Health benefits of dietary glucosinolates and its derived isothiocyanates

Abstract

The consumption of cruciferous vegetables lowers
incidences of chronic diseases like cancer. Some of the
major cruciferous vegetables consumed as fresh or cooked
are broccoli, cabbage, cauliflower, Brussels sprouts etc.
These vegetables contain biologically active compounds
like glucosinolates and its derived isothiocyanates.
Isothiocyanates are sulfur containing secondary metabolites
and possess chemopreventive activity. This review provides
information on glucosinolates and its derived
isothiocyanates and with some insights on the mechanisms
for cancer inhibition.

Full text

Indian Food Industry Mag
Vol 36 No 2, Mar-Apr 2017
3131
3131
31
TARs
Health benefits of dietary glucosinolates and its derived
isothiocyanates
Rohit Thirumdas a*, Anjineyulu Kothakotab
aDepartment of Food Engineering and Technology, Institute of Chemical Technology, Mumbai-
400019 (India)
bDepartment of Food and Agricultural Process Engineering, Kelappaji College of Agricultural
Engineering and Technology, Thavanur-679573 (India).
*E-mail: ft12rr.thirumdas@pg.ictmumbai.edu.in
Abstract
The consumption of cruciferous vegetables lowers
incidences of chronic diseases like cancer. Some of the
major cruciferous vegetables consumed as fresh or cooked
are broccoli, cabbage, cauliflower, Brussels sprouts etc.
These vegetables contain biologically active compounds
like glucosinolates and its derived isothiocyanates.
Isothiocyanates are sulfur containing secondary metabolites
and possess chemopreventive activity. This review provides
information on glucosinolates and its derived
isothiocyanates and with some insights on the mechanisms
for cancer inhibition.
Introduction
Global hunger remains an important challenge,
which is bound to elevate with the growing population
of the world. By 2050, the population on earth is
estimated to reach 10 billion, which points to the need
for innovative approaches for food production and
processing to meet the global demand for nutritional
intake. It is recognized that the chronic diseases including
degenerative diseases, in particular, cancer is the major
threat to human health. In recent years, the foods with
chemo- preventive properties are in high demand as the
consumers are turning health conscious. Under this
scenario, bioactive compounds in foods with health
benefits could prove highly valuable in dealing with such
demands. One of such bioactive compounds present in
vegetables consumed as the salads are dietary
isothiocyanates. More than 120 glucosinolates were
identified in plants which are the precursors for
isothiocyanates are known to possess the chemopreventive
and chemotherapeutic activity. Consumption of cruciferous
vegetables is subjected to lower the risk of cancer proved
in epidemiological studies. Consumption of vegetables
rich in isothiocyanates reduced the risk of lung cancer and
reduction of 57% of colon rectal cancer in individuals
(Manchali et al., 2012). Dietary isothiocyanates are the
derived compounds of glucosinolates, formed when acted
upon by enzyme myrosinase. The glucosinolates are the
major sulfur containing secondary metabolites (non-
nutritive) present in the cruciferous vegetables. The
bioactivity of these compounds, in turn depends on the
chemical structure of isothiocyanates with respect to their
side chain. These bioactive compounds are mainly
concentrated in the vegetables of cruciferous belong to
Brassicaceae family like broccoli, Brussels sprouts,
cabbage, kale, turnip, rape, mustard, radish etc. Mostly,
the vegetables of this family are consumed as the salads.
The methods for determining the glucosinolates are
generally classified in to two categories i.e. individual
derivative compound of glucosinolates using HPLC
(cyclocondensation), LC-MS/MS, GC-MS and total
glucosinolates content by using spectrophotometer (Wu et
al., 2017).
Dietary sources of glucosinolates
The cruciferous vegetables are the richest sources
of dietary isothiocyanates. Each cruciferous vegetable
contains a mixture of glucosinolates that varies according
to the cultivar of the plant. Some of the important
isothiocyanates found in Brassica family are 2-propenyl
(allyl), indole-3-methyl, 4-methylsulfinylbutyl
(sulforaphane), 3-methylsulfinylpropyl, 3-butenyl, 2-
hydroxyl-3-butenyl (IARC, 2004; Barba et al., 2015).
Chemical structure of glucosinolates and
isothiocyanates
Glucosinolates are the precursors of the
isothiocyanates and these are classified according to the
molecular structure of side-chains. The glucosinolates are
sulfur containing glycosides comprises of glucone moiety
and aglucone side-chain. The aglucone side-chain may be
aliphatic, aromatic and heterocyclic compounds containing
any one of the eight amino acids like alanine, valine,
leucine, isoleucine, phenylalanine, methionine, tyrosine,
and tryptophan (Deng et al. 2015). From the all known
glucosinolates side-chain, about 50% of glucosinolates are
derived from methionine amino acids followed by valine
and phenylalanine. The side-chain of glucosinolates
undergoes modifications like elongation, oxidation, and
hydroxylation. Myrosinase enzyme is an endogenous plant
enzyme (thioglucoside glucohydrolase EC 3.2.1.1) which

Indian Food Industry Mag
Vol 36 No 2, Mar-Apr 2017
3232
3232
32
TARs
hydrolysis the glucosinolates into isothiocyanates. These
enzymes are separated from the glucosinolates which are
present in intact cells called myrosin cells. The enzyme
is released when the tissue is disrupted during chopping
or chewing, interacts with glucosinolates and releases
isothiocyanates. The chemical structure of glucosinolate
and isothiocyanate is given below
The importance of side chain R in the structure of
glucosinolates it defines whether it is aliphatic, aromatic,
aryl or indole. Some of the important R structures observed
in the cruciferous vegetables are given in the Table 2.
Bioavailability and bioaccessibility
The term bioavailability refers to ingested nutrient

Indian Food Industry Mag
Vol 36 No 2, Mar-Apr 2017
3333
3333
33
TARs
or any bioactive compound absorbed in the systemic
circulation and is utilized. The term bioaccessibility is
defined as the quantity or fraction of nutrient released into
the gastrointestinal tract during digestion and available for
absorption. During the processing or chewing of
cruciferous vegetables the contact between the myrosinase
enzymes and glucosinolates increases and results in release
and absorption of isothiocyanates. Shapiro et al. (1998)
reported that the inactivation of myrosinase enzymes using
heat or other food processing operations like steaming or
boiling decrease the release in isothiocyanates. Table 2
presents the data of the glucosinolates and its derived
compounds observed before and after steaming of
broccoli. Apart from myrosinase enzyme present in
vegetables, the glucosinolates are hydrolyzed into
isothiocyanates by the myrosinase enzymes released by the
intestinal microflora (Getahun and Chung, 2000; Fahey et
al., 2012). The released isothiocyanates are absorbed
immediately into the blood and reached peak concentration
in the plasma after the 1 h of ingestion. The bioavailability
of the isothiocyanates in the humans was studied after
analyzing the derived compounds from the urinary extracts
of ingested volunteers. The isothiocyanates during
metabolic processing conjugates with glutathione and
further metabolized to mercapturic acids and these can be
detected in the urine. Seow et al. (1998) stated that
metabolized compounds observed in the urine have the
direct correlation to the intake of the glucosinolates. The
isothiocyanates excreted after the consumption of fresh
broccoli is three times higher than the steamed cooked

Indian Food Industry Mag
Vol 36 No 2, Mar-Apr 2017
3434
3434
34
TARs
broccoli. The main reason for the difference might be the
inactivation of myrosinase enzyme in the steamed cooked
broccoli. The supplement of external myrosinase enzymes
extract could solve the problem and result in the increase
of hydrolysis of glucosinolates before consumption.
Similarly, after the consumption of cooked watercress for
3 min, the urinary excretion reported only 1.2-7.3% of
total glucosinolates consumed whereas the consumption
of uncooked resulted up to 77.7% of isothiocyanates. The
time of chewing of cruciferous vegetables also affects the
release of isothiocyanates. Shapiro et al. (1998) observed
twice the concentration of isothiocyanates released in the
thoroughly chewed vegetables than the directly swallowed
or un-chewed.
Anti-cancer activity of isothiocyanates
The chemopreventive potential of isothiocyanates
was discovered before 30 years, from then it triggered the
research interest focusing on its health benefits. Till date,
extensive research has been done on the anti-cancer
mechanism of isothiocyanates. Tang et al. (2013) have
reported that isothiocyanates have anti-cancer action on
different cancer modules in both in-vitro and in-vivo
systems including colon, liver, bladder and oesophagus.
Isothiocyanates are sulfur containing compounds with
chemopreventive activity against cancer with induction of
apoptosis and cell cycle progression to inhibit the growth
of malignant tumors (Singh and Singh, 2013). The
anticancer activity of isothiocyanates is pertinent to
inhibition of phase-I enzymes (mainly p450) responsible
for bioactivation of carcinogens (Conaway et al., 2000).
The induction of phase-II enzymes by these isothiocyanates
help in the removal of xenobiotic metabolites form the
body which are potent anti-carcinogens (Manchali et al.,
2012). Some of the xenobiotic compounds like
phenobarbital-like compounds (CAR) and dexamethasone
and rifampin-type of agents (PXR) are removed by the
isothiocyanates (sulforaphane) (Xu et al., 2005). The
induction of these enzymes by isothiocyanates reduced the
risk of breast cancer. The induction of glutathione S-
transferase by sulforaphane was observed in prostate cancer
cells. The sulforaphane is known to arrest the cells in G2/
M phase and induction of apoptosis in prostate cancer cells
(Xiao et al., 2003). The induction of apoptosis and cell
cycle arrest in human adenocarcinoma was also observed
by sulforaphane. The major mechanism of anti-cancer
activity of isothiocyanates is through apoptosis, cell cycle
arrest, oxidative stress pathways, autophagy, alteration of

Indian Food Industry Mag
Vol 36 No 2, Mar-Apr 2017
3535
3535
35
TARs
carcinogen metabolism, induction of caspase-dependant
and independent apoptosis (Singh and Singh, 2003;
Manchali et al., 2012).
Isothiocyanates are known to have anti-angiogenic
effect and decrease the expression of vascular endothelial
growth factors and inhibit the capillary tube-like structure
formation in cancer cells. One of the important anti-
cancer activities of isothiocyanates is depletion of mutant
p53. TP53 gene which codes the p53 protein is the most
frequent target for mutation in human cancer accounts
more than half of all tumors exhibiting mutation. The
isothiocyanates directly bind to p53 and conformational
change will result in depletion of mutant p53. The
isothiocyanates inhibits the transformation of epithelial
cells to mesenchymal cells in breast cancer cells (Singh
and Singh, 2003).
Other health benefits
The consumption of cruciferous vegetables is
related to decrease in the risk of cardiovascular diseases
by reduction of oxidative stress, ability to reduce LDL and
combat with free radicals. Isothiocyanates are known to
detoxify by involving in the Nrf2 or NFE2L2 (Nuclear factor
(erythroid-derived 2)-like 2) dependent signaling pathway.
Nrf2 is a basic leucine zipper protein which regulates the
expression of the antioxidants and xenobiotics genes that
protects against oxidative damage. Isothiocyanates are also
responsible for the prevention of metabolic disorders,
Alzheimer’s disease, reduction of obesity and these
bioactive compounds are also potential antimicrobial
agents. They have a significant effect on the gram negative
bacteria compared to gram positive bacteria.
Global consumption of cruciferous vegetables
Overall, the cruciferous vegetables are mostly
consumed in cooked state globally contributing to 80%
except in the Greece. The most commonly consumed
vegetable is cabbage accounting for 25% followed by
broccoli. The highest consumption of cruciferous vegetables
was reported for China, consumes more than 100 g/day.
Other Asian countries like Japan and Singapore consumes
40 to 80 g/day. Total estimated consumption in North
America is around 25-30 g/day, while the population of
South America and India consumes fewer quantities
approximately 14 g/day and 20 g/day respectively (IARC,
2004).
Conclusion
Cruciferous vegetables contain health beneficial
bioactive sulfur containing compounds like glucosinolates
and its derived compounds like isothiocyanates. The
isothiocyanates are biologically active compounds has been
proved to possess several health benefits like anti-cancer
activity. The chemopreventive activity of the isothiocyanates
mainly depends on the chemical structure of side chain.
The consumption of unprocessed or raw cruciferous
vegetables is more beneficial than the cooked or steamed.
The key mechanism of isothiocyanates anti-cancer activity
is through activation of enzymes and induction of
apoptosis in cancer causing cells. Through the
biotechnology approaches and other agricultural practices,
the increase in cultivation of cruciferous vegetables with

Indian Food Industry Mag
Vol 36 No 2, Mar-Apr 2017
3636
3636
36
TARs
the optimum content of these biologically active
compounds will be greatly beneficial for the consumers.
Further reading
Conaway CC, Getahun SM, Liebes LL, Pusateri DJ,
Topham DK, Botero-Omary M, Chung FL (2000).
Disposition of glucosinolates and sulforaphane in
humans after ingestion of steamed and fresh
broccoli. Nutr. & Cancer 38(2):168-178.
Deng Q, Zinoviadou KG, Galanakis CM, Orlien V,
Grimi N, Vorobiev E , Barba FJ (2015). The effects
of conventional and non-conventional processing
on glucosinolates and its derived forms,
isothiocyanates: extraction, degradation, and
applications. Food Eng Rev. 7(3): 357-381.
Getahun SM, Chung FL (1999). Conversion of
glucosinolates to isothiocyanates in humans after
ingestion of cooked watercress. Cancer Epidemiol.
Biomarkers & Prev. 8(5):447-51.
Fahey JW, Wehage SL, Holtzclaw WD, Kensler TW,
Egner PA, Shapiro TA, Talalay P (2012). Protection
of humans by plant glucosinolates: efficiency of
conversion of glucosinolates to isothiocyanates by
the gastrointestinal microflora. Cancer Prev. Res.
5(4):603-611.
International agency for research on Cancer (2004). IARC
handbooks of cancer prevention (Vol. 9). The
Agency.
Manchali S, Murthy KNC, Patil BS (2012). Crucial facts
about health benefits of popular cruciferous
vegetables. J. Funct Foods. 4(1): 94-106.
Seow A, Shi CY, Chung FL, Jiao D, Hankin JH, Lee HP,
Yu MC (1998). Urinary total isothiocyanate (ITC)
in a population-based sample of middle-aged and
older Chinese in Singapore: relationship with
dietary total ITC and glutathione S-transferase M1/
T1/P1 genotypes. Cancer Epidemiol. Biomarkers &
Prev. 7(9): 775-781.
Shapiro TA, Fahey JW, Wade KL, Stephenson KK,
Talalay P (1998). Human metabolism and
excretion of cancer chemoprotective glucosinolates
and isothiocyanates of cruciferous
vegetables. Cancer Epidemiol Biomarkers &
Prev. 7(12): 1091-1100.
Singh SV, Singh K (2012). Cancer chemoprevention with
dietary isothiocyanates mature for clinical
translational research. Carcinogenesis. 33(10):
1833-1842.
Song L, Thornalley P.J (2007). Effect of storage,
processing and cooking on glucosinolate content
of Brassica vegetables. Food & Chemical
Toxicol. 45(2): 216-224.
Tang L, Paonessa JD, Zhang Y, Ambrosone CB, McCann
SE (2013). Total isothiocyanate yield from raw
cruciferous vegetables commonly consumed in the
United States. J. Fun. Foods. 5(4): 1996-2001.
Verkerk R, Schreiner M, Krumbein A, Ciska E, Holst B,
Rowland I, De Schrijver R, Hansen M, Gerhäuser
C, Mithen R, Dekker M (2009). Glucosinolates in
Brassica vegetables: the influence of the food
supply chain on intake, bioavailability and human
health. Molecular Nutri. & Food Res. 53: S219-
S265.
Vallejo F, Tomás-Barberán F, Garcia-Viguera C (2002).
Glucosinolates and vitamin C content in edible
parts of broccoli florets after domestic cooking.
European Food Res. & Technol. 215(4): 310-316.
Vallejo F, Tomás-Barberán F, García-Viguera C (2003).
Health-promoting compounds in broccoli as
influenced by refrigerated transport and retail sale
period. J. Agric. & Food Chem. 51(10): 3029-3034.
Wu X, Sun J, Haytowitz DB, Harnly JM, Chen P,
Pehrsson PR. (2017). Challenges of developing a
valid dietary glucosinolate database. J. Food Comp.
& Analys. In press, corrected proof.
Xiao D, Srivastava SK, Lew K, Zeng Y, Hershberger P,
Johnson CS, Singh, SV (2003). Allyl
isothiocyanate, a constituent of cruciferous
vegetables, inhibits proliferation of human prostate
cancer cells by causing G 2/M arrest and inducing
apoptosis. Carcinogenesis 24(5): 891-897.
Xu C, Li CY, Kong AN (2005). Induction of phase I, II
and III drug metabolism/transport by xenobiotics.
Arch. Pharma. Res. 28(3):249-268.