Bioactive Compounds in Wild Nettle (Urtica dioica L.) Leaves and Stalks: Polyphenols and Pigments upon Seasonal and Habitat Variations

Abstract

This study evaluated the presence of bioactives in wild nettle leaves and stalks during the phenological stage and in the context of natural habitat diversity. Thus, wild nettle samples collected before flowering, during flowering and after flowering from 14 habitats situated in three different regions (continental, mountain and seaside) were analyzed for low molecular weight polyphenols, carotenoids and chlorophylls using UPLC-MS/MS and HPLC analysis, while the ORAC method was performed for the antioxidant capacity measurement. Statistical analysis showed that, when compared to the stalks, nettle leaves contained significantly higher amounts of analyzed compounds which accumulated in the highest yields before flowering (polyphenols) and at the flowering stage (pigments). Moreover, nettle habitat variations greatly influenced the amounts of analyzed bioactives, where samples from the continental area contained higher levels of polyphenols, while seaside region samples were more abundant with pigments. The levels of ORAC followed the same pattern, being higher in leaves samples collected before and during flowering from the continental habitats. Hence, in order to provide the product’s maximum value for consumers’ benefit, a multidisciplinary approach is important for the selection of a plant part as well as its phenological stage with the highest accumulation of bioactive compounds.

Phenolic Profile, Antioxidant Capacity and Antimicrobial Activity of Nettle Leaves Extracts Obtained by Advanced Extraction Techniques

“…The phenolic profile of obtained MAE and PLE extracts did not differ qualitatively, unlike with the CE extract, where some compounds (myricetin and caffeic acid) could not be detected. A detailed description of phenolic composition with accompanying identification pathways for compounds lacking reference standards of nettle leaves from the Croatia region was reported previously [7], and is in accordance with results of this study. A total of 27 phenolic compounds were identified, belonging to the classes of benzoic, cinnamic and other phenolic acids, flavonols, flavan-3-ols, flavones and coumarins (Figure 2).…”

“…Acetone suitability for extraction of plant polyphenols has been reported previously [23] and can be attributed to its ability to inhibit and/or break polyphenol-protein interactions and therefore prevent the formation of insoluble complex and consequently increase the polyphenolic yield [24]. According to Rezaie et al (2015) [25] acetone is suitable for the extraction of non-glycosidic polyphenols due to its poor ability to form hydrogen bonds, so its high effectiveness in extraction of nettle leaves polyphenols can be related to the predominance of phenolic acids and non-glycosylated flavonoid derivates in nettle polyphenolic profile [7]. Temperature was also shown to be a significant factor for the isolation of nettle leaves polyphenols during MAE.…”

“…Zeković et al (2017) [5] Molecules 2021, 26, 6153 2 of 16 reported that the predominant phenolic compound in nettle leaves is rutin, followed by sinapic acid. Ince et al (2012) [6] listed gallic, caffeic, chlorogenic and p-coumaric acid as well as naringenin and naringin as the main phenolic compounds in nettle extracts, while Repajić et al (2021) [7] reported cinnamic acids and flavonols as the most abundant phenolic classes in nettle leaves. Apart from its medicinal and dietary use, nettle shows a great potential for application in the food industry as natural preservative [2].…”

Electrically assisted ionic gelling encapsulation of enzymatically extracted zinc‐chlorophyll derivatives from stinging nettle (Urtica urens L.)

“…Still, the accumulation of color pigments varies with climate and habitat diversity. Plants grown in cold climates generally exhibit more antioxidant properties as a result of oxidative stress defense, while color pigment synthesis is increased due to exposure to higher temperatures and more sunlight (González‐Talice, Yuri, & del Pozo, 2013; Repajić et al, 2021; Saini, Nile, & Park, 2015). Besides all the stability of chlorophyll varied according to the subspecies of stinging nettle.…”

Indigenous Knowledge and Consumer’s Perspectives of Stinging Nettle (Urtica Simensis) in the Central and Southeastern Highlands of Oromia Regional States of Ethiopia

“…Recent studies reported that young nettle leaves extracts are a good source of polyphenols and phytochemicals that render them with nutritional, nutraceutical and functional properties. Polyphenols content of nettle leaves showed a decreasing trend with the phenological stage, total polyphenols decreased for almost 50% by the 3rd phenological stage (Repajić et al, 2021).…”