Consuming cooked or processed broccoli may result in less of the potential anti-cancer compounds being available for absorption, suggests a new study from TNO Quality of Life.
Consumption of the cooked vegetable led to lower levels of a compound called sulforaphane being measured in the blood and urine, compared to consuming raw broccoli, according to findings published in the Journal of Agricultural and Food Chemistry.
The bioavailability of sulforaphane was calculated to be 37 per cent from the raw vegetable, and only 3.4 per cent from cooked broccoli, reported Martijn Vermeulen and co-workers from TNO Quality of Life.
The study extends out understanding of the potential anti-cancer benefits of broccoli, and may offer important information to companies involved in the production of broccoli extracts for the functional food and dietary supplements industry.
Sulforaphane is the main isothiocyanate from broccoli. The tissue of cruciferous vegetables, like broccoli, cauliflower, cabbage and Brussels sprouts, contain high levels of the active plant chemicals glucosinolates. These are metabolised by the body into isothiocyanates, which are known to be powerful anti-carcinogens.
Glucoraphanin, also known as sulforaphane glucosinolate (SGS), is the precursor of sulforaphane.
The Netherlands-based researchers recruited eight men to participate in the study. The men consumed 200 grams of crushed raw or cooked broccoli with a warm meal. The randomised, free-living, open cross-over trial used blood and urine levels of sulforaphane to elucidate the bioavailability of the proposed anti-carcinogen.
Vermeulen and co-workers report that the glucoraphanin content of the cooked broccoli was 61.4 micromoles, while glucoiberin and glucobrassicins were also detected. On the other hand, raw broccoli contained 9.92 micromoles of sulforaphane, and no other isothiocyanates.
“The sulforaphane content of raw broccoli was lower than the glucoraphanin content of cooked broccoli, 9.92 and 61.4 micromoles, respectively. It seems that the conversion from glucosinolate to isothiocyanate was incomplete or that another reaction occurred,” they wrote.
In addition to less sulforaphane being measured in the blood and urine when cooked broccoli was consumed, compared to raw broccoli, the absorption of the compound was delayed when the broccoli was cooked: the optimal levels were observed after six hours for the cooked broccoli, compared to only 1.6 hours after consumption of raw broccoli.
“Consumption of raw broccoli resulted in faster absorption, higher bioavailability, and higher peak plasma amounts of sulforaphane, compared to cooked broccoli,” wrote the researchers.
“In future research, care should be taken that glucoraphanin is not hydrolyzed into other metabolites when broccoli is crushed,” they concluded.
Source: Journal of Agricultural and Food Chemistry
Published online ahead of print, ASAP Article, doi: 10.1021/jf801989e
“Bioavailability and Kinetics of Sulforaphane in Humans after Consumption of Cooked versus Raw Broccoli”
Authors: M. Vermeulen, I.W.A.A. Klopping-Ketelaars, R. van den Berg, W.H.J. Vaes