Oxidation Of Vanillin Research Articles

Manganese cobalt sulfide nanoparticles wrapped by reduced graphene oxide: a fascinating nanocomposite as an efficient electrochemical sensing platform for vanillin determination

In this work, a fascinating nanocomposite based on manganese-cobalt sulfide (MnS/Co3S4) wrapped by electrochemically reduced graphene oxide (ERGO) has been successfully synthesized on the surface of a glassy carbon electrode (GCE) by a facile hydrothermal assisted electrochemical reduction method. The modified electrode was fully characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The morphological results illustrate that MnS/Co3S4 are embedded in the ERGO layers, resulting in a rough surface and three-dimensional (3D) microstructure. The as-synthesized MnS/Co3S4-ERGO/GCE displays distinctly enhanced electrocatalytic activity for vanillin oxidation in comparison with that of the ERGO/GCE and MnS/Co3S4/GCE. Therefore, the MnS/Co3S4-ERGO/GCE can be used as an effective electrochemical sensing platform for the sensitive determination of vanillin, and the fabricated sensor displays a wide linear range of 0.02−1.00 μmol/L and 1.0−40.0 μmol/L, low detection limit of 4.0 nmol/L and satisfactory recoveries between 98.0% and 102.8%.

Enhanced ozonation of vanillin catalyzed by highly efficient magnetic MnFe2O4/ZIF-67 catalysts: Synergistic effects and mechanism insights.

In this study, we synthesized magnetic MnFe2O4/ZIF-67 composite catalysts using a straightforward method, yielding catalysts that exhibited outstanding performance in catalyzing the ozonation of vanillin. This exceptional catalytic efficiency arose from the synergistic interplay between MnFe2O4 and ZIF-67. Comprehensive characterization via x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FE-SEM), and energy dispersive spectroscopy (EDS) confirmed that the incorporation of MnFe2O4 promoted the creation of oxygen vacancies, resulting in an increased presence of l adsorbed oxygen (Oads) and the generation of additional ·OH groups on the catalyst surface. Utilizing ZIF-67 as the carrier markedly enhanced the specific surface area of the catalyst, augmenting the exposure of active sites, thus improving the degradation efficiency and reducing the energy consumption. The effects of different experimental parameters (catalyst type, initial vanillin concentration, ozone dosage, initial pH value, and catalyst dosage) were also investigated, and the optimal experimental parameters (300 mg/L1.0-MnFe2O4/ZIF-67, vanillin concentration = 250 mg/L, O3 concentration = 12 mg/min, pH = 7) were obtained. The vanillin removal efficiency of MnFe2O4/ZIF-67 was increased from 74.95% to 99.54% after 30 min of reaction, and the magnetic separation of MnFe2O4/ZIF-67 was easy to be recycled and stable, and the vanillin removal efficiency of MnFe2O4/ZIF-67 was only decreased by about 8.92% after 5 cycles. Additionally, we delved into the synergistic effects and catalytic mechanism of the catalysts through kinetic fitting, reactive oxygen quenching experiments, and electron transfer analysis. This multifaceted approach provides a comprehensive understanding of the enhanced ozonation process catalyzed by MnFe2O4/ZIF-67 composite catalysts, shedding light on their potential applications in advanced oxidation processes. PRACTITIONER POINTS: A stable and recyclable magnetic composite MnFe2O4/ZIF-67 catalyst was synthesized through a simple method. The synergistic effect and catalytic mechanism of the MnFe2O4/ZIF-67 catalyst were comprehensively analyzed and discussed. A kinetic model for the catalytic ozone oxidation of vanillin was introduced, providing valuable insights into the reaction dynamics.

Detection of vanillin in food products over Cu - laser induced graphene nanocomposite using the combined electrochemistry and UV–Vis spectroscopy principles

Vanillin is the fragrant phenolic compound widely used as a food additive. However, an excessive consumption of vanillin can have adverse effects on human health. Therefore, the development of a sensor for the rapid and precise measurement of vanillin is essential. In this study, vanillin is successfully measured using the UV–Vis spectroelectrochemical (SEC) method. The method uses the laser induced graphene (LIG)-supported Cu nanoparticles coated over an indium tin oxide (ITO) as the electrode. The precursor material for Cu-LIG is synthesized using the suspension polymerization of phenol and formaldehyde, with the in-situ inclusion of Cu during gel formation step. The resulting polymeric film is subjected to calcination, hydrogen-reduction, and laser ablation to create a conductive Cu-LIG layer. The synthesized material exhibits a high electrochemical surface area of 0.907 cm2/cm2 and electrical conductance of 0.002 S, rendering it a suitable electrocatalyst for the oxidation of vanillin. The Cu-LIG/ITO electrode is used in detecting the oxidized species of vanillin at 370 nm-wavelength post two cyclic voltammetry (CV) cycles over 0–1.3 V potential. The sensor shows an excellent linear response (R2 value ∼ 0.993) over the concentration range 0.25–40 μg/mL, with 0.14 μg/mL limit of detection. Owing to the anti-interference ability of the SEC sensor, the intensity of UV–Vis absorbance at 370 nm remains unaffected against common interferents including glucose, fructose, ascorbic acid, and uric acid found in real food substances. This study has clearly shown the advantages of the combined electrochemistry and UV–Vis spectroscopy principles in quantitatively detecting oxidizable compounds in commercial food products.

Oxidative Depolymerisation of Kraft Lignin: From Fabrication of Multi‐Metal‐Modified Electrodes For Vanillin Electrogeneration via Pulse Electrolysis To High‐Throughput Screening of Multi‐Metal Composites

AbstractThe production of green hydrogen may be greatly aided by the use of an alternative anode reaction replacing oxygen evolution to increase energy efficiency and concomitantly generate value‐added products. Lignin, a major component of plant matter, is accumulated in large amounts in the pulp and paper industry as waste. It has excellent potential as a source of aromatic compounds and can be transformed into the much more valuable aroma chemical vanillin by electrochemical depolymerisation. We used a flow‐through model electrolyser to evaluate electrocatalyst‐modified Ni foam electrodes prepared by a scalable spray‐polymer preparation method for oxidative lignin depolymerisation. We demonstrate how pulsing, i. e. continuously cycling between a lower and a higher applied current, increases the amount of formed vanillin while improving the energy efficiency. Further, we present a scanning droplet cell‐assisted high‐throughput screening approach to discover suitable catalyst materials for lignin electrooxidation considering that a suitable electrocatalyst should exhibit high activity for lignin depolymerization and simultaneously a low activity for vanillin oxidation and oxygen evolution. Combining electrosynthesis and electrocatalysis can aid in developing new customised materials for electrochemical processes of potential industrial interest.

Voltammetric Sensor Based on the Poly(p-aminobenzoic Acid) for the Simultaneous Quantification of Aromatic Aldehydes as Markers of Cognac and Brandy Quality.

Cognac and brandy quality control is an actual topic in food analysis. Aromatic aldehydes, particularly syringaldehyde and vanillin, are one of the markers used for these purposes. Therefore, simple and express methods for their simultaneous determination are required. The voltammetric sensor based on the layer-by-layer combination of multi-walled carbon nanotubes (MWCNTs) and electropolymerized p-aminobenzoic acid (p-ABA) provides full resolution of the syringaldehyde and vanillin oxidation peaks. Optimized conditions of p-ABA electropolymerization (100 µM monomer in Britton-Robinson buffer pH 2.0, twenty cycles in the polarization window of -0.5 to 2.0 V with a potential scan rate of 100 mV·s-1) were found. The poly(p-ABA)-based electrode was characterized by scanning electron microscopy (SEM), cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Electrooxidation of syringaldehyde and vanillin is an irreversible two-electron diffusion-controlled process. In the differential pulse mode, the sensor allows quantification of aromatic aldehydes in the ranges of 0.075-7.5 and 7.5-100 µM for syringaldehyde and 0.50-7.5 and 7.5-100 µM for vanillin with the detection limits of 0.018 and 0.19 µM, respectively. The sensor was applied to cognac and brandy samples and compared to chromatography.

Poly(hexylene vanillate): Synthetic Pathway and Remarkable Properties of a Novel Alipharomatic Lignin-Based Polyester

The negative environmental effects of conventional polymeric materials have intensified the research toward the production of biobased counterparts. Vanillic acid (VA), a vanillin oxidation product, is a relatively new and most promising aromatic monomer for the synthesis of biobased polyesters. In this work, the synthesis of a new, high molecular weight alipharomatic polyester, poly(hexylene vanillate) (PHV), using 4-(6-hydroxyethoxy)-3-methoxybenzoic acid via a two-stage melt polycondensation method is reported. The success of the polymerization was confirmed using nuclear magnetic resonance spectroscopy (NMR) and Fourier-transformed infrared spectroscopy (FTIR), while the number-average molecular weight (Mn) was estimated by size-exclusion chromatography (SEC). Moreover, the thermal behavior of PHV was determined with differential scanning calorimetry (DSC), and insights on the thermal stability and degradation mechanism of PHV were given. The mechanical and thermomechanical properties of the synthesized material were investigated, revealing a thermoplastic elastomer behavior, with elastic recovery at room temperature, associated with the formation of a mesophase status. Finally, rheological tests were applied, indicating that PHV is easily processable and fully recoverable upon yielding and flow cessation.

Reduced Graphene Oxide and Poly (phenylalanine) Composite Modified Electrode for the Electrochemical Determination of Vanillin

In this study, a simple, low cost and stable electrochemical sensor for vanillin is reported based on glassy carbon electrode (GCE) modified with poly (phenylalanine) and electrochemically reduced graphene oxide (ERGO) composite (poly (phenylalanine)/ERGO/GCE). The surface structure of the bare and modified electrodes was characterized by Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The electrochemical behavior of vanillin at phenylalanine)/ERGO/GCE) was also studied by CV. Poly (phenylalanine)/ERGO/GCE) exhibited high electrocatalytic activity for the electrochemical oxidation of vanillin due to the synergetic effects of poly (phenylalanine) and ERGO. From linear sweep voltammetry (LSV) study, the electrode reaction of vanillin is adsorption-controlled process. Furthermore, several electrochemical parameters such as number of electrons transferred (n = 2), number of protons transferred (H+ = 2), electron transfer coefficient (α = 0.66) and surface concentration of vanillin (Ґ = 0.32 nmol cm−2) were calculated. SWV was used for quantitative determination of vanillin at phenylalanine)/ERGO/GCE). Under the optimum conditions, the oxidation peak current of vanillin increased linearly with its concentration in the range 0.25–120 μM with a low detection limit of 0.025 μM. The developed sensor was successfully applied for the determination of vanillin in food and soft drink samples.

A review on nanomaterial-based electrochemical sensors for determination of vanillin in food samples.

Vanillin is an organic compound that not only acts as a flavoring and fragrance enhancer in some foods, but also can have antioxidant, anti-inflammatory, anti-cancer and anti-depressant effects. Nevertheless, its excessive use can be associated with side effects on human health. Consequently, there is a need to achieve a rapid vanillin determination approach to enhance food safety. The diversity and high sensitivity of analytical approaches has led researchers to use more advanced and efficient methods providing quantitative and qualitative outcomes in complex matrices. Among these, prominent attention has been drawn to electrochemical sensors for reasons such as reliability, simplicity, cost-effectiveness, portability, selectivity, and ease of operation, especially for the determination of vanillin. Nanomaterials are a good candidate for sensor construction due to their commendable physicochemical attributes. Some advanced nanostructures with promising platforms for high-sensitivity, highly selective, and long-lasting electrochemical sensors include graphene (Gr) and its derivatives, graphite carbon nitride (g-C3N4), carbon nanotubes (CNTs), metal nanoparticles, metal organic frameworks, carbon nanofibers (CNFs) and quantum dots. Study about sizes, dimensions, and morphologies of nanomaterials makes strong candidates for improving sensitivity or selectivity according to electrocatalytic abilities. The low LOD and wide linear range of samples demonstrated an excellent catalytic performance towards the vanillin oxidation. Some investigations have reported the synergistic effects like great conductivity of carbon nanomaterials which improved the electrocatalytic performance of nanocomposites which demonstrated the estimable sensitivity of nanomaterial-supported electrochemical sensors for determination of vanillin concentrations. The sensors which have reported have a commendable response to practical potential and evaluated in biscuit, pudding powder, chocolate, custard specimens and etc. sensitivity, stability, reproducibility and repeatability of suggested sensor were investigated. The present review article scrutinizes recent advances in the fabrication of nanomaterial-based electrochemical sensors to detect vanillin in various food matrices.

Combustion synthesis of Pr6O11 nanoparticles as an effective and sensitive sensor for detection of vanillin in the presence of uric acid

This research work describes a simple, sensitive, and disposable modified carbon paste electrode that has been constructed using praseodymium oxide nanoparticles (Pr6O11 NPs) as a modifier. These Pr6O11 NPs were prepared by combustion method and their characteristic features were studied by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDX). The prepared modified carbon paste electrode (Pr6O11/CPE) was explored by voltammetric techniques such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), differential pulse voltammetry (DPV), and electron impedance spectroscopy (EIS). The electrochemical oxidation of vanillin (VN) with uric acid (UA) in 0.1 M PBS (pH 7.0), the modified Pr6O11/CPE provides a significant current enhancement over the bare carbon paste electrode (BCPE). Some variable parameters, such as electroactive surface area, effect of modifier concentration, scan rate effect, effect of pH, and electron transfer kinetics have been investigated using the modified electrode. The electrooxidation of VN shows a diffusion-controlled process at modified Pr6O11/CPE. The detection limit of VN was found to be 0.57 µM in the range of 1-4 µM was studied by DPV method. The proposed modified sensor was fruitfully employed to measure the ingredient of VN in real sample. The stability, sensitivity, and limit of detection for VN study demonstrated the feasibility of the modified Pr6O11/CPE.

Aqueous secondary organic aerosol formation from the direct photosensitized oxidation of vanillin in the absence and presence of ammonium nitrate

Abstract. Vanillin (VL), a phenolic aromatic carbonyl abundant in biomass burning emissions, forms triplet excited states (3VL∗) under simulated sunlight leading to aqueous secondary organic aerosol (aqSOA) formation. Nitrate and ammonium are among the main components of biomass burning aerosols and cloud or fog water. Under atmospherically relevant cloud and fog conditions, solutions composed of either VL only or VL with ammonium nitrate were subjected to simulated sunlight irradiation to compare aqSOA formation via the direct photosensitized oxidation of VL in the absence and presence of ammonium nitrate. The reactions were characterized by examining the VL decay kinetics, product compositions, and light absorbance changes. Both conditions generated oligomers, functionalized monomers, and oxygenated ring-opening products, and ammonium nitrate promoted functionalization and nitration, likely due to its photolysis products (⚫OH, ⚫NO2, and NO2- or HONO). Moreover, a potential imidazole derivative observed in the presence of ammonium nitrate suggested that ammonium participated in the reactions. The majority of the most abundant products from both conditions were potential brown carbon (BrC) chromophores. The effects of oxygen (O2), pH, and reactants concentration and molar ratios on the reactions were also explored. Our findings show that O2 plays an essential role in the reactions, and oligomer formation was enhanced at pH <4. Also, functionalization was dominant at low VL concentrations, whereas oligomerization was favored at high VL concentrations. Furthermore, oligomers and hydroxylated products were detected from the oxidation of guaiacol (a non-carbonyl phenol) via VL photosensitized reactions. Last, potential aqSOA formation pathways via the direct photosensitized oxidation of VL in the absence and presence of ammonium nitrate were proposed. This study indicates that the direct photosensitized oxidation of VL may be an important aqSOA source in areas influenced by biomass burning and underscores the importance of nitrate in the aqueous-phase processing of aromatic carbonyls.

OXIDATION OF VANILLIN BY IODATE IN AQUEOUS ACETIC ACID MEDIUM: A KINETIC AND MECHANISTIC STUDY

The kinetics and mechanism of the oxidation of vanillin by iodate in aqueous acetic acid medium is studied. The reaction exhibits first order in [Iodate], fractional order in [vanillin] and [acid]. Variation of ionic strength had no effect on the reaction rate. Increase in the reaction rate by a decrease in the dielectric constant of the medium is observed. The reaction was studied at four different temperatures and the related activation and thermodynamic parameters were calculated. The product of oxidation was confirmed as vanillic acid by spectral analysis. Based on the results a plausible mechanism has been proposed and the appropriate rate law has been derived.

Separate and simultaneous determination of vanillin, theophylline and caffeine using molybdenum disulfide embedded polyaniline/graphitic carbon nitrite nanocomposite modified glassy carbon electrode

Electrochemical detection and quantitative analysis VAN, TP and CAF in food stuffs, energy drinks and pharma products using modified MoS2/PANI@g-C3N4 electrode (GCE) has been fascinating researches for many years. In this study polyaniline (PANI), molybdenum disulfide (MoS2) and graphitic carbon nitride (g-C3N4) nanocomposite modified glassy carbon electrode (MoS2/PANI@g-C3N4/GCE) was successfully used for separate and simultaneous sensing of vanillin (VAN), theophylline (TP) and caffeine (CAF). Compared to pure g-C3N4/GCE, MoS2/GCE and PANI/GCE, with MoS2/PANI/g-C3N4@GCE displayed high sensitivity and good selectivity and electrocatalytic activity towards the oxidation of VAN, TP and CAF under optimal experimental conditions. The modified electrode was also used simultaneous detection of VAN, TP and CAF, with high oxidation peak currents and well separated voltammetric peaks, using differential pulse voltammetry measurements. The sensitivity of the fabricated electrode was 8.5 μAμM−1 cm−1, 10.43 μAμM−1 cm−1 and 6.96 μAμM−1 cm−1 and the limit of detection (LOD) was estimated to be 0.043, 0.052 and 0.061 μM for VAN, TP and CAF, respectively. Furthermore, the modified electrode exhibited excellent stability and good reproducibility. In addition, the MoS2/PANI@g-C3N4 electrode was also successfully employed for the determination of these three species in real samples like food stuff, energy drinks and pharma products. These results demonstrate that the MoS2/PANI@g-C3N4 composite modified GCE could be a promising electrode material for the development of high-performance electrochemical sensor.

Theoretical investigation on the mechanisms and kinetics of OH/NO3-initiated atmospheric oxidation of vanillin and vanillic acid

Vanillin and vanillic acid are two kinds of lignin pyrolysis products that are generated by biomass combustion. The gas-phase oxidation mechanisms of vanillin and vanillic acid initiated by OH/NO3 radicals were investigated by using density functional theory (DFT) at M06–2X/6-311+G(3df,2p)//M06–2X/6-311+G(d,p) level. The initial reactions of vanillin and vanillic acid with OH/NO3 radicals can be divided into two patterns: OH/NO3 addition and H-atom abstraction. For vanillin reacted with OH radical, the OH addition mainly occurs at C2-position to produce highly chemically activated intermediate (IM2). The oxidation products 3,4-dihydroxy benzaldehyde, malealdehyde, methyl hydrogen oxalate, methylenemalonaldehyde, carbonyl and carbonyl compounds are formed by the subsequent reactions of IM2. H-atom abstracting from aldehyde group occurs more easily than from the other positions. In addition, vanillin reacting with NO3 radicals principally proceeds via NO3-addition at C1 sites and H-atom abstracting from OH group (C1) to generate HNO3. The primary reaction mechanisms of vanillic acid with OH/NO3 radicals were similar to vanillin. The Rice-Ramsperger-Kassel-Marcus (RRKM) theory was performed to calculate the rate constants of the significant elementary reactions. The total rate constants for OH-initiated oxidation of vanillin and vanillic acid are 5.72 × 10−12 and 5.40 × 10−12 cm3 molecule−1 s−1 at 298 K and 1 atm. The atmospheric lifetimes were predicted to be 48.56 h and 51.44 h, respectively. As a supplement, the kinetic calculations of NO3 radicals with two reactants were also discussed. This work investigates the atmospheric oxidation processes of vanillin and vanillic acid, and hopes to provide useful information for further experimental research.

A Novel Sensitive and Selective Amperometric Detection Platform for the Vanillin Content in Real Samples

AbstractAccurate and sensitive determination of vanillin in commercial samples is significant for food safety & quality. In the proposed study, copper particles were coated on an indium tin oxide electrode (ITO) by cyclic voltammetry (CV) for the determination of vanillin in food samples. CV studies indicated that the electrodeposition of Cu particles provides a good electrocatalytic effect towards the oxidation of vanillin. The fabricated sensor determines vanillin linearly between 0.50 μM–2.0 mM (Limit of detection: 0.15 μM). The Cu/ITO was successfully tested on vanillin samples and the recommended method provides accurate and selective determination of vanillin in daily samples.

Laccase treatment of phenolic compounds for bioethanol production and the impact of these compounds on yeast physiology

Laccase treatment of phenolic compounds found in lignocellulosic hydrolysates is an alternative to reduce the growth inhibitory effect of these compounds on fermenting microorganisms. In order to determine the main factors that affect the efficiency of this biocatalytic approach, laccase oxidation of individual and mixtures of phenolic compounds was evaluated. Additionally, the effect of phenolic compounds on Saccharomyces cerevisiae cell physiology and their effect on yeast membrane liposome models were evaluated. Trametes versicolor laccase showed complete oxidation of six phenolic compounds, while Agaricus bisporus laccase showed oxidation percentages ranging between 30–100%. High Performance Liquid Chromatography (HPLC) analyses suggested that compounds such as syringic acid, catechol and gallic acid were not completely polymerised after laccase treatment, which could explain the increase of negative effects observed when they were added to S. cerevisiae cultures. Ferulic acid and vanillin oxidation led to a 6.4 and 6.5-fold increase in ethanol production, respectively, compared with the untreated cultures. In phenolic mixtures, chemical interactions between phenolic compounds led to biotransformation of these compounds since different by-products were observed in HPLC chromatograms. Moreover, after laccase treatment, the negative effects of these mixtures were reduced, resulting in an increase in ethanol production yields. No correlation was observed between growth inhibition data, the effect on liposomes and the detoxification efficiencies. Thus, the efficiency of laccase detoxification was not related to the toxicity of the compounds but could be conditioned by the heterogeneity in the chemical structure and properties of these compounds (functional side groups, hydrophobicity, pKa).

Facile Fabrication of CeO2/Electrochemically Reduced Graphene Oxide Nanocomposites for Vanillin Detection in Commercial Food Products.

In this paper, CeO2 nanoparticles were synthesized by the solvothermal method and dispersed uniformly in graphene oxide (GO) aqueous solution by ultrasonication. The homogeneous CeO2-GO dispersion was coated on the surface of a glassy carbon electrode (GCE), and the CeO2/electrochemically reduced graphene oxide modified electrode (CeO2/ERGO/GCE) was obtained by potentiostatic reduction. The results of X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) showed that CeO2 nanocrystals were uniformly coated by gossamer like ERGO nanosheets. The electrochemical behavior of vanillin on the CeO2/ERGO/GCE was studied by cyclic voltammetry (CV). It was found that the CeO2/ERGO/GCE has high electrocatalytic activity and good electrochemical performance for vanillin oxidation. Using the second derivative linear sweep voltammetry (SDLSV), the CeO2/ERGO/GCE provides a wide range of 0.04–20 µM and 20 µM–100 µM for vanillin detection, and the detection limit is estimated to be 0.01 µM after 120 s accumulation. This method has been successfully applied to the vanillin detection in some commercial foods.

Directly Microwave-Accelerated Cleavage of C-C and C-O Bonds of Lignin by Copper Oxide and H2 O2.

Model erythro, phenolic, and nonphenolic lignin β-O-4 dimer compounds are treated with copper oxide and H2 O2 at the electronic field maximum position of a single-mode 2.45 GHz microwave system equipped with a cavity resonator. The products obtained through microwave heating and oil-bath heating with the same reaction vessel and temperature profile are quantitatively compared. Dimer degradation is found to proceed through consecutive elementary reactions. The phenolic dimer is dehydroxylated and this is followed by the spontaneous cleavage of Cα -Cβ and C-O-C bonds to produce guaiacol, vanillin, and vanillic acid. The reaction of the nonphenolic dimer produces veratric acid, veratraldehyde, and guaiacol. Microwave irradiation accelerates cleavage of the side chain and the oxidation of vanillin to vanillic acid. However, no acceleration of veratraldehyde oxidation to veratric acid or aromatic ring cleavage to produce dicarboxylic acids is observed. The selective acceleration of elementary reactions during the degradation of model lignin compounds indicates that microwaves interact with reaction intermediates that are sensitive to electromagnetic waves.

Differential Activation of Ferulic Acid Catabolic Pathways of Amycolatopsis sp. ATCC 39116 in Submerged and Surface Cultures

Amycolatopsis sp. ATCC 39116 catabolizes ferulic acid by the non-oxidative deacetylation and β-oxidation pathways to produce vanillin and vanillic acid, respectively. In submerged culture, vanillin productivity decreased more than 8-fold, when ferulic, p-coumaric, and caffeic acids were employed in pre-cultures of the microorganism in order to activate the ferulic acid catabolic pathways, resulting in a carbon redistribution since vanillic acid and guaiacol productivities increased more than 5-fold compared with control. In contrast, in surface culture, the effects of ferulic and sinapic acids in pre-cultures were totally opposite to those of the submerged culture, directing the carbon distribution into vanillin formation. In surface culture, more than 30% of ferulic acid can be used as carbon source for other metabolic processes, such as ATP regeneration. In this way, the intracellular ATP concentration remained constant during the biotransformation process by surface culture (100μg ATP/mg protein), demonstrating a high energetic state, which can maintain active the non-oxidative deacetylation pathway. In contrast, in submerged culture, it decreased 3.15-fold at the end of the biotransformation compared with the initial content, showing a low energetic state, while the NAD+/NADH ratio (23.15) increased 1.81-fold. It seems that in submerged culture, low energetic and high oxidative states are the physiological conditions that can redirect the ferulic catabolism into β-oxidative pathway and/or vanillin oxidation to produce vanillic acid.

High sensitive voltammetric sensor for nanomolarity vanillin detection in food samples via manganese dioxide nanowires hybridized electrode

Vanillin is widely used as a flavoring and fragrance enhancer in foods. Rapid detection of vanillin is of vital significance and necessity for food safety. In this work, a sensitive voltammetric sensor to detect trace vanillin of nanomolarity in food samples was demonstrated by using manganese dioxide nanowires hybridized electrode. Firstly, a modified glassy carbon electrode was prepared using manganese dioxide nanowires functionalized reduced graphene oxide as a modifier (MnO2 NWs-rGO/GCE). Then the MnO2 NWs-rGO/GCE were characterized by scanning electron microscopy, X-ray diffraction (XRD) and cyclic voltammetry (CV). Vanillin's electrochemical behavior in the solution of 0.1 M H2SO4 was studied in detail. The results showed that the modified electrode had an electrocatalytic activity for vanillin oxidation. The adsorption capacity (Γs) and standard rate constant (ks) on the modified electrode were calculated by chronocoulometry (CC). Subsequently, after systematic investigation of second derivative linear sweep voltammetry (SDLSV) under the optimal conditions, the oxidation peak current was linearly correlated with vanillin concentration in the separate ranges of 0.01–20 μM (R2= 0.9808) and 20–100 μM (R2= 0.9964), yielding the detection limit of 6.0 nM (S/N = 3). In addition, MnO2 NWs-rGO/GCE showed the advantages of surface renewal, excellent reproducibility, good stability, and simple preparation. The method was applied to the nanomolarity determination of vanillin in commercial foods with satisfactory results.

Chromatographic and Mass Spectrometric Studies of the Features of Vanillin Desorption during Regeneration of a Highly Basic Anion Exchanger

The occurrence of side chemical reactions during regeneration of the highly basic anion exchanger AB-17-2P with adsorbed vanillin with an alkali solution in the presence of atmospheric oxygen was confirmed by the method of gas chromatography/mass spectrometry. A number of the vanillin transformation products were identified. The method of mass spectrometry with matrix-activated laser desorption/ionization demonstrated the presence of the products of vanillin oxidation and polymerization, as well as benzoin condensation in the studied regeneration solution.