3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
P87 IODINE IN MILK ON ThE CZECh MARKET
RADEK KAVříK, IREnA řEHůřKOVá and JIří
RUPRICH
National Institute of Public Health – Centre for Hygiene of
Food Chains, Palackého 3a, 612 42 Brno, Czech Republic
kavrik@chpr.szu.cz
Introduction
Iodine is an essential trace element. Biological role of
this trace element is related to the hormonal system of thyroid
gland where iodine is a constituent of thyroid hormones.
Therefore iodine is very important element also for human
population. natural sources of iodine are e.g. seaweed, seafood
and also plants grown on iodine-rich soil 1 .
Iodine deficit is typical problem for areas where there
is low content of iodine in the diet especially in areas where
seafood consumption is low 2 . It is well known that Europe
and therefore also the Czech Republic belong between countries
with known iodine deficiency. Usual public health protection
measure is fortification of salt with iodine.
Many studies have been published about problem of
dietary intake of iodine for the Czech population. Summary
study about situation in the Czech Republic published Scientific
Committee on Food in 2007 3 .
The national Institute of Public Health in Prague, Centre
of Hygiene of Food Chains in Brno is involved in “The Project
on Dietary Exposure to Selected Chemical Substances” 4 .
The objective of the project is to describe the dietary exposure
of the population of the Czech Republic. In the framework of
this project iodine has been monitored since 1998.
Since year 2000 to 2003 has been observed increasing
trend of iodine intake. This effect causes mainly usage of fortified
salt in kitchen and during industrial food processing.
Doses observed in the 2003 reached 3.59 μg kg –1 b.w./day
(230 μg/person/day) 5 . This value matches 153 % of recommended
daily intake by Czech law (Regulation 446/2004).
As a biomarker of short term (24 hours) intake of iodine
the urinary level is mostly used. The national Institute
of Public Health in Prague and some other institutes monitor
urinary level of iodine for many years. It was recognized that
average iodine concentration in adult’s urine increased from
85 μg dm –3 to 251 μg dm –3 (ref. 6 ) during years 1995–2005.
This increase can be attributed to some specific foods in
our diet. High concentrations of iodine were measured in fish,
meat products, instant soups, milk and milks products. It was
recognized that significant exposure sources are mainly milk
and milks products, bread, meat products and eggs (descending
order to total exposure dose).
Probabilistic modelling was used to estimate usual daily
intake of iodine from various kinds of foodstuffs for age
groups in the Czech population 3,7 . It was observed that milk
is the most important source of iodine for various age groups
in the Czech Republic. Results of that modelling (it did not
take added salt after cooking into account) also support an
idea that high intake of iodine can be a certain risk for young
s774
children (< 10 years) where milk and dairy produces represent
very important parts of their diet 7 .
That was the reason why our laboratory focused its
research on iodine concentration in marketed consumer
milk.
Experimental
Twice a year, in May and november, 24 samples of milk
(12 semi-skimed and 12 skimed milks) were purchased from
markets in twelve towns in the Czech Republic. These samples
were analyzed as one composite sample. Milk samples
have been also analysed as individual samples since 2007 to
get better imagination about distribution of iodine concentrations.
For determination of iodine was used Sandell-Kolthoff
method. The principle of this method is in catalytic function
of iodide in oxidation-reduction reaction Ce(IV) and As(III).
Samples are transferred to refractory glass tube. Solutions
of potassium hydroxide and zinc sulphate are added.
These mixtures are stirred and tubes are placed in an oven at
105 °C to dry the samples and then in a cold muffle furnace
where are left until temperature gradually rises to 600 °C.
The tubes are taken out. At this stage the food samples are
not completely digested. The samples are soaked with 0.5 ml
of water and then placed in a cold muffle furnace and digestion
process is repeated. now the samples are completely
digested. Into each tube containing the digest, 6 ml of water
is added and stirred to dissolution of the water-soluble part
of the digest. The suspension is transferred into a centrifuge
tube and centrifuged for 10 min at 2500 rev min –1 .
Aliquot of the supernatant liquid is transferred to the glass
tube and refilled with water to 2 ml. Then 2 ml of arsenic(III)
solution is added and the tube is placed in the cooling bath
(10 min). Then 2 ml of cerium(IV) solution is added and the
tube is placed in the water bath at 40 °C (20 min) and then in
the cooling bath (10 min). Then 0.5 ml of brucine is added
and the tube is placed in an oven at 105 °C (15 min). After
adding of every solution thorough stirring is important.
Finally, a light absorption is measured by spectrometer
at 430 nm. Limit of quantification is 15 μg kg –1 . This method
is accredited according to CSn En ISO/EC 17025:2005 by
the Czech Accreditation Institute.
Results
Average concentration of iodine in milk analysed since
1998 to 2007 is 268 μg kg –1 . The results are shown in Fig. 1.
Average concentration of iodine in milk composite samples
has been higher since 2003.
In 2007, after publishing of results clarifying a key
role of milk in iodine intake, we analyzed all of 24 samples
from the Czech market individually. Results for semi-skimed
milks are shown in Fig. 2. and for skimed milk in Fig. 3.
Semi-skimed milk from town no. 7 (May, 07) has not been
determined.
Average content of iodine in semi-skimed milk was
344 μg kg –1 in May and 277 μg kg –1 in november. Average