Ascorbic Acid Oxidase Activity Research Articles

Nanozyme-mediated signal amplification on g-C3N4/NaBiO3 Z-scheme heterojunction photoelectrode toward ultrasensitive photoelectrochemical immunoassay for prostate-specific antigen

A sandwich-type photoelectrochemical (PEC) immunosensor for prostate-specific antigen (PSA) detection was developed using the g-C3N4/NaBiO3 (CN/NBO) Z-scheme heterojunction as the photoelectrode and glutathione-Cu/Cu2O nanozyme (GSH-Cu/Cu2O NPs) as the signal amplifier. The unique Z-scheme charge-carrier migration pathway of the CN/NBO heterojunction significantly promotes the separation and migration of photogenerated electron-hole pairs, producing a high photocurrent response of the photoelectrode. GSH-Cu/Cu2O NPs with ascorbic acid oxidase (AAO) activity were introduced into the PEC immunosensing system through immunoreactions for signal amplification. Signal amplification was achieved through double photocurrent quenching of the GSH-Cu/Cu2O NPs on the photoelectrode. On the one hand, GSH-Cu/Cu2O NPs as AAO catalyzed ascorbic acid (AA), an electron donor in the PEC system, to produce dehydroascorbic acid (DHA), leading to a decrease in the photocurrent response. On the other hand, the GSH-Cu/Cu2O NPs prevented AA transfer from the detection solution to the interface of the photoelectrode, further aggravating the PEC signal quenching effect. Benefiting from the excellent performance of the Z-scheme heterojunction-based photoelectrode, the dual signal quenching effect of GSH-Cu/Cu2O NPs, the PEC immunosensor showed an ultralow detection limit of 5.1 × 10−15 g mL−1. By coupling a Z-scheme heterojunction-based photoelectrode with a nanozyme-mediated signal amplification strategy, this study provides a novel avenue for the construction of ultrasensitive and convenient biosensing systems.

Natural Enzyme-Inspired Design of the Single-Atom Cu Nanozyme as Dual-Enzyme Mimics for Distinguishing Total Antioxidant Capacity and the Ascorbic Acid Level.

Although various oxidase mimetic or peroxidase (POD) mimetic nanozymes have been extensively studied, their poor substrate selectivity significantly inhibits their practical applications. Nanozymes with specific biomolecules as substrates, especially ascorbic acid oxidase (AAO) mimetic nanozymes with ascorbic acid (AA) as a substrate, have scarcely been studied. Herein, inspired by the multi-Cu atom sites and the redox electron transfer pathway of Cu2+/Cu+ in the natural AAO, atomically dispersed Cu sites immobilized on N-doped porous carbon (Cu-N/C) are artificially designed to simulate the function of natural AAO. Compared with their natural counterparts, the Cu-N/C catalysts exhibited higher catalytic efficiency and superior stability. Combined theoretical calculation and experimental characterizations reveal that the Cu-N/C nanozymes could catalyze the AA oxidation through a 2e- oxygen reduction pathway with H2O2 as the product. Moreover, the Cu-N/C nanozymes also possess high POD activity. As a proof-of-concept application, Cu-N/C can simultaneously realize AA detection in fluorescent mode based on its AAO activity and total antioxidant capacity detection in colorimetric mode utilizing its POD activity.

Variations in Oxidative and Antioxidant Responses of Rice Plant to Arsenic Contaminated Areas of Assam

Rice is a common food in the state of Assam, and because it is grown in arsenic contaminated soil, eating it might expose people to arsenic. Standard procedures were used while analysing arsenic content in various parts of rice plant and other biochemical indicators related to arsenic stress. In descending order, the rice plant's parts that accumulate arsenic are root, straw, leaf, husk, and grain. With a reduction in the build-up of arsenic, it was observed that the catalase activity increased, although the ascorbic acid oxidase activity, hydrogen peroxide content, malondialdehyde content, and proline content all decreased. It is clear from the current study that the amount of arsenic in the rice grain (0.094 to 0.147 ppm) is below the permissible limit prescribed by FAO/WHO, but since the local population typically eats rice three times a day, which may cause bioaccumulation so efforts can be made to check arsenic in the cooked rice as well.

Transcriptome Analysis Reveals the Genes Related to Pollen Abortion in a Cytoplasmic Male-Sterile Soybean (Glycine max (L.) Merr.).

Cytoplasmic male sterility (CMS) lays a foundation for the utilization of heterosis in soybean. The soybean CMS line SXCMS5A is an excellent CMS line exhibiting 100% male sterility. Cytological analysis revealed that in SXCMS5A compared to its maintainer SXCMS5B, its tapetum was vacuolated and abnormally developed. To identify the genes and metabolic pathways involving in pollen abortion of SXCMS5A, a comparative transcriptome analysis was conducted between SXCMS5A and SXCMS5B using flower buds. A total of 372,973,796 high quality clean reads were obtained from 6 samples (3 replicates for each material), and 840 differentially expressed genes (DEGs) were identified, including 658 downregulated and 182 upregulated ones in SXCMS5A compared to SXCMS5B. Among them, 13 DEGs, i.e., 12 open reading frames (ORFs) and 1 COX2, were mitochondrial genome genes in which ORF178 and ORF103c were upregulated in CMS lines and had transmembrane domain(s), therefore, identified as CMS candidate mitochondrial genes of SXCMS5A. Furthermore, numerous DEGs were associated with pollen wall development, carbohydrate metabolism, sugar transport, reactive oxygen species (ROS) metabolism and transcription factor. Some of them were further confirmed by quantitative real time PCR analysis between CMS lines with the same cytoplasmic source as SXCMS5A and their respective maintainer lines. The amount of soluble sugar and adenosine triphosphate and the activity of catalase and ascorbic acid oxidase showed that energy supply and ROS scavenging decreased in SXCMS5A compared to SXCMS5B. These findings provide valuable information for further understanding the molecular mechanism regulating the pollen abortion of soybean CMS.

Modulation of inner filter effect between persistent luminescent particles and 2, 3-diaminophenazine for ratiometric fluorescent assay of ascorbic acid and ascorbate oxidase activity

Ascorbate oxidase (AAO) and ascorbic acid (AA) play an important role in delaying lives senescence and metabolism. In this study, a sensitive ratiometric fluorescence sensing system based on the inner filter effect (IFE) between persistent luminescent particles (PLPs) and 2, 3-diaminophenazine (DAP), was designed for the detection of AA and AAO activity. Wherein, PLPs emit blue fluorescence at 475 nm with an excitation wavelength of 370 nm. CoOOH nanosheets with oxidase-like activity can oxidize o-phenylenediamine (OPD) to produce 2, 3-diaminophenazine (DAP) with orange fluorescence at 558 nm. The generated DAP quenched the fluorescence of PLPs by an inner filter effect (IFE). When AA was introduced to the system, CoOOH nanosheets were destroyed and reduced to Co2+, thereby inhibiting the oxidization of OPD and effectively preserving the blue fluorescence of PLPs at 475 nm. Besides, AAO can catalyse AA to produce the oxided dehydroascorbic acid (DHA). The dissipative AA can recover orange fluorescence of DAP with weakening the blue fluorescence of PLPs. Therefore, a sensitive ratio fluorescence sensing strategy was established by using PLPs as the reference signal and DAP as a reported signal for the detection of AA and AAO activity. Under optimal conditions, the obtained linear ranges were 1–45 μM and 1–20 mU/mL, and detection limits were 0.2 μM and 0.25 mU/mL, respectively. Finally, this proposed ratiometric fluorescent analytical strategy was used to detect AA in real samples (lemon, orange, tomato), which exhibited satisfactory results comparing with commercial kit.

Lanthanum Promotes Bahiagrass (Paspalum notatum) Roots Growth by Improving Root Activity, Photosynthesis and Respiration

Lanthanum (La), one of the most active rare earth elements, promotes the growth of turfgrass roots. In this study, the mechanisms by which La influences bahiagrass (Paspalum notatum) growth were evaluated by the analyses of root growth, root activity, cell wall polysaccharide content, respiration intensity, ascorbic acid oxidase (AAO) and polyphenol oxidase (PPO) activity, the subcellular distribution of mitochondria, transcription in roots, photosynthetic properties, chlorophyll fluorescence parameters, and chlorophyll content. The application of 0.3 mM La3+ increased root activity, respiration intensity, AAO activity, and the number of mitochondria in the mature cells of bahiagrass roots. La could significantly improve the net photosynthetic rate, transpiration rate, and chlorophyll fluorescence of bahiagrass. Differentially expressed genes identified by high-throughput transcriptome sequencing were enriched for GO (Gene Ontology) terms related to energy metabolism and were involved in various KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways, including oxidative phosphorylation, TCA (Tricarboxylic Acid) cycle, and sucrose metabolism. These findings indicate that La promotes bahiagrass root growth by improving root activity, photosynthesis, and respiration, which clarifies the mechanisms underlying the beneficial effects of La and provides a theoretical basis for its use in artificial grassland construction and ecological management projects.

60Coγ-ray irradiation inhibits germination of fresh walnuts by modulating respiratory metabolism and reducing energy status during storage

Postharvest germination negatively affects the development of fresh walnut industry. Our previous research showed that 60Coγ-ray irradiation with 0.3 kGy effectively inhibited the germination of fresh walnuts during storage, but the underlying mechanism in respiratory metabolism remains still unclear. The untreated and 0.3 kGy-irradiated fresh walnuts were stored at 25 °C for 24 d, and then the indicators related to respiratory metabolism in kernels and embryos were determined. The results found that the 0.3 kGy irradiation decreased the respiration intensity after 15d and completely inhibited the germination of fresh walnuts with the declined adenosine triphosphate (ATP) content and energy charge (EC) levels in kernels except from 12 to 15 d and polyphenol oxidase (PPO), cytochrome C oxidase (CCO) and ascorbic acid oxidase (AAO) activities in both tissues except the stimulated PPO activity in embryos during storage. Moreover, the irradiation promoted the glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activities but reduced the isocitrate lyase (ICL) activity in both tissues, and decreased the nicotinamide adenine dinucleotide reduced form (NADH) content but increased the nicotinamide adenine dinucleotide phosphate reduced form (NADPH) content in kernels of fresh walnuts during storage. The irradiation induced the JRG6PDH and JR6PGDH expression levels in both tissues, as well as the JRICL and JRMS expression levels in kernels before 12 d but suppressed those after 12 d of storage. In conclusion, the germination inhibition of fresh walnuts by gamma irradiation is attributed to suppressed terminal oxidases activities, decreased ratio of Embden–Meyerhof–Parnas pathway-tricarboxylic acid cycle (EMP-TCA) and glyoxylate cycle (GAC), increased level of pentose phosphate pathway (PPP) and reduced energy status.

Biogenic copper nanoparticles from Avicennia marina leaves: Impact on seed germination, detoxification enzymes, chlorophyll content and uptake by wheat seedlings.

Biogenic copper nanoparticles (Cu NPs) were synthesized using the aqueous crude extract of mangrove leaves, Avicennia marina (CE). GC-MS metabolite profiling of CE showed that their carbohydrates are mainly composed of D-mannose (29.21%), D-fructose, (18.51%), L-sorbose (12.91%), D-galactose (5.47%) and D-Talose (5.21%). Ultra-fine nanoparticles of 11.60 ±4.65 nm comprising Cu2O and Cu(OH)2 species were obtained with a carbohydrate and phenolic content of 35.6±3.2% and 3.13±0.05 mgGA/g, respectively. The impact of the biogenic Cu NPs on wheat seedling growth was dose-dependent. Upon treatment with 0.06 mg/mL of Cu NPs, the growth was promoted by 172.78 ± 23.11 and 215.94 ± 37.76% for wheat root and shoot, respectively. However, the lowest relative growth % of 81.94 ± 11.70 and 72.46 ± 18.78% were recorded for wheat root and shoot, respectively when applying 0.43 mg/mL of Cu NPs. At this concentration, peroxidase activity (POX) of the germinated wheat seeds also decreased, while ascorbic acid oxidase (AAO) and polyphenol oxidase (PPO) activities increased. Higher uptake of copper was observed in the root relative to the shoot implying the accumulation of the nanoparticles in the former. The uptake was also higher than that of the commercial Cu NPs, which showed an insignificant effect on the seedling growth. By treating the wheat leaves in foliar application with 0.06 mg/mL of Cu NPs, their contents of Chlorophyll a, Chlorophyll b, and total chlorophyll were enhanced after 21 days of application. Meanwhile, the high concentration (0.43 mg/mL) of Cu NPs was the most effective in reducing the leaf content of chlorophyll (a, b, and total) after the same time of application. The findings of this study manifest the potential of utilizing controlled doses of the prepared biogenic Cu NPs for inhibition or stimulation of seedling growth.

CPPU-induced changes in energy status and respiration metabolism of grape young berry development in relation to Berry setting

The energy status, the level of respiration metabolism are improtant index reflecting plant growth state, participates in many growth processes. However, their relationship to berry setting remain unclear. In this study, the grape of ‘kyoho’ of CPPU [CPPU, N-(2-coloro-4-pyridinyl)-N-phenylurea] treated were used to measurement physiological indicators. The results showed that CPPU treatment reduced respiratory rate, reduced Cytochrome C oxidase (CCO) and ascorbic acid oxidase (AAO) activity, reduced NAD kinase (NADK) activity, maintained low nicotinamide adenine denucleotie phosphate (NADP) and nicotinamide adenine denucleotie phosphate reduced form (NADPH) levels, reduced nicotinamide adenine denucleotie (NADH) levels, and slowed down the reduction of energy charge. These results provided strong evidence that CPPU treatment promoted grape berry setting due to increased energy status, increased Embden-Meyerhof pathway (EMP) and the tricarboxylic acid (TCA) cycle respiratory metabolic pathways, decreased pentose phosphate pathway (PPP), and decreased CCO and AAO activity of respiratory terminal oxidase.

Seedling Priming with Sodium Nitroprusside Rescues Vigna radiata from Salinity Stress-Induced Oxidative Damages

The main focus of this manuscript was to highlight the efficacy of seedling priming with 0.06 mM sodium nitroprusside (SNP), a potent NO donor in the alleviation of salt-induced oxidative and ionic stress in Vigna radiata. Treatment of seedlings with 100 mM NaCl reduced their overall growth and severely affected the basic growth and physiological parameters such as fresh weight, dry weight, root, shoot and leaf length, and relative water content and led to chlorophyll loss, accumulation of H2O2 and malondialdehyde (MDA) and induced the ascorbic acid oxidase (AAO) activity. Priming with SNP enhanced the level of protective metabolites such as proline, reducing sugars, total amino acids and total phenolics, lowered the AAO activity, and modulated the activity of antioxidative enzymes such as catalase, ascorbate peroxidase, superoxide dismutase and guaiacol peroxidase that efficiently scavenged the H2O2 formed, lowered the MDA level and chlorophyll loss, and improved the overall physiological traits. The activity of polyphenol oxidase, nitrate reductase and α-amylase was also induced in presence of SNP during salt stress that ensured better utilization of polyphenolic compounds for defence, and improved the nitrogen assimilation efficiency with better mobilization of stored starch, so as to facilitate germination and enhance seedling tolerance in response to salinity. Our communication clearly established the prospects of seedling priming with SNP as a cost-effective strategy to develop salt-tolerant V. radiata seedlings with better survival capacity.

Comparative Study on Redox State of Ascorbic Acid and Ascorbate Oxidase Activity in Vacuoles and Leucoplasts of Red Beet Taproots during Physiological Dormancy

Vacuoles and leucoplasts were isolated from red beet (Beta vulgaris L.) taproots and compared in terms of ascorbic acid concentration and ascorbate oxidase (AO) activity. The total amount of ascorbic acid (AAtot) was greater in vacuoles than in the plastids. The content of oxidized form of ascorbic acid, i.e., dehydroascorbic acid (DHA), was also higher in vacuoles than in the leucoplasts. However, the content ratios of reduced ascorbic acid (AA) to its oxidized form (AA : DHA) were similar in vacuoles and leucoplasts. The studied organelles displayed a relatively high AO activity. The oxidation of AA was catalyzed by ascorbate oxidase in vacuoles, whereas it was mediated by ascorbate oxidase and polyphenol oxidase in leucoplasts. The oxidases catalyzing AA oxidation are presumed to regulate the redox state of ascorbic acid in these organelles.

AN INVESTIGATION OF THE BIOCHEMICAL COMPOSITION OF NORWAY MAPLE (ACER PLATANOIDES L.) IN THE CONDITIONS OF TECHNOGENIC STRESS

A reasonably large number of publications devoted to the study of the role of antioxidant substances in plants growing under anthropogenic stress have appeared in scientific journals. However, these problems and issues are not studied sufficiently. This study aimed to reveal the biochemical composition features of Norway maple (Acer platanoides L.) in the conditions of urban plantations (by the example of the large industrial center in the city of Naberezhnye Chelny). The paper presents the results of investigations of biochemical composition features of Norway maple in the conditions of a large industrial center, the city of Naberezhnye Chelny (the Republic of Tatarstan). In the circumstances of intensive technogenic load, Norway maple shows higher ascorbic acid oxidase activity at the initial stages of active vegetation and lower activity at the end of vegetation, in comparison with plants in the conventional control zones (CCZ). At the same time, the content of ascorbic acid in the leaves also decreases during the vegetation of plants in the buffer zone plantations of industrial enterprises and trunk plantations. In the buffer zone plantations of industrial enterprises and trunk plantations, Norway maple was characterized by an increase in polyphenol oxidase activity, in comparison with the control plantings. The rise in polyphenol oxidase activity is accompanied by a decrease in the content of tannins. Norway maple in trunk plantations has lower peroxidase activity in its leaves in the conditions of the most intense load in July than in plantations of CCZ, and in August, this activity is higher than in the control group.

Seed priming with calcium compounds abrogate fluoride-induced oxidative stress by upregulating defence pathways in an indica rice variety.

The aim of this manuscript was to investigate the role of calcium compounds, viz., Ca(OH)2, Ca(NO3)2, and CaCl2 (each used at 0.3mM and 0.5mM concentration) as seed priming agents to ameliorate fluoride toxicity in rice. The stressed seedlings exhibited high fluoride bioaccumulation, severe growth retardation, and cellular damages. Calcium compounds improved plant performance by increasing seed germination, seedling biomass, and root and shoot length, avoiding chlorophyll degeneration and leakage of electrolytes, along with lowering the levels of malondialdehdye, H2O2, and endogenous fluoride. Calcium-regulated defence was mediated by proline synthesised due to increased Δ1-pyrroline 5-carboxylate synthetase (P5CS) and lowered proline dehydrogenase (PDH) expression, and glycine betaine synthesised due to betaine aldehyde dehydrogenase 1 (BADH1) expression. While the stress-mediated lowering of carotenoids and total phenolics was relieved by calcium priming, stress-enhanced flavonoids and ascorbic acid content was restored to the normal condition, along with releasing the fluoride-induced inhibition of ascorbic acid oxidase (AAO) activity. The activities of antioxidant enzymes like catalase, guaiacol peroxidase, and superoxide dismutase, and the expression of catalase and superoxide dismutase genes were also affected by calcium priming. The elevated endogenous calcium level, brought about by priming, enhanced the expression of genes related to calcium signalling pathway, particularly the calcineurin-B-like 10 (CBL10) gene. Ca(OH)2 (0.3mM) appeared to be the most efficient of all the three priming agents. Overall, the present work highlighted the efficacy of calcium compounds as priming agents in abrogating fluoride toxicity in rice.

A carbon dot-based ratiometric fluorometric and colorimetric method for determination of ascorbic acid and of the activity of ascorbic acid oxidase.

A dual-mode method was developed for the determination of ascorbic acid (AA) and of ascorbic acid oxidase (AA-Ox) activity. It combines the advantages of ratiometric fluorometry and colorimetry. The assay is based on the oxidation of o-phenylenediamine (OPDA) by permanganate (KMnO4). A yellow substance (referred to as oxOPDA) with an absorption peak at 425nm is rapidly produced in the presence of the oxidant. oxOPDA reduces the blue fluorescence of carbon dots (C-dots) peaking at 450nm (upon 380-nm excitation), and a new emission peak is found at 565nm. If AA is pesent, it consumes acertain fraction of KMnO4, so that less OPDA will be oxidized. This is accompanied by a decrease in the intensity of the fluorescence at 565nm and an increase in the intensity at 450nm. In parallel, the color of the solution changes from yellow to colorless. The determination of the activity of ascorbic acid oxidase (AA-Ox) is performed as follows: AA is oxidized by AA-Ox. This causes the fluorescence and colors to change in the opposite directions compared with AA detection. The ratio of fluorescences (I565/I450) becomes larger if the color the solution turns from colorless to yellow. Thus, the fluorescence intensity ratio (I565/I450) and colorimetric "bare-eye" readout can be used for determination of both the concentration of AA and the activity of AA-Ox. The fluorometric assay for AA has a linear range that extends from 0.6 to 40μM, and the colorimetric assay from 0.2 to 70μM. The respective data for AA-Ox activity are 0.04 ~ 5mU·mL-1 and 0.04 ~ 8mU·mL-1, respectively. The limits of detection for AA are 9 and 40nM, and the LODs for AA-Ox activity are 0.017 and 0.012mU·mL-1. Graphical abstract Schematic presentation of the assay. Permanganate (KMnO4) rapidly oxidizes ortho-phenylenediamine oxide to form a product (oxOPDA) having a yellow fluorescence peaking at 565 nm. The yellow color of oxOPDA can be detected visually. It also reduces the intensity of the blue fluorescence of carbon dots (C-dots) peaking at 450 nm. Ascorbic acid (AA) can consume permanganate, and this results less oxidation of OPDA. Ascorbic acid oxidase (AA-Ox) catalyzes the oxidization of AA by oxygen, and this - in turn - causes the changes in absorbance and fluorescence to change in the opposite directions.

Changes in Enzymatic content of Rice var. ADT 36 as influenced by bioinoculant, plant activator and sheath blight pathogen inoculation

The Pot culture studies were undertaken to investigate the changes of enzymatic compound in rice as influenced by Bioinoculant Pseudomonas fluorescens, plant activator salicylic acid and Sheath blight pathogen Rhizoctonia solani inoculation. Among the various treatments seed treatment with P. fluorescens (Pf) @ 10 g/kg of seeds along with foliar application of plant activator Salicylic acid (SA) @ 50 ppm on 15 Days After transplanting (DAT) recorded the minimum disease incidence followed by foliar application of plant activator Salicylic acid @ 50 ppm on 15 DAT and 30 DAT which were statistically at par. Foliar application of Pf @ 1% on 30 DAT was the least effective when compared to fungicide, Hexaconazole 5 SC @ 0.2% and control treatments. Also, the results exploited that the same treatment increased activity of Ascorbic acid oxidase, PAL, PPO and PO activity due to treatment with combined application of resistance inducing chemical, bioinoculant and pathogen alone inoculated control when compared to control treatments. The activity of PO, Ascorbic acid oxidase and PAL increased up to 14th day of sampling and then decreased in plants treated with the combination treatment consisting of Pf, SA and challenge inoculated with the pathogen whereas the activity of Polyphenol oxidase showed increase up to the maximum period of observation (up to 21st day). The cost benefit ratio 1: 2.63 proved the worthiness of the new treatment combination developed in this study.

Biochemical characterization of superior seedless variety of grape (Vitis vinifera L.) for resistance to anthracnose

Superior seedless is a promising variety of grape under moist and warm conditions may severely get hampered by anthracnose caused by Gloeosporium ampelophagum (Pass.) Sacc. To evaluate the biochemical reaction of the variety to the pathogen, the study was undertaken at Ludhiana (Punjab) in 2016. The percent disease index (0–9) scale, the morphological and anatomical characteristics were studied in the grape leaves. Chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, total soluble proteins and free amino acid content decreased by 28.16, 3.94, 15.93, 85.86, 45.05 and 46.21%, respectively in anthracnose infected leaves as compared to healthy ones, while total soluble sugars, total phenols, ortho-dihydroxy phenols, flavonoids, ascorbic acid, proline, α-tocopherol, MDA content, peroxidase and polyphenol oxidase activity increased significantly by 9.75, 36.60, 21.80, 36.48, 23.04, 62.75, 90.47, 8.81, 10.49 and 3.12%, respectively. Increase in concentration of these chemical indicates the initiation of defense against G. ampelophagum in variety superior seedless.

A dual-model strategy for fluorometric determination of ascorbic acid and of ascorbic acid oxidase activity by using DNA-templated gold-silver nanoclusters.

Methods are described for the fluorometric and colorimetric determination of ascorbic acid (AA) and the activity of ascorbic acid oxidase (AA-Ox). The method for AA is based on AA-induced growth and aggregation of DNA-templated gold/silver nanoclusters (DNA-Au/Ag NC), which is accompanied by quenching of fluorescence emission at 605nm upon 260nm excitation and a visible color change of the solution from colorless transparent to yellow. The determination of the activity of AA-Ox is based on the finding that it catalyzes the oxidation of AA which results in the inhibition of growth and aggregation. AA can be determined with a 0.6μmol·L-1 detection limit over the 5 to 150μmol·L-1 concentration range. AA-Ox can be determined with a 0.0048U·mL-1 detection limit over the 0.01 to 0.20U·mL-1 range. Graphical abstract Schematic of a novel fluorometric and colorimetric platform for determination of ascorbic acid and ascorbic acid oxidase activity based on the use ofDNA-templated gold-silver nanoclusters.

English

The effects of microwave (MW) dry blanching of mango in comparison with conventional water blanching and blanching in closed plastic bags prior to hot air drying (70°C) were evaluated on the retention of vitamin C and β-carotene and on the activity of polyphenol oxidase (PPO) and ascorbic acid oxidase (AAO) enzymes. Blanching conditions for MW and water blanching were 2 min at 90°C high temperature and short time (HTST) or for 10 min at 70°C low temperature and low time (LTLT). PPO was completely inactivated by the blanching treatments, while low AAO activity remained. High retentions (~100%) of vitamin C were found in dried mango after blanching treatments HTST with MW and blanching in closed plastic bags, while lower retention was observed after LTLT with MW (81.8 ± 4.5%), and conventional water blanching 86.7 ± 2.6% (HTST) and 78.6 ± 2.5% (LTLT). Blanching resulted in partial oxidation of L-AA into dehydroascorbic acid (DHAA). Lower retention of all-trans-β-carotene was obtained in MW and HTST water blanched dried mango (82 to 90%) compared with LTLT water blanched dried mango (~100%). In all dried blanched mango samples the levels of 13-cis-β-carotene isomer increased. A slight darkening of colour was observed only in conventional blanched mango samples.   Key words: Microwave heating, mango, β-carotene, vitamin C, ascorbic acid oxidase.

Effect of microwave assisted blanching on the ascorbic acid oxidase inactivation and vitamin C degradation in frozen mangoes

Abstract The effect of microwave assisted and conventional water blanching of mango (Mangifera indica) under two different blanching scenarios, High Temperature Short Time (HTST) and Low Temperature Long Time (LTLT) on ascorbic acid oxidase (AAO) inactivation and on vitamin C ( l -ascorbic acid & dehydroascorbic acid) retention were comparatively studied. The impact of alternative blanching processes and subsequent frozen storage on enzymatic inactivation and vitamin C was kinetically modelled. Both water and microwave HTST as well as LTLT microwave treatments of mango pieces showed high degree of AAO inactivation. An approximately 30% residual AAO activity was observed and was described through a first order fractional conversion model. Microwave assisted blanching led to higher retention of total vitamin C in both LTLT and HTST treatments. In LTLT water blanching, vitamin C loss was mainly caused by mass transfer phenomena rather than temperature degradation, while after HTST treatments the decrease of total vitamin C content seemed to be mainly related to thermal degradation than due to the leakage of the nutrients in the blanching medium. Further inactivation of the thermostable fraction of AAO and degradation of total vitamin C were observed after frozen storage for 130 days at −18.63 ± 0.48 °C.

Interaction effects of fructan and Salicylic acid on chickpea in both biochemical and traditional agronomic indicators

Starch and fructans are accumulated for carbohydrate storage in legumes, while fructans accumulated large amounts than starch. The uses of this natural and biodegradable material counteract stress as cheaper and safer alternatives. Therefore, fructan (F, 0.5 %) and salicylic acid (SA, 0.5 mM) priming were used as exogenous growth enhancers to stimulate chickpea (Cicer arietinum L.) seed vigor against salt stress. The main aim of this study was to address whether priming chickpea with F, SA and F+SA could bring about supplementary benefits particularly against salt stress. Exogenous application of F- or SA-alone improved chickpea development in the presence of salt stress. Nevertheless, the best results in terms of growth, seed vigor and total phenolic – flavonoids, chlorophyll – carotenoids contents, phenylalanine ammonia-lyase (PAL), ascorbic acid oxidase (AAO) activities and lipid peroxidation level (LPO) were determined in the combined F+SA treatment against salt stress