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1.
Food Chem ; 332: 127150, 2020 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-32659696

RESUMO

We report an optical biosensor using imine, 5-((anthrcene-9-ylmethylene) amino)-2,3dihydrophthalazine) 1-4-dione (ADD) for direct detection of ascorbic acid (AA) via FRET quenched. The ADD was successfully prepared by using simple ultra - sonication method, which was characterized by various spectroscopic techniques. The fluorescence intensity of ADD probe was drastically quenched in presence of AA, and shown excellent selectivity towards the detection of AA in presence of possible biological active interferences. A wide linear range from 0.25 to 190 µM was achieved towards the detection of AA with a LOD of 10 nM. The occurrence of FRET mechanism is due to intermolecular hydrogen bonding between ADD and AA, which was confirmed by Density Functional Theory calculations. Moreover, the biosensor was successfully applied for the detection of AA in real samples such as fruits and vegetables to demonstrate the practicability. In addition, the developed biosensor could be a simple and economically cheap platform for the detection of AA in food samples.


Assuntos
Ácido Ascórbico/análise , Técnicas Biossensoriais/métodos , Frutas/química , Luminol/análogos & derivados , Fenômenos Ópticos , Sonicação , Verduras/química , Técnicas de Química Sintética , Limite de Detecção , Luminol/síntese química , Luminol/química
2.
An Acad Bras Cienc ; 92(2): e20190328, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32556050

RESUMO

The degradation kinetics of vitamin C in different citrus juice types (tangerine, grapefruit, orange and lime) were investigated during four hours storage at temperatures of 4 and 25°C under different storage conditions in terms of light and oxygen presence. The loss of vitamin C at each sample followed the first-order kinetic model. During storage, predicted half-life of vitamin C ranged from 137.586 to 467.486 min for tangerine; 105.444 to 203.100 min for grapefruit; 365.702 to 1044.668 min for orange and 540.076 to 722.016 min for lime juices. These results indicated that the highest and lowest retentions of vitamin C were observed in orange and grapefruit juices respectively during storage. Additionally, storage time, light penetration and oxygen presence were the most effective factors on vitamin C degradation while the storage temperature revealed no significant effect on the vitamin C content.


Assuntos
Ácido Ascórbico/análise , Citrus , Armazenamento de Alimentos , Sucos de Frutas e Vegetais/análise , Meia-Vida , Cinética , Temperatura
3.
Food Chem ; 329: 127213, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-32516713

RESUMO

Chitosan and whey protein isolate (WPI) conjugate films were prepared as a novel matrix for encapsulating and extending the postharvest shelf life of strawberries. Film forming solutions of chitosan, WPI, and chitosan-WPI conjugate were mixed with glycerol, casted for films at 60 ± 2 °C and assessed for their colour, water vapour and oxygen transfer rate, textural, functional groups and secondary structure, thermal, crystallinity, and antioxidant properties. Chitosan-WPI conjugate films were applied as an edible coating on strawberries, and studied for storage stability at 5 °C and 20 °C by assessing physical and biochemical parameters. A considerable reduction in colour indices, weight loss, pH and titratable acidity, reducing sugars, ascorbic acid, total phenolics, DPPH and ABTS assay was noted in the coated strawberries over the control at both the studied temperatures. The control strawberries had a shelf life of 5 and 3 days, whereas coating enhanced the shelf life of strawberries to 8 and 5 days when stored at 5 °C and 20 °C, respectively.


Assuntos
Quitosana/química , Conservação de Alimentos/métodos , Proteínas do Soro do Leite/química , Antioxidantes/química , Ácido Ascórbico/análise , Varredura Diferencial de Calorimetria , Cor , Fragaria/química , Fragaria/metabolismo , Frutas/química , Frutas/metabolismo , Glicerol/química , Concentração de Íons de Hidrogênio , Fenóis/análise , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura
4.
Food Chem ; 326: 126935, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32447160

RESUMO

Carbon dots (CDs) have been a new class of fascinating carbon-based fluorescent nanomaterials. In the present work, new N-doped CDs with highly crystalline graphite structures are prepared from renewable precursors, chitosan and tartaric acid, and are well characterized. The prepared CDs are applied as a biocompatible fluorescent sensor for the sequential detection of Fe3+ and AA. Among various transition metal ions, Fe3+ can selectively quench the fluorescence of CDs. Upon the further addition of AA, the quenched fluorescence of CDs is then restored as Fe3+ is reduced to Fe2+ by AA, which can be utilized for the fluorescent determination of AA. A good linear relationship in the range of 0-150 µM of AA concentration is established with a low detection limit of 0.02 µM. Moreover, the practical applications of this fluorescent sensing method in measurement of AA in food samples are successfully realized with satisfactory results.


Assuntos
Ácido Ascórbico/análise , Carbono/química , Compostos Férricos/análise , Nanoestruturas/análise , Espectrometria de Fluorescência/métodos , Fluorescência , Limite de Detecção , Nitrogênio/química , Pontos Quânticos/química , Espectrometria de Fluorescência/instrumentação
5.
Food Chem ; 326: 126966, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32416419

RESUMO

Phenolic compounds and ascorbic acid were analyzed in one yellow and four purple-flesh potato cultivars grown at 13 °C and 18 °C and harvested at different stages of tuber development, using HPLC-DAD and UHPLC-MS. The expression of genes in the phenylpropanoid pathway was studied at transcription level using qPCR. Petunidin-3-p-coumaroylrutinoside-5-glucoside was the most abundant anthocyanin in 'Blue Congo', 'Blaue Schweden', and 'Synkeä Sakari', whereas malvidin-3-p-coumaroylrutinoside-5-glucoside dominated in 'Blaue Veltlin'. In mature tubers, the purple cultivar 'Synkeä Sakari' showed the highest content of anthocyanins (2.4 mg/g freeze-dried sample), and 'Blaue Veltlin' had the highest content of phenolic acids (5.5 mg/g). Cultivar was the main variable affecting the biosynthesis of the studied metabolites, whereas the temperatures studied did not show different impact. The content of the main phenolic acids and anthocyanins in the potato cultivars correlated positively with the expression levels of the genes involved in the phenylpropanoid pathway.


Assuntos
Ácido Ascórbico/metabolismo , Fenóis/metabolismo , Tubérculos/química , Solanum tuberosum/química , Solanum tuberosum/crescimento & desenvolvimento , Antocianinas/metabolismo , Ácido Ascórbico/análise , Cromatografia Líquida de Alta Pressão , Glucosídeos/metabolismo , Espectrometria de Massas , Fenóis/análise , Pigmentação , Tubérculos/crescimento & desenvolvimento , Tubérculos/metabolismo , Solanum tuberosum/genética , Solanum tuberosum/metabolismo , Temperatura
6.
Food Chem ; 320: 126646, 2020 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-32229398

RESUMO

Wild edible plants are recently recognized as an important source of acquiring macro and micro nutrients beneficial for human health. Hence, the present study was undertaken to assess the antidiabetic and antioxidant potentials, polyphenolic profile, - as well as the ascorbic acid, proximate and mineral compositions of five selected Bangladeshi wild plants. The studied samples were rich in ash, fiber, protein, vitamin C and low in fat. The undertaken plant samples were found to have good amounts of total phenolic, total flavonoid, and antioxidant capacities, documented by DPPH, FRAP, and TEAC assays. They also exhibited varying spectrum of polyphenols estimated by HPLC. Significant inhibition of α-amylase activity by plant extracts was also observed. Evaluation by principal component analysis revealed clear separation among the wild plant varieties. The study findings would enrich the food composition table of Bangladesh and allow the population to consume more wild plants and increase their production.


Assuntos
Antioxidantes/análise , Plantas Comestíveis/química , Polifenóis/análise , Ácido Ascórbico/análise , Bangladesh , Cromatografia Líquida de Alta Pressão , Flavonoides/análise , Hipoglicemiantes/análise , Extratos Vegetais/química
7.
Food Chem ; 322: 126753, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32283366

RESUMO

This paper investigated the effects of radio-frequency (RF) energy and conventional hot-water blanching (95 °C for 2 min) on the peroxidase (POD) activity, physiochemical properties, and changes in the cellular morphology of stem lettuce. The relative residual POD activity significantly decreased (P < 0.05) from 66.03% to 6.46% with increased RF heating temperature (65 °C-85 °C). The weight loss (3.06%-7.64%), color, texture, relative electrolyte leakage (23.45%-67.90%), and residual vitamin C content (72.22%-16.67%) significantly changed (P < 0.05) with increased RF heating temperature (65 °C-85 °C). Micrographs indicated that the changes in physiochemical property can be attributed to the destruction of cell membranes, loss of cell turgor, reduced rigidity of cell walls, and loose adhesion between adjacent cells. Samples treated by RF heating at 75 °C showed lesser cell damage and better nutrient retention than those treated by hot-water blanching at a similar level of POD inactivation.


Assuntos
Alface/metabolismo , Peroxidase/metabolismo , Ondas de Rádio , Ácido Ascórbico/análise , Parede Celular/química , Eletrólitos/metabolismo , Temperatura Alta , Alface/efeitos da radiação , Alface/ultraestrutura , Paladar , Água/química
8.
Food Chem ; 322: 126713, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32283370

RESUMO

Pre-harvest application of exogenous compounds has been employed in many crops, as a cultural practice, to promote their adaptation to a new climate-changing environment. Effect of foliar pre-harvest application of salicylic acid, glycine-betaine complex and seaweed extract (Ascophyllum nodosum) on the cherry quality from 'Staccato' cultivar was studied. Treatments significantly affected (p < 0.01) the fruit size, soluble solids content, pH, colour, polyphenols, vitamin C and antioxidant activity. Glycine-betaine and A. nodosum treated cherries presented higher dimensions, soluble solids content and pH and lower acidity. In addition, these cherries had a higher content of polyphenols and vitamin C and antioxidant capacity, but lower values of L*, C*ab and hue angle, meaning that both treatments can rise the fruit ripening process. Therefore, the pre-harvest application of glycine-betaine and A. nodosum can be a good alternative to promote the adaptation of sweet cherry tree to stressful environmental conditions, without compromising the fruit quality.


Assuntos
Ascophyllum/química , Betaína/farmacologia , Conservação de Alimentos/métodos , Conservantes de Alimentos/farmacologia , Glicina/farmacologia , Extratos Vegetais/farmacologia , Prunus avium/química , Alga Marinha/química , Antioxidantes/análise , Ácido Ascórbico/análise , Cor , Frutas/química , Frutas/efeitos dos fármacos , Prunus avium/efeitos dos fármacos , Controle de Qualidade
9.
Food Chem ; 319: 126509, 2020 Jul 30.
Artigo em Inglês | MEDLINE | ID: mdl-32193056

RESUMO

In this paper, a simple, sensitive and precise electroanalytical method was developed using flow injection analysis (FIA) with amperometric detection and reduced graphene oxide sensor for ascorbic acid determination in samples of multivitamin beverages, milk, fermented milk, and milk chocolate. The advantages of this sensor include a potential displacement of 450 mV and a 2-fold peak current increase for electrochemical oxidation of ascorbic acid, which resulted in a highly sensitive method. No interference of sample matrix was observed, avoiding solvent extraction procedures (samples were only diluted). The FIA allowed a high analytical frequency, approximately 96 injections per hour, together with adequate detection limit of 4.7 µmol L-1. Good precision (RSD < 7%) and accuracy (recoveries between 91 and 108%) evidenced the robustness of the method. The method was compared with ultra-fast liquid chromatography (UFLC) obtaining statistically similar results (95% confidence level). The ascorbic acid content in samples varied from 0.065 to 2.53 mmol L-1.


Assuntos
Ácido Ascórbico/análise , Bebidas/análise , Grafite/química , Animais , Cromatografia Líquida de Alta Pressão , Análise de Injeção de Fluxo , Limite de Detecção , Leite/química , Vitaminas/análise
10.
Food Chem ; 318: 126506, 2020 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-32126473

RESUMO

Orange peels were applied as precursors to synthesize carbon dots (CDs) via a one-step green hydrothermal method. The relationship between quantum yield and volatile oils in 14 different varieties of orange peels were investigated. The CDs showed strong blue fluorescence and were further modified with EDTA. Compared with the CDs, the CDs@EDTA exhibited higher sensitivity for Cr(VI) detection with a LOD of 10 nM. The CDs@EDTA was proved to be an effective fluorescent sensor element for Cr(VI) detection in water samples with recoveries ranged from 92.09% to 104.87% (RSD < 5%). Moreover, CDs@EDTA/Cr(VI) system was further developed as a fluorescent "off-on" sensor for ascorbic acid (AA) detection with a LOD of 0.1 µM. Further, the sensor had been successfully applied for the analysis of AA in fresh oranges and commercial orange juices. The recoveries of AA in fresh oranges and orange juices were 92.58-106.76% and 91.54-104.95%, respectively.


Assuntos
Ácido Ascórbico/análise , Carbono/química , Citrus sinensis/química , Sucos de Frutas e Vegetais/análise , Espectrometria de Fluorescência/métodos , Cromo/química , Ácido Edético/química , Fluorescência , Frutas/química , Pontos Quânticos/química , Sensibilidade e Especificidade
11.
Food Chem ; 318: 126549, 2020 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-32151920

RESUMO

Cornelian cherry (CC) fruits a source of bioactive compounds that are still being underutilized. In this study, a comprehensive characterization of 11 Montenegrin CC local or introduced genotypes and cultivars collected in the wild or from organic orchards is provided. Their potential utilizations as natural antioxidants, colorants and organic food ingredients were exploited. CC fruits had high level of vitamin C (48-108 mg/100 g), malic acid (104-375 mg/100 g), and total polyphenols (158-591mgGAE/100 g). They also displayed high antioxidant activity based on DPPH (623-1903µmolTE/100 g), ABTS (441-1475µmolTE/100 g), and FRAP (1509-5954µmolFe2+/100 g) assays. UHPLC-PDA-HESI-MS/MS analyses were used to quantify the concentration of phenolic acids (7.69-19.87 mg/100 g), flavonoids (10.87-44.34 mg/100 g), anthocyanins (11.85-195.43 mg/100 g) and iridoids (129.07-341.20 mg/100 g). For each of this groups, the most abundant were caftaric acid (12.24 mg/100 g), quercetin 3-glucuronide (29.66 mg/100 g), cyanidin 3-O-galactoside (130.93 mg/100 g) and loganic acid (303.3 mg/100 g), respectively. PCA and cluster heatmap analysis highlighted potentials for further exploitation of local genotypes and cultivars through organic food processing and breeding program.


Assuntos
Cornus/química , Cornus/genética , Antocianinas/análise , Antioxidantes/análise , Ácido Ascórbico/análise , Cromatografia Líquida de Alta Pressão , Flavonoides/análise , Análise de Alimentos/métodos , Frutas/química , Galactosídeos/análise , Iridoides/análise , Montenegro , Fenóis/análise , Polifenóis/análise , Espectrometria de Massas em Tandem
12.
Artigo em Inglês | MEDLINE | ID: mdl-32197136

RESUMO

Vitamin C is a crucial antioxidant and cofactor for both plants and humans. Apple fruits generally contain low levels of vitamin C, making vitamin C content an interesting trait for apple crop improvement. With the aim of breeding high vitamin C apple cultivars it is important to get an insight in the natural biodiversity of vitamin C content in apple fruits. In this study, quantification of ascorbic acid (AsA), dehydroascorbic acid (DHA), and total AsA (AsA + DHA) in apple pulp of 79 apple accessions at harvest revealed significant variation, indicating a large genetic biodiversity. High density genotyping using an 8 K SNP array identified 21 elite and 58 local cultivars in this germplasm, with local accessions showing similar levels of total AsA but higher amounts of DHA compared to elite varieties. Out of the 79 apple cultivars screened, ten genotypes with either the highest or the lowest concentration of total AsA at harvest were used for monitoring vitamin C dynamics during fruit development and storage. For all these cultivars, the AsA/DHA ratio in both apple pulp and peel increased throughout fruit development, whereas the AsA/DHA balance always shifted towards the oxidized form during storage and shelf life, putatively reflecting an abiotic stress response. Importantly, at any point during apple fruit development and storage, the apple peel contained a higher level of vitamin C compared to the pulp, most likely because of its direct exposure to abiotic and biotic stresses.


Assuntos
Ácido Ascórbico/análise , Frutas/química , Malus/química , Antioxidantes/análise , Genótipo , Malus/genética , Melhoramento Vegetal , Polimorfismo de Nucleotídeo Único
13.
J Food Sci ; 85(4): 1248-1255, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32144763

RESUMO

Nondairy fermented products, such as fruit and vegetable juices, are gaining popularity among consumers worldwide for health-related and economic reasons. The purpose of this study was to determine the changes in microbiological quality; antimicrobial and antioxidant activity; and phenolic, vitamin C, minerals, and cadmium content occurring during spontaneous fermentation of curly kale juice. The fermentation process contributed to a significant growth of lactic acid bacteria, enterococci, and yeasts, while no pathogens of Escherichia coli and Salmonella spp. were observed. The antimicrobial properties of the obtained juice improved during fermentation for all indicator microorganisms. Total phenolic content and antioxidant activity increased from 48 to 116 mg gallic acid equivalent/100 mL and from 4.5 to 6.8 mM Trolox/100 mL, respectively, while the content of vitamin C decreased. The results indicated that 100 mL of juice provided a significant contribution to the recommended mineral intake. Moreover, the content of heavy metal Cd was within acceptable limit (6 µg/kg). Overall, our findings indicate that fermented curly kale juice may become popular in the functional food sector, especially among vegetarians and consumers with lactose intolerance or allergy to milk proteins. PRACTICAL APPLICATION: As the market for fermented fruit and vegetable products grows, new plant materials rich in biologically active compounds are being sought. Considering the high demand for sauerkraut, the fermentation of other cruciferous vegetables seems interesting. One example is curly kale, which has been classified as "superfood" due to its numerous beneficial health properties, such as strong antioxidant activity, high vitamins, and minerals content. In addition, a market niche exists due to a lack of fermented green curly kale products on the market, making our study particularly relevant.


Assuntos
Bactérias/efeitos dos fármacos , Brassica/química , Sucos de Frutas e Vegetais/microbiologia , Fungos/efeitos dos fármacos , Valor Nutritivo , Antioxidantes/análise , Ácido Ascórbico/análise , Brassica/microbiologia , Fermentação , Frutas/química , Sucos de Frutas e Vegetais/análise , Fenóis/análise , Vitaminas
14.
Food Chem ; 315: 126295, 2020 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-32014671

RESUMO

Effect of nano-SiO2 packing on postharvest quality and antioxidant capacity of two different loquat cultivars (white-flesh 'Qingzhong' and red-flesh 'Dawuxing') were determined. Results showed that nano-SiO2 packing significantly inhibited internal browning, retarded the decline of total soluble solids, titratable acidity, ascorbic acid content and extractable juice in both cultivars. Decay index of nano-SiO2 packing in 'Dawuxing' and 'Qingzhong' was 53.25% and 42.84% lower than control after the day 12, respectively. Meanwhile, nano-SiO2 packing enhanced the contents of individual phenolic compounds and soluble sugar compounds, induced higher superoxide dismutase and catalase activities, which contributed to improving 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radical scavenging capacity. Furthermore, the contents of total soluble solids, ascorbic acid and soluble sugar were higher in 'Qingzhong' than those in 'Dawuxing', which dedicated to better quality. These results indicated that nano-SiO2 packing was a promising approach in inhibiting decay, maintaining quality and expanding shelf life of loquats.


Assuntos
Antioxidantes/farmacologia , Eriobotrya/efeitos dos fármacos , Dióxido de Silício/farmacologia , Ácido Ascórbico/análise , Eriobotrya/química , Armazenamento de Alimentos , Frutas/química , Frutas/efeitos dos fármacos , Nanoestruturas , Fenóis/análise , Superóxido Dismutase/metabolismo , Temperatura
15.
PLoS One ; 15(1): e0227192, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-31923191

RESUMO

BACKGROUND: Rootstock has a significant impact on plant growth and development, including fruit maturation. However, the existence of mutual interaction between scion and rootstock is often neglected. To explore the origin of different fruit quality traits in citrus, we studied the effect of rootstock and the reciprocal interaction between scion and rootstock of nine combinations; three mandarin varieties grafted on three different rootstocks. We analyzed the metabolic profile of juice via gas and liquid chromatography-mass spectrometry (GC-MS and LC-MS, respectively). Additionally, we profiled phloem sap composition in the scion and the rootstock. Quality traits of fruit and their physio-chemical characteristics were also evaluated. RESULTS: For all three cultivars, rootstock was found to affect fruit yield and biochemical fruit quality parameters (sugar and acidity) in interactions with the scions. In mandarin juice, eight of 48 compounds (two primary and six secondary) were related directly to the rootstock, and another seven (one primary and six secondary) were interactively affected by scion and rootstock. In scion and rootstock sap, six and 14 of 53 and 55 primary metabolites, respectively, were directly affected by the rootstock, while 42 and 33 were affected by rootstock interactively with scion, respectively. CONCLUSION: In this work, we show for the first time a reciprocal effect between rootstock and scion. Based on our results, the scion and rootstock interaction might be organ, distance or time dependent.


Assuntos
Citrus/crescimento & desenvolvimento , Citrus/metabolismo , Sucos de Frutas e Vegetais/análise , Metabolômica/métodos , Floema/metabolismo , Raízes de Plantas/metabolismo , Brotos de Planta/metabolismo , Ácido Ascórbico/análise , Frutas/crescimento & desenvolvimento , Israel , Metaboloma , Açúcares/análise
16.
Anal Chim Acta ; 1097: 153-160, 2020 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-31910955

RESUMO

Ascorbic acid (AA) is very important for maintaining the normal physiological processes of the organism. In order to overcome the shortcomings of existing methods, such as lower sensitivity, complex operations and expensive instruments, it is urgent to develop a simple and rapid method for the determination of AA in the field of food and pharmaceutical preparations. Conjugated polymer nanoparticles (CPNs) have lately aroused wide concerns because of excellent optical properties, biocompatibility and stability. In our work, a CPNsPBOC-COOH fluorescence platform based on Poly [3-{2,5-bis (2-ethyl-hexyloxy)]-phenyl}-vinyl}-9-octyl-carbazole] (PBOC) and Polystyrene-maleic anhydride (PSMA), was prepared for the quantitative detection of AA. Experimental results were showed that this platform was highly selective and sensitive to AA. The concentration of AA detected by the fluorescence platform has a linear relationship in the range of 0.57-17.10 µM. The limit of detection (LOD) is 10 nM, which is lower than other methods reported. More interestingly, the fluorescence of CPNsPBOC-COOH can be controlled by logic gates with Fe3+ and AA. Finally, the designed fluorescence platform has been successfully applied to the analysis of AA in actual samples (vitamin C tablets, mouse serum and plasma), indicating the designed platform with a good feasibility.


Assuntos
Ácido Ascórbico/análise , Fluorescência , Nanopartículas/química , Polímeros/química , Animais , Camundongos , Estrutura Molecular , Tamanho da Partícula , Polímeros/síntese química , Espectrometria de Fluorescência , Propriedades de Superfície
17.
Sensors (Basel) ; 20(2)2020 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-31941118

RESUMO

We describe the voltammetric behavior of an anion-exchange membrane, hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI). The anion-exchange properties of HMT-PMBI chemically modified electrodes were investigated using K4Fe(CN)6 and K2IrCl6 as redox probes. The permselectivity properties of HMT-PMBI chemically modified electrodes were ascertained using tris(2-2')bipyridyl-ruthenium(II) chloride Ru(bpy)32+. Cyclic voltammetry and chronoamperometry were utilized to extract parameters such as the concentration of the redox mediators inside the films and the apparent diffusion coefficients. We found the concentration of K4Fe(CN)6 and K2IrCl6 redox species within HMT-PMBI-coated films to be on the order of 0.04-0.1 mol·dm-3, and values of Dapp ca. 10-10-10-9 cm2·s-1. To evaluate the possibility of using such a polymer coating in electroanalysis, HMT-PMBI-modified electrodes were utilized for the voltammetric detection of uric acid in artificial urine, Surine® and ascorbic acid in Vitamin C samples. The results showed that HMT-PMBI-coated electrodes can detect uric acid in Surine® with a limit of detection (LoD) of 7.7 µM, sensitivity of 0.14 µA·µM-1·cm-2, and linear range between 5 µM and 200 µM, whereas for Vitamin C tablets, the LoD is 41.4 µM, the sensitivity is 0.08 µA·µM-1·cm-2, and the linear range is between 25 µM and 450 µM.


Assuntos
Ácido Ascórbico/análise , Benzimidazóis/química , Carbono/química , Eletroquímica , Vidro/química , Ácido Úrico/análise , Eletrodos , Oxirredução , Comprimidos
18.
Talanta ; 210: 120649, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-31987173

RESUMO

Nitrogen and copper co-doped carbon dots (Cu-NCDs) were prepared by solvothermal carbonization of folic acid and CuCl2. The N-containing groups including sp2-hybridized CN, porphyrin C-N-C and amino N in N-(C) 3 or H-N-(C) 2, and the Cu-containing group, N-Cu-N, have formed on the surface and framework of Cu-NCDs. The Cu-NCDs were monodisperse with the average particle diameter of 3.57 nm and exhibited dual fluorescence emission peaks at 410 and 470 nm with the excitation wavelength of 340 nm. The new emission center of 410 nm might originate from the Cu doping which changed the structural network and surface state of the carbon dots. The Cu-NCDs exhibited good fluorescence quenching response towards ascorbic acid (AA) from 0.02 to 40 µM (R2 = 0.992), and the limit of detection was 17.8 nM. The mechanism of the quenching process is non-oxidation reduction strategy based static quenching (SQE). Cu doping can improve the selectivity and sensitivity for Cu-NCDs towards AA benefiting from its chelation effect towards multi-hydroxyl in AA. Cu and N doping cause positively charged surface of Cu-NCDs, improving the interaction towards AA and then the stable Cu-NCD-based non-luminescent compounds formed, which resulted SQE. The Cu-NCDs possessed low cellular toxicity and showed good uptake by HepG2 cells.


Assuntos
Ácido Ascórbico/análise , Carbono/química , Cobre/química , Nitrogênio/química , Imagem Óptica , Pontos Quânticos/química , Células Hep G2 , Humanos , Estrutura Molecular , Tamanho da Partícula , Propriedades de Superfície
19.
Talanta ; 210: 120653, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-31987208

RESUMO

In this work, nitrogen-doped carbon dots (N-CDs) were successfully utilized as a photoluminescent platform for multi-mode sensing of chromium(VI) [Cr(VI)], 2,4,6-trinitrophenol (TNP) and ascorbic acid (AA). The N-CDs with green fluorescent emission were synthesized via one-pot method using p-phenylenediamine and ammonia as precursors. The structure and optical properties were characterized by Fourier transform infrared spectroscopy, ultraviolet visible spectroscopy and fluorescence spectroscopy, respectively. Cr(VI) and TNP were able to absorb the excitation band and emission band of N-CDs and decreased the photoluminescence of N-CDs from internal filtration effect (IFE). Besides, the construction of N-CDs/Cr(VI) mixture can implement as a fluorescence platform for further detection of AA on the basis of the oxidation-reduction reactions between Cr(VI) and AA. Meanwhile, as-prepared N-CDs exhibit strong photostability, low toxicity and great biocompatibility. Moreover, the as-fabricated N-CDs have been smoothly achieved bioimaging in SMMC7721 cells owing to its low toxicity. It is prospective that N-CDs can be applied as a rapid multi-function sensing platform to biosensing and biomedical optical imaging.


Assuntos
Ácido Ascórbico/análise , Carbono/química , Cromo/análise , Nitrogênio/química , Picratos/análise , Pontos Quânticos/química , Água Potável/química , Fluorescência , Sucos de Frutas e Vegetais/análise , Voluntários Saudáveis , Humanos , Imagem Óptica , Tamanho da Partícula , Propriedades de Superfície
20.
J Sci Food Agric ; 100(4): 1694-1701, 2020 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-31803938

RESUMO

BACKGROUND: Extreme temperatures are among the primary abiotic stresses that affect plant growth and development. Ascorbic acid (AsA) is an efficient antioxidant for scavenging relative oxygen species accumulated under stress. Folates play a significant role in DNA synthesis and protect plants against oxidative stress. Sweet corn (Zea mays L.), a crop grown worldwide, is sensitive to extreme temperatures at seedling stage, which may cause yield loss. This study was conducted to explore the biosynthetic regulative mechanism of AsA and folates in sweet corn seedlings under temperature stress. RESULTS: The AsA and folate composition and relative gene expression in sweet corn seedlings grown under different temperature stresses (10, 25, and 40 °C) were evaluated. The imposition of temperature stress altered the AsA content mainly by modulating the expression of Zm DHAR, whose encoded enzyme dehydroascorbic reductase (DHAR) is essential in the AsA recycle pathway. Low temperature stress raised the expressions of relative genes, leading to folate accumulation. High temperature stress modulated the folate content by influencing the expression of the correspondence gene for aminodeoxychorismate synthase, Zm ADCS, as well as downstream genes that connected with DNA methylation. CONCLUSION: These results provided a theoretical basis, at a genetic level, for understanding the stress responses mechanism in sweet corn seedlings, offering guidance for sweet corn cultivation. © 2019 Society of Chemical Industry.


Assuntos
Ácido Ascórbico/metabolismo , Ácido Fólico/metabolismo , Zea mays/metabolismo , Ácido Ascórbico/análise , Ácido Fólico/análise , Regulação da Expressão Gênica de Plantas , Estresse Oxidativo , Oxirredutases/genética , Oxirredutases/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Plântula/química , Plântula/genética , Plântula/metabolismo , Temperatura , Zea mays/química , Zea mays/genética
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