The bioactive metabolites of glucosinolates, such as isothiocyanates, contained in cruciferous vegetables have been shown to reduce the risk of cancers through the induction of detoxification enzymes. However, cruciferous vegetables are commonly processed before consumption, significantly altering the phytochemical composition of these vegetables. Compared to freeze-dried Brussels sprouts, oven-dried Brussels sprouts contain low concentrations of glucosinolates (22.14 and 0.85 μmol/g, respectively) and isothiocyanates (3.68 and 0.15 μmol/g, respectively). The effect of oven-dried Brussels sprouts on the expression of detoxification enzymes was evaluated in vitro and in vivo. Treatment of immortalized human hepatoma cells with the aqueous extract from oven-dried Brussels sprouts significantly increased quinone activity (0.5 and 1.5 mg/mL) and the activity of the antioxidant response element (EC50=2.39 mg/mL) and xenobiotic response element (EC50 2.92 mg/mL). C3H/HeJ mice fed a diet containing 20% oven-dried Brussels sprout diets for 2 wk demonstrated significantly higher expression than animals fed a nutrient-matched control diet of CYP1A1, CYP1A2, and epoxide hydrolase in the liver and CYP1A1, CYP1A2, CYP1B1, epoxide hydrolase, UGT1A1, thioredoxin reductase, and heme oxygenase in the lungs. The low concentrations of glucosinolates and isothiocyanates in oven-dried Brussels sprouts suggest that other compounds, such as the Maillard reaction products that are produced during heating, are responsible for the induction of detoxification enzymes in vitro and in vivo.
Practical application: The manner in which cruciferous vegetables are processed prior to consumption has significant effects on what compounds people are exposed to. The presence of glucosinolates or isothiocyanates can be a good indicator of the ability of cruciferous vegetables to induce detoxification enzymes. However, the data presented here demonstrate that while heat processing of Brussels sprouts greatly reduced the concentrations of glucosinolates and isothiocyanates, their ability to induce detoxification enzymes in vitro and in vivo was retained.