DNA adsorption and desorption on mica surface studied by atomic force microscopy

The adsorption of DNA molecules on mica surface and the following desorption of DNA molecules at ethanol-mica interface were studied using atomic force microscopy. By changing DNA concentration, different morphologies on mica surface have been observed. A very uniform and orderly monolayer of DNA molecules was constructed on the mica surface with a DNA concentration of 30 ng/μL. When the samples were immersed into ethanol for about 15 min, various desorption degree of DNA from mica (0-99%) was achieved. It was found that with the increase of DNA concentration, the desorption degree of DNA from the mica at ethanol-mica interface decreased. And when the uniform and orderly DNA monolayers were formed on the mica surface, almost no DNA molecule desorbed from the mica surface in this process. The results indicated that the uniform and orderly DNA monolayer is one of the most stable DNA structures formed on the mica surface. In addition, we have studied the structure change of DNA molecules after desorbed from the mica surface with atomic force microscopy, and found that the desorption might be ascribed to the ethanol-induced DNA condensation.     

Solid-state fermentation for production of phytase by Rhizopus oligosporus

Solid-state fermentation of coconut oil cake has been carried out with Rhizopus oligosporus for the production of phytase. Phytase is used commercially in the animal feed industry to improve animal performance because there is a substantial and growing interest among swine and poultry producers in the application of phytase to improve the nutritional quality in animal feeds. Demonstrated benefits include improved feed yield ratios and reduction in the environmental costs associated with the disposal of animal wastes. We report the production of extracellular phytase by R. oligosporus under solid-state fermentation using coconut oil cake as substrate. Maximal enzyme production (14.29 U/g of dry substrate) occurred at pH 5.3, 30°C, and 54.5% moisture content after 96 h of incubation. The addition of extra nutrients to the substrate resulted in inhibition of product formation. The results indicate the scope for production of phytase using coconut oil cake as solid substrate without additional nutrients.     

Relationship between coffee husk caffeine degradation and respiration of Aspergillus sp. LPBx in solid-state fermentation

Studies were carried out in a packed-bed column fermentor using coffee husk as substrate in order to verify a relationship between caffeine degradation and the respiration of Aspergillus sp. LPBx. Fermentation conditions were optimized by using factorial design experiments. The kinetic study showed that the caffeine degradation was related to the development of mold and its respiration and also with the consumption of reducing sugars present in coffee husk. From the values obtained experimentally for oxygen uptake rate and CO₂ evolved, we determined a biomass yield of 3.811 g of biomass/g of consumed O₂ and a maintenance coefficient of 0.0031 g of consumed O₂/(g of biomass·h). The maximum caffeine degradation achieved was 90%.     

Determination of ethanol in beverages by flow injection, pervaporation and density measurements

A fast, clean and easy to automate flow injection-pervaporation method for the determination of ethanol in different beverages using density measurements is proposed. The method is based on separation of the ethanol from the sample using a pervaporation module; the analyte being collected in water as acceptor liquid. The density of this water-alcohol mixture is measured at the detector. After optimisation by either a univariate or multivariate approach as required, a linear range between 0 and 40% was established. Then, the assessment of the method versus a reference one was studied in terms of repeatability (0.12% v/v), reproducibility (0.32% v/v), detection limit (0.11% v/v) and traceability. The sample throughput was 15 samples h⁻¹. The method was in agreement with the reference methods used in the European Union.     

The role of co-adsorbed O2 on the catalytic reduction of NO with C2H5OH on the surface of Pt(3 3 2)

The influence of pre-dosed O₂ on the catalytic reduction of NO with ¹³C₂H₅OH on the surface of stepped Pt(3 3 2) was investigated using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). We show that the oxidation of ¹³C₂H₅OH with O₂ is a very effective reaction, occurring at 150 K and giving rise to acetate. The presence of NO does not lead to any evident oxidation of ¹³C₂H₅OH irrespective of the annealing temperature. For the case of O₂ + ¹³C₂H₅OH + NO co-adlayers, oxidation of ¹³C₂H₅OH also takes place at 150 K. However, no new surface species that are supposed to be an intermediate for the production of N₂ are detected.The influence of O₂ on the production and desorption of N₂ is intimately related to both O₂ and ¹³C₂H₅OH coverage. The presence of pre-dosed O₂ does not greatly promote N₂ desorption. In fact, N₂ desorption is suppressed quantitatively with increasing O₂ coverage, after which unreacted, or left-over O atoms appear and remain on steps. It is concluded that the presence of pre-dosed O₂ does not play a role of activating reactants in the catalytic reduction of NO with ¹³C₂H₅OH on the surface of Pt(3 3 2).     

SiO2 Xerogel: A Suitable Inert Support for Microbial Growth

A silica xerogel was prepared at pH 2 by the hydrolysis-condensation reactions of the sol-gel method. Silica xerogel was used as a support for the growth of two filamentous fungi: Aspergillus niger ATCC 9642 and Phanerochaete chrysosporium A594. In both cases, an apparent abundant mycelia growth (5.5 mg biomass/g dry xerogel and 4.7 mg biomass/g dry xerogel respectively) was observed. A phase of rapid consumption of glucose which lasted until 96 h of culture with sugar consumption rate of 0.075 mg sugar/g support h and 0.042 mg sugar/g support h respectively, was also observed. Scanning electron microscopy (SEM) showed a superficial colonisation of both strains even in the occasional imperfections and crevices of the xerogel. This novel application of sol-gel metallic oxide systems suggests the potential use of an inert and versatile support which could be valuable, for example for solid state fermentation fundamental studies.     

Effect of oxygen addition on the hydrogen production from ethanol steam reforming in a Pd–Ag membrane reactor

In this communication, a porous stainless steel (PSS) tube was electrolessly plated into Pd–Ag membrane reactor which was used for separating hydrogen produced in an ethanol steam reforming reaction with the addition of oxygen, which has not been reported before. Palladium and silver were deposited on porous stainless steel tube via the sequential electroless plating procedure with an overall film thickness of 20 μm and Pd/Ag weight ratio of 78/22. Ethanol–water mixture (n_water/n_ethanol = 1 or 3) and oxygen (n_oxygen/n_ethanol = 0.2 or 0.7) were fed concurrently into the membrane reactor packed with MDC-3. The reaction temperatures were set at 593–723 K and the pressures 3–10 atm. The effect of oxygen addition plays a vital role on the ethanol steam reforming reaction, especially for the Pd–Ag membrane reactor in which a higher flux of hydrogen is required. If oxygen in the feed is not sufficient, it would be possible that steam reforming reaction prevails. Inversely, high O₂ addition will shift the reaction scenario to be partial oxidation dominating, and selectivity of CO₂ increases with increasing oxygen feed. At high pressure, autothermal reaction of ethanol would be easily reached.     

Hydrogen Production by Steam Reforming of Ethanol: A Two Step Process

A two-layer fixed-bed catalytic reactor for hydrogen production by steam reforming of ethanol is proposed. In this reactor ethanol is first converted to acetaldehyde over a Cu-based catalyst and then acetaldehyde is converted to a hydrogen-rich mixture over a Ni-based catalyst. It is shown that the use of such type of reactor prevents coke formation and provides hydrogen yields closed to equilibrium.