Maximizing The Sulforaphane Content of Broccoli and Broccoli Sprouts

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Glucosinolates

Glucosinolates are natural components of many pungent plants that occur as secondary metabolites of most of the Brassicales family, or the cruciferous vegetables.   When these vegetables are chewed, a pungent taste arises due to the breakdown products of glucosinolates.

Each vegetable, sprout and seed usually contains more than one glucosinolate.  However, certain vegetables, sprouts and seeds may contain a predominant amount of one glucosinolate.  An example is the following:

  • Broccoli and broccoli sprouts contain large amounts of glucoraphanin
  • Mustard seeds and Brussel sprouts contain a large amount of Sinigrin
  • Garden cress and cabbage contain a large amount of glucotropaeolin
  • Watercress contains a large amount of gluconasturtiin

The total number of documented glucosinolates from nature can be estimated to around 132, as of 2011.  1  For purposes of this article, we will focus on the 4 most important glucosinolates and the ones that have been the subject of the majority of medical research.  These 4 glucosinolates include:

  • Gluconasturtiin
  • Glucoraphanin
  • Glucotropaeolin
  • Sinigrin

Gluconasturtiin, also known as phenethylglucosinolate, is a widely distributed glucosinolate in cruciferous vegetables.  The name is derived from it occurrence in watercress which has the botanical name Nasturtium officinale.

Glucoraphanin is a glucosinolate distributed in broccoli, Brussel sprouts, cabbage and cauliflower.  It is also found in large amounts in young sprouts of cruciferous vegetables, like broccoli sprouts.

Glucotropaeolin is a phytochemical from Tropaeolum majus, which is commonly known as garden nasturtium, Indian cress or monks cress.  It is also found in cabbage.

Sinigrin is widely distributed in the plants of the Brassicaceae such as Brussel sprouts, broccoli, horseradish and black mustard seeds.

Myrosinase

Each of the vegetables, sprouts and seeds contain the enzyme myrosinase, which is activated when the vegetable, sprout or seeds is damaged (chopped or chewed) in the presence of water.  The glucosinolate converts to an isothiocyanate (or thiocyanate) through the enzymatic activity of myrosinase.  These isothiocyanates are the defensive substances of the plant.

Thus glucosinolates are the precursors to isothiocyanates through the breakdown of the enzyme myrosinase.  Myrosinase activity on the glucosinolate also continues in the gastrointestinal tract through intestinal bacteria which allows for some further formation and absorption of isothiocyanates. 2

Image result for glucosinolates myrosinase pathway

Figure 1:  Glucosinolates Hydrolysis by Myrosinase  (Source:  Linus Pauling Institute – Isothiocyanates)

Sulforaphane

Sulforaphane is obtained from cruciferous vegetables such as broccoli, broccoli sprouts, Brussels sprouts, and cabbages. It is produced when the enzyme myrosinase transforms glucoraphanin into sulforaphane upon damage to the plant (such as from chewing), which allows the two compounds to mix and react.

When the enzyme myrosinase acts on glucoraphanin, an unstable intermediate is produced.  This unstable intermediate is then acted on by a protein called epithiospecifier protein (ESP) to produce sulforaphane or sulforaphane nitrile.

If epithiospecifier protein (ESP) is abundant in the plant and is active, it will convert this unstable intermediate to a sulforaphane nitrile.  This sulforaphane nitrile has no anti-cancer activity.  3 

If epithiospecifier protein (ESP) is not abundant and is low-active, then it will convert this unstable intermediate into sulforaphane.  Sulforaphane has anti-cancer activity.  4

Image result for sulforaphane nitrile

Figure 2.  ESP converts into sulforaphane and sulforaphane nitrile  (Source

Decreasing Epithiospecifier Protein Activity

A research paper entitled “Heating decreases epithiospecifier protein activity and increases sulforaphane formation in broccoli”, published in Phytochemistry in 2004, examined the effects of heating broccoli florets and sprouts on sulforaphane and sulforaphane nitrile formation, to determine if broccoli contains ESP activity, then to correlate heat-dependent changes in ESP activity, sulforaphane content and bioactivity, as measured by induction of the phase II detoxification enzyme quinone reductase (QR) in cell culture.  5

Researchers experimented with cooking broccoli at different temperatures and at different times periods.  They then measured the point at which the epithiospecifier protein is destroyed. 

What they learned was that they only had to heat the broccoli for a short time in order to destroy the epithiospecifier protein thus yielding more sulforaphane and little to no sulforaphane nitrile.

Specifically, to maximize the sulforaphane in broccoli, they found that heating it for 10 minutes at 140 degrees Fahrenheit (60 degrees Celsius).  This can translate to steaming broccoli lightly for about 3 to 4 minutes.

When they heated the broccoli for 10 minutes at 158 degrees Fahrenheit (70 degrees Celsius) it not only destroyed the epithiospecifier protein but also the sulforaphane content. 

Broccoli sprouts

Broccoli sprouts are germinated from broccoli seeds for about 3 days minimum and 5 days maximum. 

Image result for broccoli sprouts

Figure 3.  Broccoli sprouts

Broccoli sprouts that are 3 days old have very concentrated sources of glucoraphanin.  It is estimated that broccoli sprouts have 10 to 100 times more glucoraphanin by weight than mature broccoli plants.  6

Three-day-old broccoli sprouts have been shown to be highly effective in reducing the incidence, multiplicity, and rate of development of mammary tumors in dimethylbenz(a)anthracene-treated rats.  7  Small quantities of crucifer sprouts may protect against the risk of cancer as effectively as much larger quantities of mature vegetables of the same variety.

The activity of the epithiospecifier protein (ESP) in broccoli sprouts fluctuates based on the number of days the sprouts have grown.  8

ESP activity increases up to day 2 after germination before decreasing again to seed activity levels at day 5.

Thus, the optimal amount of days to grow broccoli sprouts is probably 5 days since the amount of glucoraphanin in broccoli seeds remains more or less constant as those seeds germinate and grow into mature plants.  9

When the researchers heated broccoli sprouts for 10 minutes at 158 degrees Fahrenheit (70 degrees Celsius) in water, it minimized the epithiospecifier protein and maximized the sulforaphane content.

Heating broccoli sprouts in water under these exact specifications will increase the sulforaphane content for maximum anti-cancer benefit.

Compare the technique of heating broccoli sprouts in water with the study from China where they increased the sulforaphane yield by freezing the broccoli sprouts:

An example of heating broccoli sprouts in water using the specifications of the researchers can be viewed in the experiment conducted by Dr. Rhonda Patrick: