SOME QUESTIONS CONCERNING THE IODINE CONTENT IN MILK

Sucman E., Z. Cvak, F. Kalous, O. Synek: Some Questions Concerning the Iodine Content in Milk. Acta Vet. Brno, 53, 1984: 65-69. The determination of iodine level in milk from various regions of Czechoslovakia was carried out. Average iodine contents found were ranging from 140 to 225 fl-g/l. A short-term application of Jodonal M caused a marked increase in iodine concentration in milk from the average value 122 fl-g/I up to 831 fl-g/I, the increased levels being sustained for 14 days from the beginning of application. A short pause followed by a new application of Jodonal M induced again an increased iodine concentration in milk. This, however, lasted for a shorter period of time, the maximum achieved iodine concentration (373 fl-g/I) being also considerably lower with regard to the first period. Iodide, ion selective electrode, iodophores. The concentration of iodine in various foodstuffs has been a subject of interest for a longer period of time, this being understandable when one takes into account the importance of this trace element for the biochemical functions of living organism. Milk, as a principal component of human nutrition, particularly of children, has been subjected to a close examination, especially during last years. The problems connected with the iodine content in milk have gained importance with the introduction of disinfectants, based on active iodine (so called iodophores), employed for disinfection of mammary glands of dairy cows as well as that of milking devices. All these measures were taken within the program of mastitis eradication. In this country several preparations have been commercialized under the trade name Jodonal (produced by Lachema). The iodine content in milk, as published by various authors during last years, varies within a wide range from 10 to 4840 fl-g/I the most frequent concentration being found within 100-300 fl-g/I (J oerin and Bowering 1972; Iwarson and Ekman 1973; Barrios 1976; Dunsmore 1976; Kalous, Oliveriusova 1977; Bruhn, Franke 1978; Hemken 1978; Miles 1978; Sucman et al. 1978; Lacroix, Wong 1980; Sheldrake et al. 1980). The iodine level in milk depends on two important factors: 1. Intake of iodine in various amounts and in its various chemical forms in food. 2. External application of active iodine-based disinfectants (the application way, the treatment of mammary glands before milking, active iodine concentration in the applied preparation). The problems connected with point 1) have been dealt with e. g. in works of Hi 1m an and Curtis (1980), Hemken et al. (1981) or Laarveld et al. (1981). As to the use of iodophores, i. e. point 2), the reviews have been published e. d. by Hemken (1979), Piekacz (1979) and Wheeler (1979). All the authors agreed that the application of iodophores is always accompanied by the increase of iodine level in milk, the extent of this increase being, however, dependent on the type of preparation, the concentration of active iodine, the application form and other factors. The studies related to the application of iodophores and the iodine concentration in milk were also published by Iwarson and Ekman (1973), Barrios (1976), Sheldrake et al. (1980) or Hemken et al. (1981).

The determination of iodine level in milk from various regions of Czechoslovakia was carried out.Average iodine contents found were ranging from 140 to 225 fl-g/l.A short-term application of Jodonal M caused a marked increase in iodine concentration in milk from the average value 122 fl-g/I up to 831 fl-g/I, the increased levels being sustained for 14 days from the beginning of application.A short pause followed by a new application of Jodonal M induced again an increased iodine concentration in milk.This, however, lasted for a shorter period of time, the maximum achieved iodine concentration (373 fl-g/I) being also considerably lower with regard to the first period.
The concentration of iodine in various foodstuffs has been a subject of interest for a longer period of time, this being understandable when one takes into account the importance of this trace element for the biochemical functions of living organism.Milk, as a principal component of human nutrition, particularly of children, has been subjected to a close examination, especially during last years.The problems connected with the iodine content in milk have gained importance with the introduction of disinfectants, based on active iodine (so called iodophores), employed for disinfection of mammary glands of dairy cows as well as that of milking devices.All these measures were taken within the program of mastitis eradication.In this country several preparations have been commercialized under the trade name Jodonal (produced by Lachema).
The iodine content in milk, as published by various authors during last years, varies within a wide range from 10 to 4840 fl-g/I the most frequent concentration being found within 100-300 fl-g/I (J oerin and Bowering 1972;Iwarson and Ekman 1973;Barrios 1976;Dunsmore 1976;Kalous, Oliveriusova 1977;Bruhn, Franke 1978;Hemken 1978;Miles 1978;Sucman et al. 1978;Lacroix, Wong 1980;Sheldrake et al. 1980).The iodine level in milk depends on two important factors: 1. Intake of iodine in various amounts and in its various chemical forms in food.2. External application of active iodine-based disinfectants (the application way, the treatment of mammary glands before milking, active iodine concentration in the applied preparation).
The problems connected with point 1) have been dealt with e. g. in works of Hi 1m an and Curtis (1980), Hemken et al. (1981) or Laarveld et al. (1981).As to the use of iodophores, i. e. point 2), the reviews have been published e. d. by Hemken (1979), Piekacz (1979) and Wheeler (1979).All the authors agreed that the application of iodophores is always accompanied by the increase of iodine level in milk, the extent of this increase being, however, dependent on the type of preparation, the concentration of active iodine, the application form and other factors.The studies related to the application of iodophores and the iodine concentration in milk were also published by Iwarson and Ekman (1973), Barrios (1976), Sheldrake et al. (1980) or Hemken et al. (1981).
The analytical method of iodine determination in milk is another very important question.A review published by TuSl (1981) concerns the possibilities of iodine determination in foodstuffs.Apart from the classical photometric method which is nowadays used mostly in automatic high performance continuous flow-through analysers of a great output (Barrios 1976;Sheldrake et al. 1980) there is a whole range of suitable methods of instrumental analysis such as the method of X-ray fluorescence (Crecelius 1975;Craven and Griffith 1977), radiochemical methods (see e. g.Ohmo 1980; Dermalj 1981), gas chromatography (Bakker 1977), differential pulse polarography (Propst 1977;Curtis and Hamming 1982).During last years the methods employing the iodide ion selective electrode have become particularly attractive due to their relative simplicity, rapidity, low equipment price and low running costs (Crecelius 1975;Craven;Griffith 1977;Bruhn and Franke 1978;Sucman et al. 1978;Lacroix and Wong 1980 and others).
It was the purpose of this work to obtain both informative values concerning the iodine level in milk coming from various regions of Czechoslovakia and to asses the degree to which iodine may be transferred to milk during a short term application of Jodonal M.

Materials and Methods
The samples of milk for the iodine level determination were randomly taken from the production lines of various dairies such as Lacrum Brno, Laktos Praha and PMV Works Opocno and Hradec Kr:ilove.The samples were taken in the course of the fourth quarter of 1979 and the first quarter of 1980.No preservatives were used for milk and the iodine levels were determined within 24 hours at the latest, using the iodide ion selective electrode (Sucman et al. 1978).The samples were stored at ca 4 DC until analysed.
The experiment with a short-term application of Jodonal M was carried out in July and 1980 on the state farm Smecno, locality Kladno.No iodophores had been applied on this farm before.Forty dairy cows were included in the experiment, 20 of this number serving as controls.The remaining 20 animals were treated with solutions of Jodonal M (active iodine concentration 17 gil) using the teat dipping method.The experiment was divided into four parts: 1. Preparatory phase -Iodine levels in milk of both groups were determined for 16 days prior to start of the experiment.2. 1st application -For the period of 19 days the Jodonal M solution of a given concentration was applied to the experimental group.3. Interruption -The application as described above was interrupted for 8 days.4. 2nd application -For the period of 6 days the Jodonal M solution was reapplied as in the case of the first application.
The samples of bulk milk were taken twice a day from both groups of animals for the whole duration of experiment.Two parallel iodine determinations were carried out for each sample.
In the field, the experiment was carried out by Dairy Research Institute Prague and Central State Veterinary Institute Prague, the analyses being effected partially at the University of Veterinary Science, Bmo, and partially at the above-mentioned laboratories.All calculations pertinent to the evaluation of analyses were carried out at the University of Veterinary Science, Brno using the programs that were worked out for the desk-top programmable computer EMG 666 (Hungary).

Results and Discussion
The experimental results concerning the iodine content in milk of various regions of Czechoslovakia are summed up in Table 1.As a relatively small amount of samples was analysed, these data should be considered as only informative values.They are, however, in good agreement with the iodine levels in raw milk as published elsewhere.
The experiment with an interrupted short-term application of J odonal M may  As to the experimental group, there was a marked increase in iodine level in milk during the first application of Jodonal M which lasted for 14 days.The maximum value of 831 flg/l was observed in the 7th day of application.A similar increase, although with a lower maximum value, appeared also during the second Jodonal M application following the eight day pause.In this case the maximum value of 373 flg/1 was noted already on the 3rd day of the experiment.It is believed that the faster onset of the maximum iodine concentration in milk during the second aplication ofJodonal M, as well as its lower value and a faster decline to the original value, is connected with the adaptation mechanism of dairy cows.These results are in good agreement with our preliminary experiment in which the iodophore was applied only once for a short time period (Synek et al. 1980).Here, the maximum concentration of iodine in milk was achieved in the 8th day of application, the return to initial state being observed after two-weeks application of the preparation.The time course of iodine concentration in milk of dairy cows is for both experimental groups shown in Fig. 1.
Also the literature data reported on a similar increase of iodine concentration in milk induced by the application of iodophores (Iwarson and Ekman 1973;Barrios 1976;Dunsmore 1976;Hemken 1979;Piekacz 1979;Sheldrake et al. 1980;Hemken et al. 1981).There are,however, no literature reports describing the influencing of iodine concentration by a short-term interruption of the iodophore application as reported in this paper.
The content of residues in milk and its effect is, in the case of iodine, important from the viewpoint of milk as the raw material for dairy products.It seems that the iodine content should be checked mainly in such cases when the milk is to be used for making various kinds of dried milk products for child nutrition.Also this work is hoped to be a contribution to the solution of this problem.
C J x Samples of milk bulk from experimental and control groups ---------'------'------------------'--~~n number of analysed samples c average determined concentration (mean of three parallel determinations) emin' c max minimal and maximal concentration found within the set of samples of common origin.67 be evaluated as follows.Average iodine levels in milk of 40 dairy cows prior to our experiment was 122 flg/l, the variation ranging from 60 to 175 flg/l.The iodine concentration to 100 flg/l was found in 19 % of analysed samples in this period; 101-150 flg/l was found in 63 % of samples.During the actual experiment the iodine concentration in milk was within 40-196 flg/l (average 118 flg/l) for the control group.The values to 100 flg/l were found in 39 % of analysed samples while 45 % of samples exhibited the values within the range 100-150 flgjl.

Fig. 1 .
Fig. 1.Iodine concentration in milk during application of J odonal M.