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Abstract

Selenium is known as an essential element for humans and animals. It is mainly in taken with food, where content is usually low. Content in plants varies from less than 0.1 µg Se/g to 0.8 µg Se/g, while in other food products, such as fish, selenium content is normally higher. To overcome low selenium content in food and low selenium status in humans, biofortification of plants is promising approach. Moreover, simultaneous biofortification with selenium and iodine is next logical step, due to low iodine intake and close relationship between selenium and iodine in thyroid gland functioning, thyroid hormone biosynthesis and metabolism. Before introduction of selenium fortified food into food chain, selenium content and distribution of selenium compounds need to be evaluated. Determination of selenium and its compounds is challenging task due to normally low content in samples, its volatility and lack of reference material for selenium compounds.
In this doctoral dissertation, plants from different families were fortified with selenium in forms of Se(IV) and Se(VI) with different fortification methods – seeds soaking and foliar application. In selected plants, selenium content and presence of selenium compounds were determined. Iodine, known as essential element for humans and animals, was simultaneously added in forms of I(–I) and I(V) to fortified solution to found out the effect of its presence on content of selenium and its compounds.
First, relevant analytical parameters for microwave oven digestion of plant samples for the determination of selenium content and method for separation and determination of selenium compounds with anion exchange column were optimized. Due to changed analytical parameters, stability tests of selenium compounds were performed. For accuracy and precision of optimized method, certified reference materials were used. In addition, other chromatographic techniques were used to verify determined selenium compounds.
With optimized methods, selenium content and compounds were measured in pea (Pisum sativum L.), pumpkin (Cucurbita pepo L.) and buckwheat (Fagopyrum esculentum Moench) sprouts, grown from seeds, soaked in the 10 mg Se(IV)/L and 10 mg Se(VI)/L solution. In all fortified sprouts, selenium content was enhanced according to control plants. Almost in all treatments, SeMeSeCys, SeMet, Se(IV) and Se(VI) were present. Presence of iodine (1000 mg I(–I)/L and 1000 mg I(V)/L) in soaking solution had different effect on obtained content of selenium and its compounds with no general rule.
Selenium content and its compounds were determined also in edible parts of plants – pea seeds, pumpkin seeds, buckwheat achenes and chicory leaves (Cichorium intybus L.) after foliar application with selenium solution (10 mg Se(IV)/L and 10 mg Se(VI)/L). In addition, selenium content was determined in other parts of pea plant. Selenium content was increased in all edible parts of fortified plants in different levels. The main selenium compound in all treated plants was SeMet, regardless of solution and plant species. The effect of iodine (1000 mg I(–I)/L and 1000 mg I(V)/L) presence on selenium and its compounds depend on the forms of iodine and plant species. Selenium compounds in pumpkin seeds and buckwheat achenes were not effect by iodine.
The effect of selenium on content of iodine and its compounds in sprouts and adult plants are described in the doctoral dissertation by Jerše (2017).
In the last part of doctoral dissertation, selenium and its compounds were determined in aquatic plant water speedwell (Veronica anagallis-aquatica) and sediment sampled in the three Slovenian watercourses where different activities were present: daily farming, stock raising and extensive agriculture. Before determination of selenium content in sediment samples, analytical method was optimized. Results showed no effect of agriculture on selenium content in sediments. On the other hand, V. anagallis-aquatica accumulated great amount of selenium without showing symptoms of toxicity. Selenium compounds Se(VI) and Se(IV) were found. Moreover, selenium content and compounds were compared with cultivated plant from present study. Despite high selenium content in V. anagallis-aquatica, selenium was not present in form of SeMet like we expected.