Ascorbic acid: a review of its chemistry and reactivity in relation to a wine environment

Development of a model to study browning caused by tyrosinase in grape must

Enzymatic browning caused by polyphenol oxidases, tyrosinase and laccase, continues to be one of the main problems in winemaking. Therefore, wineries are very interested in studying the mechanisms of browning and procedures for decreasing the use sulphur dioxide. This research proposes a model to study tyrosinase activity from grape must using different substrates: one monophenol (p-hydroxybenzoic acid), two diphenols (caftaric acid and (-)-epicatechin) and one triphenol (gallic acid). The kinetic constants of tyrosinase, Vmax and KM, indicate that caftaric acid is the best substrate for tyrosinase, followed in decreasing order by (-)-epicatechin, gallic acid and p-hydroxybenzoic acid. This last acid does not appear to be susceptible to browning by the action of grape must tyrosinase. The influence of pH, temperature and ethanol on grape must tyrosinase were also determined and the results indicate that tyrosinase Vmax increases when pH and temperature are higher and that the presence of ethanol reduces it.

Carboxymethyl chitosan-N-alkylimine derivatives: Synthesis, characterization and use for preservation of symbiotic biofertilizer bacteria on chickpea seeds

A series of carboxymethyl chitosan-N-alkylimine derivatives with side chain length of 4 to 10 carbons (CMCS-n, n = 4, 6, 8, 10) was prepared in a one-step solvent-free synthesis using Schiff base chemistry. The modified polysaccharides were characterized by their spectral, thermal and physical properties. The prepared polymers demonstrated an ability to spontaneous self-assembly with a clear correlation between critical aggregation concentration and the chain length of the alkyl substituent. N-alkylimine-CMCS derivatives were found to deliver hydrophobic (curcumin) and hydrophilic (ascorbic acid) active agents in unfavorable environments of water and oil, respectively. Then, N-alkylimine-CMCS derivatives were used as a platform for the delivery of symbiotic gram-positive bacteria Bacillus subtilis CJ onto chickpea seeds. These bacteria demonstrated a significantly higher survival rate (106 CFU/mL) in dried CMCS-6 derivative film than in other films tested. The seeds treated with N-alkylimine-CMCS coatings that contained B. subtilis CJ demonstrated up to 100-fold increase of this bacterial population on the seedlings in comparison to the pristine CMCS.

Kinetic Modeling Assisted Analysis of Vitamin C-Mediated Copper Redox Transformations in Aqueous Solutions

The kinetics of oxidation of micromolar concentrations of ascorbic acid (AA) catalyzed by Cu(II) in solutions representative of biological and environmental aqueous systems has been investigated in both the presence and absence of oxygen. The results reveal that the reaction between AA and Cu(II) is a relatively complex set of redox processes whereby Cu(II) initially oxidizes AA yielding the intermediate ascorbate radical (A•-) and Cu(I). The rate constant for this reaction was determined to have a lower limit of 2.2 × 104 M-1 s-1. Oxygen was found to play a critical role in mediating the Cu(II)/Cu(I) redox cycle and the oxidation reactions of AA and its oxidized forms. Among these processes, the oxidation of the ascorbate radical by molecular oxygen was identified to play a key role in the consumption of ascorbic acid, despite being a slow reaction. The rate constant for this reaction (A • - + O 2 → DHA + O 2 • - ) was determined for the first time with a calculated value of 54 ± 8 M-1 s-1. The kinetic model developed satisfactorily describes the Cu/AA/O2 system over a range of conditions including different concentrations of NaCl (0.2 and 0.7 M) and pH (7.4 and 8.1). Appropriate adjustments to the rate constant for the reaction between Cu(I) and O2 were found to account for the influence of the chloride ions and pH on the kinetics of the process. Additionally, the presence of Cu(III) as the primary oxidant resulting from the interaction between Cu(I) and H2O2 in the Cu(II)/AA system was confirmed, along with the coexistence of HO•, possibly due to an equilibrium established between Cu(III) and HO•.

Variations in physicochemical characteristics, antioxidant activity, phenolic and volatile profiles, and sensory attributes of tea-flavored Chardonnay wine during bottle aging

A novel Chardonnay wine flavored with either green tea or black tea was subjected to bottle aging for 9 months, and the physicochemical properties, antioxidant capacity, total phenolic content, volatile content and sensory properties were monitored. There were 272 phenolic and non-phenolic compounds characterized in the aged Chardonnay wines, including newly formed 9, 1, 3 and 8 phenolic compounds and 10, 6, 1 and 6 non-phenolic compounds after aging for 1, 3, 6 and 9 months, respectively. For all the aged wines, catechin was determined as the most abundant phenolic compound, and epigallocatechin mainly contributed toward the antioxidant power. A total of 54 volatile compounds were identified in the aged Chardonnay wines, including 17 odor-active compounds. The aging process diminished floral and fruity odors, but intensified green odor. The consumer study revealed the highest consumer liking for 1% (w/v) black tea infused wine. This study revealed the quality and bioactivity of this novel flavored wine type during aging which is critical to understand the shelf-life and functionality of the product.

Supercritical CO2 Processing of White Grape Must as a Strategy to Reduce the Addition of SO2

In winemaking, sulfur dioxide addition is the most common procedure to prevent enzymatic and microbial alterations. However, the enological industry looks for safer alternatives to preserve enological products, and high-pressure treatments with supercritical CO2 are a suitable alternative. This study evaluates the effectiveness of this process in the stabilization and preservation of white grape must, studying the influence of time, pressure, and CO2 percentage on must characteristics. In spite of the percentage of CO2 turned out to be the variable that affects the most the process, no remarkable differences were observed in pH, acidity, and color intensity between untreated and treated musts. Moreover, this technique has proven to be very efficient in the reduction of aerobic mesophilic microorganisms as well as in the reduction of residual polyphenol oxidase activities, being lower than those obtained with SO2 addition (60 and 160 mg/L). Based on the results, the most convenient conditions were 100 bar and 10% CO2, for 10 min treatment.

Linker Independent Regioselective Protonation Triggered Detoxification of Sulfur Mustards with Smart Porous Organic Photopolymer

The development of efficient metal-free photocatalysts for the generation of reactive oxygen species (ROS) for sulfur mustard (HD) decontamination can play a vital role against the stockpiling of chemical warfare agents (CWAs). Herein, one novel concept is conceived by smartly choosing a specific ionic monomer and a donor tritopic aldehyde, which can trigger linker-independent regioselective protonation/deprotonation in the polymeric backbone. In this context, the newly developed vinylene-linked ionic polymers (TPA/TPD-Ionic) are further explored for visible-light-assisted detoxification of HD simulants. Time-resolved-photoluminescence (TRPL) study reveals the protonation effect in the polymeric backbone by significantly enhancing the life span of photoexcited electrons. In terms of catalytic performance, TPA-Ionic outperformed TPD-Ionic because of its enhanced excitons formation and charge carrier abilities caused by the donor-acceptor (D-A) backbone and protonation effects. Moreover, the formation of singlet oxygen (1 O2 ) species is confirmed via in-situ Electron Spin Resonance (ESR) spectroscopy and density functional theory (DFT) analysis, which explained the crucial role of solvents in the reaction medium to regulate the (1 O2 ) formation. This study creates a new avenue for developing novel porous photocatalysts and highlights the crucial roles of sacrificial electron donors and solvents in the reaction medium to establish the structure-activity relationship.

Acidic enol electrooxidation-coupled hydrogen production with ampere-level current density

Hydrogen production coupled with biomass upgrading is vital for future sustainable energy developments. However, most biomass electrooxidation reactions suffer from high working voltage and low current density, which substantially hinder large-scale industrial applications. Herein, we report an acidic hydrogen production system that combined anodic ascorbic acid electrooxidation with cathodic hydrogen evolution. Unlike C-H and O-H bonds cleavage with slow kinetics in conventional organic oxidation, the highly active enol structure in ascorbic acid allows for an ultralow overpotential of only 12 mV@10 mA/cm² using Fe single-atom catalysts, and reaches 1 A/cm² at only 0.75 V (versus reversible hydrogen electrode) with approximately 100% Faraday efficiency for hydrogen production. Furthermore, the fabricated two-electrode membrane-free electrolyser delivers an industrial current density of 2 A/cm²@1.1 V at 60 °C (2.63 kWh/Nm³ H₂), which requires half of the electricity consumption in conventional water electrolysis (~5 kWh/Nm³ H₂). This work provides a new avenue for achieving industrial-scale hydrogen production from biomass.

Effects of Plant-Derived Polyphenols on the Antioxidant Activity and Aroma of Sulfur-Dioxide-Free Red Wine

Significant efforts have been made in recent years to produce healthier wines, with the primary goal of reducing the use of sulfur dioxide (SO₂), which poses health risks. This study aimed to assess the effectiveness of three plant-derived polyphenols (dihydromyricetin, resveratrol, and catechins) as alternatives to SO₂ in wine. After a three-month aging process, the wines were evaluated using analytical techniques such as high-performance liquid chromatography, colorimetry, gas chromatography-olfactometry-mass spectrometry, as well as electronic nose and electronic tongue analyses, with the purpose to assess parameters including antioxidant activity, color, contents of volatile aroma compounds, and sensory characteristics. The results demonstrated various degrees of improvement in the antioxidant activity, aromatic intensity, and sensory characteristics of wines using polyphenols. Notably, dihydromyricetin (200 mg/L) exhibited the strongest antioxidant activity, with increases of 18.84%, 23.28%, and 20.87% in 2,2-diphenyl-1-picrylhydrazyl, 2,2'azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), and ferric-ion-reducing antioxidant power assays, respectively. Resveratrol (200 mg/L) made the most significant contribution to volatile aroma compounds, with an 8.89% increase in the total content of alcohol esters. In E-nose analysis, catechins (200 mg/L) showed the highest response to aromatic compounds and the lowest response to volatile sulfur compounds, while also exhibiting the best sensory characteristics. Therefore, the three plant-derived polyphenols investigated here exhibited the potential to enhance wine quality as alternatives to SO₂. However, it is important to consider the specific impact of different polyphenols on wine; hence, suitable antioxidants should be selected in wine production according to specific requirements.

Ascorbic acid addition to rosé: Impact on the oxidative and reductive development of bottled wine

The impact of ascorbic acid on the oxidative and reductive development of rosé wine during bottle ageing has not been previously established. A rosé wine that contained 0.25 mg/L of Cu was bottled with levels of 0, 50 or 500 mg/L of ascorbic acid and different total packaged oxygen concentrations (3 and 17 mg/L), and was stored for 15 months at 14 °C in darkness. Ascorbic acid increased the first-order oxygen consumption rate from 0.030 ± 0.001 to 0.040 ± 0.001 days^-1, and decreased the mole ratio of total SO₂ consumed to oxygen consumed from 1.0:1 to 0.7:1. Although ascorbic acid did accelerate the loss of a Cu form that can suppress reductive aromas, it did not induce reductive aromas. These results indicate that ascorbic acid can accelerate the removal of oxygen from bottled rosé wine while maintaining higher concentrations of sulfur dioxide, however, it did not promote reductive development.

The Biochemistry and Effectiveness of Antioxidants in Food, Fruits, and Marine Algae

It is more effective to maintain good health than to regain it after losing it. This work focuses on the biochemical defense mechanisms against free radicals and their role in building and maintaining antioxidant shields, aiming to show how to balance, as much as possible, the situations in which we are exposed to free radicals. To achieve this aim, foods, fruits, and marine algae with a high antioxidant content should constitute the basis of nutritional elements, since natural products are known to have significantly greater assimilation efficiency. This review also gives the perspective in which the use of antioxidants can extend the life of food products, by protecting them from damage caused by oxidation as well as their use as food additives.

Chestnut Lily Beverage (CLB) Processing Using Ultrasound-Assisted Nisin: Microbiota Inactivation and Product Quality

We evaluated the effects of ultrasound (US) and ultrasound combined with nisin (NUS) treatments on the properties of chestnut lily beverages (CLB) using conventional thermal pasteurisation (TP) as a control. After CLB samples were treated with US and NUS for 20, 40, or 60 min, the polyphenol oxidase activity (PPO), microbial inactivation effect, colour, pH value, total phenolic content, and antioxidant capacity of the CLB were observed. It was found that the inactivation rate of PPO in CLB after NUS treatment was higher than that in the US, indicating that NUS treatment aggravated PPO inactivation. Treatment time was important in the inactivation of microorganisms by US and NUS; NUS had a lethal synergistic lethal effect on microorganisms in CLB and when compared with US, NUS reduced changes in the CLB colour value. Notably, the total phenolic content and antioxidant capacity of the US- and NUS-treated CLB significantly increased relative to the TP group. These results that suggest NUS has a potential application value in the development of CLB because it reduces the risk of microorganism contamination and helps improve the quality of CLB. This study provides technical support and a theoretical basis for the improved production of CLB.

Ozone Gas for Low Cost and Environmentally Friendly Desulfurization of Mute Grape Must

Ozone is widely used for storage and processing facilities and food sanitization. In this research, ozone was tested as an alternative to high temperature vacuum must desulfurization in order to make a more sustainable process. Bubbling ozone in highly sulfited red must (mute must) at two treatment temperatures, a significant reduction in total and free sulfites from around 1000 mg/L to 200 and 120 mg/L at 20 and 10 °C, respectively, was observed in 24 h, but already after 4 h the concentration was halved. Air flushing of the mute must did not reduce the SO₂ content. To evaluate the potential ozone effect on polyphenol oxidation, we carried out the ozone treatment on a water solution with tannins, ascorbic acid, or potassium metabisulfite (MBK) as single and as mixture. In 1 h, 2/3 of sulfite disappeared with the treatment, but the reduction was greater with ascorbate and tannins; the same was observed for ascorbate, whereas tannins decreased to a lesser extent when combined with ascorbate and MBK. Taken together, the results indicate that ozone could be an environmentally friendly, low cost, treatment for desulfurization, especially for white must, and is also easy to use by small wineries.

Comparison of a Rapid Light-Induced and Forced Test to Study the Oxidative Stability of White Wines

The oxidation processes of white wines can occur during storage and commercialization due to several factors, and these can negatively affect the color, aroma, and quality of the wine. Wineries should have faster and simpler methods that provide valuable information on oxidation stability of wines and allow fast decision-making procedures, able to trigger suitable technological interventions. Using a portable prototype instrument for light irradiations at different wavelengths and times was considered and evaluated on sensorial, spectrophotometric, and colorimetric parameters of white wines. The sensorial analysis revealed that white and light blue were the most significant, after only 1 h of irradiation. The experimental results showed that hydrogen peroxide could enhance the effect of light treatment, allowing a contemporary evaluation of the oxidation stability of wine against light and chemical stresses. As expected, a good correlation (R² > 0.89) between optical density at 420 nm and b* parameter was highlighted. The synergic effect of light and H₂O₂ was also studied on the hydrolyzable and condensed tannins' additions to white wine. The proposed methodology could be used to evaluate the oxidative stability of white wines, but also to evaluate the effect of some oenological adjuvants on wine stability.

Essential features for antioxidant capacity of ascorbic acid (vitamin C)

Vitamin C or ascorbic acid is an indispensable micronutrient for human health found principally on citrus species such as lemon and orange fruits and vegetables. It was involved in the production of proteins such as collagen. Its biochemical mechanism is related to its antioxidant capacity; however, its function at the cellular level is still unclear. Several theoretical studies about antioxidant and redox mechanisms for ascorbic acid were suggested; however, no derivative was proposed. Thereby, an electronic study of antioxidant capacity for ascorbic acid derivatives was performed using theoretical chemistry at the DFT/ B3LYP/6-311 +  + (2d,2p) level of theory. Simplified derivatives show that enol hydroxyls are more important than any other functional group. The vicinal enolic hydroxyl on β position is more important for antioxidant capacity of ascorbic than hydroxyl on α position. According to our molecular modifications, the keto-alkene compound showed the best values when compared to ascorbic acid in some molecular characteristics. No lactone derivatives have superior application potential as antioxidant when compared with ascorbic acid. Several structures are possible to be proposed and were related to spin density contributions and the increase of chemical stability. New promising structural derivatives related to ascorbic acid can be developed in the future.

Red Wine Oxidation Characterization by Accelerated Ageing Tests and Cyclic Voltammetry

In order to obtain information on the oxidative behavior of red wines, oxygen consumption rates and electrochemical changes (cyclic voltammetry) were measured for nine red wines subject to three different accelerated ageing tests: chemical (with hydrogen peroxide), enzymatic (with laccase from Trametes versicolor), and temperature (at 60 °C). Oxidative behavior depended both on the wine sample and accelerated ageing test type. A good correlation was observed between electrochemical parameters of charges for reference/non-oxidized wines, in accordance with their antioxidant capacity, and the variation of charges after enzymatic and temperature tests, meaning that cyclic voltammetry could be used in order to predict these two oxidation tests and reflect the wine sensitivity towards respective oxidation targets. However, it was not possible to predict wine chemical oxidation test based on hydrogen peroxide from the electrochemical measurements.

Vitamins in wine: Which, what for, and how much?

Vitamins are essential compounds to yeasts, and notably in winemaking contexts. Vitamins are involved in numerous yeast metabolic pathways, including those of amino acids, fatty acids, and alcohols, which suggests their notable implication in fermentation courses, as well as in the development of aromatic compounds in wines. Although they are major components in the course of those microbial processes, their significance and impact have not been extensively studied in the context of winemaking and wine products, as most of the studies focusing on the subject in the past decades have relied on relatively insensitive and imprecise analytical methods. Therefore, this review provides an extensive overview of the current knowledge regarding the impacts of vitamins on grape must fermentations, wine-related yeast metabolisms, and requirements, as well as on the profile of wine sensory characteristics. We also highlight the methodologies and techniques developed over time to perform vitamin analysis in wines, and assess the importance of precisely defining the role played by vitamins in winemaking processes, to ensure finer control of the fermentation courses and product characteristics in a highly complex matrix.

Ascorbate oxidation by iron, copper and reactive oxygen species: review, model development, and derivation of key rate constants

Ascorbic acid is among the most abundant antioxidants in the lung, where it likely plays a key role in the mechanism by which particulate air pollution initiates a biological response. Because ascorbic acid is a highly redox active species, it engages in a far more complex web of reactions than a typical organic molecule, reacting with oxidants such as the hydroxyl radical as well as redox-active transition metals such as iron and copper. The literature provides a solid outline for this chemistry, but there are large disagreements about mechanisms, stoichiometries and reaction rates, particularly for the transition metal reactions. Here we synthesize the literature, develop a chemical kinetics model, and use seven sets of laboratory measurements to constrain mechanisms for the iron and copper reactions and derive key rate constants. We find that micromolar concentrations of iron(III) and copper(II) are more important sinks for ascorbic acid (both AH2 and AH-) than reactive oxygen species. The iron and copper reactions are catalytic rather than redox reactions, and have unit stoichiometries: Fe(III)/Cu(II) + AH2/AH-  + O2 → Fe(III)/Cu(II) + H2O2 + products. Rate constants are 5.7 × 104 and 4.7 × 104 M-2 s-1 for Fe(III) + AH2/AH- and 7.7 × 104 and 2.8 × 106 M-2 s-1 for Cu(II) + AH2/AH-, respectively.

Experimental and theoretical study on the hydrogen bond interactions between ascorbic acid and glycine

Cyclic voltammetry, 1H nuclear magnetic resonance and quantum chemistry calculations were applied to explore the hydrogen bond interactions between ascorbic acid (AA) and glycine. The experimental results demonstrate the existence of hydrogen bonds in AA-glycine system, which has a significant effect on the oxidation peak potentials and currents of AA and the chemical shifts of glycine. The formation of hydrogen bonds between AA and glycine were further confirmed by the density functional theory, quantum theory of atoms in molecules and natural bond orbital analyses.

Photografting of biochelator onto polypropylene film as an antioxidant clean label

A ligand film with citric acid (CA) on the surface as a biochelator was prepared via photografting. Polypropylene film was photochemically brushed by immobilizing glycidyl methacrylate onto the film surface (PP-g-GMA) in the presence of benzophenone. The ligand film (PP-g-GMA-g-CA) was developed via a ring-opening reaction between PP-g-GMA and CA. The chemical structure was examined using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Microstructure and grafting morphology were observed using scanning electron microscopy and atomic force microscopy, and brushed-like configuration and porous surface morphology were described. A large amount of carboxylic acid (215 ± 11 nm) was detected on the surface of PP-g-GMA-g-CA and afforded chelation of Fe³⁺ (215 ± 11 nm). This ligand film exhibited chelating activity in vitamin C and virgin olive oil (p < 0.05), which extended the shelf-life of these foods. Moreover, overall migration analysis demonstrated that it can be considered as a non-migratory antioxidant.

Bottle Aging and Storage of Wines: A Review

Wine is perhaps the most ancient and popular alcoholic beverage worldwide. Winemaking practices involve careful vineyard management alongside controlled alcoholic fermentation and potential aging of the wine in barrels. Afterwards, the wine is placed in bottles and stored or distributed in retail. Yet, it is considered that wine achieves its optimum properties after a certain storage time in the bottle. The main outcome of bottle storage is a decrease of astringency and bitterness, improvement of aroma and a lighter and more stable color. This is due to a series of complex chemical changes of its components revolving around the minimized and controlled passage of oxygen into the bottle. For this matter, antioxidants like sulfur oxide are added to avoid excessive oxidation and consequent degradation of the wine. In the same sense, bottles must be closed with appropriate stoppers and stored in adequate, stable conditions, as the wine may develop unappealing color, aromas and flavors otherwise. In this review, features of bottle aging, relevance of stoppers, involved chemical reactions and storage conditions affecting wine quality will be addressed.

Effects of antioxidant and elemental sulfur additions at crushing on aroma profiles of Pinot Gris, Chardonnay and Sauvignon Blanc wines

The antioxidants sulfur dioxide (50 ppm) and ascorbic acid (100 ppm) were added to grapes soon after harvest at crushing. The chemical composition and sensory profile of Sauvignon Blanc, Pinot Gris and Chardonnay wines were examined, made from grapes collected at three different sites for each variety. With good antioxidant protection of the juices, reflected in low absorbances at 420 nm, remarkable increases in the polyfunctional mercaptans, 3-mercaptohexanol (3MH) and its acetate ester (3MHA), were seen in the wines. Moreover, high levels of these compounds were produced in the Pinot Gris and Chardonnay wines, equally high as with Sauvignon Blanc. The Pinot Gris wines maintained varietal characteristics in sensory profiles, even with high levels of polyfunctional mercaptans. When elemental sulfur was included with the grapes at crushing, extra increases in polyfunctional mercaptans were observed. However, this led to the production of unwanted reductive aroma compounds in some wines.

The effects of reaction parameters on the non-enzymatic browning reaction between l-ascorbic acid and glycine

The non-enzymatic browning (NEB) reaction between l-ascorbic acid (ASA) and glycine (Gly), including the effects of temperature (110–150 °C), time (10–150 min) and pH (4.5, 6.8, 8.0 and 9.5) on the formation of un-colored intermediate products (UIPs), browning products (BPs) and volatile products (VPs), were investigated. The results showed that pH had a remarkable effect on the reaction. The characteristics of zero-order kinetics for the formation of UIPs and BPs were discussed, and the corresponding activation energy (E a ) was also calculated. When the pH was 4.5, the E a for the formation of UIPs was approximate 53.76 kJ/mol and less than that at other pH values; while the E a for BPs formation was approximate 94.06 kJ/mol and much higher than that at other pH values. The results suggested that an acidic environment facilitated the generation of UIPs, but did not remarkably promote the formation of BPs. The possible reaction pathway between ASA and Gly was proposed according to the experimental results.

Kinetic insights into the peroxygenase activity of cellulose-active lytic polysaccharide monooxygenases (LPMOs)

Lytic polysaccharide monooxygenases (LPMOs) are widely distributed in Nature, where they catalyze the hydroxylation of glycosidic bonds in polysaccharides. Despite the importance of LPMOs in the global carbon cycle and in industrial biomass conversion, the catalytic properties of these monocopper enzymes remain enigmatic. Strikingly, there is a remarkable lack of kinetic data, likely due to a multitude of experimental challenges related to the insoluble nature of LPMO substrates, like cellulose and chitin, and to the occurrence of multiple side reactions. Here, we employed competition between well characterized reference enzymes and LPMOs for the H₂O₂ co-substrate to kinetically characterize LPMO-catalyzed cellulose oxidation. LPMOs of both bacterial and fungal origin showed high peroxygenase efficiencies, with k_cat/K_mH2O2 values in the order of 10⁵-10⁶ M^-1 s^-1. Besides providing crucial insight into the cellulolytic peroxygenase reaction, these results show that LPMOs belonging to multiple families and active on multiple substrates are true peroxygenases.

Oxidative Potential Induced by Ambient Particulate Matters with Acellular Assays: A Review

Acellular assays of oxidative potential (OP) induced by ambient particulate matters (PMs) are of great significance in screening for toxicity in PMs. In this review, several typical OP measurement techniques, including the respiratory tract lining fluid assay (RTLF), ascorbate depletion assay (AA), dithiothreitol assay (DTT), chemiluminescent reductive acridinium triggering (CRAT), dichlorofluorescin assay (DCFH) and electron paramagnetic/spin resonance assay (EPR/ESR) are discussed and their sensitivity to different PMs species composition, PMs size distribution and seasonality is compared. By comparison, the DTT assay tends to be the preferred method providing a more comprehensive measurement with transition metals and quinones accumulated in the fine PMs fraction. Specific transition metals (i.e., Mn, Cu, Fe) and quinones are found to contribute OPDTT directly whereas the redox properties of PMs species may be changed by the interactions between themselves. The selection of the appropriate OP measurement methods and the accurate analysis of the relationship between the methods and PM components is conducive to epidemiological researches which are related with oxidative stress induced by PMs exposure.

Biologically active PET/polysaccharide-based nanofibers post-treated with selenium/Tragacanth Gum nanobiocomposites

Polysaccharide-based nanofibers from Tragacanth Gum (TG) and polyethylene terephthalate (PET) were post-treated with selenium nanoparticles (Se NPs) and also stabilized with TG (SeNPs/TG). DLS, FE-SEM, EDX, TEM, and XRD were employed to verify the synthesis of Se NPs. The relatively narrow size distribution of SeNPs/TG showed through TEM and DLS investigations comparing with Se NPs. The Se NPs formation with and without TG was studied with FTIR confirmed the final stabilized solution due to the bonded hydroxyl groups of TG with Se NPs. Also, a relatively higher antioxidant reported on SeNPs/TG at 0.5-5 mg/mL using DPPH scavenging ability. The Se NPs and SeNPs/TG solutions specified remarkable inhibition against Staphylococcus aureus and Candida albicans; however, no significant antibacterial activities observed on the treated nanofibers. Finally, the uniform migration of fibroblast cells in wound healing of the treated nanofibers with SeNPs/TG proved the value of the products in medical applications.

Production of hydrogen peroxide in formulated beverages is associated with the presence of ascorbic acid combined with selected redox-active functional ingredients

Hydrogen peroxide (H₂O₂) is a reactive oxygen species (ROS) that mediates essential signaling in vivo but may cause irreversible tissue damage under dysregulated or acute exposure conditions. Beverages containing redox-active compounds might produce H₂O₂ during shelf storage and potentially be consumed. Concentrations of H₂O₂ in selected 'functional' (including energy, E, n = 28), 'non-functional' flavored, (S, n = 6) and mineral water (W, n = 6) drinks were measured under ambient (i.e., produced in situ) and 'potentiated' conditions (i.e., H₂O₂ production enhanced by addition of a reducing agent, to simulate availability of reducible substrates in vivo). Under air-saturated conditions, mean H₂O₂ contents were: 15.60 ± 15.84; 1.39 ± 2.06 and 0.30 ± 0.21 µM in E, S and W drinks, respectively. Under air-saturated, potentiated conditions, mean rates of H₂O₂ production were 21.7 ± 33.3, 0.98 ± 2.84, and -0.38 ± 1.18 µM/h for E, S and W drinks, respectively. Using multivariate statistics, the ingredient significantly associated with H₂O₂ production in combination with other ingredients was found to be ascorbic acid.

Effect of Different Reducing Agents on Aromatic Compounds, Antioxidant and Chromatic Properties of Sauvignon Blanc Wine

Sulfur dioxide (SO2) is widely the most used enological additive with reductive, antiseptic and dissolving properties. According to increasing health concerns and the gradual decrease in total SO2 concentrations allowed in wine, alternative and supplementary agents for preservation are being investigated. For this reason, the current study was focused on the impact of different commercial reductive agents on white wine antioxidant activity and chemical composition. The effect of additives that combine sulfites, ascorbic acid and enological tannins were compared against standard 5% sulfurous acid (H2SO3) during the pre-fermentative treatments of Sauvignon Blanc must (Vitis vinifera L.). The basic parameters of quality, free amino-nitrogen and total polyphenoliccompounds in must were analyzed. Gas chromatography and spectrophotometric methods were used to investigate the overall volatile composition, antioxidant and chromatic parameters in wines. The obtained results undoubtedly pointed out the positive effect of sulfuric acid on the fermentation dynamics. Furthermore, application of combined reducing additives with potassium metabisulfite, L-ascorbic acid, gallotannins and ellagitannins, resulted in a higher antioxidant capacity and increased concentration of aromatic compounds and their odor activity values in Sauvignon Blanc wine.

Analysis of factors related to browning of Dangshan pear (Pyrus spp.) wine

The effects of different dissolved oxygen concentrations (DOC) on the browning degree, amino acids, total phenols, reducing sugars, polyphenoloxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL) of pear wine, and the relationship between various quality indicators and browning degree were investigated. Dynamic model fitting analysis of the changes of physiochemical indicators of pear wine in the storage process were performed. The importance of the physiochemical indicators effect on the browning of pear wine during the storage process was analyzed by OPLS (orthogonal partial least squares discriminant analysis), and the effect of dissolved oxygen on the browning of pear wine was systematically revealed. The results showed that dissolved oxygen, total phenols and amino acids had the greatest influence on the browning degree of pear wine. It provided a theoretical basis for revealing the browning mechanism and inhibiting the browning of pear wine.

Potential of Different Natural Antioxidant Substances to Inhibit the 1-Hydroxyethyl Radical in SO2-Free Wines

The potential of different natural antioxidants to inhibit the 1-hydroxyethyl radical formation in SO₂-free wines was analyzed by electron paramagnetic resonance (EPR). Chitosan, glutathione, inactive dry yeast, oak and grape seed extracts, and ascorbic acid were tested in white and red wines. The ability of these substances to prevent the formation of acetaldehyde after the Fenton reaction and the oxygen consumption capacity were measured. Ascorbic acid was the antioxidant substance that offered higher percentages of 1-hydroxyethyl radical inhibition at 30 min of reaction. However, wines with ascorbic acid showed higher concentrations of acetaldehyde after the Fenton reaction. Grape seed extract and chitosan provided higher percentages of radical inhibition in red wine than those in white wine, in contrast to the inactive dry yeast that only produced radical inhibition in white wine. Although oak extract did not produce changes in the 1-hydroxyethyl radical, wines with that extract had lower concentrations of acetaldehyde.

Sulfide-binding to Cu(II) in wine: Impact on oxygen consumption rates

This study investigates the relationship between the two main forms of Cu in wine and their impact on the rate of oxygen consumption. The Cu forms were differentiated by medium exchange constant current stripping potentiometry, which classified the Cu as either bound to sulfide or not. Oxygen consumption rates were determined in red, white and model wines after saturation with oxygen. The results for white wines showed that the oxygen consumption was sensitive to the non-sulfide-bound Cu concentration when ascorbic acid was present, and the first order rates ranged from 0.02 to 0.11 h^-1. However, the same was not true for wines without added ascorbic acid that showed little influence of Cu form on oxygen decay rates. Cu forms were also found to significantly change in some wines during the oxygen decay experiment. Ascorbic acid is critical in enabling the form of Cu to significantly influence the oxygen reaction rate in wine.

Cu-based metal–organic framework HKUST-1 as effective catalyst for highly sensitive determination of ascorbic acid

In this work, a Cu-based nanosheet metal–organic framework (MOF), HKUST-1, was synthesised using a solvent method at room temperature. Its morphology, structure and composition were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy, nitrogen adsorption and desorption isotherms, energy dispersive X-ray spectroscopy (EDS) and elemental analysis (EA). This material was then loaded onto the surface of an indium tin oxide (ITO) electrode to catalyse the electrochemical oxidation of ascorbic acid (AA). An equal-electron-equal-proton reaction was deduced from the pH investigation, and a diffusion-controlled process was reinforced by the dynamics study. Under optimal conditions, the oxidation peak current at +0.02 V displayed a linear relationship with the concentration of AA within the ranges of 0.01–25 and 25–265 mM, respectively. The limit of detection (LOD) was 3 μM at S/N of 3. The superb response could be ascribed to the porous nanosheet structure of HKUST-1, which enhanced both the effective surface area and the electron transfer ability significantly. Moreover, the novel AA sensor demonstrated good reproducibility, favourable stability and high sensitivity towards glucose, uric acid (UA), dopamine (DA) and several amino acids. It was also successfully applied to the real sample testing of various AA-containing tablets.

In this work, a Cu-based nanosheet metal–organic framework (MOF), HKUST-1, was synthesised using a solvent method at room temperature and it demonstrated high capability and sensitivity towards the oxidation of ascorbic acid (AA).

Ascorbic acid induced activation of persulfate for pentachlorophenol degradation

In the present study, ascorbic acid (AA) induced persulfate activation was investigated for the further exploration of organic pollutants oxidation by persulfate. We interestingly found that AA showed a significant catalytic activity to persulfate. Under neutral pH and room temperature condition, about 71.3% of pentachlorophenol (PCP, 10 mg L^-1) was decomposed in 180 min with 40 mmol L^-1 persulfate and 1.0 mmol L^-1 AA, while only 15.4% and 3.2% of PCP was removed by alone persulfate and AA respectively. The result of EPR spectra identified sulfate radical (SO₄^•-) and hydroxyl radical (OH) were generated during the reaction between persulfate and AA. Quenching experiments confirmed that both SO₄^- and OH contributed to the decomposition of PCP. With the addition of AA augmented from 0 to 1 mmol L^-1, the PCP degradation ratio continuously increased. However, excess AA could consume the generated reactive oxygen species (ROSs) that led to the inhibition of PCP degradation. Meanwhile, the PCP degradation by persulfate-AA was strongly pH dependent. The PCP degradation rate was declined as the initial pH increased from 3.5 to 10.5. At pH above 12.5, the base activation began to predominate over AA activation of persulfate. Furthermore, it was observed that the AA inducing persulfate activation was related to the extent of AA ionization, while C₆H₈O₆ promoted the highest persulfate activation for the PCP degradation, and C₆H₆O₆^2- induced the lowest persulfate activation. This study indicates the high potential of AA induced persulfate activation for treatment of organochlorine contaminated water.

The Management of Compounds that Influence Human Health in Modern Winemaking from an HACCP Point of View

The undesirable effects of some hazardous compounds involved in the different steps of the winemaking process may pose health risks to consumers; hence, the importance of compliance with recent international food safety standards, including the Hazard Analysis and Critical Control Point (HACCP) standards. In recent years, there has been a rise in the development of new technologies in response to the hazardous effects of chemical compounds detected during the winemaking process, whether naturally produced or added during different winemaking processes. The main purpose was to reduce the levels of some compounds, such as biogenic amines, ethyl carbamate, ochratoxin A, and sulfur dioxide. These technological advances are currently considered a necessity, because they produce wines free of health-hazardous compounds and, most importantly, help in the management and prevention of health risks. This review shows how to prevent and control the most common potential health risks of wine using a HACCP methodology.

Alternative Methods to SO2 for Microbiological Stabilization of Wine

The use of sulfur dioxide (SO₂ ) as wine additive is able to ensure both antioxidant protection and microbiological stability. In spite of these undeniable advantages, in the last two decades the presence of SO₂ in wine has raised concerns about potential adverse clinical effects in sensitive individuals. The winemaking industry has followed the general trend towards the reduction of SO₂ concentrations in food, by expressing at the same time the need for alternative control methods allowing reduction or even elimination of SO_2. In the light of this, research has been strongly oriented toward the study of alternatives to the use of SO₂ in wine. Most of the studies have focused on methods able to replace the antimicrobial activity of SO₂ . This review article gives a comprehensive overview of the current state-of-the-art about the chemical additives and the innovative physical techniques that have been proposed for this purpose. After a focus on the chemistry and properties of SO₂ in wine_, as well as on wine spoilage and on the conventional methods used for the microbiological stabilization of wine, recent advances on alternative methods proposed to replace the antimicrobial activity of SO₂ in winemaking are presented and discussed. Even though many of the alternatives to SO₂ showed good efficacy, nowadays no other physical technique or additive can deliver the efficacy and broad spectrum of action as SO₂ (both antioxidant and antimicrobial), therefore the alternative methods should be considered a complement to SO₂ in low-sulfite winemaking, rather than being seen as its substitutes.

Enhanced Antioxidant Activity under Biomimetic Settings of Ascorbic Acid Included in Halloysite Nanotubes

Antioxidant activity of native vitamin C (ascorbic acid, AH₂) is hampered by instability in solution. Selective loading of AH₂ into the inner lumen of natural halloysite nanotubes (HNT) yields a composite nanoantioxidant (HNT/AH₂), which was characterized and investigated for its reactivity with the persistent 1,1-diphenyl-2-picrylhydrazyl (DPPH•) radical and with transient peroxyl radicals in the inhibited autoxidation of organic substrates, both in organic solution (acetonitrile) and in buffered (pH 7.4) water in comparison with native AH₂. HNT/AH₂ showed excellent antioxidant performance being more effective than native ascorbic acid by 131% in acetonitrile and 290% (three-fold) in aqueous solution, under identical settings. Reaction with peroxyl radicals has a rate constant of 1.4 × 10⁶ M-1 s-1 and 5.1 × 10⁴ M-1 s-1, respectively, in buffered water (pH 7.4) and acetonitrile, at 30 °C. Results offer physical understanding of the factors governing HNT/AH₂ reactivity. Improved performance of HNT/AH₂ is unprecedented among forms of stabilized ascorbic acid and its relevance is discussed on kinetic grounds.

Kinetic insights into the role of the reductant in H2O2-driven degradation of chitin by a bacterial lytic polysaccharide monooxygenase

Lytic polysaccharide monooxygenases (LPMOs) are monocopper enzymes that catalyze oxidative cleavage of glycosidic bonds in polysaccharides in the presence of an external electron donor (reductant). In the classical O₂-driven monooxygenase reaction, the reductant is needed in stoichiometric amounts. In a recently discovered, more efficient H₂O₂-driven reaction, the reductant would be needed only for the initial reduction (priming) of the LPMO to its catalytically active Cu(I) form. However, the influence of the reductant on reducing the LPMO or on H₂O₂ production in the reaction remains undefined. Here, we conducted a detailed kinetic characterization to investigate how the reductant affects H₂O₂-driven degradation of ¹⁴C-labeled chitin by a bacterial LPMO, SmLPMO10A (formerly CBP21). Sensitive detection of ¹⁴C-labeled products and careful experimental set-ups enabled discrimination between the effects of the reductant on LPMO priming and other effects, in particular enzyme-independent production of H₂O₂ through reactions with O₂ When supplied with H₂O₂, SmLPMO10A catalyzed 18 oxidative cleavages per molecule of ascorbic acid, suggesting a "priming reduction" reaction. The dependence of initial rates of chitin degradation on reductant concentration followed hyperbolic saturation kinetics, and differences between the reductants were manifested in large variations in their half-saturating concentrations (K _mR ^app). Theoretical analyses revealed that K _mR ^app decreases with a decreasing rate of polysaccharide-independent LPMO reoxidation (by either O₂ or H₂O₂). We conclude that the efficiency of LPMO priming depends on the relative contributions of reductant reactivity, on the LPMO's polysaccharide monooxygenase/peroxygenase and reductant oxidase/peroxidase activities, and on reaction conditions, such as O₂, H₂O₂, and polysaccharide concentrations.

Photocurable coatings prepared by emulsion polymerization present chelating properties

Herein, we present a method to synthesize a photocurable metal chelating copolymer coating via emulsion polymerization to enable a facile coat/cure preparation of metal chelating materials. The copolymer coating was a poly(n-butyl acrylate) based polymer (79 mol %) synthesized by emulsion polymerization, with iminodiacetic acid (2 mol %) and benzophenone moieties (19 mol %) to impart metal chelating and photocrosslinking properties, respectively. The copolymer was applied onto polypropylene films and was photocured (365 nm, 225 mW/cm², 180 s) to produce metal chelating film. The resulting metal chelating film had activity towards Fe³⁺ by chelating 10.9 ± 1.9 nmol/cm², 47.9 ± 5.3 nmol/cm², and 156.0 ± 13.8 nmol/cm² of Fe³⁺ at pH 3.0, pH 4.0, and pH 5.0, respectively. The metal chelating film controlled transition metal induced ascorbic acid degradation by extending half-life of ascorbic acid degradation from 6 days to 20 days at pH 3.0, and from 3 days to 6 days at pH 5.0, demonstrating its potential as an antioxidant active packaging material. Despite the introduction of polar iminodiacetic acid chelating moieties, the poly(n-butyl acrylate) based coatings retained low surface energies (24.0 mN/m) necessary to mitigate fouling and enable product release in packaging applications. This work overcomes a major knowledge gap in the area of functional coatings, by demonstrating a method by which critical properties such as control of surface energy, retention of mechanical properties, and scalability are integrated into the structure of a functional coating. The photocurable polymer coatings as reported here enable scalable production of active materials with metal chelating functionality, with applications in water treatment, trace metal detection, protein purification, and active packaging.

Untargeted voltammetric approaches for characterization of oxidation patterns in white wines

Chemical and electrochemical changes associated with controlled oxidation were measured in thirteen commercial white wines, in order to evaluate the potential of linear sweep voltammetry to provide relevant information on the oxidative behavior of individual wines. For a given amount of oxygen consumed, substantial diversity of oxidative behaviors was observed. A good correlation (R² = 0.69) was observed between the rate of O₂ consumption of individual wines and the total charged passed during linear sweep voltammetry, but not with their Folin-Ciocalteu values. Onset potential of anodic oxidation was also related to oxygen consumption capacity of wine, indicating an important contribution of easily oxidizable substrates. Subtraction of voltammograms of oxidized wines from their corresponding non-oxidized controls generated new voltammograms representative of the global changes induced by oxidation. These new voltammograms contained several features related to oxygen consumption rates of each wine, and could be considered as a 'wine oxidation signature'.