Total isothiocyanate contents in cooked vegetables frequently consumed in Singapore

Jiao, D.; Yu, M.C.; Hankin, J.H.; Low, S.H.; Chung, F.L.

Total isothiocyanate contents in cooked vegetables frequently consumed in Singapore

1998

Jiao, D. | Yu, M.C. | Hankin, J.H. | Low, S.H. | Chung, F.L.

The degradation products of glucosinolates in cruciferous vegetables, organic isothiocyanates (ITCs), inhibit carcinogenesis in numerous animal models including cancers of the lung, esophagus, forestomach, colon, mammary gland, and pancreas. To assist investigations aimed at understanding the role of dietary ITCs in the protection of human cancers, we examined ITC contents in various cooked vegetables frequently consumed 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 product of ITCs and 1,2-benzenedithiol after treatment of vegetable juices with myrosinase, we analyzed a total of 102 vegetable specimens. The results show considerable variation in ITC contents in the nine types of cruciferous vegetables analyzed, ranging from 4.9 micromol/100 g wet weight in bok choi (Brassica chinensis0 to 81.3 micromol/100 g wet weight in watercress. ITCs were not detected in any of the noncruciferous vegetables examined. ITCs also were not detected in most of the cooked cruciferous vegetables prior to myrosinase treatment, indicating that only glucosinolates are present in these cooked vegetables. This study demonstrated the usefulness of the cyclic condensation reaction of ITCs with a dithiol reagent for quantifying total ITC contents in vegetables and the potential application of the assay in epidemiologic studies.

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