Real-time assessment of fluid flow generated by appendage movements of Daphnia using standing square-wave chronamperometry

Standing square-wave chronoamperometry (SSWCA) was applied to the analysis of the microfluid flow generated by the movement of the appendages of the Crustacea Daphnia. This novel approach provided for the first time real-time assessment and analysis of the breathing rate/fluid flow of individual organisms. An electrochemical tracer was delivered into the fluid inflow of the organism and a carbon fiber microelectrode placed in the fluid outflow's path. The variation of the net concentration/flux of the electroactive tracer, dopamine, at the electrode surface was measured with SSWCA. The observed chronoamperometric peaks (with fine structure) of the outflow are seen as a direct representation of appendage movement and, too, the workings and responses of the organism to its environment, e.g., external stimuli such as food or chemicals. It was concluded that SSWCA follows primarily the variation of the convective component of the Nernst-Plank equation for flux and, to lesser extent, diffusion and migration. In this work, SSWCA can clearly be used to monitor changes in the Daphnia-generated fluid outflow on a different time scale than was previously possible. This new application of SSWCA is faster and likely more accurate than using high-speed video.     

Indium tin oxide-coated glass modified with reduced graphene oxide sheets and gold nanoparticles as disposable working electrodes for dopamine sensing in meat samples

Sensitive, rapid, and accurate detection of dopamine (DA) at low cost is needed for clinical diagnostic and therapeutic purposes as well as to prevent illegal use of DA in animal feed. We employed a simple approach to synthesize reduced graphene oxide sheets (rGOS) and gold nanoparticles (AuNPs) at room temperature on indium tin oxide-coated glass (ITO) slides as disposable working electrodes for sensing DA. Graphene oxide (GO) was directly reduced on ITO to remove oxygenated species via a rapid and green process without using chemical reducing reagents. AuNPs were electrochemically deposited in situ on rGOS-ITO with fairly uniform density and size. The sensitivity of the AuNPs-rGOS-ITO sensor for DA detection is 62.7 μA mM(-1) cm(-2) with good selectivity against common electrochemically interfering species such as ascorbic acid (AA) and uric acid (UA), and the detection limit measured by differential pulse voltammetry (DPV), at a signal-noise ratio of 3, was 6.0 × 10(-8) M. The electrochemical catalysis of DA was proven to be a surface process with an electron transfer coefficient (α) of 0.478 and a rate constant (k(s)) of 1.456 s(-1). It correlates well with the conventional UV-vis spectrophotometric approach (R = 0.9973) but with more than thrice the dynamic range (up to 4.5 mM). The sensor also exhibited good stability and capability to detect DA in beef samples, and thus is a promising candidate for simple and inexpensive sub-nanomolar detection of DA, especially in the presence of UV-absorbing compounds.     

Strain-level characterization of nonstarter lactic acid bacteria in Norvegia cheese by high-resolution melt analysis

The nonstarter lactic acid bacteria (NSLAB) constitute an important microbial group found during cheese ripening and they are thought to be fundamental to the quality of cheese. Rapid and accurate diagnostic tests for NSLAB are important for cheese quality control and in understanding the cheese ripening process. Here, we present a novel rapid approach for strain-level characterization through combined 16S rRNA gene and repetitive sequence-based high-resolution melt analysis (HRM). The approach was demonstrated through the characterization of 94 isolates from Norvegia, a Gouda-type cheese. The HRM profiles of the V1 and V3 variable regions of the 16S rRNA gene of the isolates were compared with the HRM profiles of 13 reference strains. The HRM profile comparison of the V1 and V3 regions of the 16S rRNA gene allowed discrimination of isolates and reference strains. Among the cheese isolates, Lactobacillus casei/paracasei (62 isolates) and Lactobacillus plantarum/Lactobacillus pentosus (27 isolates) were the dominant species, whereas Lactobacillus curvatus/Lactobacillus sakei were found occasionally (5 isolates). The HRM profiling of repetitive sequence-based PCR using the (GTG)(5) primer was developed for strain-level characterization. The clustering analysis of the HRM profiles showed high discriminatory power, similar to that of cluster analysis based on the gel method. In conclusion, the HRM approach in this study may be applied as a fast, accurate, and reproducible method for characterization of the NSLAB microflora in cheese and may be applicable to other microbial environments following selective plate culturing.     

The effect of crowding stress on bacterial growth and sensory properties of chilled Atlantic salmon fillets

Abstract: Atlantic salmon were subjected to minimal preslaughter crowding stress (Control), short‐term crowding for 20 min (SS‐group), or long‐term crowding for 24 h (LS‐group). The fish were filleted prerigor, cut into 270 g pieces, and packaged in modified atmosphere (60% CO₂ and 40% N₂). Fillet quality analyses were determined during 22 d of storage at 0.3 °C. Bacterial growth and unpleasant sensory properties increased earlier in the LS‐group. The negative effects of long‐term preslaughter stress were more pronounced for raw than cooked samples, and more pronounced for odor than flavor. Sequence analyses of bacterial DNA at the end of storage revealed that 100% of the bacteria were comprised by Photobacterium phosphoreum of the SS‐ and LS‐group, whereas the Control group also contained 21% of Carnobacterium maltaromaticum (lactic acid bacteria, LAB). Counting of LAB, using Man‐Rogosa‐Sharke agar, similarly showed higher numbers of the Control group after 15 d of storage. A total bacterial count of log 6 CFU/g was observed after 15 d of storage of the LS‐group, which was 3 and 7 d earlier compared with the Control and SS‐group, respectively. Fillet color, texture, and liquid losses were not negatively affected by preslaughter crowding stress. From the sensory and bacterial analyses, it is concluded that long‐term crowding stress accelerates bacterial growth and development of unpleasant sensory properties, hence reduces the shelf life of prerigor modified atmosphere packaged (MAP) salmon. Practical Application: Stressful handling of Atlantic salmon before slaughter resulted in faster reduction of fresh taste and smell, faster bacterial growth, and hence shorter shelf life. The deteriorative effects were more pronounced of raw compared to cooked salmon. Therefore, salmon should be handled carefully in connection with slaughter to avoid impaired welfare and fillet quality, in particularly for fish that is consumed raw, such as sushi.     

Impact of ‘oxidizing’ and ‘reducing’ buckwheat sourdoughs on brown rice and buckwheat batter and bread

The influence of reducing and oxidizing buckwheat sourdoughs on the rheological, protein, and bread properties of buckwheat and brown rice flour was investigated. Batters and breads prepared with chemically acidified doughs, fresh pre-doughs, and fresh pre-doughs containing glutathione (3 mM) were used as controls. No significant differences were observed after the addition of reducing and oxidizing sourdoughs in all trials. Proteolysis was observed after proofing time in buckwheat and brown rice batters, respectively. Acidified doughs increased the elasticity and the gelatinization temperature of buckwheat batters. No notable microstructure changes were detected in brown rice batters. The extension of fermentation time in sourdough caused a slight decrease in bread volumes in all trials. Sourdoughs increased the bread volume and decreased the crumb hardness of buckwheat breads. In trials with brown rice flour, the addition of sourdough did not show relevant volume differences as compared to the controls, except big voids in sourdough bread crumb. Linear correlations between hardness, volume, and cells’ density were observed. However, no clear correlations among rheological parameters and bread characteristics could be detected. These results indicated that the applied strains were responsible for the leavening capacity of the yeast during the proofing time and for crumb structure in trials with buckwheat and brown rice flour. Applied sourdoughs were able to change the molecular, and bread properties of buckwheat and brown rice bread.     

Bioactive compounds, antioxidant, xanthine oxidase inhibitory, tyrosinase inhibitory and anti-inflammatory activities of selected agro-industrial by-products

Evaluation of abundantly available agro-industrial by-products for their bioactive compounds and biological activities is beneficial in particular for the food and pharmaceutical industries. In this study, rapeseed meal, cottonseed meal and soybean meal were investigated for the presence of bioactive compounds and antioxidant, anti-inflammatory, xanthine oxidase and tyrosinase inhibitory activities. Methanolic extracts of rapeseed meal showed significantly (P < 0.01) higher phenolics and flavonoids contents; and significantly (P < 0.01) higher DPPH and nitric oxide free radical scavenging activities when compared to that of cottonseed meal and soybean meal extracts. Ferric thiocyanate and thiobarbituric acid tests results showed rapeseed meal with the highest antioxidant activity (P < 0.01) followed by BHT, cotton seed meal and soybean meal. Rapeseed meal extract in xanthine oxidase and tyrosinase inhibitory assays showed the lowest IC(50) values followed by cottonseed and soybean meals. Anti-inflammatory assay using IFN-γ/LPS stimulated RAW 264.7 cells indicated rapeseed meal is a potent source of anti-inflammatory agent. Correlation analysis showed that phenolics and flavonoids were highly correlated to both antioxidant and anti-inflammatory activities. Rapeseed meal was found to be promising as a natural source of bioactive compounds with high antioxidant, anti-inflammatory, xanthine oxidase and tyrosinase inhibitory activities in contrast to cotton and soybean meals.     

Numerical simulation of three‐dimensional gas‐solid particle flow in a horizontal pipe

A three‐dimensional model of particulate flows using the Reynolds Averaged Navier‐Stokes method is presented. The governing equations of the gas–solids flow are supplemented with appropriate closure equations to take into account all the relevant forces exerted on the solid particles, such as particle‐turbulence interactions, turbulence modulation, particle–particle interactions, particle–wall interactions, as well as gravitational, viscous drag, and lift forces. A finite volume numerical technique was implemented for the numerical solution of the problem. The method has been validated by comparing its results with the limited number of available experimental data for the velocity and turbulence intensity of the gas–particle flow. The results show that the presence of particles in the flow has a significant effect on all the flow variables. Most notably, the distribution of all the parameters becomes asymmetric, because of the gravitational effect on the particles and particle sedimentation. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Impact of the reaction conditions on the photocatalytic reduction of water on mesoporous polymeric carbon nitride under sunlight irradiation

Sacrificial hydrogen evolution was studied with sol–gel prepared carbon nitride photocatalysts loaded in-situ with platinum in a photocatalytic setup with defined geometry and a solar simulator as light source. Reaction conditions (e.g. photocatalyst concentration, triethanolamine concentration, amount of Pt precursor, water quality, etc.), and catalyst properties (e.g. BET surface area) were varied to optimize the catalysts for hydrogen evolution. We found that most of the parameters strongly influence the in-situ co-catalyst loading. The optimum platinum loading is between 0.03 and 0.09 wt%, which is less than 5% of the initial amount of platinum. A long term stability test was conducted showing a stable hydrogen evolution rate for more than 10 days indicating a stable catalyst under applied reaction conditions. We found that a change in the BET surface area affects the photocatalytic activity rather than the experimental conditions.     

数值模拟与极限平衡方法在复杂边坡优化中的应用研究

露天矿山最终边坡角的设计是否合理,将对边坡的稳定性、矿山的生产安全和经济效益产生重大影响。结合一露天矿山的二期扩采需要,采用大型非线性固-流耦合FLAC数值模拟方法进行了边坡多种方案的应力场、破坏场、监测点位移、位移速度变化趋势等多种指标分析,并采用传统的极限平衡分析方法对数值模拟分析推荐的边坡设计方案进行稳定性计算, 最后,综合分析得出最佳方案。研究表明,数值模拟方法和极限平衡方法相结合是进行复杂边坡优化的一条合理有效途径,该方法可为矿山提出安全、经济、切实可行的边坡设计方案。