The last article posted on the subject of broccoli microgreens pointed out that adding a sulfur rich hydroponic fertilizer increased broccoli sprouts content of sulforaphane. This confirms we can produce more nutraceutically potent microgreens with an adjusted blend of nutrients.
However the redacted description of referenced study, below, compares sulforaphane at all stages of growth and in comparison to mature broccoli flowers. It concludes that 3 days is best and that at 15 days the microgreens will have lost potency in comparison. The comparisons were made using a hot water extract from the sprouts. Boiling water with sprouts in water can also be used to sterilize. The boiled water extract contains the nutrients. Though eating them, instead, would be more satisfying.
Take home message. Sprouts are better than the microgreens which are about equivalent to the mature plant. When growing sprouts for consumption use caution to prevent contamination. It doesn’t require solvents as used in the study but know your precautions.
For more on the dosage and uses of the broccoli sprout extract, see the link at the Denver Naturopath.
Proc Natl Acad Sci U S A. 1997 September 16; 94(19): 10367–10372.
Jed W. Fahey, Yuesheng Zhang, and Paul Talalay*
Brassica Chemoprotection Laboratory and Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
To whom reprint requests should be addressed at: Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, 725 North Wolfe Street (Wood Basic Science, Room 406), Baltimore, MD 21205. e-mail: email@example.com
Contributed by Paul Talalay
Thus, edible plants belonging to the family Cruciferae and genus Brassica (e.g., broccoli and cauliflower) contain substantial quantities of isothiocyanates (mostly in the form of their glucosinolate precursors) some of which (e.g., sulforaphane or 4-methylsulfinylbutyl isothiocyanate) are very potent inducers of phase 2 enzymes. Unexpectedly, 3-day-old sprouts of cultivars of certain crucifers including broccoli and cauliflower contain 10–100 times higher levels of glucoraphanin (the glucosinolate of sulforaphane) than do the corresponding mature plants.
Extracts of 3-day-old broccoli sprouts (containing either glucoraphanin or sulforaphane as the principal enzyme inducer) were highly effective in reducing the incidence, multiplicity, and rate of development of mammary tumors
)anthracene-treated rats. Notably, sprouts of many broccoli cultivars contain negligible quantities of indole glucosinolates, which predominate in the mature vegetable and may give rise to degradation products (e.g., indole-3-carbinol) that can enhance tumorigenesis. Hence, 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.
RESULTS AND DISCUSSION
Comparison of Inducer Activity of Fresh and Frozen Mature Stage Vegetables.
By using triple solvent for extracting glucosinolates and converting them to their bioactive isothiocyanates with myrosinase, we compared phase 2 enzyme inducer activities from a variety of cruciferous plants (arugula, broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, crambe, daikon, kale, kohlrabi, mustard, red radish, turnip, and watercress).
Because broccoli extracts were typically the most potent, we compared the inducer activities of 7 samples of frozen broccoli (five national brands) with those of 22 randomly collected fresh broccoli samples (cultivars unknown) obtained from local supermarkets.
The inducer activities of the fresh broccoli samples were unrelated to their physical appearance or whether grown under conventional or organic conditions. In all 7 samples of frozen broccoli and in 21 of 22 triple solvent extracts of fresh mature broccoli, no inducer activity was detectable before addition of myrosinase.
Therefore, we conclude that the contribution of phytochemicals other than glucosinolates to the inducer activity of these extracts is negligible. The generally lower potencies of frozen broccoli samples may have been due to unfavorable storage conditions or to removal of glucosinolates during the blanching process. Both cultivar and many environmental factors have significant effects on glucosinolate content and, consequently, on inducer potency.
Effects of Plant Age on Inducer Potencies of Cruciferous Vegetables.
Preliminary experiments indicated that inducer potencies (expressed per g of plant) of extracts of young sprouts of arugula, bok choy, broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, cress, daikon, kale, kohlrabi, mustard, turnip, and watercress ranged from 10 to 100 times those of mature field-grown plants. Similarly, in sprouts of eight broccoli cultivars, grown without exogenous nutrients, the inducer activity (nearly all of which arose from glucosinolates) per unit plant weight declined initially in an exponential manner from a maximum in the seed (Fig. (Fig.3)3
) and continued to decline thereafter, approaching the values in mature broccoli heads after about 15 days (data not shown), whereas the total inducer activity per plant remained constant. The inducer activity fell from 1.8 million units/g of seeds to 180,000 units/g fr. wt. at 9 days, largely due to an increase in plant weight from seeds (3.3 mg) to 9-day-old sprouts (60 mg). Apparently no significant net synthesis of glucosinolates occurred under these conditions.
Indole glucosinolates, however, accounted for only 3% of the total glucosinolates in these sprouts, compared with 68% of those in the mature plant. There are 20 times more methylsulfinylalkyl glucosinolates (glucoraphanin and glucoerucin) in the sprouts compared with the mature broccoli. A 100-g serving of mature broccoli would, therefore, provide 108 μmol of methylsulfinylalkyl glucosinolates and 229 μmol of indole glucosinolates, whereas consumption of an equivalent quantity of methylsulfinylalkyl glucosinolates via a much smaller serving of sprouts (5 g) would result in the consumption of only 11.2 μmol of indole glucosinolates.
These differences in glucosinolate profiles between young sprouts and mature broccoli are of considerable interest and potential importance in devising chemoprotective strategies in humans. The methylsulfinylalkyl glucosinolates contained in high concentrations in sprouts are monofunctional inducers (see above, and ref. 15
Consequently, there are potential limitations to the use of indole glucosinolates as chemoprotectors in humans because they (i
) are weak inducers of phase 2 enzymes, (ii
) are bifunctional inducers that activate phase 1 enzymes, (iii
) may have estrogen receptor binding activity (30
), and (iv
) are potential tumor promoters.
Large quantities of inducers of enzymes that protect against carcinogens can be delivered in the diet by small quantities of young crucifer sprouts (e.g., 3-day-old broccoli sprouts) that contain as much inducer activity as 10–100 times larger quantities of mature vegetables. Moreover, the inducer activity arises primarily from glucoraphanin (the glucosinolate of sulforaphane) and such sprouts contain relatively low quantities of indole glucosinolates, which are potential tumor promoters. Because little is known of the metabolism of glucosinolates in humans, we have undertaken studies (to be published separately) that demonstrate efficient conversion of glucosinolates to isothiocyanates in humans in the absence of plant myrosinase.