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. 2021 Oct 12;26(20):6153.
doi: 10.3390/molecules26206153.

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

Ivona Elez Garofulić  1 , Valentina Malin  2 , Maja Repajić  1 , Zoran Zorić  1 , Sandra Pedisić  1 , Meta Sterniša  2 , Sonja Smole Možina  2 , Verica Dragović-Uzelac  1
Affiliations

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

Ivona Elez Garofulić et al. Molecules. .

Abstract

Nettle is a widely known plant whose high biological activity and beneficial medicinal effects are attributed to various bioactive compounds, among which polyphenols play an important role. In order to isolate polyphenols and preserve their properties, advanced extraction techniques have been applied to overcome the drawbacks of conventional ones. Therefore, microwave-assisted extraction (MAE) has been optimized for the isolation of nettle leaves polyphenols and it was compared to pressurized liquid extraction (PLE) and conventional heat-reflux extraction (CE). The obtained extracts were analyzed for their individual phenolic profile by UPLC MS2 and for their antioxidant capacity by ORAC assay. MAE proved to be the more specific technique for the isolation of individual phenolic compounds, while PLE produced extracts with higher amount of total phenols and higher antioxidant capacity. Both techniques were more effective compared to CE. PLE nettle extract showed antimicrobial activity against bacteria, especially against Gram-negative Pseudomonas fragi ATCC 4973 and Campylobacter jejuni NCTC 11168 strains. This suggests that PLE is suitable for obtaining a nettle extract with antioxidant and antimicrobial potential, which as such has great potential for use as a value-added ingredient in the food and pharmaceutical industry.

Keywords: ORAC; UPLC MS2; advanced extraction techniques; antimicrobial activity; antioxidant capacity; microwave-assisted extraction; nettle leaves; plant polyphenols; pressurized liquid extraction.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
3D graphs of TPC extraction evolution during MAE using 30% acetone as extraction solvent: (a) TPC extraction evolution at fixed extraction time of 5 min, (b) TPC extraction evolution at fixed microwave power of 300 W, (c) TPC extraction evolution at fixed extraction temperature of 60 °C.
Figure 2
Figure 2
UPLC ESI-MS2 chromatogram in MRM acquisition mode from nettle leaves extracts obtained under (a) optimized MAE conditions, (b) PLE and (c) CE. (1) Umbelliferone, (2) Protocatechuic acid, (3) Isorhamnetin 3-O-rutinoside, (4) Kaempferol-3-O-rutinoside, (5) Kaempferol hexoside, (6) Apigenin hexoside, (7) Myricetin, (8) Luteolin, (9) Caffeic acid, (10) Esculetin, (11) Gentisic acid, (12) Quinic acid, (13) Quercetin-3-rutinoside, (14) p-coumaric acid, (15) Cinnamic acid, (16) Apigenin, (17) Epigallocatechin gallate, (18) Ferulic acid, (19) Kaempferol pentoside, (20) Kaempferol rhamnoside, (21) Quercetin-acetyl-rutinoside, (22) p-hydroxybenzoic acid, (23) Gallic acid, (24) Epicatechin, (25) Kaempferol-pentosyl-hexoside, (26) Epicatechin gallate, (27) Kaempferol.
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