LEVELS OF IODINE IN SRI LANKAN FOOD VARIETIES
by
Wathure Vidanalage Shirani Manel Perera
Thesis submitted to the University of Sri Jayawardenepura
Master of Philosophy in Chemistry on 14.12.2000
164614
for the award of the degree of
VIII
Levels of Iodine in Sri Lankan food varieties
by
Wathure Vidanalage Shirani Manel Perera
ABSTRACT
Iodine is needed for the synthesis of thyroid hormones which are necessary for mental
and physical health of both humans and animals. It cannot be synthesized in the human
body and therefore should be provided in the daily diet. Daily requirement
150 ug for an adult.
is around
The non availability of this amount regularly can lead to iodine
deficiency disorders (IDD) of which the best known manifestation
is endemic goiter.
One approach for elimination and prevention of iodine deficient disorders in Sri Lanka
would be from iodine rich dietary sources without
recourse
iodization of salt.
of Sri Lankan
The inclusion
of iodine content
to measures
such as
foods in food
composition tables can make the public aware of the iodine levels in foods consumed in
their daily diet. Thus the objective of this study was to determine the levels of iodine in
Sri Lankan food varieties.
This involved the use of Sandell and Kolthoff reaction which
is a the redox reaction between Ce(IV) and As(III) catalyzed by trace amounts of iodide
ions in acidic medium.
Kinetics are monitored over longer reaction times and a different
calibration plot to those previously
published was employed
in the determination
of
iodide concentration.
The method is relatively sample and sensitive and the minimum
working concentration
was found to be 4 ng cm-3 in the working iodide solution.
The
IX
accuracy was found to be satisfactory
and low levels of iodide.
included prawns,
crabs,
and coconut/king
coconut
The Sri Lankan
fish, cereals,
6 ug/l l Og).
concentrated
significant loss of iodide
iodide content
with and
The iodide
both at high
for iodide
in this study
tap/ground
water
Penaeus indicus (Indian
in the edible
prawn)
collected
content
was
under
study,
semisulcatus
highest
iodide
loss being greater
prawns
with the exo-skeleton
flesh.
The mean iodide
exo-skeleton)
collected
(Green
from Negombo
was
tiger
on
three
Penaeus indicus
in
found
rather than in the edible flesh. Boiling
with relative
boiling
without
analyzed
fruits, vegetables,
(Giant tiger prawn),Penaeus
For all species
in the exo-skeleton
skeleton. Moreover,
spices,
ensis (Greasyback
different days was determined.
±
pulses,
analyzed
of four marine prawn species,namely,
white prawn), Penaeus monodon
prawn), and Metapenaus
food variety
solution
water.
The iodide content
(121
for all the standard
to be largely
of prawns
when boiled
without
leads to
the exo-
intact leads to an increase
levels of raw prawn
on three different
species
the
(both
days are not significant
(p> 0.5).
The iodine
sanguinolentus
determined.
content
and
Marine
of three crab species
Scylla serrata
crab
flesh
collected
namely
Neptunus pelagicus,
on different
(Neptunus pelagicus,
days
62.3
from
Neptunus
Negombo
± 2.8 1lg/100g; Neptunus
Sanguinolentus, 95.8 ± 4.9 ug/I OOg) is a rich source of iodine, compared
to lagoon crab
(Scylla Serrata, 29.4 ± 1.9 ug/l ~Og). The most of the iodine in crabs are concentrated
the gills.
Iodine
in raw crab flesh was lost on boiling
percentage
iodine
loss from marine
crabs (33.5
was
(35 - 55%)
± 3.7) significantly
in
and the relative
lower
than lagoon
x
crabs (49.9 ± 4.7).
The relative percentage loss of iodine from crabs was in the same
range as prawns.
The iodine content of twenty seven species of marine/fresh
water fish collected
from different areas of Sri Lanka on different days has also been determined.
The iodine
content in marine fish was found to be significantly higher (three to five times) than fresh
water fish except in the case Histophorous
gladius which had a very low iodine level.
Large marine pelagics had a significantly lower level of iodine than small pelagics.
species under study lost iodine on boiling. A comparison of the means (p
zx:
All
0.05) of the
relative percentage loss of iodine in marine/fresh water fish during boiling indicates that
the loss in large marine pelagics and fresh water fish is significantly higher than small
marine pelagics and marine fish respectively.
The iodide content of five types of pulses namely Phaseofus
bean/Green gram), Cicer arietinum (Chick-peaslKadala),
aureus (Mung
Lens esculentas (Mysoor dhal),
Cajanus cajan (Bengal grarn/Kadala parippu), & Vigna sinensis (black pea/cowpea) and
three types of cereals namely Oryza sativa (rice: sudu kekulu (polished), rathu kekulu
(raw), samba
(parboiled),
(milletlkurakkan)
purchased
Triticum
vulgarae
(wheat
flour)
& Eleusine
from two areas in Sri Lanka was determined
coracana
using the
Sandell and Kolthoff reaction.
Of all species analyzed, Phaseolus aureus falls into the iodine rich category and
can provide the daily recommended
quantity of iodine with one single meal. Boiling of
these foodstuffs leads to loss of iodine with the relative loss being greater for cereals than
for pulses.
XI
Significant differences (p < 0.05) were seen in the mean iodide levels of each
pulse analyzed from the two areas whereas same with cereals were largely non significant
(p> 0.05).
The iodine content of coconut/king coconut water, tap water, ground water, fruits,
vegetables and spices has been determined
using the Sandell and Kolthoff reaction.
Coconut/king coconut water is a rich source of iodine compared to tap/ground water and
their iodide content fluctuate with maturity.
poor sources of iodide.
Among
In general, vegetable, fruits and spices are
the spices, however,
higher
levels are found in
Cumminum cyminum (cumin), Murraya koenigii (curry leaves) and Foenniculum
vulgare
(maduru). Among the fruits, highest level of iodine was found in Annona squamosa
(20.9 ± 0.8 ug/l Oug).
In vegetables,
fruit vegetable showed higher levels of iodine
compared to earth and herbage vegetables.
I
Table of Contents
Page no.
List of tables
IV
List of figures
v
List of plates
VI
Acknowledgements
VII
Abstract
VIII
CHAPTER 1
1.1
1.2
1.3
1.4
1.5
1.6
Importance of iodine
The iodine cycle
Iodine deficiency disorders
Thyroid hormone synthesis -involves thyroglobulin and
iodide metabolism
Transport and metabolism ofthyroid hormones
Prevention and control of iodine deficiency disorders
CHAPTER 2
2.1
2.2
2.3
2.4
LITERATURE
REVIEW
Determination of trace amounts of iodine using Sandell
and Kolthoff reaction
Spectrophotometric methods used in the micro determination
of iodide other than the Sandell and Kolthoff reaction
Other methods used in the determination of trace levels of iodine
other than kinetic methods
Scope of the thesis
CHAPTER 3
3.1
3.2
INTRODUCTION
METHODOLOGY
Reagents
Preparation of reagents
3.2.1 Preparation of 0.02M Ce(IV) Solution
3.2.2 Preparation of 0.12 M As(III) Solution
3.2.3 Preparation of standard iodide solutions
3.2.4 Preparation of 0.52 mol dm-3 zinc sulphate solution
3.2.5 Preparation of 1 mol dm-3 potassium hydroxide
1
1
2
3
12
18
19
26
26
30
37
38
40
40
42
42
42
42
43
43
II
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.13
3.14
3.15
3.16
3.17
3.18
3.19
3.20
3.21
3.22
3.23
Instruments used
Cleaning of glassware
Sample collection
Identification of samples
Sample storage
Moisture determination
Procedure for ashing
Preparation of ash solution
Effect of boiling
The theory involved in the determination of trace levels of iodide
by iodide catalyzed Ce(TV)/As(TTI) redox reaction
Selection of wave length
Temperature control of the reaction
Order 0 f adding reagents
Calibration curve
Estimation of the iodide content in a given sample
Analysis of prawns
3.18.1 Sampling of prawns for analysis
3.18.2 Ashing of samples
3.18.3 Effect of boiling
3.18.4 Determination of iodide in prawn samples
3.18.5 Determination of moisture
Analysis of crabs
3.19.1 Sampling of crabs for analysis
3.19.2 Ashing of samples
3.19.3 Effect of boiling
3.19.4 Determination of iodide in crab samples
3.19.5 Determination of moisture
Analysis of fish
3.20.1 Sampling of fish for analysis
3.20.2 Ashing of samples
3.20.3 Effect of boiling
3.20.4 Determination of iodide in fish samples
3.20.5 Determination of moisture
Analysis of cereals and pulses
3.21.1 Sampling of cereals and pulses
3.21.2 Ashing of sam les
3.21.3 Effect ofboilmg
3.21.4 Determination of iodide in pulses and cereals
Analysis of Cocos nucifera (king coconut/coconut water)
3.22.1 Sampling
3.22.2 Determination of iodide in king coconut/coconut water
Analysis of tap water/ground water
3.23.1 Sampling
3.23.2 Determination of iodide in tap water/well water
44
44
44
45
45
45
45
46
47
47
50
50
51
52
55
62
62
62
63
63
64
64
64
64
64
64
65
65
65
65
65
66
66
66
66
66
67
67
68
68
68
68
68
69
III
3.24
3.25
3.26
Analysis of spices/fruits/vegetables
3.24.1 Sampling
3.24.2 Ashing
3.24.3 Determination of iodide in fruits, spices and vegetables
Precision, detection limit and accuracy
Statistical analysis of results
CHAPTER 4
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
Iodine
Iodine
Iodine
Iodine
Iodine
Iodine
Iodine
Iodine
RESULTS
in
in
in
in
in
in
in
in
prawns and crabs
marine/fresh water fish
pulses and cereals
spices
vegetables
fruits
coconut/king coconut (Cocos nucifera)
ground water
CHAPTERS
5.1
5.2
5.3
5.4
5.5
5.6
69
69
69
69
70
70
71
71
80
81
83
83
84
84
86
DISCUSSION
106
in prawns
in crabs
in marine/fresh water fish
in pulses and cereals
in king coconut/coconut water
in tap water and ground water
in spices
in fruits
in vegetables
106
107
5.9
Iodine
Iodine
Iodine
Iodine
Iodine
Iodine
Iodine
Iodine
Iodine
6.
Conclusions
114
7.
References
116
8.
Appendix
I
124·
9.
Appendix
II
132
5.7
5.8
108
109
110
III
112
113
113