plants Article Major and Trace Element Content of Tribulus terrestris L. Wildlife Plants Kirill Tkachenko 1, Marina Frontasyeva 2,* , Atanas Vasilev 3, Latchezar Avramov 4 and Lei Shi 5 1 Komarov Botanical Institute of Russian Academy of Sciences, Peter the Great Botanical Gardens, 197376 Saint-Petersburg, Russia; [email protected] 2 Joint Institute for Nuclear Research, Frank Laboratory of Neutron Physics, 141980 Dubna, Russia 3 Faculty of Physics, Sofia University “St. Kliment Ohridski”, 1164 Sofia, Bulgaria; [email protected] 4 Academician Emil Djakov Institute of Electronics of Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria; [email protected] 5 Institute of Botany of Chinese Academy of Sciences, Key laboratory for Plant Resources Botanical Garden, Beijing 100093, China; [email protected] * Correspondence: [email protected]; Tel.: +7-903-260-6369 Received: 21 October 2020; Accepted: 10 December 2020; Published: 13 December 2020 Abstract: The genus Tribulus L. (Zygophyllaceae) includes 12 species, the most important of which is Tribulus terrestris L. This annual herb grows in temperate and tropical climates, and has a rich chemical composition of biologically active substances and chemical elements. Medicinal plants, and the phytopreparations obtained from them, are becoming more and more popular in world practice as they are used to successfully treat human diseases. Their therapeutic effect is due to the presence in them, of a variety of natural compounds and biologically important trace elements, especially in higher concentrations present in higher doses. T. terrestris is becoming more and more popular for the treatment of diseases of the human genital area and sexual dysfunctions. The elemental content in the tissues of leaf, flower, and fruit of T. terrestris was determined by using multi-element instrumental epithermal neutron activation analysis. For the first time, 26 essential and trace elements were observed in the plant species collected in Russia (from cultivated) and China (wild growing). It was confirmed that the elemental composition of T. terrestris grass varies depending on the habitat (geographic zones). The place of growth affects the accumulation of elements by the plant. Keywords: herbal medicinal products; epithermal neutron activation analysis; elemental content; bioavailability; complementary foods 1. Introduction The medicinal value of plants lies in some chemical substances that produce a definite physiological action in the human body. Medicinal plants contain both organic and inorganic constituents. The pharmacological properties of medicinal plants have been attributed to the presence of active chemical constituents that are responsible for important physiological functions in living organisms. The steroidal saponins of Tribulus terrestris L. (Zygophyllaceae) are considered the factor responsible for the biological activity of products derived from this plant. Its various parts contain a variety of medicinally important chemical constituents, such as flavonoids, flavonol glycosides, steroidal saponins, and alkaloids. The activity depends on the concentration and the composition of active saponins, which in turn is influenced by the geographical origin of plant material [1–6]. Since the levels of Na, Mg, K, Ca, and Zn in analyzed samples of T. terrestris are higher than the levels considered as reference, the importance of the contribution by T. terrestris in the daily human needs can be considered Plants 2020, 9, 1764; doi:10.3390/plants9121764 www.mdpi.com/journal/plants Plants 2020, 9, 1764 2 of 11 Plants 2020, 9, x FOR PEER REVIEW 2 of 12 insignificant.The Ca, Fe, The Zn element content determination of the tested canraw be materials important of inT. controllingterrestris, although the quality high, of the cannot raw materialbe used forto supplement standardized the extracts intake, (especially since any heavyplant sources metal content) that have [7– 13a ].high content of bi- or tri-valent ions haveThe a low Ca, bioavailability Fe, Zn content ofdue the to tested their raw content materials of phytic of T. terrestris acid, polyphenols,, although high, and cannot tannins, be usedwhich to supplementdrastically limits the intake, absorption. since anyDespite plant other sources favorable that have effects, a high phytic content acid ofis an bi- antinutrient or tri-valent regarding ions have amineral low bioavailability intake [10,12,13]. due to their content of phytic acid, polyphenols, and tannins, which drastically limitsA absorption.number of herbal Despite preparations other favorable from e ffT.ects, terrestris phytic have acid been is an produced antinutrient in Bulgaria regarding for mineral many intakeyears. Consequently, [10,12,13]. many works have been devoted to the study of this species in nature [14,15]. It has beenA number shown of that herbal this preparations plant species from accumulatesT. terrestris flavonoids,have been produced which provides in Bulgaria biological for many activity years. Consequently,[16]. many works have been devoted to the study of this species in nature [14,15]. 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Tribulus terrestris terrestris L.L. (family (family Zygophyllaceae) Zygophyllaceae) (Figure (Figure 1) is1) ais widespread a widespread pantropic pantropic weed, weed, which whichgrows as grows a weed as aon weed sandy on soils sandy in subtropical, soils in subtropical, and desert and climate desert regions climate arou regionsnd the around world: the in world:South inand South East Europe and East (Mediterranean), Europe (Mediterranean), in Asia (India, in Asia China, (India, Vietnam China, etc.), Vietnam South etc.), Africa, South USA, Africa, Mexico. USA, T. Mexico.terrestris T.L. terrestrisis widelyL. known is widely as a known medicinal as a medicinalplant whose plant herb whose is the herb basis is for the a basis number for a of number