REPOSITORY > RESULTS

Abstract

Selenium (Se) has been demonstrated to be an essential trace element for maintenance of animal and
human health. Se is incorporated into proteins to make selenoproteins, which are important antioxidant
enzymes. The antioxidant properties of selenoproteins help to prevent cellular damage caused by radicals.
Radicals are natural by-products of oxygen metabolism that may contribute to the development of chronic
diseases, such as cancer and heart disease. Other selenoproteins help to regulate thyroid function and play a
protective role in the immune system.
In majority of countries throughout the world plant foods contain insufficient amount of Se. The content
of Se in food depends on the Se content in soil where the plants are grown or animals are raised, and this is
mainly poor.
The growth interest in the production of Se-enriched cultural plants and nutritional supplements
parallels the need to develop and optimise analytical methodologies for characterization of Se species in
these matrices. Several analytical steps were examined in this doctoral dissertation that should make a
significant contribution to further research. In this regard, an analytical method for separation and detection
of soluble (HPLC-ICP-MS) and volatile Se species (GC-MS) was developed. Before chromatographic
separation, the analytes must be extracted from the solid sample in which identification and determination
of Se species is required. The most frequently used extraction technique for Se speciation analysis is to
transform Se species from protein-bounder to soluble forms with enzymatic hydrolysis. Thus, several
commercially available enzymes were evaluated in order to obtain the highest Se extraction efficiency in
samples of different origin. Moreover, we checked if commercially available enzymes are pure enough to
be used for Se speciation analysis and what contribution could the impurities make to Se determination of a
real sample. The stability of Se species in the matrix considered is rarely reported in the literature. The
matrix may affect the analyte, therefore we considered the reactions that can take place between the Se
species and the matrix components during the extraction. Furthermore, the distribution of Se between
insoluble, soluble and volatile fractions (mass balance calculations) is often overlooked, but was considered
in this dissertation.
Plants vary considerably in their physiological response to Se; the question of the essentiality of Se in
plants still remains unanswered. Although it has not been confirmed to be an essential micronutrient for
higher plants, the number of evidence that Se functions as an antioxidant in plants is increasing. Some plant
species are Se tolerant and accumulate very high concentrations of Se (Se accumulators), but most plants
are Se non-accumulators and are Se-sensitive. However, the specific physiological mechanisms that
underlie the positive effects of Se in plants have not been clearly elucidated. This thesis makes
contributions to our knowledge of the physiology and biochemistry of Se-enriched non-accumulating
plants, often present in Slovenian nutrition (common buckwheat (Fagopyrum esculentum) sprouts, cultivar
Darja, potato tubers (Solanum tuberosum L., cultivar Desiree) and the leafy vegetables: chicory (Cichorium
intybus L. cv. ‘Anivip’ and ‘Monivip’), dandelion (Taraxacum officinale Waggner), garden rocket (Eruca
sativa Mill.) and wild rocket (Diplotaxis tenuifolia DC.)), particularly with regard to Se uptake,
incorporation into proteins and volatilisation.
The Se human status can be improved with consumption of food supplements that contain different Se
species, and nowadays market is overflowed with them. Since there is no verification of Se and its species
content in food supplements, they were studied with regard to quality in meeting declared and
recommended intakes.