Glucosinolates are sulfur-containing compounds found in cruciferous vegetables like broccoli and cabbage. They are hydrolyzed by the enzyme myrosinase into isothiocyanates and other compounds. Indole glucosinolates were discovered in these vegetables and are synthesized from tryptophan. Key indole glucosinolates include glucobrassicin and neoglucobrassicin. Their breakdown products can induce various drug metabolizing enzymes and may have anticancer effects, though they also have some goitrogenic effects on the thyroid. Their reaction with nitrites can form potentially carcinogenic nitrosamines.

1. GLUCOSINOLATES IN
VEGETABLE CROPS
PRESENTEDBY,
VANISREE PADMANABHAN
2019534005
DEPT OF VEGETABLE SCIENCE

2. INTRODUCTION
 The medicinal properties of the volatile, pungent oils obtained
from members of the family Cruciferae.
 The volatile oils were isothiocyanates which were not present in
the plant as such, but as involatile precursors, and that they were
only obtained after the plant or seed was crushed in water.
 Two such nonvolatile precursors (mustard oil glycosides or
glucosinolates) were iso- lated from species of mustard and later a
general structure for glucosinolates was suggested by Gadamer
(1897).

3. CONTD.,
 Glucosinolates are hydrolysed by an enzyme, myrosinase which
is also present in the plant tissue, and most yield volatile alkyl or
aryl isothiocyanates amongst other products (notably sulphate and
glucose).
 A second, very much smaller, group of glucosinolates give cyclic
thioamides.
 These latter products, such as oxazolidine-2-thiones, have been
shown to be the causative agents in 'brassica seed goitre.

4. DISCOVERY OF INDOLE
GLUCOSINOLATES
 Indole-3-acetonitrile isolated from cabbage, and showed it to
possess rather less activity as a growth agent than indoleacetic
acid. Shortly afterwards, following much research, Czech
 Later a bound form of ascorbic acid (ascorbigen) isolated from
cabbage and other brassicas contained an indole group
(Prochazka, 1954).
 The first two indole glucosinolates - gluco- brassicin and neo-
glucobrassicin and the realization that the observed products were
a result of their enzymic hydrolysis.

5. OCCURENCE AND BIOSYNTHESIS
 The occurrence of indole glucosinolates in etiolated seedlings
Schraudolf & Bergman (1965) considered both glucobrassicin
and neoglucobrassicin to be present in the Capparadaceae.
 The co-occurence of serotonin (5-hydroxytryptamine) and indole
gluco- sinolates in Tovaria pendula is especially interesting, and
has led to speculation that 5-hydroxyglucobrassicin may yet be
found in this plant.
 Within individual plants indole glucosinolates are found in
increasing amounts in young shoots and growing leaves they are
present in relatively small amounts in senescing tissue and in
etiolated plants

6. INTERMEDIATE COMPOUNDS
 An important intermediate in the biosynthesis of indole
glucosinolates appears to be indole-3-acetal- doxime.
 Labelled indole-3-acetaldoxime (derived bio- synthetically from
tryptophan) has been converted to glucobrassicin in woad leaves
(together with glucobrassicin-l-sulphonate) and Sinapis alba
shoots.

7. METHODS OF ANALYSIS
 The most common methods of detection involve reaction of the released
ion with ferric salts and spectrophotometric measurement of the intensely
red complex thus formed (Josefsson, 1968).
 A second approach involves oxidation of thiocyanate and quantification
using spectrophotometry, or less commonly, gas chromatography (GC).
 The analysis of thiocyanate ion, released by indole glucosinolates, in
forage brassicas has been automated with a continuous flow analysis
(Gosden, 1978).
 The detection and determination of individual indole glucosinolates was
originally carried out by TLC, using Ehrlich's reagent or p-dimethyl-
amino cinnamaldehyde solution for visualization.

8. LEVELS OF INDOLE GLUCOSINOLATES

9. CONTD.,

10. BREAKDOWN OF INDOLE GLUCOSINOLATES
Enzymic breakdown

11. GLUCOBRASSICIN – chemical
breakdown

12. BIOLOGICAL EFFECTS OF GLUCOBRASSICIN
 In a similar study (Pantuck et al. 1976) rats were dosed orally
with diindolylmethane (175 mg/kg body weight), indole-3-
carbinol (100mg/kg) or indole-3- acetonitrile (95 mg/kg) twice
daily for 3 days.
 The rats were killed 18 hr after the last dose of indole. Intestinal
metabolism of phenacetin, 7-ethoxy- coumarin, hexobarbitone
and benzo[a]pyrene were increased by all three indole
glucosinolate hydrolysis products.
 Indole-3-carbinol was the most potent inducer, increasing
intestinal 7-ethoxycoumarin and benzo[a]pyrene hydroxylation
16- and 22-fold, respectively.

13. BIOLOGICAL EFFECT
Goitrogenicity
 The goitrogenic potential of Brassica vegetables is well established (Fenwick et al.
1983).
 This effect on the thyroid has been linked to the hydrolysis products of two
glucosinolates, namely 5-vinyloxazolidine-2-thione (goitrin) and thio- cyanate ion.
 The former, derived from progoitrin is the more potent, exerting its effect via
interference of thyroid hormone synthesis.
 In contrast, thiocyanate ion, derived from glucobrassicin (and presumably other indole
glucosinolates) competes with iodine for uptake by the thyroid gland.
 In a recent study in which human volunteers were given diets containing Brussels
sprouts, there was no effect on thyroid function as determined by measurement of
thyroid stimulating hormone, triiodothyronine and thyr- oxine.

14. NITROSATION OF INDOLE COMPOUNDS:
 A possible hazard from indoles in the diet is an ability of this type
of chemical to react with nitrites to form carcinogenic N-nitroso
compounds.
 A recent study (Wakabayashi et al. 1985b) has shown that indole-
3-acetonitrile can react with nitrite in vitro to form compounds
that are mutagenic in the Ames test.
 The high ascorbic acid content of cruciferous vegetables may,
therefore, inhibit nitrosation reactions.