The tissue of cruciferous vegetables, like broccoli, cauliflower, cabbage and Brussels sprouts, contains high levels of the active plant chemicals glucosinolates. These are metabolized in the body into isothiocyanates, which are known to be antioxidants and powerful anti-carcinogens. The main isothiocyanate from broccoli is sulforaphane.
Some consumers, however, do not enjoy eating broccoli but still seek out the potential benefits of isothiocyanates may turn to a wide range of broccoli supplements on the market.
According to new findings published in Pharmacological Research, some of these supplements may not deliver the same benefits as the whole food.
Researchers from Oregon State University and The Ohio State University report that the bioavailability of sulforaphane and another isothiocyanate called erucin is “dramatically lower” when broccoli supplements are consumed, compared to fresh broccoli sprouts.
The scientists point to the inactivity of an enzyme called myrosinase in broccoli supplements. Myrosinase is the enzyme that converts glucosinolates to isothiocyanates. The only sources we have for this enzyme is from the plant itself, or from our own microflora.
The Oregon and Ohio-based scientists said that many supplements do not contain active myrosinase due to the processing methods employed in the production of the broccoli extract.
Twelve volunteers were recruited to analyze if there may indeed be a difference in the bioavailability of isothiocyanates between supplements and whole foods.
The volunteers consumed 40 g of fresh broccoli sprouts (Sprouters Northwest, Inc.) followed by a one month washout period. The same 12 subjects then took 6 pills of a commercial broccoli supplement (BroccoMax, Jarrow Formulas).
A second set of four volunteers acted as controls and were given 40 g of alfalfa sprouts and then placebo pills.
Results showed that “the bioavailability of sulforaphane and erucin is dramatically lower when subjects consume broccoli supplements compared to fresh broccoli sprouts”, reported the researchers.
The data is reportedly the first to detailed analysis of sulforaphane and erucin in humans using ultra-high performance liquid chromatographic tandem mass spectroscopy (UHPLC–MS/MS).
“This study confirms that consumption of broccoli supplements devoid of myrosinase activity does not produce equivalent plasma concentrations of the bioactive isothiocyanate metabolites compared to broccoli sprouts.
“This has implications for people who consume the recommended serving size (1 pill) of a broccoli supplement and believe they are getting equivalent doses of isothiocyanates,” concluded the researchers.
Question of pH?
Commenting on the study’s findings, a spokesperson for Jarrow Formulas told NutraIngredients-USA: “The basic problem is that sulforaphane is formed in a high pH environment rather than a low pH one.
“Broccoli seed sprouts are relatively high pH and tend to elevate the pH (alkalinize) of the digestive environment, whereas orange juice is low pH and therefore will not have this effect in the stomach and upper small intestine,” he explained. “In the context of the test meal, it might be expected that the spouts would yield better sulforaphane results for pH reasons alone.
“How much better cannot be determined without performing a separate test, but it is likely that the BroccoMax product would have yielded more sulforaphane had it been taken with water or milk rather than orange juice,” added the Jarrow Formulas spokesperson.
Earlier this year, researchers from the University of Illinois recently reported combining broccoli supplements with broccoli sprouts to boost the absorption of sulforaphane.
“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 U of I authors in Nutrition and Cancer (doi: 10.1080/01635581.2011.523495).
“The results show that combination improved availability, opening the door to development of products with enhanced chemoprotective potential.”
Source: Pharmacological Research
Published online ahead of print, doi:10.1016/j.phrs.2011.07.005
“Bioavailability and inter-conversion of sulforaphane and erucin in human subjects consuming broccoli sprouts or broccoli supplement in a cross-over study design”
Authors: J.D. Clarke, A. Hsu, K. Riedl, D. Bella, S.J. Schwartz, J.F. Stevens, E. Ho