Oxygen Scavenging System Research Articles

Role of exogenous salicylic acid in regulating physio-morphic and molecular changes under chromium toxicity in black- and yellow- seeded Brassica napus L.

Salicylic acid (SA) mediates tolerance mechanisms in plants against a wide spectrum of biotic and abiotic stresses. Therefore, the present study was carried out to determine how SA regulates the plant protection mechanisms in two cultivars of oilseed rape (Brassica napus L.) under chromium (Cr) stress. Exogenously applied SA enhanced plant growth, increased dry biomasses, and strengthened the reactive oxygen scavenging system by improving cell organelles that were severely damaged via Cr toxicity. The contents of Cr were significantly enhanced in both root and leaf of cultivar Zheda 622 (yellow color) compared with cultivar ZS 758 (black color). Exogenous application of SA significantly reduced the Cr contents in both plant organs as well as enhanced the SA contents under Cr stress. A dose-dependent increase was observed in reactive oxygen species (ROS) generation under Cr stress. To ease the inimical effects of ROS, plants' defense systems were induced under Cr stress, and SA further enhanced protection. Further, TEM micrographs results showed that Cr stress alone significantly ruptured the plant cell organelles of both cultivars by increasing the size of starch grain and the number of plastoglobuli, damaging the chloroplast and mitochondrion structures. However, exogenously applied SA significantly recovered these damages in the plant cells of both cultivars. It was also observed that cultivar ZS 758 was proved to be more tolerant under Cr toxicity. Gene expression analysis revealed that combined treatments of Cr and SA increased antioxidant-related gene expression in both cultivars. Findings of the present study demonstrate that SA induces the enzymatic antioxidant activities and related gene expression, secondary metabolism, and improves the cell structural changes and the transcript level of specific stress-associated proteins in root and leaf of two oilseed rape cultivars under Cr toxicity.

Characterization and properties of LDPE film with gallic‐acid‐based oxygen scavenging system useful as a functional packaging material

ABSTRACTWe prepared and characterized active, oxygen‐scavenging, low density polyethylene (LDPE) films from a non‐metallic‐based oxygen scavenging system (OSS) containing 1, 3, 5, 10, and 20% of gallic acid (GA) and potassium chloride (PC). We compared the surface morphology and mechanical, permeability, and optical properties of the oxygen‐scavenging LDPE film with those of pure LDPE film. The surface morphology, gas barrier, and thermal properties indicate that the OSS was well incorporated into the LDPE film structure. The surface roughness of the film increased with the amount of oxygen scavenging material. The oxygen and water vapor permeability of the developed film also increased with the amount of oxygen scavenging material, though its elongation decreased. The oxygen scavenging capability of the prepared film was analyzed at different temperatures. The initial oxygen content (%) in the vial headspace, 20.90%, decreased to 16.6% at 4 °C, 14.6% at 23 °C, and 12.7% at 50 °C after 7 days of storage with the film containing 20% OSS. The film impregnated with 20% organic oxygen scavenging material showed an effective oxygen scavenging capacity of 0.709 mL/cm2 at 23 °C. Relative humidity triggered the oxygen scavenging reaction. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44138.

Inactivation of Palladium‐based Oxygen Scavenger System by Volatile Sulfur Compounds Present in the Headspace of Packaged Food

An oxygen scavenger based on a catalytic system with palladium (CSP) was recently developed to remove oxygen in food packagings. Although the CSP worked with various types of food, with some foods, an inhibition of the CSP was observed. Because such catalytic systems are susceptible to poisoning by sulfur‐containing compounds, the aim of this study was to understand the inactivation of palladium‐based catalysts in presence of foods containing volatile sulfur compounds (VSCs). To achieve this, the oxygen scavenging activity (OSA) of the CSP was evaluated in presence of selected food products. Afterwards, VSCs mainly present in these foods were exposed to the CSP, and the influence on the OSA was evaluated. Finally, headspace analysis was performed with the diluted VSCs and with the packaged food products using proton transfer reaction time‐of‐flight mass spectrometry. It was found that the catalytic activity of the CSP was inhibited when VSCs were present in the headspace in concentrations ranging between 10.8–36.0 ppbv (dimethyl sulfide, DMS), 1.2–7.2 ppbv (dimethyl disulfide), 0.7–0.9 ppbv (dimethyl trisulfide), 2.1–5.8 ppbv (methional) and 4.6–24.5 ppbv (furfuryl thiol). It was concluded that in packaged roast beef and cheese, DMS may be the compound mainly responsible for the inactivation of the CSP. In packagings containing ham, the key compounds were hydrogen sulfide and methanethiol; in peanuts, it was methanethiol; and in par‐baked buns, an accumulation of methional, DMS, butanethiol and methionol. When potato chips were packaged, it was demonstrated that when VSCs are present in low concentrations, oxygen can still be scavenged at a reduced OSA.

Developmental differences in antioxidant compounds and systems in normal and small-phenotype fruit of ‘Hass’ avocado (Persea americana Mill.)

Antioxidant compounds and reactive oxygen-scavenging systems were investigated in ‘Hass’ avocado fruit set by determinate (DFS) and indeterminate floral shoots (IFS). During early development, DFS produced the largest fruit, IFS the smallest. Normal-phenotype (large) fruit (NPF) from DFS and IFS were faster growing, greater in length, diameter and weight and contained more protein than small-phenotype fruit (SPF) from DFS and IFS, resulting in SPF having greater ascorbic acid and total phenol concentrations and antioxidant capacity per g fresh weight. In contrast, NPF had greater catalase, ascorbate peroxidase, and glutathione reductase activities per g fresh weight than SPF on a greater number of sample dates; SPF had greater superoxide dismutase activity. Per mg protein, ascorbic acid and phenol concentrations, antioxidant capacity, peroxidase, polyphenol oxidase, catalase and ascorbate peroxidase activities were greater in SPF than NPF on more dates and at maturity. Thus, SPF would be a healthier food choice due to their greater antioxidant compounds and capacity compared to NPF.

Novel natural phenolic compound-based oxygen scavenging system for active packaging applications

An oxygen scavenging system containing a natural phenolic compound, pyrogallol with sodium carbonate, was developed and analyzed as a possible oxygen scavenger. The effect of several parameters, including the amount of pyrogallol and sodium carbonate, relative humidity and storage temperature, on the oxygen scavenging capability were investigated. The initial, glass vial headspace oxygen content (%) of 21.1 % (v/v) decreased to 0.26 % after 8 days of storage at room temperature when the oxygen scavenging system used a 1:1 (w/w) ratio of pyrogallol (250 mg) and sodium carbonate (250 mg). Both pyrogallol and sodium carbonate were required for optimum oxygen scavenging, otherwise the oxygen scavenging ability decreased. The oxygen content (%) decreased further to 6.55 % (v/v) when the amount of sodium carbonate decreased from 250 to 166 mg, which yielded a 2:1 ratio. In the present study, pyrogallol (250 mg) and sodium carbonate (250 mg) had highest oxygen scavenging capacity of 51.81 mL O2/g and an oxygen scavenging rate of 6.48 mL O2/g day. The oxygen absorption kinetics rate of pyrogallol and sodium carbonate confirmed that the material has good efficiency for use as an oxygen scavenger. Results indicated that the pyrogallol based oxygen scavenging system with moisture activation can be used as an effective oxygen scavenger for low water activity food packaging applications.

A rice LSD1-like-type ZFP gene OsLOL5 enhances saline-alkaline tolerance in transgenic Arabidopsis thaliana, yeast and rice.

BackgroundZinc finger proteins (ZFPs) play an important role in regulating plant responses to abiotic stress. However, little is known about the function of LSD1-like-type ZFP in saline-alkaline (SA) stress resistance of rice. In this study, OsLOL5 (GenBank No. AJ620677), containing two LSD1-like-type C2C2 domains, was isolated and analyzed its protection roles in transgenic plants and yeast. OsLOL5 was located in the nucleus as evidenced by the bombardment of onion epidermal cells.ResultsOsLOL5 expression significantly increased in rice leaves and roots under 150 mmol L-1 NaCl, 30 mM NaHCO3, and 10 mmol L-1 H2O2 treatment, respectively. Overexpression of OsLOL5 in yeast resulted in SA tolerance at significant level. Transgenic Arabidopsis plants overexpressing OsLOL5 grew well in the presence ofboth NaCl and NaHCO3 treatments, whereas wild-type plants exhibited chlorosis, stunted growth phenotype, and even death. SA stress caused significant changes in the malondialdehyde (MDA) contents in non-transgenic plants compared with those in transgenic lines. Transgenic rice overexpressing OsLOL5 exhibited stronger resistance than NT under NaHCO3 treatment, as demonstrated by its greater shoot length, and fresh weight. The genes associated with oxidative stress, such as OsAPX2, OsCAT, OsCu/Zn-SOD, and OsRGRC2, were significantly upregulated in OsLOL5-overexpressing rice. The results suggested that OsLOL5 improved SA tolerance in plants, and regulated oxidative and salinity stress retardation via the active oxygen detoxification pathway.ConclusionsThe yeast INVScI bacterium grew significantly better than the control strain under NaCl, NaHCO3, and H2O2 treatments. These findings illustrated that OsLOL5 overexpression enhanced yeast resistance for SA stress through active oxygen species. The present study showed that the OsLOL5 genes involved in the ROS signaling pathways may combine with the model plant Arabidopsis and rice in LDS1-type ZFP by ROS signaling pathways that regulate cell necrosis. We speculated that the OsLOL5 active oxygen scavenging system may have coordinating roles. The present study further revealed that OsLOL5 ZFP could regulate oxidative stress function, but could also provide a basis for salt-resistant rice strains.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2460-5) contains supplementary material, which is available to authorized users.

Preparation, characterization, and oxygen scavenging capacity of biodegradable α‐tocopherol/PLA microparticles for active food packaging applications

In this work, a biodegradable oxygen scavenger system, which consists of α‐tocopherol‐loaded poly(lactic)acid microparticles containing 40 wt% of the natural antioxidant agent, was prepared by an oil in water (O/W) emulsion‐solvent evaporation method. The preparation procedure assured high encapsulation efficiency and production yield and gives no noticeable alteration of the molecular structure of the microencapsulated active α‐tocopherol, as demonstrated by Fourier‐transform infrared and thermogravimetric analyses measurements. The produced active microparticles are semicrystalline and are characterized by suitable morphology (size and shape) to have satisfactory flowability to be used as active powder additive in conventional polymer extrusion technologies. Both the scavenging capacity and rate are in line with the values required for an effective oxygen scavenger system. POLYM. COMPOS., 38:981–986, 2017. © 2015 Society of Plastics Engineers

Construction of effective disposable biosensors for point of care testing of nitrite

In this paper we aim to demonstrate, as a proof-of-concept, the feasibility of the mass production of effective point of care tests for nitrite quantification in environmental, food and clinical samples. Following our previous work on the development of third generation electrochemical biosensors based on the ammonia forming nitrite reductase (ccNiR), herein we reduced the size of the electrodes' system to a miniaturized format, solved the problem of oxygen interference and performed simple quantification assays in real samples. In particular, carbon paste screen printed electrodes (SPE) were coated with a ccNiR/carbon ink composite homogenized in organic solvents and cured at low temperatures. The biocompatibility of these chemical and thermal treatments was evaluated by cyclic voltammetry showing that the catalytic performance was higher with the combination acetone and a 40°C curing temperature. The successful incorporation of the protein in the carbon ink/solvent composite, while remaining catalytically competent, attests for ccNiR's robustness and suitability for application in screen printed based biosensors.Because the direct electrochemical reduction of molecular oxygen occurs when electroanalytical measurements are performed at the negative potentials required to activate ccNiR (ca.−0.4V vs Ag/AgCl), an oxygen scavenging system based on the coupling of glucose oxidase and catalase activities was successfully used. This enabled the quantification of nitrite in different samples (milk, water, plasma and urine) in a straightforward way and with small error (1–6%). The sensitivity of the biosensor towards nitrite reduction under optimized conditions was 0.55AM−1cm−2 with a linear response range 0.7–370μM.

Changes in activities of antioxidant enzymes and photosynthetic attributes in triticale (×Triticosecale Wittmack) genotypes in response to long-term salt stress at two distinct growth stages

To examine the impact of long-term salinity on triticale, two salt-tolerant (ET-84-15 and ET-86-9) and two salt-sensitive (ET-85-17 and Jouvanilo) genotypes were grown in a sand culture containing Hoagland solution with 200 mM NaCl. Lipid peroxidation (LPO), hydrogen peroxide (H2O2), photosynthetic parameters, and antioxidant enzymes including catalase (CAT), guaiacol peroxidase (GPOD), superoxide dismutase (SOD), and ascorbate peroxidase (APX) were analyzed at the late tillering (LT) and flowering (FL) stages. A substantial reduction was found in the net photosynthetic rate, stomatal conductance, and transpiration rate of the triticale genotypes due to salt stress, with a more noticeable decline in the sensitive ones. Salt-treated plants indicated the presence of high amounts of H2O2 and LPO with a subsequent increase in the activities of the enzymes’ SOD, CAT, and GPOD in comparison with the control treatment. Conversely, APX activities remained unaltered or decreased slightly by salt stress. The salt-tolerant genotypes exhibited lower H2O2 and LPO, and displayed increased activities of the enzymes participating in the reactive oxygen scavenging system except for APX. The activities of the antioxidant enzymes under both the saline and non-saline conditions were found to be higher at the FL stage than at the LT one. This may explain partly the reason for why triticale is more tolerant at the FL stage. These results clearly demonstrate that the activation of SOD, CAT, and GPOD could contribute to the salt-stress tolerance in triticale.

Golgi/plastid-type manganese superoxide dismutase involved in heat-stress tolerance during grain filling of rice.

SummarySuperoxide dismutase (SOD) is widely assumed to play a role in the detoxification of reactive oxygen species caused by environmental stresses. We found a characteristic expression of manganese SOD 1 (MSD1) in a heat‐stress‐tolerant cultivar of rice (Oryza sativa). The deduced amino acid sequence contains a signal sequence and an N‐glycosylation site. Confocal imaging analysis of rice and onion cells transiently expressing MSD1‐YFP showed MSD1‐YFP in the Golgi apparatus and plastids, indicating that MSD1 is a unique Golgi/plastid‐type SOD. To evaluate the involvement of MSD1 in heat‐stress tolerance, we generated transgenic rice plants with either constitutive high expression or suppression of MSD1. The grain quality of rice with constitutive high expression of MSD1 grown at 33/28 °C, 12/12 h, was significantly better than that of the wild type. In contrast, MSD1‐knock‐down rice was markedly susceptible to heat stress. Quantitative shotgun proteomic analysis indicated that the overexpression of MSD1 up‐regulated reactive oxygen scavenging, chaperone and quality control systems in rice grains under heat stress. We propose that the Golgi/plastid MSD1 plays an important role in adaptation to heat stress.

Toward New Polymeric Oxygen Scavenging Systems: Formation of Poly(vinyl alcohol) Oxygen Scavenger Film

Active packaging is a term that refers to the use of package to do more than merely protect the food from the outside environment. Amongst active packaging, oxygen scavengers can prevent oxidative damage to flavour and colour in a wide range of foods. They offer advantages in maintaining quality and extending shelf life. We thus present the use of a cobalt(II) complex with the ligand l‐threonine as a new oxygen scavenger. This complex, in addition to its high reactivity with oxygen after water activation, can be obtained easily in large amounts and does not react with oxygen in solid state. Thus, the incorporation of the Co(II)(l‐Thr)2(OH2)2 natural complex in organic polar polymer (poly(vinyl alcohol)) by casting process was conducted. The reactivity towards oxygen of the obtained films was evaluated by oxidation kinetics monitoring using ultraviolet–visible spectrophotometry as a function of time and relative humidity. Oxygen consumption of the active film was found equal to the complex alone (2.5 mg of O2 per gramme of complex) after water activation (90.5% relative humidity). Copyright © 2014 John Wiley & Sons, Ltd.

Oxygen Depletion Speeds and Simplifies Diffusion in HeLa Cells

Many cell types undergo a hypoxic response in the presence of low oxygen, which can lead to transcriptional, metabolic, and structural changes within the cell. Many biophysical studies to probe the localization and dynamics of single fluorescently labeled molecules in live cells either require or benefit from low-oxygen conditions. In this study, we examine how low-oxygen conditions alter the mobility of a series of plasma membrane proteins with a range of anchoring motifs in HeLa cells at 37°C. Under high-oxygen conditions, diffusion of all proteins is heterogeneous and confined. When oxygen is reduced with an enzymatic oxygen-scavenging system for ≥15 min, diffusion rates increase by >2-fold, motion becomes unconfined on the timescales and distance scales investigated, and distributions of diffusion coefficients are remarkably consistent with those expected from Brownian motion. More subtle changes in protein mobility are observed in several other laboratory cell lines examined under both high- and low-oxygen conditions. Morphological changes and actin remodeling are observed in HeLa cells placed in a low-oxygen environment for 30 min, but changes are less apparent in the other cell types investigated. This suggests that changes in actin structure are responsible for increased diffusion in hypoxic HeLa cells, although superresolution localization measurements in chemically fixed cells indicate that membrane proteins do not colocalize with F-actin under either experimental condition. These studies emphasize the importance of controls in single-molecule imaging measurements, and indicate that acute response to low oxygen in HeLa cells leads to dramatic changes in plasma membrane structure. It is possible that these changes are either a cause or consequence of phenotypic changes in solid tumor cells associated with increased drug resistance and malignancy.

Antioxidant enzyme activity, proline accumulation, leaf area and cell membrane stability in water stressed Amaranthus leaves

Traditional crops are extremely important for food production in low income, food-deficit countries (LIFDCs) where they continue to be maintained by socio-cultural preferences and traditional uses. Significant potential exists to improve these crops, one of which is to select for improved productivity during moisture stress conditions. Germplasm of Amaranthus tricolor, Amaranthus hypochondriacus and Amaranthus hybridus were subjected to various screening methods to measure metabolic and physiological changes during water stress. The activities of enzymes involved in the oxygen-scavenging system during abiotic stress conditions (superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR)), free proline production, leaf area (LA), cell membrane stability (CMS), leaf water potential (LWP) and relative water content (RWC) were measured in these three amaranth species during induced water stress. This study showed significant differences in metabolic responses during water deficit of the three species tested. Moisture stress and a decrease in RWC and LWP were first experienced in A. hybridus and A. hypochondriacus, followed by A. tricolor. There was an indirect correlation between leaf water status (RWC and LWP), enzyme activity, proline production and leaf area. The combined effect of GR, APX and SOD could ensure higher levels of regulation of the toxic effect of H2O2 which could be associated with drought tolerance in Amaranthus. Distinct differences in onset of proline accumulation and the amount of accumulated in leaves upon induced water stress was noticed for the three amaranth species tested. Proline accumulation during water stress conditions in amaranth seems to be indirect and could possibly have a protective role apart from osmoregulation during stress conditions. This contention is supported by the decrease in leaf area and high cell membrane stability for two of the species tested. This study forms part of a project aimed at the development of improved traditional crops to contribute to food production and quality for subsistence farmers in areas with low precipitation or variable rainfall patterns.

Exogenous ascorbic acid and glutathione alleviate oxidative stress induced by salt stress in the chloroplasts of Oryza sativa L.

The effects of exogenous ascorbic acid (AsA) and reduced glutathione (GSH) on antioxidant enzyme activities [superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR)] and the contents of malondialdehyde (MDA) and H2O2, as well as of endogenous AsA and GSH, in the chloroplasts of two rice cultivars, the salt-tolerant cultivar Pokkali and the salt-sensitive cultivar Peta, were investigated. Exogenous AsA and GSH enhanced SOD, APX, and GR activities, increased endogenous AsA and GSH contents, and reduced those of H2O2 and MDA in the chloroplasts of both cultivars under salt stress (200 mM NaCl), but the effects were significantly more pronounced in cv. Pokkali. GSH acted more strongly than AsA on the plastidial reactive oxygen scavenging systems. These results indicated that exogenous AsA and GSH differentially enhanced salinity tolerance and alleviated salinity-induced damage in the two rice cultivars.

Single-molecule photophysics of dark quenchers as non-fluorescent FRET acceptors

Dark quencher chromophores are interesting alternatives to common single-molecule FRET acceptors. Due to their short excited state lifetime, they should be less prone to complex photophysics and bleaching. We find, however, that for common enzymatic oxygen scavenging systems and photoprotection strategies - the gold standard of single-molecule measurements - the quenchers BBQ650 and BHQ-2 induce frequent blinking of the donor molecule. They switch in a photoinduced process to what we identify as a radical anion state and back. We further make use of the broad absorption spectrum for selective bleaching of the quenchers in order to photoactivate the fluorescence of initially completely quenched dye molecules. This represents a general strategy to turn fluorescent dyes into photoactivatable probes.

Cold priming drives the sub-cellular antioxidant systems to protect photosynthetic electron transport against subsequent low temperature stress in winter wheat

Low temperature seriously depresses the growth of wheat through inhibition of photosynthesis, while earlier cold priming may enhance the tolerance of plants to subsequent low temperature stress. Here, winter wheat plants were firstly cold primed (5.2 °C lower temperature than the ambient temperature, viz., 10.0 °C) at the Zadoks growth stage 28 (i.e. re-greening stage, starting on 20th of March) for 7 d, and after 14 d of recovery the plants were subsequently subjected to a 5 d low temperature stress (8.4 °C lower than the ambient temperature, viz., 14.1 °C) at the Zadoks growth stage 31 (i.e. jointing stage, starting on 8th April). Compared to the non-primed plants, the cold-primed plants possessed more effective oxygen scavenging systems in chloroplasts and mitochondria as exemplified by the increased activities of SOD, APX and CAT, resulting in a better maintenance in homeostasis of ROS production. The trapped energy flux (TRO/CSO) and electron transport (ETO/CSO) in the photosynthetic apparatus were found functioning well in the cold-primed plants leading to higher photosynthetic rate during the subsequent low temperature stress. Collectively, the results indicate that cold priming activated the sub-cellular antioxidant systems, depressing the oxidative burst in photosynthetic apparatus, hereby enhanced the tolerance to subsequent low temperature stress in winter wheat plants.

Silencing the radicals improves Click Chemistry.

Modern fluorescence imaging microscopy in living and fixed material makes use of fluorescent probes to label targeted entities. Common labelling approaches include classical immunocytochemistry, expression of chimerically tagged fluorescent protein domains, and chemical affinity-binding or covalent labelling. Of these methods, the so-called "Click Chemistry", is emerging as one of the most influential labelling chemistries introduced in recent times, offering enormous utility for bio-orthoganol attachment of fluorescent probes to biological target entities. In this issue of Biotechnology Journal, Löschberger, Niehörster and Sauer report "ClickOx", a Click Chemistry protocol that uses an enzymatic oxygen scavenger system to reduce concurrent ROS-associated damage during Click labeling.

Click chemistry for the conservation of cellular structures and fluorescent proteins: ClickOx

Reactive oxygen species (ROS), including hydrogen peroxide, are known to cause structural damage not only in living, but also in fixed, cells. Copper-catalyzed azide-alkyne cycloaddition (click chemistry) is known to produce ROS. Therefore, fluorescence imaging of cellular structures, such as the actin cytoskeleton, remains challenging when combined with click chemistry protocols. In addition, the production of ROS substantially weakens the fluorescence signal of fluorescent proteins. This led us to develop ClickOx, which is a new click chemistry protocol for improved conservation of the actin structure and better conservation of the fluorescence signal of green fluorescent protein (GFP)-fusion proteins. Herein we demonstrate that efficient oxygen removal by addition of an enzymatic oxygen scavenger system (ClickOx) considerably reduces ROS-associated damage during labeling of nascent DNA with ATTO 488 azide by Cu(I)-catalyzed click chemistry. Standard confocal and super-resolution fluorescence images of phalloidin-labeled actin filaments and GFP/yellow fluorescent protein-labeled cells verify the conservation of the cytoskeleton microstructure and fluorescence intensity, respectively. Thus, ClickOx can be used advantageously for structure preservation in conventional and most notably in super-resolution microscopy methods.

Comparison of lignin derivatives as substrates for laccase-catalyzed scavenging of oxygen in coatings and films

BackgroundLignin derivatives are phenylpropanoid biopolymers derived from pulping and biorefinery processes. The possibility to utilize lignin derivatives from different types of processes in advanced enzyme-catalyzed oxygen-scavenging systems intended for active packaging was explored. Laccase-catalyzed oxidation of alkali lignin (LA), hydrolytic lignin (LH), organosolv lignin (LO), and lignosulfonates (LS) was compared using oxygen-scavenging coatings and films in liquid and gas phase systems.ResultsWhen coatings containing lignin derivatives and laccase were immersed in a buffered aqueous solution, the oxygen-scavenging capability increased in the order LO < LH < LA < LS. Experiments with coatings containing laccase and LO, LH or LA incubated in oxygen-containing gas in air-tight chambers and at a relative humidity (RH) of 100% showed that paperboard coated with LO and laccase reduced the oxygen content from 1.0% to 0.4% during a four-day period, which was far better than the results obtained with LA or LH. LO-containing coatings incubated at 92% RH also displayed activity, with a decrease in oxygen from 1.0% to 0.7% during a four-day period. The oxygen scavenging was not related to the content of free phenolic hydroxyl groups, which increased in the order LO < LS < LH < LA. LO and LS were selected for further studies and films containing starch, clay, glycerol, laccase and LO or LS were characterized using gel permeation chromatograpy, dynamic mechanical analysis, and wet stability.ConclusionsThe investigation shows that different lignin derivatives exhibit widely different properties as a part of active coatings and films. Results indicate that LS and LO were most suitable for the application studied and differences between them were attributed to a higher degree of laccase-catalyzed cross-linking of LS than of LO. Inclusion in active-packaging systems offers a new way to utilize some types of lignin derivatives from biorefining processes.

A Simple Chemical Oxygen Scavenging System for Improved dSTORM Tissue Imaging

dSTORM based super-resolution localization microscopy typically uses a thiol reductant such as mercapto-ethyl amine (MEA) in conjunction with an enzymatic oxygen scavenging system such as glucose oxidase & catalase in an aqueous buffer. The use of an aqueous buffer, however, is non-optimal when trying to perform tissue imaging with high NA objectives due to the considerable refractive index mismatch. In previous works we have used a modified buffer solution with a glycerol concentration of 80-90%, which gives satisfactory blinking behavior and allows better index matching. Unsurprisingly, enzymatic scavengers do not function in this high glycerol mountant, although media oxygen concentration is nonetheless substantially reduced. This reduction in oxygen concentration occurs through a reaction of the thiol with dissolved oxygen and comes at the cost of a reduced and highly variable end thiol concentration and a substantial change in solution pH.To have the thiol acting as both the blinking agent, and the principal oxygen scavenger is obviously a somewhat undesirable situation. This led us to experiment with sodium sulphite, a chemical which is commonly used as a preservative, as an oxygen scavenger in industrial processes, and in making ‘zero oxygen’ calibration solutions for dissolved oxygen sensors. When added to an MEA and glycerol containing switching buffer, sodium sulphite improves entry to the dark state, resulting in lower background levels and improved single molecule contrast. In contrast to the use of either the glucose oxidase or thiol mediated oxygen scavenging systems, the reaction of sodium sulphite with dissolved oxygen does not significantly change solution pH.