DETERMINATION OF IODINE AND SOME ASSOCIATED PARAMETERS IN SOME FOODSTUFFS
DETERMINATION OF IODINE AND SOME ASSOCIATED PARAMETERS IN SOME FOODSTUFFS
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Date
1996-04
Authors
HAJEKODUNMI, OLAYIDE BOLAJOKO
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Abstract
Fifty-two food items of various types (grains, seeds,
fruits, vegetables, roots and tubers, fish, meats and egg and
others} were analysed for their iodine contents. Moisture,
starch, crude protein, lipid, carbohydrate, ash, minerals (Na,
Ca, Fe, and Cu) and the known goitrogens, thiocyanate and
phenol, were also determined in some of the food samples.
A preliminary study of the variation of absorbance with
time for some of the samples in the determination of the
iodine content by the Moxon and Dixon method (1980) showed
that for certain foodstuffs colour development was complete
before the recommended time. Finding the optimum time for the
reaction and further dilution of some sample extracts were
found to improve the determination of iodine.
The iodine content of the samples ranged from 0.24 ppm
(Carrot) to 750 ppm (Sweet potato). The fish, meats, and egg
were generally found to be richest in iodine. The grains on
the other hand gave some of the lowest values for iodine. It
was observed that the removal of the testa of brown beans led
to a significant loss in iodine content.
As expected, the grains, roots and tubers gave the
highest values for starch, while the fruits and vegetables
showed the lowest values. Rased on their starch and iodine
contents, the foodstuffs may be grouped into three categories,
namely: (a) foods rich in iodine but low in starch, (b) foods
relatively rich in iodine and starch, and (c) foods relatively vii
poor in iodine but rich in starch.
The crude protein content of the foodstuffs ranged from
4.1% (sweet potato) to 69.7% (olarias). Cabbage, unexpectedly
was shown to be high in crude protein (21.4%). A comparison
of the crude protein and iodine contents showed that a high
crude protein is usually accompanied by a high iodine content
in the samples analysed.
The lipid content of groundnut was found to be highest
(51.4%) followed by those of beef (35.6%) and soyabeans
(21.5%). The grains showed the lowest values (below 1%). A
comparison of the lipid and iodine content for some of the
foodstuffs showed that generally, a moderate to high lipid
content (over 10%) was accompanied by a high iodine content
(over 200 ug/g). Foods rich in both lipid and crude protein
content tended to have high iodine content.
The carbohydrate content of the grains, roots and tubers
were expectedly the highest (over 20%) while those of the fish
and meat were lowest (below 4%). No distinct trend was
observed between the iodine and carbohydrate contents of the
foodstuffs.
For most of the samples studied, it. was found that the
calcium content is much lower than the sodium content. The
removal of the testa of brown beans led to a significant
reduction in both the sodium and calcium contents. A
comparision of the sodium, calcium, and iodine contents of
some foodstuffs indicates that the iodine in foodstuffs may be viii
present in forms other than the iodide and iodate of sodium
and calcium in which it occurs in nature, as there was no
obvious correlation between these parameters.
Both copper and iron were found to be relatively high in
plant materials while in the animal materials examined, high
copper content was accompanied by low iron content. A
comparision of the iodine content with the iron and copper
contents showed the Fe: I ratio to be greater than 1 for most
of the foodstuffs. Generally the Cu: I ratio was less than 1.
However, millet, guinea corn, soyabeans, yam, and garden egg
all have Cu:I ratios above 1 and may therefore be
goitrogenous.
The known goitrogen thiocyanate, was not detected in the
food items analysed but the goitrogen phenol, was observed in
onion, garri, fluted pumpkin leaf, and millet. This seems to
support the suggestions that onion, garri, and millet are
goitrogenous. The proposition that millet particularly may be
goitrogenous is supported by its low contents of iodine and
protein, a high carbohydrate content, a Cu: T ratio above 1,
and its phenolic content.
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Keywords
PARAMETERS IN SOME FOODSTUFFS, PARAMETERS IN SOME FOODSTUFFS