Extraction of phenolics and anthocyanins from purple eggplant peels by multi-frequency ultrasound: Effects of different extraction factors and optimization using uniform design

In this work, multi-frequency ultrasound (working modes for the single-, dual- and tri-frequency in simultaneous ways) was applied to extract bioactive compounds from purple eggplant peels. The single-factor experiments were performed by varying six independent variables. A six-level-five-factor uniform design (UD) was further employed to evaluate the interaction effects between different factors. It was found that extraction temperature and extraction time significantly affected the total phenolic content (TPC), whereas the total monomeric anthocyanins (TMA) was mainly influenced by ethanol concentration, extraction temperature and solid-liquid ratio. Based on partial least-squares (PLS) regression analysis, the optimal conditions for TPC extraction were: 53.6 % ethanol concentration, 0.336 mm particle size, 44.5 °C extraction temperature, 35.2 min extraction time, 1:43 g/mL solid-liquid ratio, and similar optimal conditions were also obtained for TMA. Furthermore, the TPC and TMA extraction were investigated by ultrasound in different frequencies and power levels. Compared with single-frequency (40 kHz) and dual-frequency ultrasound (25 + 40 kHz), the extraction yield of TPC and TMA with tri-frequency ultrasound (25 + 40 + 70 kHz) increased by 23.65 % and 18.76 % respectively, which suggested the use of multi-frequency ultrasound, especially tri-frequency ultrasound, is an efficient strategy to improve the TPC and TMA extracts in purple eggplant peels.     

Sonoprocessing improves phenolics profile,antioxidant capacity,structure, and product qualities of purple corn pericarp extract

For the first time, purple corn pericarp (PCP) was converted to polyphenol-rich extract using two-pot ultrasound extraction technique. According to Plackett-Burman design (PBD), the significant extraction factors were ethanol concentration, extraction time, temperature, and ultrasonic amplitude that affected total anthocyanins (TAC), total phenolic content (TPC), and condensed tannins (CT). These parameters were further optimized using the Box-Behnken design (BBD) method for response surface methodology (RSM). The RSM showed a linear curvature for TAC and a quadratic curvature for TPC and CT with a lack of fit > 0.05. Under the optimum conditions (ethanol (50%, v/v), time (21 min), temperature (28 °C), and ultrasonic amplitude (50%)), a maximum TAC, TPC, and CT of 34.99 g cyanidin/kg, 121.26 g GAE/kg, and 260.59 of EE/kg, respectively were obtained with a desirability value 0.952. Comparing UAE to microwave extraction (MAE), it was found that although UAE had a lower extraction yield, TAC, TPC, and CT, the UAE gave a higher individual anthocyanin, flavonoid, phenolic acid profile, and antioxidant activity. The UAE took 21 min, whereas MAE took 30 min for maximum extraction. Regarding product qualities, UAE extract was superior, with a lower total color change (ΔE) and a higher chromaticity. Structural characterization using SEM showed that MAE extract had severe creases and ruptures, whereas UAE extract had less noticeable alterations and was attested by an optical profilometer. This shows that ultrasound, might be used to extract phenolics from PCP as it requires lesser time and improves phenolics, structure, and product qualities.     

Synthesis of gelatin-capped gold nanoparticles with variable gelatin concentration

Gelatin-stabilized gold nanoparticles (AuNPs-gelatin) with controlled particle size were synthesized with simple variation of concentration of gelatin by reducing in situ tetrachloroauric acid with sodium citrate. The nanoparticles showed excellent colloidal stability. Transmission electron microscopy (TEM) revealed the formation of well-dispersed gold nanoparticles (AuNPs) with different sizes. The methodology produces particles 10–15 nm in size depending on the concentration of gelatin used. The measured AuNPs are 10, 11, 12, 13, 14, and 15 nm for AuNPs-gelatin 1, 0.5, 0.25, 0.1 and 0.05%, and pure AuNPs, respectively. The AuNPs-gelatin exhibit size-dependent localized surface plasmon resonance behavior as measured by UV–visible spectroscopy. UV–vis spectroscopy and TEM results suggest that higher concentration of gelatin favor smaller particle size and vice versa. FTIR spectroscopy analysis of AuNPs-gelatin revealed the amino bands and carboxyl peak of gelatin. The crystalline nature of AuNPs was investigated by X-ray diffraction.     

Ferritin as a photocatalyst and scaffold for gold nanoparticle synthesis

The ferrihydrite mineral core of ferritin is a semi-conductor capable of catalyzing oxidation/reduction reactions. This report shows that ferritin can photoreduce AuCl₄ ⁻ to form gold nanoparticles (AuNPs). An important goal was to identify innocent reaction conditions that prevented formation of AuNPs unless the sample was illuminated in the presence of ferritin. TRIS buffer satisfied this requirement and produced AuNPs with spherical morphology with diameters of 5.7 ± 1.6 nm and a surface plasmon resonance (SPR) peak at 530 nm. Size-exclusion chromatography of the AuNP–ferritin reaction mixture produced two fractions containing both ferritin and AuNPs. TEM analysis of the fraction close to where native ferritin normally elutes showed that AuNPs form inside ferritin. The other peak eluted at a volume indicating a particle size much larger than ferritin. TEM analysis revealed AuNPs adjacent to ferritin molecules suggesting that a dimeric ferritin–AuNP species forms. We propose that the ferritin protein shell acts as a nucleation site for AuNP formation leading to the AuNP-ferritin dimeric species. Ferrihydrite nanoparticles (~10 nm diameter) were unable to produce soluble AuNPs under identical conditions unless apo ferritin was present indicating that the ferritin protein shell was essential for stabilizing AuNPs in aqueous solution.     

Influence of ultrasonic amplitude,temperature, time and solvent concentration on bioactive compounds extraction from propolis

An ultrasound assisted method was investigated to extract bioactive compounds from propolis. This method was based on a simple ultrasound treatment using ethanol as an extraction medium to facilitate the disruption of the propolis cells. Four different variables were chosen for determining the influence on the extraction efficiency: ultrasonic amplitude, ethanol concentration, temperature and time; the variables were selected by Box-Behnken design experiments. These parameters were optimised in order to obtain the highest yield, and the results exhibited the optimum conditions for achieving the goal as 100% amplitude of ultrasonic treatment, 70% solvent concentration, 58 °C and 30 min. The extraction yield under modified optimum extraction conditions was, as follows: 459.92 mg GAE/g of TPC, 220.62 mg QE/g of TFC and 1.95% of balsam content. The results showed that the ultrasound assisted extraction was suitable for bioactive compounds extraction from propolis. The most abundant phenolic compound was kaempferol (228.8 mg/g propolis) followed by myricetin (115.5 mg/g propolis), luteolin (27.2 mg/g propolis) and quercetin (25.2 mg/g propolis).     

A novel strategy for producing nano-particles from date seeds and enhancing their phenolic content and antioxidant properties using ultrasound-assisted extraction: A multivariate based optimization study

Date seeds from the date palm fruit are considered as a waste and they are known to contain several bioactive compounds. Producing nanoparticles from the date seeds can enhances their effectiveness and their utilization as novel functional food ingredients. In this study, date seed nanoparticles (DSNPs) synthesized using acid (HCl) hydrolysis method (HCl concentration of 38% and hydrolysis time of 4 days) was found to have particle size between 50 and 150 nm. The obtained DSNPs were characterized by measuring particle size and particle charge (Zetasizer), morphology using scanning electron microscope (SEM), and determination of the functional groups using fourier-transform infrared spectroscopy (FTIR). DSNPs were further treated with green extraction technology [ultrasound-assisted extraction (UAE)] using water-based and methanol-based solvent for optimizing the extraction of the bioactive compounds by implementing response surface methodology (RSM). The UAE of DSNPs were analysed for set of responses including total phenolic content (TPC), total flavonoid content (TFC), 1,1-diphenyl-2-picrlthydrazyl (DPPH) radical scavenging activity, ferric ion reducing antioxidant power (FRAP), and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity. Three-factor and four-factor Box-Behnken design (BBD) of three models (Synthesis of DSNPs, UAE with water, and UAE with methanol) was performed. The results showed that in UAE of DSNPs using water-based solvent, the key independent factors effecting the TPC and TFC and antioxidant activities were S:L ratio (40:1 mg/ml) and treatment time (9 min). Whereas the methanol-based UAE of DSNPs was mostly affected by US amplitude/power (90%) and methanol concentration (80%). All models were further optimized using response optimizer in Minitab and the generated predicted values were very comparable to the actual obtained results which confirm the significance and validity of all RSM models used. The phenolic compounds identified from DSNPs consisted mainly of 3,4-Dihydroxy benzoic acid, ferulic acid, and p-coumaric acid. The present study demonstrated a successful method for synthesising DSNPs as well as documented the optimum UAE conditions to maximize the extraction of polyphenolic compounds from DSNPs and enhancing their antioxidant activities to be used in food application.     

Process intensification of synthesis of metal organic framework particles assisted by ultrasound irradiation

This study synthesized UiO-66, a typical Zr-Metal Organic Framework (MOF), by using an ultrasound-assisted synthesis method to reduce the synthesis time. This method was short-time ultrasound irradiation at the initial stage of the reaction. As compared with average particle size of conventional solvothermal method (=192 nm), averaged particle size by the ultrasound-assisted synthesis method showed particle sizes that were smaller on average, ranging from 56 to 155 nm. In order to compare the relative reaction rates of the solvothermal method and the ultrasound-assisted synthesis method, the cloudiness of the reaction solution in the reactor was observed with a video camera, and the luminance was calculated from the images obtained by the video camera. It was found that the ultrasound-assisted synthesis method showed a faster increase in luminance and shorter induction time than the solvothermal method. The slope of the luminance increase during the transient period was also found to become increase with the addition of ultrasound, which also affects the growth of particles. Observation of the aliquoted reaction solution confirmed that particle growth was faster in the ultrasound-assisted synthesis method than in the solvothermal method. Numerical simulations were also performed using MATLAB ver. 5.5 to analyze the unique reaction field generated by ultrasound. Bubble radius and temperature inside a cavitation bubble was obtained using the Keller-Miksis equation, which reproduces the motion of a single bubble. The bubble radius expanded and contracted repeatedly according to the ultrasound sound pressure, and eventually collapsed. The temperature at the time of collapse was extremely high, exceeding 17,000 K. It was confirmed that the high-temperature reaction field generated by ultrasound irradiation promoted nucleation, leading to a reduction in particle size and induction time.     

Antioxidant and anti-inflammatory polyphenols in ultrasound-assisted extracts from salvilla (Buddleja scordioides Kunth)

Salvilla is a widely distributed plant used in treatments against gastrointestinal disorders due to its phenolic antioxidant and anti-inflammatory potential. Major yield and quality of bioactive polyphenols must be obtained with no degradation during suitable processes such as Ultrasound-Assisted Extraction (UAE), which allows an efficient extraction of metabolites at appropriate parameter conditions. Salvilla extractions were made using UAE and aqueous ethanolic solutions. Variables used in UAE were sonication time, wave amplitude and percentage of ethanol in solvent. Extracts were tested for total flavonoids, antioxidant activity (ABTS, FRAP and ORAC) and an identification and quantification of phenolic compounds was carried out by UPLC-PDA-ESI-MS/MS. Once elected the better extraction conditions, an anti-inflammatory test was performed for this treatment. As a result, total flavonoids content in extracts was 147 to 288 µg catechin equivalents/mg of dry salvilla extract. All extracts have shown good antioxidant activity (86 to 280 mM Trolox eq/mg dry salvilla extract). Flavonoids contents by chromatography were higher than hydroxybenzoic and hydroxycinnamic acids specially the flavone, flavanol and flavanone groups. Treatment T6 (75% ethanol, 30% amplitude and 10 min extraction time) was the best extract in terms of significant flavonols, antioxidant activity, and higher anti-inflammatory potential.     

Optimization of ultrasound-assisted extraction of bioactive compounds from coffee pulp using propylene glycol as a solvent and their antioxidant activities

In the cosmetic and pharmaceutical industries, it has been increasingly popular to use alternative solvents in the extraction of bioactive compounds from plants. Coffee pulp, a by-product of coffee production, contains different phenolic compounds with antioxidant properties. The effects of polyols, amplitude, extraction time, solvent concentration, and liquid–solid ratio on total phenolic content (TPC) using ultrasound-assisted extraction (UAE) were examined by single-factor studies. Three main factors that impact TPC were selected to optimize the extraction conditions for total phenolic content (TPC), total flavonoid content (TFC), total tannin content (TTC), and their antioxidant activities using the Box-Behnken design. Different extraction methods were compared, the bioactive compounds were identified and quantified by liquid chromatography triple quadrupole mass spectrometer (LC-QQQ), and the cytotoxicity and cellular antioxidant activities of the extract were studied. According to the response model, the optimal conditions for the extraction of antioxidants from coffee pulp were as follows: extraction time of 7.65 min, liquid–solid ratio of 22.22 mL/g, and solvent concentration of 46.71 %. Under optimized conditions, the values of TPC, TFC, TTC, 1,1-diphenyl-2-picryl-hydrazil (DPPH) radical scavenging assay, 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical scavenging assay, and Ferric reducing antioxidant power assay (FRAP) were 9.29 ± 0.02 mg GAE/g sample, 58.82 ± 1.38 mg QE/g sample, 8.69 ± 0.25 mg TAE/g sample, 7.56 ± 0.27 mg TEAC/g sample, 13.59 ± 0.25 mg TEAC/g sample, and 10.90 ± 0.24 mg FeSO₄/g sample, respectively. Compared with other extraction conditions, UAE with propylene glycol extract (PG-UAE) was significantly higher in TPC, TFC, TTC, DPPH, ABTS, and FRAP response values than UAE with ethanol (EtOH-UAE), maceration with propylene glycol (PG-maceration), and maceration with ethanol (EtOH -maceration) (p < 0.05). Major bioactive compounds detected by LC-QQQ included chlorogenic acid, caffeine, and trigonelline. At higher concentrations starting from 5 mg/ml, PG-UAE extract showed higher cell viability than EtOH-UAE in both cytotoxicity and cellular antioxidant assays. The researcher expects that this new extraction technique developed in this work could produce a higher yield of bioactive compounds with higher biological activity. Therefore, they can be used as active ingredients in cosmetics (anti-aging products) and pharmaceutical applications (food supplements, treatment for oxidative stress-related diseases) with minimal use of chemicals and energy.     

Biological Production of Gold Nanoparticles at Different Temperatures: Efficiency Assessment

The study aims to compare different approaches and efficacies during the biological production of nanoparticles (NPs). Gold nanoparticles (AuNPs) are produced by Fusarium oxysporum at two different temperatures. One flask is incubated at 37 °C (“Common”) and the other is directly heated for 5 min at 80 °C (“Heat-treated”). Obtained AuNPs are analyzed and compared by spectrophotometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Graphite furnace atomic absorption spectroscopy (GF-AAS) is used to determine the particle concentration after the AuNPs production. The AuNPs prepared by both (the Common and the Heat-treated) methods exhibit maximum absorption peaks at 541 and 528 nm, respectively, and have round shapes and sizes of less than 50 nm. Their zeta potential is about −28 mV. GF-AAS shows that the efficiency of AuNP production in Common- and Heat-treated samples is equal, between 65% and 68%. Since the Heat-treated sample shows a better size distribution, the use of higher temperature and shorter time period is preferable for the bioproduction of AuNPs. It seems that shortening the time for the production of AuNPs prevents the formation of larger NPs.     

ICP-MS: a powerful technique for quantitative determination of gold nanoparticles without previous dissolving

A direct and simple inductively coupled plasma mass spectroscopy (ICP-MS) method for the determination of gold nanoparticles (AuNP) with different particle sizes ranging from 5 to 20 nm and suspended in aqueous solutions is described. The results show no significant difference compared to the determination of the same AuNPs after digestion, as claimed by the literature. The obtained limit of quantification of the method is 0.15 μg/L Au(III) that corresponds to 4.40 × 10⁹ AuNP/L, considering spherical AuNPs 15 nm sized. Spike recovery experiments have shown that the sample matrix is a significant factor influencing the accuracy of the measurement. Spike recoveries from 93% to 95% are found for AuNP samples prepared in trisodium citrate, while for deionized H₂O a spike recovery of around 80% was obtained. The sample preparation mode along with the ICP-MS parameters have been optimized and found to be crucial so as to achieve the required accuracy for the direct quantification of AuNP suspensions. The effect of the nanoparticle size upon the ICP-MS signal also was studied, and only significant differences due to the chemical environment and not to the AuNPs size were found.     

Ultrasound-assisted alkaline proteinase extraction enhances the yield of pecan protein and modifies its functional properties

To enhance the extraction yield of pecan protein and modify its functional properties, this study investigated whether both ultrasound and enzyme have a synergistic impact on the extraction of pecan (Carya illinoinensis (Wangenh.) K. Koch) protein. The highest protein extraction rate (25.51%) was obtained under the conditions of 1415.43 W^.cm⁻², 15 min, pH 10.0, 50 °C, and 1% (w/w) alkaline proteinase. Owing to its high shear, mechanical energy and cavitation, the ultrasound process increased the solubility of the substrate making it readily accessible to the enzyme, thereby accelerating the chemical reaction and improving the yield of the protein. The optimized ultrasound-assisted enzymatic method (400 W, 20 kHz, 5 s/3s) effectively changed the secondary and tertiary structure of the pecan protein. The results of surface hydrophobicity, intrinsic fluorescence spectra, sulfhydryl content and scanning electron microscopy all indicated the unfolding of protein and exposure of hydrophobic groups and sulfhydryl groups. Moreover, the protein obtained by this method showed higher solubility (70.77%), higher emulsifying activity (120.56 m²/g), smaller particle size (326.7 nm), and better dispersion (0.305) than single ultrasound and non-ultrasound methods (p < 0.05). To conclude, ultrasound-assisted enzymatic method could be an appropriate technique to improve the yield and quality of the pecan protein. The study also provides a theoretical basis for the application of pecan protein in food processing.     

Improved synthesis of aluminium nanoparticles using ultrasound assisted approach and subsequent dispersion studies in di-octyl adipate

The present work reports on an efficient and simple one pot synthetic approach for aluminium nanoflakes and nanoparticles based on the intensification using ultrasound and provides a comparison with the conventional approach to establish the cutting edge process benefits. In situ passivation of aluminium particles with oleic acid was used as the method of synthesis in both the conventional and ultrasound assisted approaches. The aluminium nanoflakes prepared using the ultrasound assisted approach were subsequently dispersed in di-octyl adipate (DOA) and it was demonstrated that a stable dispersion of aluminium nanoflakes into di-octyl adipate (DOA) is achieved. The morphology of the synthesized material was established using the transmission electron microscopy (TEM) analysis and energy dispersive X-ray analysis (EDX) and the obtained results confirmed the metal state and nano size range of the obtained aluminium nanoflakes and particles. The stability of the aluminium nanoflakes obtained using ultrasound assisted approach and nanoparticles using conventional approach were characterized using the zeta potential analysis and the obtained values were in the range of −50 to +50 mV and −100 to +30 mV respectively. The obtained samples from both the approaches were also characterized using X-ray diffraction (XRD) and particle size analysis (PSA) to establish the crystallite size and particle distribution. It was observed that the particle size of the aluminium nanoflakes obtained using ultrasound assisted approach was in the range of 7–11 nm whereas the size of aluminium nanoparticles obtained using conventional approach was much higher in the range of 1000–3000 nm. Overall it was demonstrated that the aluminium nanoflakes obtained using the ultrasound assisted approach showed excellent morphological characteristics and dispersion stability in DOA showing promise for the high energy applications.     

Synthesis of sub-micronic and nanometric PMMA particles via emulsion polymerization assisted by ultrasound: Process flow sheet and characterization

PMMA particle synthesis was performed from MMA (methyl methacrylate) and water mixtures, exposed to different ultrasonic systems and frequencies. The sonication sequence was 20 kHz → 580 kHz → 858 kHz → 1138 kHz, and the solution was sampled after each irradiation step for polymerization. Effects of sonication parameters (time, power), polymerization method (thermo-initiated or photo-initiated), use of small amounts of surfactant (Triton X-100™ or Tween® 20) and initial MMA quantity were investigated on particle size and synthesis yields. Particle size and size distribution were measured by DLS (Dynamic Light Scattering), and confirmed via SEM (Scanning Electron Microscopy) images. Synthesis yield was calculated using the dry weight method. Particle composition was estimated using FTIR (Fourier Transform Infra-Red) spectroscopy. PMMA (polymethylmethacrylate) monodispersed particles were successfully synthesized, with a possibility of control in the 78–310 nm size range. These sized-controlled particles were synthesized with a 7.5–85% synthesis yield (corresponding to 7.5–40 g/L particle solid content), depending on operational parameters. Furthermore, a trade-off between particle size and synthesis yield can be proposed: 20 kHz → 10 min waiting time → 580 kHz → 858 kHz leading to 90 nm particles diameter with 72% yield in less than 40 min for the whole sequence. Thus, the synthesis under ultrasound can be found easy to implement and time efficient, ensuring the success of the scale-up approach and opening up industrial applications for this type of polymeric particles.     

Therapeutic Pretargeting with Gold Nanoparticles as Drug Candidates for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a binary approach for cancer treatment in which boron-10 atoms and thermal neutrons need to colocalize to become effective. Recent research in the development of BNCT drug candidates focuses increasingly on nanomaterials, with the advantages of high boron loadings and passive targeting due to the enhanced permeability and retention (EPR) effect. The use of small boron-rich gold nanoparticles (AuNPs) in combination with a pretargeting approach is proposed. Small sized polyethylene glycol–stabilized AuNPs (core size 4.1 ± 1.5 nm), are synthesized and functionalized with thiolated cobalt bis(dicarbollide) and tetrazine. To enable in vivo tracking of the AuNPs by positron emission tomography (PET), the core is doped with [⁶⁴Cu]CuCl₂. For the pretargeting approach, the monoclonal antibody Trastuzumab is functionalized with trans-cyclooctene-N-hydroxysuccinimide ester. After proving in vitro occurrence of the antibody conjugation onto the AuNPs by click reaction and the low toxicity of the AuNPs, the boron delivery system is evaluated in vivo using breast cancer xenograft bearing mice and PET imaging. Tumor uptake due to the EPR effect can be witnessed with ≈5% injected dose (ID) cm⁻³ at 24 h postinjection, but with slower clearance than expected. Therefore, no increased retention can be observed using the pretargeting strategy.     

Titania Gold Composite: Effect of Illumination on Size of Gold Nanoparticles with Consequent Implication on Photocatalytic Water Splitting

This work deals with the study of photodeposition (PD) of gold nanoparticles (AuNPs) on TiO₂ by using different illumination sources, Medium pressure Mercury lamp (ML), Solar Simulator equipped with AM 1.5 (SL) and Tungsten lamp (WL). Different particle size of AuNPs on TiO₂ were obtained by photodeposition method under different illumination sources, which clearly proves the influence of light source on the synthesis of Au–TiO₂. The plasmonic activity of Au–TiO₂ photocatalyst for water splitting reaction was observed to be strongly influenced by the particle size of Au as well as illumination source. Amongst the three different illumination sources used, smallest particle size for AuNP–TiO₂ were observed under ML followed by SL and WL, as revealed by TEM analysis. Different illumination sources were also investigated to evaluate the activity of Au–TiO₂ samples thus prepared under different illumination conditions. The order of hydrogen evolution rate (HER) observed for Au–TiO₂ with different source of illuminations is ML > SL > WL. The highest HER of 1709 μmol/h was observed for Au–TiO₂, which was synthesized and evaluated under ML irradiation. This may be explained on the basis of reduced catalytic activity and photothermal effect of Au nanoparticles with increasing particle size.     

Green synthesis and characterization of gold nanoparticles using extract of anti-tumor potent Crocus sativus

In the present study, we have explored anti-tumor potent Crocus sativus (saffron) as a reducing agent for one pot size controlled green synthesis of gold nanoparticles (AuNps) at ambient conditions. The nanoparticles were characterized using UV–vis, scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and FTIR analysis. The prepared AuNPs showed surface Plasmon resonance centered at 549 nm with average particle size of 15±5 nm. Stable, spherical and triangular crystalline AuNPs with well-defined dimensions were synthesized using anti-tumor potent Crocus sativus (saffron). Crystalline nature of the nanoparticles is confirmed from the HR-TEM, SAED and SEM images, and XRD patterns. From the FTIR spectra it is found that the biomolecules are responsible for capping in gold nanoparticles.     

Sonosynthesis of gold nanoparticles from a geranium leaf extract

A rapid in situ biosynthesis of gold nanoparticles (AuNPs) is proposed in which a geranium (Pelargonium zonale) leaf extract was used as a non-toxic reducing and stabilizing agent in a sonocatalysis process based on high-power ultrasound. The synthesis process took only 3.5 min in aqueous solution under ambient conditions. The stability of the nanoparticles was studied by UV–Vis absorption spectroscopy with reference to the surface plasmon resonance (SPR) band. AuNPs have an average lifetime of about 8 weeks at 4 °C in the absence of light. The morphology and crystalline phase of the gold nanoparticles were characterized by transmission electron microscopy (TEM). The composition of the nanoparticles was evaluated by electron diffraction and X-ray energy dispersive spectroscopy (EDS). A total of 80% of the gold nanoparticles obtained in this way have a diameter in the range 8–20 nm, with an average size of 12 ± 3 nm. Fourier transform infrared spectroscopy (FTIR) indicated the presence of biomolecules that could be responsible for reducing and capping the biosynthesized gold nanoparticles. A hypothesis concerning the type of organic molecules involved in this process is also given. Experimental design linked to the simplex method was used to optimize the experimental conditions for this green synthesis route. To the best of our knowledge, this is the first time that a high-power ultrasound-based sonocatalytic process and experimental design coupled to a simplex optimization process has been used in the biosynthesis of AuNPs.     

Ultrasound pretreatment of wheat dried distiller’s grain (DDG) for extraction of phenolic compounds

Wheat Dried distiller’s grain (DDG), a coproduct from the ethanol production process, is rich in potentially health-promoting phenolic compounds. In the extraction of phenolic compounds from DDG, the DDG cell wall is an important barrier for mass transfer from the inside to the outside of the cell. The effect of high-power ultrasound pretreatment on destruction of DDG cell walls and extraction yield and rate was investigated. Direct sonication by an ultrasound probe horn at 24 kHz was applied and factors such as ultrasound power and treatment time were investigated. The method of nitrogen (N₂) adsorption at 77 K was used as a means to determine and compare the changes in physical properties (specific surface area, pore volume and pore size) of the treated samples at different levels of ultrasound power and treatment time. Increasing specific surface area, pore volume and pore size caused by ultrasonic treatment implied development of new or larger pores and damaged cell walls. Also, it was observed that the ultrasound pretreatment of DDG particles increased the extraction yield and rate of phenolic compounds from DDG by 14.29%. Among tested ultrasound conditions, 100% ultrasound power for 30 s was evaluated as the best pretreatment condition.     

Ultrasound-alkaline combined extraction improves the release of bound polyphenols from pitahaya (Hylocereus undatus 'Foo-Lon') peel: Composition,antioxidant activities and enzyme inhibitory activity

In this study, ultrasound-assisted alkaline hydrolysis was used to extract polyphenols from pitahaya peel. The effects of sonication time, ultrasonic density, NaOH concentration and the liquid–material ratio on the total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity of the extracts were studied. The composition and content difference of the extracts were analyzed and the inhibitory effect of α-amylase and α-glucosidase was measured. The results of single-factor analysis showed that when the sonication time was 45 min, the ultrasonic density was 32 W/L, the NaOH solution concentration was 6 M and the liquid–material ratio was 30 mL/g, the release of phenolic compounds was the largest and the antioxidant activity was the strongest. An UPLC-QTOF-MS/MS method was used to analyze the components and contents of the extracts. We found that there was a great difference in the component content of the free polyphenol extract and the bound polyphenol extract. From the results, we concluded that there was a strong correlation between the type and content of phenolic compounds and antioxidant activities, indicating that phenolic compounds were the main compounds of these biological activities. Moreover, the bound polyphenol extracts showed a significant inhibitory effect on α-amylase and α-glucosidase was stronger than that of the free polyphenol extracts. In addition, scanning electron microscopy showed that ultrasound-assisted extraction is crucial to the destruction of the cell wall and the release of bound polyphenols. Therefore, the pitahaya peel has the potential for therapeutic, nutritional, and functional food applications, and ultrasound-assisted alkaline hydrolysis is an effective means to release phenolic compounds.