Isothiocyanate concentrations and interconversion of sulforaphane to erucin in human subjects after consumption of commercial frozen broccoli compared to fresh broccoli

Institute of Food Research, Norwich Research Park, Norwich, UK.
Molecular Nutrition & Food Research (Impact Factor: 4.91). 12/2012; 56(12). DOI: 10.1002/mnfr.201200225
Source: PubMed

ABSTRACT Sulforaphane (a potent anticarcinogenic isothiocyanate derived from glucoraphanin) is widely considered responsible for the protective effects of broccoli consumption. Broccoli is typically purchased fresh or frozen and cooked before consumption. We compared the bioavailability and metabolism of sulforaphane from portions of lightly cooked fresh or frozen broccoli, and investigated the bioconversion of sulforaphane to erucin.
Eighteen healthy volunteers consumed broccoli soups produced from fresh or frozen broccoli florets that had been lightly cooked and sulforaphane thio-conjugates quantified in plasma and urine. Sulforaphane bioavailability was about tenfold higher for the soups made from fresh compared to frozen broccoli, and the reduction was shown to be due to destruction of myrosinase activity by the commercial blanching-freezing process. Sulforaphane appeared in plasma and urine in its free form and as several thio-conjugates forms. Erucin N-acetyl-cysteine conjugate was a significant urinary metabolite, and it was shown that human gut microflora can produce sulforaphane, erucin, and their nitriles from glucoraphanin.
The short period of blanching used to produce commercial frozen broccoli destroys myrosinase and substantially reduces sulforaphane bioavailability. Sulforaphane was converted to erucin and excreted in urine, and it was shown that human colonic flora were capable of this conversion.

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    • "The anaerobic incubation ex vivo of ceacal microbiota from male F344 rats with glucoraphanin yielded only the hydrolysis product erucin NIT in relatively low concentrations [9]. Similarly, glucoraphanin metabolism in human gut microbiota showed the bioconversion of glucoraphanin to glucoerucin and the production of sulforaphane (trace amounts), erucin and corresponding NITs [10]. However, there was no identification of bacterial strains responsible for this bioconversion. "
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    ABSTRACT: Certain myrosinase-positive human gut bacteria can metabolize glucosinolates (GSLs) to produce isothiocyanates (ITC) as chemopreventive agents. We investigated glucoerucin, glucoiberin, and glucoraphanin (present in broccoli) metabolism by human gut strains. All tested bacteria metabolized glucoerucin to completion within 16 h to erucin and erucin nitrile (NIT). Lactobacillus agilis R16 metabolized only 10% of glucoiberin and glucoraphanin with no detectable products. Enterococcus casseliflavus CP1, however, metabolized 40-50% of glucoiberin and glucoraphanin producing relatively low concentrations of iberin and sulforaphane. Interestingly, Escherichia coli VL8 metabolized 80-90% of glucoiberin and glucoraphanin and also bioconverted glucoraphanin and glucoiberin to glucoerucin and glucoiberverin, respectively, producing erucin, erucin NIT, iberverin, and iberverin NIT from the two GSLs. The putative reductase enzyme in the cell-free extracts of this bacterium required both Mg(2+) and NAD(P)H as cofactors for bioconversion. The cell-free extract of E. coli VL8 containing the reductase enzyme was able to reduce both the GSL glucoraphanin and its hydrolysis product sulforaphane to glucoerucin and erucin/erucin NIT, respectively. The composition and metabolic activity of the human gut bacteria can indirectly impact on the potential chemopreventive effects of GSL-derived metabolites.
    Molecular Nutrition & Food Research 04/2014; 58(4). DOI:10.1002/mnfr.201300377 · 4.91 Impact Factor
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    • "Interestingly, more recent SF bioavailability studies in human subjects consuming broccoli showed its bioconversion into isothiocyanate erucin (isothiocyanato-4- (methylthio)-butane) (ER), a sulfide analog [25] [26]. Whether this conversion from SF to ER is important for the health promoting effects of glucosinolate still remains to be determined although some reports provide a glimpse into the possibility of differing activities between these two isothiocyanates [27– 29]. "
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    Oxidative medicine and cellular longevity 08/2013; 2013:415078. DOI:10.1155/2013/415078 · 3.36 Impact Factor
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    ABSTRACT: There is a growing interest in the health benefits of broccoli. Sulforaphane, the major bioactive component in broccoli, is an unstable isothiocyanate stored in the plant as glucoraphanin. Myrosinase enzymes release sulforaphane when the plant is crushed. Extraction during supplement formulation or heat processing can destroy myrosinase. When myrosinase activity is lost, colonic microbiota perform this hydrolysis in vivo. Here we review hydrolysis by myrosinase and microbiota. Myrosinase acts fast to generate a bolus of SF that is rapidly absorbed high in the gut and rapidly excreted. Microbial metabolism is slow and delayed. Sulforaphane absorption, distribution and excretion are discussed.
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