NaSCN Research Articles

The Investigation of General Properties of Carbon Fiber (CF) Composites - Preliminary Study

The most commonly used materials in the production of high-performance CFs are cellulose, polyacrylonitrile, and pitch. Polyacrylonitrile (PAN)-based fibers dominate the market (representing nearly 90% of total CF production), with some companies producing more than 10,000 tons per year. However, the current technique's high cost (the combined cost of the precursors and stabilization accounts for 70% of total CF synthesis cost) limits the technology's applicability. Carbon fiber manufacturing is characterized by a high energy demand due to long processing times and energy intensive thermal processes. PAN-based CFs are difficult to commercialize due to the time-consuming pre-oxidation step, which significantly raises the manufacturing cost. As a result, advanced processing technologies aimed at reducing CF production costs should be developed. They were consisting of a thin but strong crystalline filament of carbon. This experimental study was to learn the mechanical properties of carbon fiber using Universal Testing Machine (UTM). There was a section where we made a phone case out of Polyacrylonitrile (PAN) carbon fiber and compared it to other materials for phone cases. The phone cases of carbon fiber composites as the one examples of consumer product was made from the woven carbon fiber then was hardened by hard epoxy mixed with resin epoxy. Then, the phone cases were tested with UTM machine to compare the tensile strength and high modulus. Other than that, there were few samples with different composition of PAN powder mixed with different composition of sodium thiocyanate. The results of the testing shows that the carbon fiber had the high tensile strength than the other materials of phone cases which were silicone and thermoplastic polyurethanes (TPU). The microstructure of carbon fiber has a significant impact on its mechanical properties.

Elucidating the concentration-dependent effects of thiocyanate binding to carbonic anhydrase

Many proteins naturally carry metal centers, with a large share of them being in the active sites of several enzymes. Paramagnetic effects are a powerful source of structural information and, therefore, if the native metal is paramagnetic, or it can be functionally substituted with a paramagnetic one, paramagnetic effects can be used to study the metal sites, as well as the overall structure of the protein. One notable example is cobalt(II) substitution for zinc(II) in carbonic anhydrase. In this manuscript we investigate the effects of sodium thiocyanate on the chemical environment of the metal ion of the human carbonic anhydrase II. The electron paramagnetic resonance (EPR) titration of the cobalt(II) protein with thiocyanate shows that the EPR spectrum changes from A-type to C-type on passing from 1:1 to 1:1000-fold ligand excess. This indicates the occurrence of a change in the electronic structure, which may reflect a sizable change in the metal coordination environment in turn caused by a modification of the frozen solvent glass. However, paramagnetic nuclear magnetic resonance (NMR) data indicate that the metal coordination cage remains unperturbed even in 1:1000-fold ligand excess. This result proves that the C-type EPR spectrum observed at large ligand concentration should be ascribed to the low temperature at which EPR measurements are performed, which impacts on the structure of the protein when it is destabilized by a high concentration of a chaotropic agent.

On the Use of Pseudo-Protic Ionic Liquids to Extract Gold(III) from HCl Solutions.

Solvent extraction of gold(III) from HCl media using pseudo-protic ionic liquids (PPILs) dissolved in toluene as the extractant phase is investigated. Three PPILs are generated from the reaction of commercially available amines and 1 M HCl solution and named as pri-NH2H+Cl- (derived from the primary amine Primene 81R), sec-NHH+Cl- (derived from the secondary amine Amberlite LA2) and ter-NH+Cl- (derived from the tertiary amine Hostarex A327). In the above structures, -NH2H+Cl-, -NHH+Cl- and -NH+Cl- represented the active groups (anion exchangers) of the respective PPIL. In the case of gold(III) extraction, the experimental variables investigated included the equilibration time (2.5-30 min), temperature (20-60 °C), HCl concentrations (1-10 M) in the aqueous phase, gold(III) concentration (0.005-0.05 g/L) in this same phase, and PPILs concentrations in the organic phase. From the experimental data, and using the Specific Interaction Theory, the interaction coefficients (ε) for the pair AuCl4-, H+ are estimated for the systems involving the three PPILs. Gold(III) is recovered from the metal-loaded organic phases using sodium thiocyanate solutions, and from these, gold is finally recovered by the precipitation of zero-valent gold (ZVG) nanoparticles.

Al2O3@Ag composite structure as SERS substrate for sensitive detection of sodium thiocyanate.

Sodium thiocyanate (NaSCN) can be added to fresh milk to enhance the sterilization ability of the lactoperoxidase system (LP system) in milk, extending shelf life. However, excessive intake of NaSCN can be harmful to human health because it can prevent absorption of iodine leading to disease. Also NaSCN can be used as a marker to distinguish smokers from non-smokers. In this work, we successfully synthesized meatball-like Al2O3@Ag composite structures as surface-enhanced Raman scattering (SERS) substrates using a simple wet chemical method adapted to conventional laboratory conditions. The substrate exhibited strong SERS enhancement for NaSCN. Under the optimal experiment conditions, we obtained a detection limit of 0.28μg L-1 and a quantification limit of 1μg L-1, R2 = 0.992. Based on the analysis of the intensity of SERS characteristic peak, the substrate had good reproducibility and uniformity. In summary, the Al2O3@Ag composite structure achieved sensitive SERS detection of NaSCN. Combining the facile and low-cost methods, we believe that the SERS detection method developed in this work can be used as a potential candidate for biosensing applications in the future.

Risk factors for the development of bronchopulmonary pathology in workers producing synthetic polyacrylonitrile fiber

Aim of the study was to assess the risk of bronchopulmonary pathology in workers of the production of synthetic polyacrylonitrile fiber as a result of exposure to harmful chemicals and smoking tobacco products . Material and methods . During the periodic medical examination , the function of external respiration and adherence to smoking in 137 employees were studied , medical records were analyzed (025/u accounting form ). Hygienic assessment of working conditions was carried out on the basis of the results of in-situ sanitary and hygienic studies . Results and discussions . As a result of a hygienic assessment of working conditions , it was found that workers engaged in the production of polyacrylonitrile fiber are subject to the combined intermittent effects of harmful chemicals of hazard classes 1–3 ( acrylonitrile , methyl acrylate , hydrocyanide , ammonia , sodium rhodanide , sulfuric acid , methanol , isopropyl alcohol , ethylene glycol ), the content of which in the working area exceeded the maximum permissible concentrations in 1.6% of samples . The occupational risk of developing bronchopulmonary diseases in groups of workers who smoke is assessed as unacceptably high , while in people exposed to harmful chemicals , its level is 28.46 times higher than in people who are not exposed to these effects . The risk of the formation of ventilation disorders in groups of smoking workers is unacceptably high , while its level is 2.46 times higher in workers exposed to harmful chemicals than in non-workers in such conditions . In groups of workers exposed to harmful chemicals , the occupational risk of obstructive disorders is unacceptably high , in the group of smokers the risk is 2.32 times higher . Conclusions . Among the employees of the enterprise producing synthetic polyacrylonitrile fiber , the influence of tobacco smoking on the development of bronchopulmonary pathology is higher than the influence of harmful working conditions , and the use of smoking tobacco products significantly increases the negative effect of chemical pollutants .

Rhenium-molybdenum separation in an alkaline leaching solution of a waste superalloy by N263 extraction

The recovery of rhenium from waste superalloys has always been a research focus. This study focuses on the performance of extraction of rhenium and its separation with molybdenum in alkali leaching solution of waste superalloy by methyl trioctylammonium chloride (N263). Minitab 17 Statistical Software (Trial version, Techmax, USA) was used to create a four-factor (N263 concentration, sec-octyl alcohols concentration, extraction time and organic to aqueous ratio (O/A ratio)) two-level orthogonal experiment table. According to the orthogonal experiment results of rhenium extraction and rhenium molybdenum separation coefficient, rhenium extraction model, rhenium molybdenum separation coefficient model and the corresponding regression equation were established. The rhenium extraction performance of N263 was investigated by the rhenium equilibrium curve and NaSCN concentration. It was found that the N263 concentration was the main factor affecting rhenium extraction, and the regression equation of rhenium extraction was Re extraction/% = 0.672 + 9.880 [N263]. Moreover, N263 concentration and O/A ratio are the main factors affecting rhenium molybdenum separation coefficient. The regression equation of rhenium molybdenum separation coefficient is βRe/Mo = 37.5 + 116.88* [N263] −24.3 *(O/A ratio) −20.62 [N263]*(O/A ratio). At the same concentration of the rhenium stripping agent, the rhenium stripping efficiency is perchloric acid > nitric acid > sodium thiocyanate. However, the strong oxidability of perchloric acid and nitric acid destroys the organic phase, making the organic phase produce visible destruction. The rhenium stripping was about 75.8 % with 40 times the theoretical amount of sodium thiocyanate. The results showed that Re was easy to be extracted in the alkali solution, but it was not easy to be stripped from the loaded N263 phase.

Performance of pseudo‐specific cryogel in lysozyme purification from chicken egg white

AbstractThe application of cryogels for biomolecule purification has expanded due to their adsorption efficiency and operational advantages. In this study, polyacrylamide cryogels functionalized with l‐phenylalanine (cryogel‐Phe) via the glutaraldehyde method were designed for lysozyme adsorption. Cryogel functionalization was confirmed by Fourier‐transform infrared spectroscopy and Kjeldahl analysis, indicating the immobilization of 458.65 mgphenylalanine gcryogel−1. Cryogel‐Phe showed high porosity (0.95) and a Young's modulus of 526.71 kPa. Thermogravimetric analysis indicated that thermal degradation occurred above 200°C. Differential scanning calorimetry and X‐ray diffraction confirmed that the cryogel material was amorphous. In addition, the column presented a hydraulic permeability of 4.15 × 10−13 m2, axial dispersion ranging from 10−7 to 10−6 m2 s−1, and a height equivalent to a theoretical plate ranging from 0.10 to 0.21 cm. The highest adsorption of lysozyme (67.65 mg g−1) was obtained using sodium thiocyanate saline solution (0.025 mol L−1, pH 5.0). The ability of the cryogel‐Phe column to capture and purify lysozyme was confirmed by high enzymatic activity (1294.17 U ml−1), purity (87.92%), purification factor (11.49), and sulphate‐polyacrylamide electrophoresis gel (SDS‐PAGE) electrophoresis gel.

Defect passivation via incorporation of sodium thiocyanate for achieving high-performance MAPbI3-based perovskite solar cells with enhanced stability

The high density of defects in MAPbI3 perovskite films brings about severe carrier nonradiative recombination, which lowers the photovoltaic performance and the stability of MAPbI3-based perovskite solar cells (PSCs). To tackle this issue, we prepared stable and efficient MAPbI3-based PSCs with incorporation of sodium thiocyanate (NaSCN). NaSCN can increase grain size and improve crystallization quality of the perovskite films due to an Ostwald ripening effect of SCN- and surface passivation of Na+ which can effectively passivate the defect states and inhibit nonradiative recombination for an ultimate improvement of the device performance and stability. The excellent characteristics lead to a significant enhancement of the power conversion efficiency (PCE) from 18.1 % to 19.4 % both for MAPbI3-based and Cs0.06MA0.15FA0.79PbI2.5Br0.5-based PSCs, respectively. The unencapsulated NaSCN-treated PSCs also shows a improved stability after aging under a relative humidity of 40 ± 5 % for 15 days.

Development of High-Performance Fiber Cement: A Case Study in the Integration of Circular Economy in Product Design

A new fiber cement (FC) is designed with the integration of circular economy (CE) concepts, in particular a product that is recyclable yet maintains performance. The FC samples were prepared from the mixtures of ordinary Portland cement (OPC), sand, and cellulose fibers, and required an inclusion compound (IC) and water. From the heat of hydration tests, the most effective IC, IC1, was prepared from lithium silicate, sodium thiocyanate, alkylbenzene sulfonate, and hydrochloric acid. The FC samples were recycled by crushing and grinding, then used as sand replacement in varying amounts to produce new FC samples. The results from the mechanical tests showed that the 50%replacement of the sand provided FC samples with the highest modulus of rupture (MOR) of 10.64 MPa and a modulus of elasticity (MOE) of 7706.40 MPa. The samples with/without the recycled product passed both the freeze–thaw resistance test and flammability test for durability. Most importantly, results showed that the mechanical properties of the produced FC samples remained the same over 5 to 50 recycles.

Direct Access to Thiocyano-Thioesters from Cyclic Thioacetals via Photoredox Catalysis: An Introduction of Two Functional Groups in One Pot.

The cyanation of organic compounds is an important synthetic transformation and mainly relies on a toxic CN source. Undeniably, thiocyanate salt has emerged as a very mild and environmentally benign CN source, yet its synthetic utility for cyanation is highly limited to very few types of organic compounds. Herein, we report the direct cyanation of cyclic thioacetals for accessing compounds with two different functional groups (thiocyano-thioesters) in one pot using sodium thiocyanate via photoredox catalysis. The protocol has been further extended for the direct cyanation of disulfides and diselenide to access aryl thiocyanates and aryl selenocyanate. A plausible mechanism has been proposed based on a series of control experiments, cyclic voltammetry and Stern-Volmer studies.

Fabrication and Characterization of Flexible Solid Polymers Electrolytes for Supercapacitor Application.

In this work, solid flexible polymer blend electrolytes (PBE) composed of polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) with different amounts of sodium thiocyanate (NaSCN) salt mixed in double-distilled water (solvent) are prepared via solution casting method. The obtained films are characterized using several techniques. The study of the surface morphology of the polymer blend salt complex films via the POM technique reveals the presence of amorphous regions due to the NaSCN effect. FTIR spectra studies confirm the complex formation between PVA, PVP, and NaSCN. The addition of 20 wt% NaSCN salt in the composition PVA: PVP (50:50 wt%) polymer blend matrix leads to an increase in the number of charge carriers and thus improves the ionic conductivity. The ionic conductivity of each polymer blend electrolyte was studied using the electrochemical impedance spectroscopy (EIS) method. The highest room temperature ionic conductivity of 8.1 × 10−5 S/cm S cm−1 is obtained for the composition of PVA: PVP (50:50 wt%) with 20 wt% NaSCN. LSV test shows the optimized ion-conducting polymer blend electrolyte is electrochemically stable up to 1.5 V. TNM analysis reveals that 99% of ions contribute for the conductivity against 1% of electrons only in the highly conductive polymer electrolyte PVA: PVP (50:50 wt%) + 20 wt% NaSCN. A supercapacitor device was fabricated using the optimized ion-conducting polymer blend film and graphene oxide (GO) coated electrodes. The GCD curve clearly reveals the behavior of an ideal capacitor with less Faradic process and low ESR value. The columbic efficiency of the GO-based system is found to be 100%, the GO-based electrode exhibits a specific capacitance of 12.15 F/g and the system delivers the charge for a long duration. The specific capacitance of the solid-state supercapacitor cell was found to be 13.28 F/g via the CV approach close to 14.25 F/g obtained with EIS data at low frequency.

The use of 1-ethyl-3-methylimidazolium iodide ionic liquid in dye sensitized solar cells: A joint experimental and computational perspective

The photovoltaic performance of dye-sensitized solar cells (DSSCs) significantly depends on the components of electrolyte solution. In this study, the electrolytes involving acetonitrile (ACN) solvent and various salts namely potassium iodide (KI), 1-ethyl-3-methylimidazolium iodide ionic liquid ([C2mim]I ∼ Emim-I IL), sodium thiocyanate (NaSCN), and ammonium thiocyanate (NH4SCN) were fabricated and their effects on the DSSC performance were explored. Among the different inorganic (KI) and organic (Emim-I) iodide sources, the DSSC showed high performance when KI and Emim-I mixed. In the meantime, without KI, by increasing Emim-I concentration from 0.3 M to 1.2 M, the best efficiency of DSSC was obtained for 0.9 M concentration. The results indicated that the best performance of the cells can be obtained when Emim-I and NH4SCN were added to the 0.6 M of KI solution. Power conversion efficiency as high as 11.07 % was obtained under the best operation conditions. Beside experiments, the interface of solid/liquid electrolyte was also studied as a key element of DSSCs by using molecular dynamics simulations. The influence of cations such as K+, and 1-ethyl-3-methylimidazolium (Emim+), Na+, and NH4+ on the double-layer structure in ACN-based electrolytes at the anatase TiO2(101) and platinum surfaces was studied. Particularly, a strong impact of cations on the I− and SCN− anions density distribution at the interface was found.

A monomeric iron(III) compound containing N-(2-pyridylmethyl)iminodiisopropanolate and thiocyanato ligands: structure, magnetic and catalytic properties

The reaction of Fe(NO3)3·9H2O, sodium thiocyanate, and N-(2-pyridylmethyl)iminodiisopropanol (H2pmidip) in methanol/water mixture solution leads to the formation of a mononuclear iron(III) compound of [FeIII(Hpmidip)(NCS)2] (1). The iron ion of 1 has a distorted octahedral structure that is bonded by two thiocyanate anions and one Hpmidip- ligand. One of the two hydroxyl moieties in H2pmidip is deprotonated, while the other is involved in hydrogen bonding interactions to form a dimeric structure. The magnetic properties of 1 reveal a very weak antiferromagnetic interaction within the dimer with parameters J = -0.75 cm−1 and g = 2.068. 1 showed that the catalytic oxidations for a variety of olefins are selective and effective with moderate yields using meta-chloroperoxybenzoic acid (m-CPBA). For the identification of the mechanism for olefin epoxidation in 1, the OO bond cleavage of peroxyphenylacetic acid (PPAA) and competitive experiments of cis- and trans-2-octene have been investigated.

Pickering Emulsions Stabilized by Polystyrene Particles Possessing Different Surface Groups.

Colloidal polystyrene (PS) latex particles in water can undergo interesting charge reversal in the presence of particular electrolytes. It is worth exploring the effect of charge reversal on the properties of Pickering emulsions they stabilize. Herein, emulsions stabilized by PS latex particles possessing different surface groups (sulfate, amidine, or carboxyl) were prepared in the presence of tetrapentylammonium bromide (TPeAB) or sodium thiocyanate (NaSCN) electrolytes. The effect of salt concentration on the charge of the particles and their colloid stability was measured. Emulsions were prepared from aqueous dispersions, and their type and stability were determined. The three-phase contact angle of particles at the planar oil–water interface was also measured using a gel trapping technique. It was found that the type of emulsion stabilized by latex particles is dominated by the hydrophobic PS portion on particle surfaces, although their surface charge is strongly affected by electrolyte addition. Preferred emulsions were always water-in-oil with dodecane, and charge reversal had little influence on the emulsion type and stability. However, transitional phase inversion of emulsions stabilized by carboxyl latex particles occurred on adding salt when the oil was a low-viscosity polydimethylsiloxane.

Synthesis, crystal structure, and DFT studies of a new phenoxo-bridged dinuclear zinc(II) Schiff base complex with two different geometries

A new dinuclear Zn(II) complex Zn2L(H2O)(NCS)2 (1) is synthesized by the reaction of the tetradentate Schiff base ligand N,N'-bis(5-bromosalicylidene)-1,3-diaminopropane (H2L) with Zn(OAc)2·2H2O in the presence of sodium thiocyanate. The ligand and complex 1 are characterized by microanalytical and spectroscopic techniques. The structure of the complex is established by single crystal X-ray diffraction studies. In the phenoxo-bridged zinc complex, one Zn atom is five-coordinated in a square-pyramidal geometry while another is four-coordinated in a tetrahedral geometry. To gain insight into the structural features of complex 1, DFT studies are performed. The calculations reveal a strong effect of the intermolecular interaction, namely the π—π stacking interaction, on the geometry of the complex.

Effect of Lactoperoxidase Enzyme System in Improving Shelflife of Raw Milk from Dairy Farms in Khartoum State, Sudan

Lactoperoxidase enzyme (LP) is a natural component in milk with broad spectrum of antimicrobial activity applications in in vivo and in vitro. LP system (LPS) was developed to eliminate the growth of bacterial pathogens and augment the shelf life of raw milk. The aim of this study was to evaluate the effect of activation of LPS on the growth and survival of bacterial pathogens and preserving raw milk quality. A checklist was developed and filled in ten farms at the time of milking to detect the hygienic measures in these farms. Two liters of milk were collected in sterile containers and warmed to 37°C/15min. LPS was activated by dissolving 40mg and 30mg of sodium thiocyanate and sodium percarbonate, respectively, in one liter of milk and followed by thorough mixing. 50ml from this liter of milk was added to two new containers and designated as group B and C. Moreover, group C was supplied with E. coli (106-107 cfu/ml). While milk in group D, LPS was not activated, instead milk was only supplied with E. coli (106-107 cfu/ml). Group A was considered as the control group (neither activated nor supplied with Escherichia coli). Tenfold serial dilution was performed to determine the bacterial total viable count (TVC) and milk clotting time (per seconds) in each group for 2, 4, 6, 8 and 10 hrs. The TVC and the milk clotting time in each group were statistically expressed as pairs between the groups (A versus B; C versus D) with significance probability of P≤0.05. The checklist analysis reflected the bad hygiene measures in the dairy farms. For TVC, in 2hrs incubation; no significant difference was observed between group A versus group B. While group C versus group D showed high significant difference. After 4hrs incubation, TVC showed prominent significance difference between the control compared to group B. While group C versus group D showed no statistical significance differences. At 6hrs time period, a significant difference was observed between the compared groups. However, no significance differences were observed between the groups after 8hrs and 10hrs of incubation. For clotting time, in 2hrs incubation, a significant difference between the compared groups was observed. After 4hrs incubation, a significant difference between the control compared to group B was prominent, while group C versus group D showed no statistical differences in clotting time. However, no significant differences were observed between the groups after 6, 8 and 10hrs of incubation in the clotting times. Taken together these results indicated that the LPS system was efficient until 6hrs and could prolong milk shelf life and prevent milk clotting.

Identification and Characterization of mRNA Biomarkers for Sodium Cyanide Exposure.

Biomarkers in exposure assessment are defined as the quantifiable targets that indicate the exposure to hazardous chemicals and their resulting health effect. In this study, we aimed to identify, validate, and characterize the mRNA biomarker that can detect the exposure of sodium cyanide. To identify reliable biomarkers for sodium cyanide exposure, critical criteria were defined for candidate selection: (1) the expression level of mRNA significantly changes in response to sodium thiocyanate treatment in transcriptomics results (fold change > 2.0 or <0.50, adjusted p-value < 0.05); and (2) the mRNA level is significantly modulated by sodium cyanide exposure in both normal human lung cells and rat lung tissue. We identified the following mRNA biomarker candidates: ADCY5, ANGPTL4, CCNG2, CD9, COL1A2, DACT3, GGCX, GRB14, H1F0, HSPA1A, MAF, MAT2A, PPP1R10, and PPP4C. The expression levels of these candidates were commonly downregulated by sodium cyanide exposure both in vitro and in vivo. We functionally characterized the biomarkers and established the impact of sodium cyanide on transcriptomic profiles using in silico approaches. Our results suggest that the biomarkers may contribute to the regulation and degradation of the extracellular matrix, leading to a negative effect on surrounding lung cells.

A sensitive method for detecting sodium thiocyanate using AgNPs and MIL-101(Fe) combined as SERS substrate

Sodium thiocyanate (NaSCN) is normally used as a kind of food preservative in daily life, but using excessive NaSCN in milk would cause the low absorption of iodine in human body, and then would make the normal secretion of thyroid hormone disorder. In this study, we developed a method combines AgNPs and MIL-101(Fe) which is a kind of Metal organic frameworks materials as a kind of composite Surface Enhanced Raman Scattering (SERS) substrate and achieved the determination of NaSCN in spiked milk. The characteristic peak of NaSCN at 2110 cm−1 showed obvious SERS enhancement and has good linearity with the concentration of NaSCN in milk. Through the simple and rapid detection, the limit of detection in water and milk was calculated as 18.5 μg/L and 96.3 μg/L with the correlation coefficient of 0.991 and 0.988 respectively. This work provides a new method to detect NaSCN in milk and expands the application of SERS in food detection.

A High Selective Chemiluminescent Probe Derived fromIso‐luminol Enabling High Sensitive Determination of Ferrous Ions in the Environmental Waters

Main observation and conclusionA new chemiluminescence (CL) reagent named 4‐amino‐5‐thiocyanato‐phthalyl‐hydrazine (iso‐luminol‐SCN) is synthesized by the bromide‐mediated substitution reaction ofiso‐luminol with sodium thiocyanate in dimethyl formamide (DMF) at room temperature. Strong CL is observed foriso‐luminol‐SCN oxidized by hydrogen peroxide (H2O2) in the presence of Fe2+, with the CL intensity strongly depending on the concentration of Fe2+and being hardly interferred by other common metal ions. Based on this fact, a flow injection CL method is established for the high sensitive and selective determination of Fe2+. The CL intensity was linearly correlated with the concentration of Fe2+in the range of 1.0 × 10–8mol·L–1to 1.0 × 10–5mol·L–1following the equation CLnet= 166.3c+ 57.7 (c, ×10–6mol·L–1;n= 7;R2= 0.9988). The detection limit is calculated to be 3.2 × 10–9mol·L–1Fe2+based on the 3S0/K principle. The relative standard deviation (RSD) was 3.7% for 1.0 × 10–6mol·L–1Fe2+(n= 11), a support for the precision of Fe2+measurement. The recoveries of Fe2+were obtained in the range of 98.8%—101.6% in three real water samples, showing the applicability and reliability by the proposed method. The possible CL mechanism is proposed based on the kinetic characteristic of the CL reaction and the CL spectrum.

Lactose oxidase: An enzymatic approach to inhibit Listeria monocytogenes in milk

Listeria monocytogenes is a ubiquitous pathogen that can cause morbidity and mortality in immunocompromised individuals. Growth of L. monocytogenes is possible at refrigeration temperatures due to its psychrotrophic nature. The use of antimicrobials in dairy products is a potential way to control L. monocytogenes growth in processes with no thermal kill step, thereby enhancing the safety of such products. Microbial-based enzymes offer a clean-label approach for control of L. monocytogenes outgrowth. Lactose oxidase (LO) is a microbial-derived enzyme with antimicrobial properties. It oxidizes lactose into lactobionic acid and reduces oxygen, generating H2O2. This study investigated the effects of LO in UHT skim milk using different L. monocytogenes contamination scenarios. These LO treatments were then applied to raw milk with various modifications; higher levels of LO as well as supplementation with thiocyanate were added to activate the lactoperoxidase system, a natural antimicrobial system present in milk. In UHT skim milk, concentrations of 0.0060, 0.012, and 0.12 g/L LO each reduced L. monocytogenes counts to below the limit of detection between 14 and 21 d of refrigerated storage, dependent on the concentration of LO. In the 48-h trials in UHT skim milk, LO treatments were effective in a concentration-dependent fashion. The highest concentration of LO in the 21-d trials, 0.12 g/L, did not show great inhibition over 48 h, so concentrations were increased for these experiments. In the lower inoculum, after 48 h, a 12 g/L LO treatment reached levels of 1.7 log cfu/mL, a reduction of 1.3 log cfu/mL from the initial inoculum, whereas the control grew out to approximately 4 log cfu/mL, an increase of 1 log cfu/mL from the inoculum on d 0. When a higher challenge inoculum of 5 log cfu/mL was used, the 0.12 g/L and 1.2 g/L treatments reduced the levels by 0.2 to 0.3 log cfu/mL below the initial inoculum and the 12 g/L treatment by >1 log cfu/mL below the initial inoculum by hour 48 of storage at refrigeration temperatures. After the efficacy of LO was determined in UHT skim milk, LO treatments were applied to raw milk. Concentrations of LO were increased, and the addition of thiocyanate was investigated to supplement the effect of the lactoperoxidase system against L. monocytogenes. When raw milk was inoculated with 2 logcfu/mL, 1.2 g/L LO alone and combined with sodium thiocyanate reduced~0.8 logcfu/mL from the initial inoculum on d 7 of storage, whereas the control grew out to >1 logcfu/mLfrom the initial inoculum. Furthermore, in the higher inoculum, 1.2 g/L LO combined with sodium thiocyanate reduced L. monocytogenes counts from the initial inoculum by >1 log cfu/mL, whereas the control grew out 2 log cfu/mL from the initial inoculum. Results from this study suggest that LO is inhibitory against L. monocytogenes in UHT skim milk and in raw milk. Therefore, LO may be an effective treatment to prevent L. monocytogenes outgrowth, increase the safety of raw milk, and be used as an effective agent to prevent L. monocytogenes proliferation in fresh cheese and other dairy products. This enzymatic approach is a novel application to control the foodborne pathogen L. monocytogenes in dairy products.