Micellar Extraction of Active Components from Spices and Evaluation of the Ce(IV)-Based Reducing Capacity of the Extracts

Abstract: We found the conditions for the micellar extraction of active components from spices using 0.1 M Brij® 35 as an extractant and intensifying the process with ultrasonic treatment. A single extraction for 10 min ensures the maximum recovery of active components. The raw material-to-extractant ratio varies widely depending on the type of the spice. To characterize the extracts obtained, the Ce(IV)-based reducing capacity was used, based on the interaction of the extract components with electrogenerated Ce(IV). Using ascorbic acid as an example, we proved that the Brij® 35 micellar medium does not affect the current efficiency of the coulometric titrant. Stoichiometric coefficients of several biologically active compounds with electrogenerated Ce(IV) were determined. The Ce(IV)-based reducing capacity of 20 spices was determined. The results were compared with total antioxidant parameters

Voltammetric Evaluation of Polyphenol–Protein Interactions and Their Influence on the Antioxidant Capacity of Tea

© 2020, Pleiades Publishing, Ltd. Abstract: A voltammetric method for evaluating polyphenol–protein interactions was developed based on the oxidation of polyphenols at an electrode modified with multi-walled carbon nanotubes and electropolymerized quercetin. Tea polyphenols (catechin and epigallocatechin gallate) and milk proteins (casein, bovine serum albumin, and β-lactoglobulin) were considered as model systems. It was found that proteins bind the test polyphenols (from 10 to 60%) with increasing protein content (from 1 : 0.25 to 1 : 1.5, by volume) in the mixture by decreasing the fraction of free polyphenol. The developed approach was used to assess the effect of milk on the antioxidant properties of tea (green, white, oolong, and black teas), which were expressed through the antioxidant capacity (AOC) parameter. A statistically significant decrease in the AOC of tea by a factor of 1.8–23 in the presence of 20 vol % milk was demonstrated

An electrode based on electropolymerized naringin for voltammetry

The working conditions of naringin electropolymerization on the glassy carbon electrode modified with multi-walled carbon nanotubes (MWNT/GCE) under the conditions of potentiodynamic electrolysis have been found. The effect of monomer concentration, polarization window, potential scan rate, and number of cycles on the electrochemical properties of the polynaringin-modified electrode has been evaluated using hexacyanoferrate(II) ions as a redox standard. The best results have been observed for the polymeric coverage obtained from 0.20 mM naringin by tenfold potential cycling in the range of 0.2–0.8 V at a scan rate of 75 mV/s in the Britton-Robinson buffer solution, pH 8.0. The surface of the glassy carbon and modified electrodes has been characterized by scanning electron microscopy, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The high porosity of the polynaringin layer leads to an increase of the electrode effective surface area in comparison to GCE (8.2 ? 0.3 and 12.6 ? 0.6 mm2 for GCE and polynaringin/MWNT/GCE, respectively). The electrochemical impedance spectroscopy data indicate an increase of the electron transfer rate on the polynaringin-modified electrode in comparison to GCE and MWNT/GCE (6.0 ? 0.5 kΩ vs. 181 ? 5 and 6.8 ? 0.3 kΩ, respectively)

Chaga extracts and melanins after plasma treatment of raw material

The extracts and melanins of chaga (Inonotus obliquus (Pers.) Pil.) obtained by raw material pretreatment with high-frequency capacitive low-pressure plasma (RF-plasma) under different technological conditions were studied. The advantages of RF-plasma treatment of raw materials in three different plasma-forming media (argon, air, and nitrogen) were shown. In all cases, the modification of the natural particles surface affecting the extraction process was observed. Optimization of the extraction parameters demonstrated that best results (increase of the extractive compounds yield and higher antioxidant capacity) were achieved with the air-based plasma. The surface topology of the melanins under investigation was evaluated by atomic force microscopy (AFM). The difference of melanins structural features by roughness degree, height, and diameter of single particles in relation to the raw material RF-plasma treatment mode was shown that enabled a deeper insight into the nature of fungal melanins. Preliminary RF-plasma treatment of raw material can be recommended for Inonotus obliquus (Pers.) Pil. extraction while producing medications on their basis

Voltammetric Determination of Quercetin and Rutin on Their Simultaneous Presence on an Electrode Modified with Polythymolphthalein

© 2020, Pleiades Publishing, Ltd. Abstract: A voltammetric method is developed for the determination of quercetin and rutin in the simultaneous presence on a glassy carbon electrode modified with carbon nanofibers and polythymolphthalein. The conditions of the potentiodynamic electrolysis of thymolphthalein providing the maximum difference in the oxidation potentials of quercetin and rutin equal to 136 mV are found. Thymolphthalein electropolymerization should be carried out in a 100 μM solution by the 10-fold cycling of the potential from 0 to 1.7 V at a sweep rate of 75 mV/s in phosphate buffer solution with pH 7.0. The electrode modified with polythymolphthalein is characterized by scanning electron microscopy, cyclic voltammetry, and electrochemical impedance. It is found that the oxidation of quercetin proceeds irreversibly, and that of rutin, quasi-reversibly with the participation of two electrons and two protons and is controlled by the adsorption of analytes on the electrode surface. The analytical range is 0.025–1.00 μM for both analytes, and the limits of detection are 7.3 nM for quercetin and 4.7 nM for rutin. The selectivity of the electrode response to quercetin and rutin in the presence of inorganic ions, saccharides, and ascorbic and p-coumaric acids is shown. The developed method is tested on real samples (linden Tilia L. flowers and onions)

An Electrode Based on Electropolymerized Sunset Yellow for the Simultaneous Voltammetric Determination of Chlorogenic and Ferulic Acids

Abstract: We developed an electrode based on multi-walled carbon nanotubes and electropolymerized Sunset Yellow FCF for the simultaneous voltammetric determination of chlorogenic and ferulic acids. Poly(Sunset Yellow) was obtained potentiostatically under chronoamperometric conditions. Variation of the pH of the supporting electrolyte, monomer concentration, and electrolysis conditions showed that the maximum difference between the oxidation potentials of phenolic acids (190 mV) and high currents were achieved for a coating obtained in an alkaline medium from 50 μM monomer solution at a potential of 1.1 V for 30 s. Poly(Sunset Yellow) consists of spherical particles and their aggregates with a diameter of 26–75 nm, which leads to an increase in the effective surface area of the electrode (44.0 ± 0.6 mm2 compared to 26.1 ± 0.6 mm2 for a glassy carbon electrode modified with carbon nanotubes). The data of electrochemical impedance spectroscopy indicate an increase in the rate of electron transfer on modified electrodes. The data of cyclic voltammetry proved that the electrooxidation of phenolic acids on the polymer-modified electrode is controlled by diffusion and proceeds with the participation of two electrons and two protons with the formation of corresponding o-quinones. The linear dynamic range is 0.10–4.0 µM for chlorogenic acid and 0.5–4.0 µM for ferulic acid with the limits of detection 0.076 and 0.098 µM, respectively. The proposed method was applied to determine these acids in coffee

Chronoamperometric Evaluation of the Antioxidantcapacity of Micellar Spice Extracts

The oxidation potentials of micellar spice extracts on a glassy carbon electrode modified with cerium dioxide nanoparticles in the Brij®35 micellar medium in phosphate buffer solution have been found. A chronoamperometric approach for evaluation of the antioxidant capacity (AOC) of micellar spice extracts based on the oxidation of their antioxidants under the conditions of potentiostatic electrolysis at 1.1 V has been developed. It has been shown that steady-state electrolysis is attained in 100 s. The AOC has been expressed in gallic acid equivalents recalculated per 1 g of dry spices. The dynamic analytical range of gallic acid was 7.50–2500 μM with the limits of detection and quantification of 2.27 and 7.50 μM, respectively. The approach has been tested on the extracts of 20 spices. Their AOC varied in a wide range (from 109.0 ± 0.2 mg/g for clove to 1.9 ± 0.1 mg/g for caraway) owing to the composition and contents of active components in raw plant materials. Positive correlations have been found between the AOC of spices and their antioxidant activity based on the reaction with 2,2-diphenyl-1-picrylhydrazyl (r = 0.8990 at rcrit = 0.497) and ferric reducing power (r = 0.9066 at rcrit = 0.497)

Optimizing Pretreatment of Medicinal Raw Materials by RFC Plasma before Extraction

Optimization of the RF-plasma treatment modes of chaga raw materials using the Statistica 6.0 software package has been performed. Mathematical design has been carried out to calculate the optimum parameters of RF-plasma treatment using three plasma-forming gases – argon, air, and nitrogen. Plasma treatment of chaga raw materials has been undertaken at the constant parameters: pressure P = 30.0 Pa, anodic current J = 0.7 A, gas consumption G = 0.04 g/s; the variable parameters were power U = 5.0÷7.0 kV and treatment duration at the high-frequency capacitor category of the lowered pressure t = 30÷60 min. Optimization of four key parameters for extraction of chaga raw materials (solid residue, melanin yield, antioxidant activity of both extract and chaga melanin) depending on the chosen plasma-forming gas (argon, air, or nitrogen) has been achieved. The optimum modes of RF-plasma treatment allowing to obtain the extracts and melanin of chaga mushroom with the improved physicochemical and antioxidant characteristics have been calculated

Investigation of Inonotus obliquus (Pers.) Pil. Extracts and Melanins after RF-plasma Treatment of Raw Material

High-frequency capacitive discharge (RF plasma) at low pressure was used as preliminary stage for the intensification of extraction from natural medicinal raw material. RF-plasma treatment was carried out in two modes differed by the nature of plasma-forming gas. Chaga (Inonotus obliquus (Pers.) Pil.) known as the birch mushroom was selected as a perspective source of raw material. Extraction was carried out in two ways – remaceration and maceration. The analy-sis of chaga extracts and melanins was performed using traditional techniques including determination of physical and chemical, antioxidant and spectral characteristics. The obtained extracts and melanins were compared to the control samples and literature data. RF-plasma treatment of medicinal raw material increased the yield of extractive substances, in particular of the main active component of chaga – melanin. The antioxidant activity of chaga extracts grew, while for melanins it remained at the level similar to that of control samples. The IR spectral characteristics of the studied chaga melanins are similar and agree well with the literature data. Insignificant deviations in the position and intensity of absorption strips were observed for the samples after RF treatment. IR spectra of the studied chaga melanins are similar to those for mushroom melanins, thereby confirming the similarity in their nature. RF-plasma treatment of chaga medicinal raw materials allows to modify them partially. The structural and mechanical properties of melanins modified by RF plasma remain the same