Study Questions Bioavailability of Sulforaphane in Green Supplements

September 16, 2011

The bioactive component of cruciferous vegetables may have poor bioavailability in dietary supplements due to the absence of a key enzyme.

Is your greens supplement doing all that it can? New research suggests that sulforaphane, a bioactive component of cruciferous vegetables, may have little bioavailability in dietary supplements due to the common absence of a key enzyme.

Cruciferous vegetables like broccoli sprouts, broccoli, and kale are staples for most green supplements because they contain high amounts of glucosinolates, compounds which can convert into the anticarcinogen sulforaphane. But in order for glucosinolates to turn into sulforaphane, a hydrolysis reaction must occur with the enzyme myrosinase-an enzyme killed from the heating process used to make many dietary supplements.

New research published online at the British Journal of Nutrition supports the notion that including myrosinase in the consumption of glucoraphanin (a widespread glucosinolate) will greatly increase bioavailable sulforaphane.

Researchers from the University of Illinois at Urbana-Champaign gave adult men four meals (separated by one week) of dry cereal and yogurt with broccoli sprouts (equivalent to 70 μmol of sulforaphane), glucoraphanin-rich powder (equivalent to 120 μmol of sulforaphane), both ingredients, or neither ingredient.

Analysis for sulforaphane metabolites in urine yielded a recovery of 65%, 60%, and 24% for combined ingredients, broccoli sprouts, and glucoraphanin powder, respectively. These numbers suggest that the vegetable source with the enzyme undamaged can yield significantly more sulforaphane and improve sulforaphane yield from a glucoraphanin-rich powder.

The results of this study complement a February study by the researchers, which found sulforaphane metabolites at 74%, 49%, and 19% with consumption of air-dried broccoli sprouts, sprouts and glucoraphanin-rich broccoli powder, or glucoraphanin-rich powder alone, respectively.

In an interview with Nutritional Outlook, lead researcher Elizabeth H. Jeffery warned of the implication for consumers of glucosinolate-rich products.

“One needs to read the [ingredient] label carefully,” said Jeffery. “It is likely to say broccoli or glucosinolates or even sulforaphane glucosinolate (using sulforaphane more like an adjective). These will all have been made using a heating process that kills the myrosinase.”