α-Amylases (E.C 3.2.1.1) hydrolyse starch into smaller moieties such as maltose and glucose by breaking α-1,4-glycosidic linkages. The application of α-amylases in various industries has made the ...large-scale productions of these enzymes crucial. Thermostable α-amylase that catalyses starch degradation at the temperatures higher than 50 °C is favourable in harsh industrial applications. Due to ease in genetic manipulation and bulk production, this enzyme is most preferably produced by microorganisms. Bacillus sp. and Escherichia coli are commonly used microbial expression hosts for α-amylases (30 to 205 kDa in molecular weight). These amylases can be purified using ultrafiltration, salt precipitation, dialysis, and column chromatography. Recently, affinity column chromatography has shown the most promising result where the recovery rate was 38 to 60% and purification up to 13.2-fold. Microbial thermostable α-amylases have the optimum temperature and pH ranging from 50 °C to 100 °C and 5.0 to 10.5, respectively. These enzymes have high specificity towards potato starch, wheat starch, amylose, and amylopectin. EDTA (1 mM) gave the highest inhibitory effect (79%), but Ca2+ (5 mM) was the most effective co-factor with 155%. This review provides insight regarding thermostable α-amylases obtained from microbial sources for industrial applications.
•Townsend hypothesis can explain large-scale motions near rough and smooth walls.•Is unable to describe all roughness regimes and does not scale d-type roughness.•Wall similarity hypothesis faces ...both supporting and conflicting evidence.•Roughness function can be scaled with height and effective slope of roughness.•Available models do not point to agreed conclusions or trends for all roughness types,
Surface roughness can significantly influence the fluid dynamics and heat transfer in convective flows by inducing perturbations in the velocity profile which affect surface drag, turbulent mixing and heat transfer. While surface roughness can often negatively affect the performance of systems, it can also lead to performance improvements, such as in convective flows where roughness elements have been shown to enhance heat transfer. Turbulent flows over rough surfaces have been studied for about a century leading to significant developments in this field. Direct Numerical Simulation (DNS) has made significant contributions to the knowledge of turbulent flows over rough surfaces as well as evaluation of the developed theories. Moreover, the turbulent closures model has seen wide use for simulation of rough-wall turbulent flows in practical applications where DNS is hindered by its complexity and computational resources.
Despite a significant number of experimental and CFD studies and the latest advances in this field, a recent review was not available. Therefore, this review surveys the past and recent experimental and numerical studies to address the fundamentals and theories related to the structure of turbulent flows over rough walls. This study chiefly investigates the structure of mean flow profile over rough surfaces, and its correlation with smooth wall mean flow profile. This review study can contribute to prospective experimental and CFD work, and for characterising rough-wall turbulent flows and heat transfer in different academic and engineering applications such as aerodynamics, hydraulics, meteorology, and manufacturing.
The review concludes that despite significant progress, the structure of turbulent flow is still not fully understood. This is mainly due to a lack of systematic studies on the structure of turbulent flow and also due to the variety of roughness which influence the dynamics of the flow in the roughness sublayers. The current roughness scale (sand-grain roughness height) fails to completely characterise roughness in many cases. Therefore, there is a need for a universal roughness scale that can describe every type of roughness and be used in any rough-flow regimes, including fully rough and transitionally rough regimes.
Risk assessment of ochratoxin A in food Schrenk, Dieter; Bodin, Laurent; Chipman, James Kevin ...
EFSA journal,
20/May , Letnik:
18, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The European Commission asked EFSA to update their 2006 opinion on ochratoxin A (OTA) in food. OTA is produced by fungi of the genus Aspergillus and Penicillium and found as a contaminant in various ...foods. OTA causes kidney toxicity in different animal species and kidney tumours in rodents. OTA is genotoxic both in vitro and in vivo; however, the mechanisms of genotoxicity are unclear. Direct and indirect genotoxic and non‐genotoxic modes of action might each contribute to tumour formation. Since recent studies have raised uncertainty regarding the mode of action for kidney carcinogenicity, it is inappropriate to establish a health‐based guidance value (HBGV) and a margin of exposure (MOE) approach was applied. For the characterisation of non‐neoplastic effects, a BMDL10 of 4.73 μg/kg body weight (bw) per day was calculated from kidney lesions observed in pigs. For characterisation of neoplastic effects, a BMDL10 of 14.5 μg/kg bw per day was calculated from kidney tumours seen in rats. The estimation of chronic dietary exposure resulted in mean and 95th percentile levels ranging from 0.6 to 17.8 and from 2.4 to 51.7 ng/kg bw per day, respectively. Median OTA exposures in breastfed infants ranged from 1.7 to 2.6 ng/kg bw per day, 95th percentile exposures from 5.6 to 8.5 ng/kg bw per day in average/high breast milk consuming infants, respectively. Comparison of exposures with the BMDL10 based on the non‐neoplastic endpoint resulted in MOEs of more than 200 in most consumer groups, indicating a low health concern with the exception of MOEs for high consumers in the younger age groups, indicating a possible health concern. When compared with the BMDL10 based on the neoplastic endpoint, MOEs were lower than 10,000 for almost all exposure scenarios, including breastfed infants. This would indicate a possible health concern if genotoxicity is direct. Uncertainty in this assessment is high and risk may be overestimated.
This publication is linked to the following EFSA Supporting Publications article: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2020.EN-1845/full
•In a cod protein hydrolysate the fraction <3kDa contained the highest amount of free amino acids.•All sub-fractions showed high Fe2+ chelating activity.•Peptides <600Da with His and Tyr dominated in ...fractions with high radical-scavenging activity.•Peptides rich in Arg, Tyr and Phe showed significantly higher reducing power.
This study aimed to characterise peptide fractions (>5kDa, 3–5kDa and <3kDa) with antioxidative activity obtained from a cod protein hydrolysate. The free amino acids in all fractions were dominated by Ala, Gly, Glu and Ser. The total amino acid composition had high proportions of Lys, Ala and Glu. The 3–5kDa and <3kDa fractions were further fractionated by size exclusion chromatography. All sub-fractions showed high Fe2+ chelating activity. The DPPH radical-scavenging activity of the 3–5kDa fraction was exerted mainly by one sub-fraction dominated by peptides with masses below 600Da. The DPPH radical-scavenging activity of the <3kDa fraction was exerted by sub-fractions with low molecular weight. The highest reducing power was found in a sub-fraction containing peptides rich in Arg, Tyr and Phe. Both free amino acids and low molecular weight peptides thus seemed to contribute to the antioxidative activity of the peptide fractions, and Tyr seemed to play a major role in the antioxidant activity.
The use of QSAR estimated data as basis for calculation of characterisation factors, and the further use of thosefactors for ranking based on ecotoxicity potential, was assessed as a feasible way to ...gather substance data for large datasets.However, further research and development of the guidance on how to make use of estimated data is needed to achieveimprovement of the accuracy of the results (PDF) The potential to use QSAR to populate ecotoxicity characterisation factors for simplified LCIA and chemical prioritisation. Available from: https://www.researchgate.net/publication/324503117_The_potential_to_use_QSAR_to_populate_ecotoxicity_characterisation_factors_for_simplified_LCIA_and_chemical_prioritisation accessed Jan 29 2019.
The EFSA has updated the Guidance on risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain, human and animal health. It covers the application areas within ...EFSA’s remit, including novel foods, food contact materials, food/feed additives and pesticides. The updated guidance, now Scientific Committee Guidance on nano risk assessment (SC Guidance on Nano‐RA), has taken account of relevant scientific studies that provide insights to physico‐chemical properties, exposure assessment and hazard characterisation of nanomaterials and areas of applicability. Together with the accompanying Guidance on Technical requirements for regulated food and feed product applications to establish the presence of small particles including nanoparticles (Guidance on Particle‐TR), the SC Guidance on Nano‐RA specifically elaborates on physico‐chemical characterisation, key parameters that should be measured, methods and techniques that can be used for characterisation of nanomaterials and their determination in complex matrices. The SC Guidance on Nano‐RA also details aspects relating to exposure assessment and hazard identification and characterisation. In particular, nanospecific considerations relating to in vitro/in vivo toxicological studies are discussed and a tiered framework for toxicological testing is outlined. Furthermore, in vitro degradation, toxicokinetics, genotoxicity, local and systemic toxicity as well as general issues relating to testing of nanomaterials are described. Depending on the initial tier results, additional studies may be needed to investigate reproductive and developmental toxicity, chronic toxicity and carcinogenicity, immunotoxicity and allergenicity, neurotoxicity, effects on gut microbiome and endocrine activity. The possible use of read‐across to fill data gaps as well as the potential use of integrated testing strategies and the knowledge of modes or mechanisms of action are also discussed. The Guidance proposes approaches to risk characterisation and uncertainty analysis.
This publication is linked to the following EFSA Journal article: http://onlinelibrary.wiley.com/doi/10.2903/j.efsa.2021.6769/full
This publication is linked to the following EFSA Supporting Publications articles: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2021.EN-6502/full, http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2020.EN-1948/full
We performed an environmental risk assessment for microplastics (<5 mm) in the marine environment by estimating the order of magnitude of the past, present and future concentrations based on global ...plastic production data. In 2100, from 9.6 to 48.8 particles m−3 are predicted to float around in the ocean, which is a 50-fold increase compared to the present-day concentrations. From a meta-analysis with effect data available in literature, we derived a safe concentration of 6650 buoyant particles m−3 below which adverse effects are not likely to occur. Our risk assessment (excluding the potential role of microplastics as chemical vectors) suggests that on average, no direct effects of free-floating microplastics in the marine environment are to be expected up to the year 2100. Yet, even today, the safe concentration can be exceeded in sites that are heavily polluted with buoyant microplastics. In the marine benthic compartment between 32 and 144 particles kg−1 dry sediment are predicted to be present in the beach deposition zone. Despite the scarcity of effect data, we expect adverse ecological effects along the coast as of the second half of the 21st century. From then ambient concentrations will start to outrange the safe concentration of sedimented microplastics (i.e. 540 particles kg−1 sediment). Additional ecotoxicological research in which marine species are chronically exposed to realistic environmental microplastic concentration series are urgently needed to verify our findings.
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•First ever ecological risk assessment of microplastics in the marine environment.•A safe concentration of 6650 buoyant particles m−3 was found.•On average this safe concentration will not be exceeded.•However, even today, heavily polluted sites with buoyant microplastics are at risk.•Beaches are at risk due to microplastics that wash ashore to date and in future.
We present the first-ever ecological risk assessment of microplastics in the marine environment and found a potential risk in sites that are heavily polluted with buoyant microplastics. Adverse effects of microplastics are to be expected on highly polluted beaches and in coastal ecosystems as of the second half of this century if plastics emissions are not reduced.
•The initial moisture content in CFRP tendons affects significantly the Tg values.•CFRP specimens without initial moisture content should be used for quality control.•Plasticisation effects in CFRP ...tendons due to exposure in water are reversible.•The fire performance of CFRP tendons can be affected by the initial moisture content.•The magnitude of static flexural strain and specimen geometry do not affect the Tg.
The high temperature and long-term performance of uni-directional pultruded carbon fibre reinforced polymer (CFRP) tendons in prestressed concrete relies on the integrity of the epoxy matrix and the degree of crosslinking. The dynamic glass transition temperature (Tg) obtained using Dynamic Mechanical Analysis (DMA) can be a useful indicator of the degree of cross-linking. However, variations in the epoxy plasticisation due to different initial hygrothermal equilibrium conditions in CFRP tendons can influence the measured Tg leading to inconsistent results. The dependency of Tg on the initial CFRP moisture content, and also DMA test parameters including the thermocouple position, the magnitude of static flexural strain, the static to dynamic strain ratio and the specimen geometry were investigated. Whereas the selected DMA test parameters had only a small influence on the Tg values, the initial moisture content of the CFRP tendon had a significant effect. A decrease in Tg of up to 38 °C was observed with an increase in average moisture content of up to 2.46%. Knowledge of the initial moisture content and the establishment of a comparative baseline are necessary to more accurately infer the crosslinking density and degree of cure of a resin from dynamic Tg results.
Aptamers are promising biorecognition elements with a wide applicability from therapeutics to biosensing. However, to successfully use these biomolecules, a complete characterisation of their binding ...performance in the presence of the target is crucial. Several multi-analytical approaches have been reported including techniques to describe kinetic and thermodynamic aspects of the aptamer-target interaction, and techniques which allow an in-depth understanding of the aptamer-target structures. Recent literature shows the need of a critical data interpretation, a combination of characterisation techniques and suggests the key role of the characterisation protocol design. Indeed, the final application of the aptamer should be considered before choosing the characterisation method. All the limitations and capabilities of the analytical tools in use for aptamer characterisation should be taken into account. Here, we present a critical overview of the current methods and multi-analytical approaches to study aptamer-target binding, aiming to provide researchers with guidelines for the design of characterisation protocols.
•A complete understanding of aptamer-target interactions is essential.•The design of the characterisation protocol takes into account the application.•A rational choice between label-free, labelled or immobilised approaches is key.
This study discusses the modelling of torque and speed characterisation of the double stator slotted rotor brushless DC motor (DSSR-BLDC). Most double stators have a surface mount rotor structure. ...The problem with this structure is that it has a large air gap, expensive permanent magnet, and cannot operate at high speed. In addition to flux leakage when this type of rotor structure is used. To overcome this problem, the DSSR-BLDC has been introduced. The usage of the DSSR-BLDC is to minimise the flux leakage, thus increasing the flux linkage. This will increase the torque production for the DSSR-BLDC. The aim of this research is to model the torque and speed characterisation of the DSSR-BLDC. This model uses the permeance analysis method and finite element method. The maximum torque and speed can be determined using both methods. The analyses of the electromagnetic torque, output power, and efficiency for various voltages are also presented. The simulation and measurement result show a good agreement with each other. The highest measurement value of the electromagnetic torque is 11 N m at 100 rpm. In conclusion, this study reveals that the modelling of the torque and speed characterisation of the DSSR-BLDC is suitable for portable applications.
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