Research Article Creative Commons, CC-BY
Edible Macroalgae: Beneficial Resource of Iodine
*Corresponding author: Jelena Milinovic, Department of Chemistry, Faculty of Science and Technology, NOVA University of Lisbon, Portugal.
Received: April 08, 2020; Published: April 14, 2020
Iodine is an essential element required for the synthesis of thyroid hormones. Its deficiency is correlated to goiter, while in excess can cause autoimmune thyroiditis. Worldwide exists a deficiency in iodine, and recommended daily intake should be 150μg for adults. One of the most naturally available and abundant resources of iodine is macroalgae, which may contain it in several orders different concentrations, depends primarily on species. To accomplish the recommended daily intake of iodine, it is important to know the exact concentration of iodine in macroalgae, dried and/ or processed.
Keywords: Iodine; Thyroid Hormones, Goiter; Hypothyroidism; Recommended Daily Intake; Natural Food Sources of Iodine; Macroalgae; Dried and processed Macro algae; Bioavailability
Iodine is a trace element, the essential constituent of thyroid hormones, triiodothyronine (T3) and thyroxine (T4), both having an important role in cell metabolism, reproduction and growth [1- 3]. Deficiency of iodine is associated with increased frequency of goiter, hypothyroidism, lack of strength and eventually, hypotension, lethargy and obesity [4,5]. On the other hand, excess iodine can cause autoimmune thyroiditis . Insufficient iodine intake led to problems in different groups of the population worldwide and special attention should be taken for the commercial products that have no specified iodine content . Following a request from the European Commission, after a large epidemiological study, the Panel of European Food Safety Authority (EFSA) proposed an adequate intake of iodine of 150μg/day for adults and 200μg/ day for pregnant women [5,8]. In the USA, the recommended daily intake is 220μg and 290μg for pregnant and women in a period of lactation, respectively . A significant part of the population in the world is with insufficient iodine intake [8,10]. The most affected regions are in Africa, Eastern Mediterranean and Europe, where it was estimated that the iodine intake of 42,6%, 54.1% and 56.9% of the general population, respectively . According to the current estimate, the total goiter prevalence has been increased by 62.9% in Eastern Mediterranean countries, and for around 81% in Africa and Europe . Overall, almost one-third of the population worldwide (31.7%) indicates insufficient iodine intake. These statistics clearly 2 pointed out a serious problem and as a solution, improved iodine nutrition may reflect better results in populations who are severely deficient. Since the strategy to use the salt iodization is known to be a highly cost-effective method of supplying iodine, and moreover, it may increase the risk of cardiovascular diseases, alternative resources of iodine have to be used [10,11]. The most abundant dietary resources of iodine are edible seafood and seaweeds, i.e., macroalgae that can quantitatively accumulate iodine from seawater . Traditionally, most meals in Japan include soups with macroalgae and this is changing more towards more Western foods. In Japan, 21 species of macroalgae are included in the diet, in Hawaii and Polynesian islands more than 25 species are in use as food and medicine, whereas in Korea more than 40 kinds of macroalgae are applied in gastronomy . Macroalgae are increasingly common food in the United States .
Macroalgae as a Source of Iodine
Rich in micronutrients, macroalgae contain also high levels of iodine and thus they are multipurpose as food supplements and nutraceuticals with potential health implications. Divided into three main taxonomic categories, macroalgae can be green (Chlorophytae), red (Rhodophyceae) and brown (Phaeophytae), each of them with different absorption potential for trace elements from seawater, among others iodine [15,16]. In general, macroalgae are considered rich in iodine, but total iodine contents vary amongst species and taxonomic entities, and may depend on collection sites and season, and/or processing [14,17-21]. Some species, in particular, brown macroalgae, such as Laminaria spp. (Konbu) or Laminariale spp. (Kelp), can accumulate very high levels of iodine which plays a physiological role in oxidative and salinity stress responses [22-24].
Iodine Level in Macroalgae
The overall range of the iodine level in macroalgae is very broad, because they may contain from only a few ppm to several thousand ppm of iodine [7,12,20,25-31]. Brown macroalga Laminaria sp. is the best accumulator of iodine with its average content of almost 0.3% of dry weight, thus representing 104 more concentration of this element in comparison with seawater [12,26]. In studies in the lagoon of Venice, brown macroalgae species Sargassum muticum and Undaria pinnatifida (Wakame) collected from the depth at 50 cm, showed concentrations of 177ppm and 583ppm, per dry weight (dw), respectively . Similarly, U. pinnatifida (Wakame) imported from Japan had iodine content equal to 260 ppm (dw), whereas Laminaria digitata japonica (Konbu) contained as much as 1700ppm (dw) of total iodine . Considering the recommended daily intake of iodine, the consumption of 577mg of selected Japanese species of U. pinnatifida (Wakame) or 88mg of L. digitata japonica (Konbu) per day, would satisfy the established requirement for adults [5,8,9]. Concerning the Japanese species of Konbu, even 2-4 times higher values were found for the species of Laminaria ochroleuca (Konbu) harvested in the north-western Spanish coast, and they contained from 3703 to 7088ppm (dw) of iodine . On the other hand, similarly to Japanese macroalgae Laminaria spp., Konbu from Taiwan showed an average iodine concentration of 2524ppm . Species of brown Saccharina latissima from Lysefjord in Norway, showed different values of total iodine concentration, ranging from 380 to 3965ppm dw, which depended on the seasonal variation of sampling and geographical origin of the species . Brown macroalgae belonging to Laminariale spp. (Kelp) were shown to be the richest natural source of iodine (up to 10203ppm, dw), whereas some red species of commercial macroalgae (e.g., Chondrus crispus) had two orders of concentration lower levels, i.e., 296ppm (dw) . Red macroalga Palmaria Palmata from the North Atlantic was also rich in iodine, with its total content of 2149 ppm (dw) and it meets recommended intake by daily consumption of 70mg of dried species .
Besides dried macroalgae, the effect of the cooking process on iodine level was examined as well, and it was deduced that boiling can lead to changes in the total iodine concentration in macroalgae. As an example, boiling of dried Saccharina spp. for several minutes will result in the reduction of its iodine content to approximately one-third of the initial value and after boiling up to 30 min the result will remain the same . During iodine change testing, after boiling of red macroalga Palmaria palmata, it was estimated that 68% of seaweed iodine remained, thus still representing a rich iodine source . Moreover, it was established that iodine had moderate bioavailability (49-82%) after gastrointestinal digestion . Therefore, the concerns over iodine intake from macroalgae and its bioavailability must be evaluated better, concerning all crucial parameters.
Materials and Methods
Production of β cyclodextrin clathrates with milk peptides
β CD manufactured by Roquette (France) and extensive whey/ colostrum hydrolysates (produced atlaboratory of applied biology, Faculty of Biology, BSU, Belarus) were engaged for clathrate complexing. Solutions containing β CD and hydrolysates in mass ratio 2:1 (calculated as solids) were prepared. The resulting solutions of cyclic oligosaccharide and peptides were incubated during 4h at temperature 50 °C with constant stirring (200 rpm). Organoleptic properties of liquid samples were evaluated according to the procedure described in . Samples of whey and colostrum hydrolysates were used as the control. Clathrate and hydrolysate samples were freeze-dried at temperature-53 ºС and pressure 0.1atm during 24-48h for subsequent experiments.
Thermo-gravimetric analysis of clathrates and hydrolysates
Thermal degradation parameters of clathrate and hydrolysate samples were determined by thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC) on TGA/DSCI instrument (Mettler Toledo, Switzerland). The sample weight was 20mg, resolution of analysis equalled 1μg. TGA/DSC was carried out in the range 30-600 °С, the rate of temperature rise reached 5 °С/min, the accuracy of temperature control was ±2 °С. Effective activation energy (Еа) was calculated according to Broydo method using TGA curves . Pure substances (peptides and β CD) and their mixtures in mass ratio 2:1 were chosenas the control samples.
Estimation of antioxidant activity
AOA of experimental samples was evaluated by fluorimetric method (Oxygen Radical Absorbance Capacity, ORAC). It is based on the suppression of fluorescein (Fl) fluorescence as a result of its oxidation by oxygen radicals and inhibition of this process by antioxidants. The technique presented in EI Tarun’s paper (2014)  was applied in this research. The results of 3 independent experiments were expressed as the mean value ± confidence interval.
To overcome iodine deficiency one of the useful solutions is the consumption of macroalgae, which can provide the necessary daily intake recommended for each population group. Future research should explore in more detail, the iodine content (and bioavailability) after consumption of edible macroalgae, dried and/ or processed by any recommended technique and thus, prove the beneficial effects of macroalgae in human health.
This work was supported by the project “MAR-01.03.01-FEAMP- 0016-Alga4Food” which is financed by the European Maritime and Fisheries Fund and co-financed by the Operational program MAR2020 in the field of Sustainable development of Aquaculture in the domains of Innovation, Advice and Productive Investment - Innovation and Knowledge Action. The work was also supported by the Applied Molecular Biosciences Unit- UCIBIO which is financed by national funds from FCT/MCTES (UIDB/04378/2020) and by the Associate Laboratory for Green Chemistry- LAQV which is financed by national funds from FCT/MCTES (UIDB/50006/2020).
Conflict of Interest
Authors declare that there is no financial interest or conflict of interest.
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