Recovery of Biologically Active Compounds from Stinging Nettle Leaves Part II: Processing of Exhausted Plant Material after Supercritical Fluid Extraction

Abstract

Stinging nettle (Urtica dioica L.) is one fantastic plant widely used in folk medicine, pharmacy, cosmetics, and food. This plant’s popularity may be explained by its chemical composition, containing a wide range of compounds significant for human health and diet. This study aimed to investigate extracts of exhausted stinging nettle leaves after supercritical fluid extraction obtained using ultrasound and microwave techniques. Extracts were analyzed to obtain insight into the chemical composition and biological activity. These extracts were shown to be more potent than those of previously untreated leaves. The principal component analysis was applied as a pattern recognition tool to visualize the antioxidant capacity and cytotoxic activity of extract obtained from exhausted stinging nettle leaves. An artificial neural network model is presented for the prediction of the antioxidant activity of samples according to polyphenolic profile data, showing a suitable anticipation property (the r2 value during the training cycle for output variables was 0.999).

Chemical Constituents of Stinging Nettle (Urtica dioica L.): A Comprehensive Review on Phenolic and Polyphenolic Compounds and Their Bioactivity

“…Otles and Yalcin analyzed phenolic compounds in root, stalk, and leaves. The authors reported the lack of gallic acid and catechin in analyzed parts of the plant [ 63 ], which is in agreement with other studies [ 16 , 17 ] but contrary to other studies that reported the presence of only gallic acid [ 11 , 64 ] or both compounds [ 19 , 61 ]. The results showed that leaves were the richest in polyphenolic compounds, followed by stalk and root [ 63 ].…”

“…Besides the compounds mentioned above, other phenolic acids and polyphenolic compounds were also reported in leaves but with a specific diversity because of the extraction techniques used (Table 4). Leaf [16,17] In this case, both glycosides and aglycones were reported in extracts. The presence of aglycones indicates hydrolysis during the extraction processes.…”

“…There are many different studies regarding the presence and content of these compounds in stinging nettle. However, these results differ due to several reasons, e.g., geographical, seasonal, and environmental variations and conditions, part of the plant used for extraction (root, stalk, leaves), extraction technique, and solvent or mixture of solvents used for the extraction [ 11 , 16 , 17 , 19 , 61 , 62 , 63 , 64 ]. Đurović et al reported a polyphenolic profile of stinging nettle leaves obtained using different extraction techniques and 96% ethanol as a solvent [ 11 ].…”

“…Interestingly, all these compounds, except taxifolin and daidzein, were found and quantified only in the Soxhlet extract of stinging nettle leaves. Further extraction of exhausted leaves after supercritical fluid extraction also showed the dependence of the chemical profile on the technique [ 17 ]. The authors compared the polyphenolic profile of extracts obtained from the dried plant material and plant material after the supercritical fluid extraction (SFE).…”

“…Medicinal applications consider fresh leaves and extracts for treating flailing arthritic or paralytic limbs, stimulating blood circulation, and warmth of joints and extremities [ 15 ]. The stinging nettle’s extracts showed different biological activities such as antioxidant, antimicrobial, anti-inflammatory, anti-ulcer, and analgesic [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. This plant is also used as a medicament against anemia, gout, eczema, and urinary, bladder, and kidney problems [ 14 , 24 , 25 , 26 ].…”