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Comparison of conventional Soxhlet and advanced accelerated solvent extraction in isolation of phytosterols from nettle (Urtica dioica L) roots

Stinging nettle (Urtica dioica L.) represents a desirable raw material for application in food as well other industries since various parts of the plant (leaves, stems, seeds and root) are abundant with numerous chemically diverse biologically active compounds such as polyphenols, pigments and phytosterols. The dominant source of nettle phytosterols is nettle root, but it also contains lower quantity of steryl glycosides, triterpenoids, and other compounds. The isolation of these compounds is demanding and complex, and the extraction yield depends on the applied technique and conditions. Therefore, this research compared conventional Soxhlet extraction and accelerated solvent extraction (ASE) with goal to obtain higher extraction yield. Soxhlet extraction was performed within 8 h, whereas ASE conditions were: temperature 110 oC, static extraction time 15 min and 4 cycles. In both techniques n-hexane was used as an extraction solvent. Isolated targeted bioactive molecules were identified and quantified using GC-MS and GC-FID. A total of 12 identified compounds include the following groups: (i) Δ5- sterols (campesterol, campestanol, stigmasterol, β-sitosterol, Δ5-avenasterol) ; (ii) Δ7-sterols (citrostadienol) ; (iii) triterpenoids (α-amirin, β-amirin, β-amirin acetate) and other compounds (cycloartenol, obtusifoliol as precursors and 24- methylene cycloartanol). ASE technique was more efficient when compared to Soxhlet extraction, achieving 2-fold higher extraction yield. Δ5- sterols were the predominant group in obtained lipid fraction (approximately 93%), followed by triterpenoids, Δ7-sterols and other compounds. Among all identified compounds, β-sitosterol and campesterol were the most abundant ones (approximately 80 and 10%, respectively). This study makes a significant contribution in characterisation of nettle root phytosterols and represents an excellent framework for future research directions.

nettle root, phytosterols, accelerated solvent extraction, Δ5-sterols

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