Nanotechnology offers a solution to bacterial antibiotic resistance, which poses a serious threat to global health. Green synthesis of metallic nanoparticles is gaining increasing attention due to its environmental benefits. This study aimed to biosynthesize silver nanoparticles (AgNPs) by microwave irradiation through silver nitrate reduction using starch and microalgae biomass; characterize them using UV–visible spectroscopy, scanning electron microscopy-energy-dispersive X-ray microanalysis, and X-ray diffraction; and evaluate their antibacterial activity against Escherichia coli, Bacillus clausii, and Staphylococcus aureus using disk diffusion and broth dilution methods. Synthesized AgNPs showed a single peak related to surface plasmon resonance at 430 nm. Size range of spherical AgNPs was 40–150 or 90–400 nm for starch- or biomass-mediated NPs, respectively. Biomass-mediated AgNPs exhibited antibacterial activity with the inhibition zones of 8, 12, and 10.5 mm against E. coli, B. clausii, and S. aureus, respectively; those starch-mediated showed inhibition of 7, 13, and 12 mm, respectively. AgNPs’ minimum inhibitory concentrations were 6.25 μg·mL−1 toward both E. coli and S. aureus and 12.5 μg·mL−1 against B. clausii when using starch in biosynthesis, whereas they were 19.6 μg·mL−1 against both E. coli and S. aureus and 9.81 μg·mL−1 toward B. clausii when using biomass. Synthesized AgNPs have promising antibacterial potential.
Introduction
Most recurrently available organic solvents are toxic and inflammable and pose high risks to human health. Natural deep eutectic solvents (NADESs) have been developed as promising green alternatives.
Objective
We aimed to extract polyphenolic compounds from Mentha pulegium using lactic acid‐based deep eutectic solvents. Extraction parameters were optimized by response surface methodology.
Material and Methods
Combined with ultrasound‐assisted extraction, three different lactic acid‐based deep eutectic solvents were investigated for the extraction of polyphenols. Methanol (80%, v/v) was used for comparison. The optimized influencing factors were: water content in solvent, extraction time, and temperature. The design was adopted including 17 experiments with three center points.
Results
All NADESs tested showed an excellent extraction efficacy compared to 80% methanol. Under the optimized conditions, with 45% of water, at 30°C, and for extraction 90 min, the highest extraction yields were recorded using lactic acid:sodium acetate (3:1), achieving 173.35 ± 0.02 mg gallic acid equivalents (GAE)/g dry weight (dw) of polyphenols and 95 ± 0.09% antioxidant activity. After extraction for 90 min at 80°C with 18% of water, we obtained 164.06 ± 0.01 mg GAE/g dw and 94 ± 0.02% antioxidant activity using lactic acid:glucose (5:1). Efficient recovery (64.92 ± 0.01 mg GAE/g dw and 97 ± 0.1% antioxidant activity) was achieved using lactic acid:glycine (3:1) with 31% of water, at 35°C, and extraction for 30 min.
Conclusion
Our results indicate that with optimized parameters, the proposed natural solvents are excellent alternatives to chemical ones for the extraction of phenolic compounds.
Developing of an eco-friendly, sustainable and efficient solvents with low toxicity and cost has always been a tremendously important goal for industries. In this context, green solvent, such as natural deep eutectic solvent, have been developed as a promising solvent capable of replacing organic ones. The combination of lactic acid: glucose (5:1) was investigated as an extraction medium for bioactive phenolic compounds from Thymus broussonetii. The ultrasonication method was established and optimized by a systematic investigation of the influencing factors: water content in solvent (0/35/70 %), extraction time (30/60/90 min), and temperature (30/50/80°C). A Box – Behnken design was adopted including 17 experiments with three center points. The results obtained presented an excellent efficacy of polyphenols extraction ranging from 25.53 ± 0,02 to 153.23 ± 0,03 mg GAE/g dm and a high scavenging activity attending 80.64 %, the optimized conditions selected for both responses were 66.47 min, at 80°C and a 40.72 % of water, with an extraction yields of 144.394 ±0,02 mg GAE/g dm and 75.9 % for phenolic compounds and antioxidant activity, respectively. Regression analysis showed a good fit of the experimental data which indicates the suitability of the model employed and the successful application of Box – Behnken design in optimizing the extraction conditions. Furthermore, the developed procedure represents an excellent alternative for the extraction of natural products from sample matrices.
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