Mixture Of Ascorbic Acid Research Articles

Antioxidant active packaging based on papaya edible films incorporated with Moringa oleifera and ascorbic acid for food preservation

Edible films made from papaya (Carica papaya L.) with antioxidant activity for food preservation were developed. First, film drying conditions (solvent casting at room temperature, dehydrator, and oven) were studied considering water activity, color, thickness, and sensory evaluation. The optimum drying condition was selected for subsequent steps, wherein Moringa leaf extract and ascorbic acid were incorporated into the films either individually or simultaneously at 6 wt% each. The films were characterized regarding antioxidant activity, physicochemical properties (water activity, thickness, color, pH, and content of total soluble solids), mechanical properties, bromatology, and sensory acceptance. Moreover, the performance of the films in contact with minimally processed pears was assessed by means of sensory evaluation and physicochemical properties of this food matrix. Films dried by different methods presented no significant difference as for the evaluated parameters. In this sense, the dehydrator was selected for further film-forming procedures because of the reasonable drying time (4 h) as well as suitable preservation of the in natura physicochemical and sensory properties. Films incorporated with ascorbic acid and those with the mixture of moringa and ascorbic acid presented no significant difference, with both treatments having the highest antioxidant activity. All studied physicochemical and mechanical properties had significant difference among the tested treatments, except for pH. Finally, the incorporation of both bioactive compounds showed an influence on the shelf-life stability of minimally processed pears, with the edible film incorporated with ascorbic acid presenting positive influence on the sensory acceptance of such a food matrix.

Antibacterial and antioxidant potentials of leave extracts of Helianthus annuus

Helianthus annuus has been widely used for its medicinal and nutritional properties. This study was aimed at assessing the ethyl acetate, n-hexane and methanol extracts of Helianthus annuus for antibacterial and antioxidant potentials. The phytochemical screening, total phenols, DPPH radical scavenging assay and nitric oxide radical scavenging activity were carried out following standard procedures. Preliminary screening of the antibacterial activities of the extracts was carried out on five bacterial species (Bacillus subtilis, E. coli, Pseudomonas aeruginosa, Staphylococcus aureus and Klebsiella pneumoniae), using the agar-diffusion method. Growth rate studies in presence of the extract was investigated on two bacterial species (Bacillus subtilis and E. coli). The methanol extract was observed to inhibit the growth of the five bacterial species while ethyl acetate and N-hexane extracts showed inhibition against Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa. Extended lag periods of 5 - 6 h were observed when the Bacillus subtilis and Escherichia coli were grown in broth medium that contained the respective extracts. In broth medium with mixture of extract and ascorbic acid, there was no observed growth of the Bacillus subtilis and Escherichia coli throughout the 7 h incubation period. The total phenolics content of the extracts revealed concentrations of 6.66 ±0.45, 5.58 ±0.11 and 6.06±0.41 mg TAE.g-1) for the methanol, N-hexane and ethyl acetate extracts respectively. The DPPH radical scavenging assay results displayed gradual increase in percentage inhibition from the lowest to the highest concentration across all the standard groups, a similar trend was observed with the extracts, the ethyl acetate extract showed highest percentage inhibition amongst the other extracts. All the extracts showed high reducing power ability. The nitric oxide scavenging ability of the extracts showed constant increase with increase in concentration. Helianthus annus, it could be a good source of antimicrobial and antioxidant especially in a world where resistance to antibiotic has increasingly become a global concern.

Bactericidal activity of copper-ascorbic acid mixture against Staphylococcus aureus spp.

The purpose of this study was to investigate the bactericidal activity of copper (Cu, 10 ppm) and ascorbic acid (AA, 0.3% v/v) mixture against Staphylococcus aureus (S. aureus) ATCC 25923 (methicillin-susceptible) and ATCC 700698 (methicillin-resistant) strains. Approximately 5.5 log10 CFU/ml of each strain was individually inoculated into brain heart infusion (BHI) broth containing Cu, AA, and a Cu-AA mixture, and a time-kill assay was conducted to assess the bactericidal activity. In order to determine the efficacy of Cu-AA mixture as a surface decontaminating solution, the cells were first attached to glass slides (~6.5–7.5 log10 CFU per slide) and treated with a Cu-AA mixture for 1 min. The inner membrane permeability of the S. aureus strains was determined by measuring β-Galactosidase activity. Similarly, changes in the protein profile of treated bacterial cells were analyzed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The time-kill study revealed >3.0 log10 CFU/ml reduction in both strains within 24 h of incubation at 37 °C. Attached cells on glass slides were also reduced by > 3.0 log10 CFU per slide after 1 min of exposure to the Cu-AA mixture. The results indicate that the Cu-AA mixture was bactericidal against S. aureus strains and the damage to the inner cell membrane could be attributed to this effect.

Rapid dissolution and recovery of Li and Co from spent LiCoO2 using mild organic acids under microwave irradiation

This study is aimed to recover the valuable metal ions from cathode materials of spent Li‒ion batteries (LIBs). Rapid microwave‒assisted dissolution process is investigated here to recover Li and Co from LiCoO2 of spent LIBs. In the conventional method, about 6 h is required to extract about 90% of Li and Co using a mixture of citric acid (CA) and ascorbic acid (AA) at 80 °C. On the other hand, more than 85% of Li and Co was obtained in about 25 min by microwave (180 W)‒assisted dissolution. The dissolved Co and Li ions were precipitated, selectively: Li as LiHC2O4 H2O or Li2CO3 and Co as CoC2O4 2H2O or Co‒citrate/ascorbate. The Co3O4 was formed on heating the Co precipitate at 600 °C for 2 h. It is important to note that LiCoO2 was re‒synthesized here by thermal decomposition of CoC2O4 2H2O and LiHC2O4 H2O at 750 °C for about 24 h. Thus, the microwave‒assisted hydrometallurgical method is found to be simple and rapid to recover Li and Co from spent LIBs.

Simultaneous Voltammetric Determination of Acetaminophen, Ascorbic Acid and Uric Acid by Use of Integrated Array of Screen-Printed Electrodes and Chemometric Tools

In the present work, ternary mixtures of Acetaminophen, Ascorbic acid and Uric acid were resolved using the Electronic tongue (ET) principle and Cyclic voltammetry (CV) technique. The screen-printed integrated electrode array having differentiated response for the three oxidizable compounds was formed by Graphite, Prussian blue (PB), Cobalt (II) phthalocyanine (CoPc) and Copper oxide (II) (CuO) ink-modified carbon electrodes. A set of samples, ranging from 0 to 500 µmol·L−1, was prepared, using a tilted (33) factorial design in order to build the quantitative response model. Subsequently, the model performance was evaluated with an external subset of samples defined randomly along the experimental domain. Partial Least Squares Regression (PLS) was employed to construct the quantitative model. Finally, the model successfully predicted the concentration of the three compounds with a normalized root mean square error (NRMSE) of 1.00 and 0.99 for the training and test subsets, respectively, and R2 ≥ 0.762 for the obtained vs. expected comparison graphs. In this way, a screen-printed integrated electrode platform can be successfully used for voltammetric ET applications.

Cryopreservation of grapevine (Vitis spp.) shoot tips from growth chamber-sourced plants and histological observations

Many genebanks rely on cryopreservation as a method to preserve vulnerable field collections of vegetatively propagated crops. Effective cryopreservation procedures have been identified for Vitis; however, they usually use in vitro plantlets as the shoot tip source materials. It is costly to establish Vitis collections in vitro prior to cryopreservation. We sought to determine if growth chamber derived Vitis plants could serve as the source of shoot tips for cryopreservation. Nodal sections from growth chamber derived plants were surface-disinfected and placed in tissue culture on pre-treatment medium for 2 weeks. Uniform apical shoot tips (1 mm) were first obtained from the nodal sections and then precultured for 3 days on medium containing 0.3 M sucrose, salicylic acid, glutathione (reduced form), ascorbic acid and plant preservative mixture. Half-strength PVS2 was applied for 30 min at 22 °C, prior to full-strength PVS2 treatment at 0 °C. Cryopreserved shoot tips had the highest average regrowth of 50 and 55 % without and with cold-acclimation followed with a full-strength PVS2 exposure duration of 40 and 30 min at 0 °C, respectively. This cryopreservation protocol achieved high percentages of regrowth in V. vinifera 'Chardonnay' and 'Riesling' and V. hybrid 'Oppenheim'. Histological observations revealed that shoot tips from growth chamber plants had apical as well as multiple lateral meristems that survived LN immersion. The preservation of multiple meristems in each shoot tip may increase the capacity of shoot tip regeneration in cryopreserved Vitis that originates from ex vitro sources. The high percentage of regrowth after shoot tip cryopreservation using Vitis shoot tips derived from growth chamber source plants suggest that it may be possible to cryopreserve Vitis shoot tips without first introducing each accession into tissue culture.

New strategy for determination of anti-viral drugs based on highly conductive layered composite of MnO2/graphene/ionic liquid crystal/carbon nanotubes

In the last decade, the biomedical field has benefited from the progressive development of antiviral drugs. Antiviral drugs Sofosbuvir (SOF), ledipasvir (LED) and acyclovir (ACY) are a class of medications used specifically for treating viral infections as hepatitis C (HCV) and B (HBV) viruses. Sofosbuvir (SOF) and ledipasvir (LED) in a single-tablet regimen represent a revolution in the treatment of chronic hepatitis C which inhibits viral production of HCV. The major problem with simultaneous determination of SOF, LED and ACY by electrochemical methods is the closeness of their oxidation potentials resulting in overlapped voltammetry responses. In such frame an innovative strategy is introduced, based on a novel GC/CNT/ILC/RGO/MnO2 layered electrode, obtained by modifying a glassy carbon surface with layers of multi-walled carbon nanotubes (CNT), an ionic liquid crystal (ILC), graphene (RGO) and MnO2. The layered sensor showed excellent current responses for the simultaneous electrochemical analysis of SOF, LED and ACY in human serum in the concentration ranges 0.20–150μmoldm−3, 0.0070–15μmoldm−3 and 0.010–30μmoldm−3 with low detection limit values of 9.8nmoldm−3, 0.11nmoldm−3 and 0.84nmoldm−3 respectively. Moreover, on the new layered electrode the electro-oxidation of a quinary mixture of ascorbic acid (AA), dopamine (DA), paracetamol (APAP), SOF and LED yielded five well-separated peaks. This electrochemical method is advantageous over other methods mentioned in the literature in terms of cost, time effectiveness, sensitivity, selectivity and lower detection limit. Analysis of ACY and a combination from LED and SOF in their pharmaceutical formulations were achieved with good recovery results.

Seed-Mediated Electroless Deposition of Gold Nanoparticles for Highly Uniform and Efficient SERS Enhancement.

A seed-mediated electroless deposition (SMED) approach for fabrication of large-area and uniform gold nanoparticle films as efficient and reproducible as surface-enhanced Raman scattering (SERS) substrates was presented. This approach involved a seeding pretreatment procedure and a subsequent growth step. The former referred to activation of polylysine-coated glass slides in gold seed solution, and the latter required a careful control of the reactant concentration and reaction time. With the aid of gold seeds and appropriate reaction conditions, a large-area and uniform nanofilm with evenly distributed gold nanoparticles (Au NPs) was formed on the surface of the substrates after adding a mixed solution containing ascorbic acid and trisodium citrate. The morphology of the Au nanofilm was examined by scanning electron microscopy. The size evolution of Au NPs on the surface of the substrates was analyzed in detail. The nanofilm substrate was prepared by reaction conditions of the seeded activation process: 10 mL ascorbic acid and trisodium citrate mixture and 30 min of soaking time, which exhibited an excellent uniformity and reproducibility of SERS enhancement with relative standard deviation (RSD) values of less than 8% (particularly, a RSD value of 3% can be reached for the optimized measurement). Compared to the common electroless deposition, the seed-mediated electroless deposition possessed inherent advantages in controllability, reproducibility, and economic benefit.

Studies of Electrical Characteristics of Reduced Graphene Oxide using Hybrid Mixture of Green Reducing Agents

In this work, the electrical characteristics of reduced graphene oxide reduced using various green reductants were studied. There were three types of reducing agent used, namely ascorbic acid, glucose, and trisodium citrate. The successful reduction of graphene oxide was exhibited in UV-Vis spectroscopy with the presence of 265 nm peak. Additionally, the resistance of the reduced graphene oxide was lowered about ten times using solely ascorbic acid. It was found that mixture of ascorbic acid and glucose yield rGO of lowest sheet resistance, ∼0.57 kΩ/sq compared to others. Comparison among all samples revealed the shift of conductance minimum, which could be attributed to the functionalization of rGO that have either enhanced or deteriorate their respective sheet resistance.

Spectroscopic Investigation of the Mixture of Ascorbic Acid and Sodium Benzoate

UV spectroscopy was employed to understand the possible interaction between ascorbic acid (AA) and sodium benzoate (SB). The absorbance of each of the preservatives was taken singly (285 and 291nm for SB and AA, respectively) and the spectrum of a common drink that contained the two preservatives was recorded. Then the interaction of AA with SB was monitored by varying the concentration of AA in SB, reaction temperature and exposure to sunlight. The peaks of AA and SB disappeared and a new peak emerged at higher wavelength upon addition of AA to SB, suggesting a redshift and incorporation of AA in SB. Sunlight and temperature (≤body temperature) did not cause AA and SB to react or changes in the wavelength of maximum absorbance. Addition of AA into a typical fizzy drink did not result in new peak suggesting AA did not create any new products by its addition to this product, which already contained AA and SB at the recommended level. However, the addition of a higher amount of AA into the fizzy drinks cause a noticeable red shift from 287.5 to 295nm. Thus caution should be taken when taking AA with SB containing products.

Simultaneous Kinetic Spectrophotometric Determination Of Ascorbic Acid And Cysteine With An Optical Probe By Mean Centering Of Ratio Kinetic Profiles Method

A procedure for simultaneous kinetic analysis of a binary mixture of ascorbic acid (Asc) and cysteine (Cys) was developed using the method of mean centering of ratio kinetic profiles. The method is based on the difference in the rate of reactions of Asc and Cys with the complex of iron(III) with o-phenanthroline at pH 7.05. The use of an optical probe simplifies the carrying out of kinetic measurements, allows to obtain highly reproducible (Sr=0.01-0.02) results, and significantly reduces the time of analysis. The method of mean centering of ratio kinetic profiles is superior to the H-Point standard addition method, since it does not require such a long measurement time and there is no restriction on the constancy of absorbance of one of the components. Asc and Cys can be determined in the concentration range from 1 to 10 mg/L. The method was successfully used to determine Asc and Cys in dietary supplements.

Effects of biocompatible surfactants on structural and corresponding magnetic properties of iron oxide nanoparticles coated by hydrothermal process

Effect of the biocompatible surfactants; tartaric acid, ascorbic acid and a mixture of them on the properties of the superparamagnetic iron oxide nanoparticles (SPIONs) were investigated, separately. The SPIONs were functionalized via hydrothermal process. It was observed from X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis that the nanoparticles were iron oxide and their shapes were about spherical. And, the particle sizes of all samples were calculated to be less than 8 nm from the TEM images and XRD patterns. Fourier transform infrared spectra and thermogravimetric analysis (TGA) results displayed that all nanoparticles were effectively coated with the surfactants. According to the TGA curves, tartaric acid and ascorbic acid coatings percentages for the corresponding samples are 6.1 and 15.4% at the temperature range of 30–600 °C, respectively. For consequent magnetic analysis, vibrating sample magnetometer showed that all samples were superparamagnetic and saturation magnetizations, Ms were 71.1 and 69.5 emu/g for the nanoparticles coated with tartaric acid and ascorbic acid, respectively. Furthermore, for the first time, the SPIONs were coated with a mixture of tartaric and ascorbic acid. For that, the TGA showed 26.4% mass loss at the same temperature range and the Ms value was found to be 65.2 emu/g with a smaller particle size. In this study, it can be said that considerably high Ms values were obtained. The use of the surfactants during the hydrothermal process provides a good coating of the surface of nanoparticles and the process also increases the Ms with the sizes within superparamagnetic limit and therefore can have the potential to use in biomedical applications.

A simple way to synthesize tartaric acid, ascorbic acid and their mixture coated superparamagnetic iron oxide nanoparticles with high saturation magnetisation and high stability against oxidation: Characterizations and their biocompatibility studies

Abstract A simple way to synthesise biocompatible superparamagnetic iron oxide nanoparticles coated with ascorbic acid, tartaric acid and a mixture of ascorbic acid and tartaric acid is proposed. The iron oxide nanoparticles were synthesized and coated with the surfactants in one step by co-precipitation method at room temperature in air atmosphere. The samples have the characteristic (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0) peaks of cubic spinel structure of iron oxide. Fourier Transform Infrared Spectroscopy analysis revealed that the nanoparticles were coated with the surfactants. The mean physical sizes of core obtained from the transmission electron microscopy images were 7 ± 2 nm. Magnetic measurements by vibrating sample magnetometer indicate that all samples are superparamagnetic at room temperature. And, the saturation magnetization, Ms of coated nanoparticles was around 62 emu/g. The effectiveness of the coating on the surface of nanoparticles against oxidation is also an important parameter. The coating agents successfully protected the core against oxidation since the Ms stayed almost stable (∼62) emu/g by 12 weeks and then decreased to ∼57 emu/g by 48 weeks. It can be concluded that coated superparamagnetic nanoparticles have high saturation magnetization and high stability against oxidation. Furthermore, the MTT assays were also carried out for cytotoxicity of various concentration of coated nanoparticles by using Hep3B, Saos-2 and HUVEC cell lines. From the MTT assay results, it is observed that the coated nanoparticles are non-toxic for all types of cells investigated and therefore can be biocompatible for potential biomedical applications.

APPROACHES TO THE DEVELOPMENT OF BIOANALYTICAL METHODS FOR DETERMINATION OF UNSTABLE SUBSTANCES IN BIOLOGICAL FLUIDS

The approaches to bioanalytical method development for determination of substances which contain unstable functional groups in the structure are described. The oxidation and the hydrolysis are main causes of the decomposition of substances in biological fluids. Phenolic hydroxyls contain drugs were selected as examples of oxidable compounds, glucuronides of drugs were selected as examples of hydrolysable compounds. Determination of mycophenolic acid, which contains one phenolic hydroxyl and metabolized by formation of glucuronides, in plasma was performed using high performance liquid chromatography with mass-spectrometry and tandem mass-spectrometry detection. Methyldopa, which contains two phenolic hydroxyls, in stabilized plasma was assayed by high performance liquid chromatography – tandem mass-spectrometry in the range of 0.02–3.00 μg/ml. Concentrations of desmethyl mebeverine acid, which contains in the structure one phenolic hydroxyl and metabolized by formation of phenolic glucuronide, was measured simultaneously with mebeverine acid in the range of 10–2000 ng/ml. The influence of the ion source conversion of glucuronides on the quantitative determination of the substances was studied in the initial part of methods development. The next, selection of anticoagulants based on the study of short-term stability and freeze/thaw stability of the analytes and back conversion of their glucuronides was performed. The combination of anticoagulant K3EDTA and the antioxidant solution containing a mixture of ascorbic acid, sodium sulfite and sodium hydrogen carbonate in the concentrations of 5.0 %, 0.2 % and 2.4 %, respectively, was used to prevent degradation of methyldopa.

Layered-designed composite sensor based on crown ether/Nafion®/polymer/carbon nanotubes for determination of norepinephrine, paracetamol, tyrosine and ascorbic acid in biological fluids

Parkinson's disease is the most common neurodegenerative disorders in human mainly due to insufficient norepinephrine supply. Hence, determination of trace level of norepinephrine (NE) in presence of interfering compounds in biological fluids such as paracetamol (APAP), tyrosine (TR), and ascorbic acid (AA) is essential to diagnosis some psychiatric and neurological disorders diseases. A layer-by-layer stacked composite sensor based on crown ether (crown), Nafion® (NF), poly (3-4-ethylene dioxythiophene) (PEDOT) and multi-walled carbon nanotubes (CNT) was fabricated (GC/CNT/PEDOT/NF/Crown). Each component possesses a unique feature that contributes to the remarkable electro-catalytic activity of the sensor. Crown ether allows excellent host-guest recognition and binding ability; NF has good ionic conductivity; PEDOT has high electrical conductivity and stability; and CNT has large surface area and mechanical strength. The proposed sensor was successfully applied for electro-oxidation and separation of quaternary mixture of AA, NE, APAP, and TR into four well-defined peaks with separations in potential (ΔEp) of: 210, 163 and 257 mV for AA-NE, NE-APAP and APAP-TR, respectively. The separation of these compounds in real human blood serum samples was also successful. Detection limits were 8.46 nmol L−1, 0.0862 nmol L−1, 0.0627 nmol L−1 and 0.429 nmol L−1 in linear dynamic ranges of 0.1–30 μmol L−1, 0.007–10 μmol L−1, 0.005–8 μmol L−1 and 0.06–20 μmol L−1, for AA, NE, APAP and TR, respectively.

Trypsin and ascorbic acid have a synergistic effect on the quality of apple processing by protecting apple cells from oxidative damage

Flesh browning is fundamentally important to the quality of minimally processed fruit. The development of browning is associated with reactive oxygen species accumulation in the fruit tissue. The novel superoxide scavenging activity of trypsin has been shown in our previous work. In the current study, the effects of mixtures of trypsin and ascorbic acid (AsA) on the processing quality of apple homogenate were evaluated. In the presence of trypsin and AsA, the browning of apple homogenate was significantly impeded, and changes in the titration of acid and in the concentration of soluble solids were also delayed. The mixture of trypsin and AsA could significantly reduce cell membrane damage and the activity of peroxidase. Above all, trypsin could protect the cells of the fruit due to its superoxide scavenging activity. The utilization of trypsin will provide a new strategy for controlling quality in the processing of apples or other fruits and vegetables. Practical applications Pure, natural fruit juice with fruit flavor, especially pure, cloudy juice with a variety of natural nutrients, is increasingly widely accepted. Eliminate or inhibit the free radical accumulation is one of the most efficient methods to control the browning of apple tissue. Trypsin had a significant effect on the superoxide anion scavenging activity and showed a good protective effect on the cells. This article investigates the antioxidant and cell protective activity of trypsin–ascorbic acid (AsA) mixture during the processing of apple homogenate. The application of trypsin provides a new strategy for the quality control of fruit juice. Food additives with trypsin have a broad market and development potential.

Effective and environmentally friendly recycling process designed for LiCoO2 cathode powders of spent Li-ion batteries using mixture of mild organic acids

An effective and environmentally friendly recycling process designed for LiCoO2 cathode powders of spent Li-ion batteries using mixture of mild organic acids, citric acid (CA), tartaric acid (TA) and ascorbic acid (AA), to recover the metals. Almost complete dissolution of Li and nearly 90% dissolution of Co occurred in at 80 °C for 6 h. The reducing agent, ascorbic acid (AA), converts the dissolved Co(III) to Co(II) thereby selective recovery of Co as Co(II)-oxalate is possible. The formation of Co(III)–and Co(II) complex is evident from the UV–Vis spectra of the dissolved solution as a function of dissolution time. Thus, the reductive-complexing dissolution mechanism is proposed here. These mild organic acids are environmentally benign unlike the mineral acids.

A highly sensitive colorimetric probe for Cd2+, Hg2+ and ascorbic acid determination based on trithiocyanuric acid-AuNPs

A highly sensitive and selective colorimetric assay is proposed for the detection of mercury ions (Hg2+), cadmium ions (Cd2+) and ascorbic acid (AA) using trithiocyanuric acid (TMT) functionalized gold nanoparticles (TMT-AuNPs). TMT-AuNPs are dispersed in 40 mM NaCl solution, while the presence of Hg2+ and Cd2+ can induce TMT-AuNPs aggregate due to the strong interaction of Hg2+ and Cd2+ with TMT. Then the quantitative detection of Hg2+ and Cd2+can be realized in the linear range from 5 × 10−9 to 1 × 10−6 M and 1 × 10−8 to 3 × 10−7 M, with a lower detection limit of 2.8 nM for Hg2+ and 3.5 nM for Cd2+ (S/N = 3), respectively. To distinguish Hg2+ from Cd2+, a reductive biological small molecule ascorbic acid (AA) was used based on the different redox interaction of AA with Hg2+ and Cd2+. When the mixture of AA and Hg2+ was added into TMT-AuNPs solution, the state of TMT-AuNPs was still dispersed because Hg2+ was reduced by AA. On the contrary, when the mixture of AA and Cd2+ was added into TMT-AuNPs solution, the TMT-AuNPs was aggregated and the color of the solution has no obvious change compared to the system of Cd2+-TMT-AuNPs since the weak interaction between AA and Cd2+. Thus, AA could be detected. A linear correlation exists between the ratio of A640/A520 and the concentration of AA in the range from 1 × 10−8 to 1 × 10−6 M with a detection limit of 4.8 nM (S/N = 3). Importantly, it has been successfully applied to determine Hg2+, Cd2+ in lake water and AA in vitamins C tablet.

Use of sequential injection analysis with lab-at-valve and an optical probe for simultaneous spectrophotometric determination of ascorbic acid and cysteine by mean centering of ratio kinetic profiles

Two new, simple, relatively fast and robust methods for the simultaneous kinetic determination of binary mixtures of ascorbic acid (Asc) and cysteine (Cys) were developed using the mean centering of ratio kinetic profiles method. The methods are based on the difference in the reaction rates of Asc and Cys with 18-molybdodiphosphate at pH 5.1. An optical probe as well as the sequential injection analysis lab-at-valve (SIA-LAV) method were used to carry out simultaneous kinetic analysis. The benefits of the mean centering of ratio kinetic profiles method were shown in comparison with other spectrophotometric kinetic methods. Asc and Cys can be determined in the concentration ranges 20–200 and 8–90 µmol L−1 with the batch spectrophotometric method and 10–200 and 4–40 µmol L−1 with the SI-LAV method, respectively. The method was successfully used to determine Asc and Cys in dietary supplements.

Exploring the effect of inhibitors, cooking and freezing on melanosis in snow crab (Chionoecetes opilio) clusters

Snow crab (Chionoecetes opilio) is a valuable crustacean either sold live or processed into two sections (i.e., clusters) and commercialized in a freshly-cooked or cooked-frozen form. The market value of snow crab clusters may be impaired by the development of melanosis, a blue-hued discoloration of enzymatic origin. This study explored the effectiveness of anti-melanosis treatments in solutions with commercially available melanosis inhibitors in conjunction with cooking and freezing. Digital image analysis, correlated to the response of a sensory panel, was used to determine melanosis progression during chilled storage. 4-Hexylresorcinol was the most effective melanosis inhibitor (p < 0.001). Phosphoric acid also showed a marginal, yet significant (p < 0.05), inhibitory effect. Ascorbic acid as well as cooking to a leg core temperature of 87 °C (±0.5) showed no effect on melanosis rate, which was instead accelerated by freezing or treatment with a mixture of acetic, ascorbic, citric and ethylenediaminetetraacetic acid. Overall, 4-hexylresorcinol has the potential to lower melanosis, which may otherwise occur very rapidly and markedly during chilled storage, especially in previously frozen clusters. Melanosis should be considered as a critical quality decay indicator in the shelf-life assessment of snow crab clusters.