Human metabolic fate of glucosinolates from kailan-hybrid broccoli. Differences between raw and microwaved consumption

Glucosinolates are sulphur-containing compounds present in Brassica species that are hydrolyzed by the plant enzyme myrosinase to isothiocyanates (ITC), which have previously reported chemopreventive properties. In vivo, ITC are metabolized and excreted in urine as mercapturic acids. A cross-over-design study of 7 subjects after ingestion of 200-g raw or microwaved kailan-hybrid broccoli was conducted. Total ITC equivalents in the vegetable, urine and blood samples were determined by HPLC as the cyclocondensation product of 1,2-benzenedithiol. The highest ITC metabolization (53.6. ±. 15.7% over the total ITC ingested) was observed during the first 4. h after ingestion of raw product. However, the highest ITC metabolization after consumption of microwaved samples was delayed to 4-10. h, with 23.2. ±. 27.6%. The high ITC metabolization during the first 4. h was most likely due to absorption in the small intestine, while the second peak (4-8. h) could be presumably attributed to an ITC absorption in the colon. The total ITC metabolization after raw kalian-hybrid consumption (79.1. ±. 18.8%) was approximately 2-fold higher than that from microwaved broccoli (41.3. ±. 8.8%), which was statistically significant (P, t test. =. 0.005). The ITC absorption of the kailan-hybrid was 2 times higher for raw and 3-9 times higher for cooked samples than the values previously reported in the bibliography with conventional broccoli varieties. Compared to other brassicas, kailan-hybrid can be presented as a vegetable with both, a high concentration and a great ITC metabolization. © 2013 Elsevier Ltd.