranging from 4.9 mu mol/100 g w et weight in bok choi (Brassica chinensis) to 81.3 mu mol/100 g wet we ight in watercress. ITCs were not detected in any of the noncruciferou s vegetables examined. ITCs also were not detected in most of the cook ed cruciferous vegetables prior to myrosinase treatment, indicating th at only glucosinolates are present in these cooked vegetables. This st udy demonstrated the usefulness of the cyclic condensation reaction of ITCs with a dithiol reagent for quantifying total ITC contents in veg etables and the potential application of the assay in epidemiologic st udies.