The tissue of cruciferous vegetables, like broccoli, cauliflower, cabbage and Brussels sprouts, contain high levels of the active plant chemicals glucosinolates. These are metabolized by the body into isothiocyanates, which are reported to be powerful anti-cancer agents. The main isothiocyanate from broccoli is sulforaphane, and is produced from glucoraphanin.
The potential health benefits of broccoli have led to a range of commercial supplements on the market. According to Jenna Cramer and Elizabeth Jeffery from U of I’s Department of Food Science and Human Nutrition, many such supplements contain glucoraphanin but lack the enzyme myrosinase, which catalyzes the production of sulforaphane from glucoraphanin. The lack of myrosinase in the supplements would therefore “question their ability to provide dietary sulforaphane”, said the Illinois-based scientists.
By combining broccoli powder with air dried broccoli sprouts, which are a rich source of the myrosinase enzyme, Cramer and Jeffery investigated if this would enhance the absorption of sulforaphane in human subjects.
“This is the first study to examine a commercially available powdered broccoli preparation containing only glucoraphanin and to examine effects of combining this glucoraphanin-rich broccoli preparation with an exogenous food source of myrosinase, broccoli sprouts,” they explained in the journal Nutrition and Cancer.
“The results show that combination improved availability, opening the door to development of products with enhanced chemoprotective potential.”
Study details
Four subjects each consumed four dry cereal and yogurt meals supplemented with broccoli sprouts (2 grams), broccoli powder (2 grams), a combination of both, or neither. The meals were consumed on separate occasions and 2-3 days of washout separated the meals. The broccoli products were provided by Caudill Seed, Inc., which also funded the study
Results showed that sulforaphane levels in the urine after 24 hours were 74, 49 and 19 percent of the ingested dose for the sprouts, the combination supplement, and the powder, respectively.
Moreover, the combination product and the broccoli sprout meal were both associated with faster absorption and excretion, with 44 and 37 percent of the sulforaphane excreted during the first six hours, respectively, compared with less than 10 percent of the sulforaphane excreted following ingestion of the broccoli powder meal during the same time period.
“Data from the combination meal were interesting as they identified possible synergy among the sprouts and powder at early time point measurements of plasma and urine recovered metabolites,” wrote the authors. “This indicates that endogenous myrosinase from the broccoli sprouts had the opportunity to hydrolyze glucoraphanin not only from the broccoli sprouts but also from the broccoli powder.”
From a safety perspective, the researchers report no observed liver toxicity from any of the meals.
“Combining broccoli sprouts with the broccoli powder enhanced sulforaphane absorption from broccoli powder, offering the potential for development of foods that modify the health impact of broccoli products,” concluded the researchers.
Source: Nutrition and Cancer
Published online ahead of print, doi: 10.1080/01635581.2011.523495
“Sulforaphane Absorption and Excretion Following Ingestion of a Semi-Purified Broccoli Powder Rich in Glucoraphanin and Broccoli Sprouts in Healthy Men”
Authors: J.M. Cramer, E.H. Jeffery