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

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.

Phenolic Characterization and Bioactivity of Fennel Seed (Foeniculum vulgare Mill.) Extracts Isolated by Microwave-Assisted and Conventional Extraction

“…Acetone (30%) proved to be the most effective solvent for isolation of polyphenols from fennel seeds, followed by water and 30% ethanol. These results are in accordance with a previous study on optimization of MAE of nettle leaves' polyphenols [15]. Sulaiman et al (2011) [36] reported that when compared to aqueous ethanol and aqueous methanol and water, 70% aqueous acetone was the most effective solvent for recovery of polyphenols from vegetables.…”

“…Therefore, MAE was carried out varying the extraction solvent, temperature, irradiation time and microwave power to observe the influence of extraction parameters on the recovery of phenolic compounds from fennel seeds. For the solvent effect, 30% aqueous solutions of ethanol and acetone were compared to water, according to previous literature reports confirming the suitability of these binary solvent systems for the isolation of plant polyphenols [15,[28][29][30]. The temperature, time and microwave power span taken into consideration were selected based upon previous research on MAE of polyphenols [14,15,31].…”

“…For the solvent effect, 30% aqueous solutions of ethanol and acetone were compared to water, according to previous literature reports confirming the suitability of these binary solvent systems for the isolation of plant polyphenols [15,[28][29][30]. The temperature, time and microwave power span taken into consideration were selected based upon previous research on MAE of polyphenols [14,15,31]. Table 1 shows the results of TPC determination in the obtained extracts.…”

“…The method is based on the heating of the sample through the mechanisms of ionic conduction and dipole rotation, which leads to the disruption of hydrogen bonds, thus increasing the penetration of the solvent into the sample matrix and enabling the extraction of the compounds [8]. However, as previous studies have shown [9][10][11][12][13][14][15][16], in order to exploit the full potential of the technique, extraction parameters such as solvent, temperature, irradiation time and microwave power should be optimized.…”

Variations in the Composition, Antioxidant and Antimicrobial Activities of Cystoseira compressa during Seasonal Growth

“…MBC of the seaweed extracts was determined as the lowest concentration at which no microbial growth was detected on agar plates after subcultivation of bacterial suspension pipetted from wells where MIC was determined and from wells with higher extract concentrations [53].…”