Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/11/2002
Publication Date: N/A
Interpretive Summary: Increased consumption of cruciferous vegetables such as broccoli, cabbage, and cauliflower has been shown to be associated with a decreased risk for developing cancers of the lung, colon, and prostate. Scientists have hypothesized that the special ability of cruciferous vegetables to prevent cancer development is due to the presence of compounds called glucosinolates. When cruciferous vegetables are eaten, a specific enzyme in the vegetable tissues breaks down the glucosinolates to other compounds. Recently, sprouted broccoli seeds have been promoted as being especially high in a particular compound, called sulforaphane, which has been shown to have potent anticancer activity. In the current study, we studied both the levels of glucosinolates and their breakdown compounds and found that at conditions similar to those found in human saliva and gastric juices, little or no sulforaphane was produced, although other glucosinolate degradation compounds were identified. This research indicates that factors occurring in the human digestive tract will likely be critical in determining which glucosinolate degradation products are produced. Further study of glucosinolate metabolism in the human system is needed in order to define the chemical basis for the previously reported cancer-risk reduction associated with diets enriched in cruciferous vegetables.
Technical Abstract: Total glucosinolate content and glucosinolate degradation products were examined in unsprouted `Marathon' broccoli (Brassica oleracea L., Italica group) seeds and in 1-, 2-, 3-, 5-, 7-, and 10-day-old sprouts. Glucosinolates identified were glucoiberin, glucoraphanin, gluconapin, glucoiberverin, 4-hydroxyglucobrassicin, glucoerucin, glucobrassicin, and neoglucobrassicin. While total glucosinolate levels on a fresh-weight basis were highest in seeds and 1-day-old sprouts, decreasing to approximately 10% of this level in 7- and 10-day-old sprouts, levels were highest on a dry weight basis for 1- and 5-day-old sprouts. Glucosinolate degradation products were examined by incubating macerated seeds or sprouts at 37C in aqueous solutions at either pH 1.7 (gastric juice pH) or pH 7.0 (saliva pH) with CH2Cl2, which accumulated the degradation products. At pH 1.7, only iberverin nitrile and erucin nitrile were found in seed extracts, but by day 3 erucin was also detected. At pH 7.0, sulforaphane, sulforaphane nitrile, iberin, erucin, erucin nitrile, iberverin, and iberverin nitrile were detected in seed extracts, but only erucin and erucin nitrile were found in 10-day-old sprout extracts. Sulforaphane, which has been identified as a potent inducer of phase II detoxification enzymes, was not detected in any extract at pH 1.7 and only in imbibed seeds and 1-, 2-, and 3-day-old sprouts at pH 7.0.