Constant pH Levels Research Articles

Comparative Analysis of Calcium and Hydroxyl Ion Release from Pulp Dressing Materials in Pulpotomized Premolars.

BACKGROUND The aim of this study was to evaluate the time-dependent release of calcium (Ca⁺⁺) and hydroxyl (OH⁻) ions from 3 different pulp dressing materials used to cap root canal orifices in pulpotomized premolars. MATERIAL AND METHODS Freshly extracted (n=40) premolars were subjected to standardized pulpotomy procedure and finally restored in 5 groups using resin-modified glass ionmmer liner (RMGI) and bonded resin composite directly against the pulp chamber's floor (Control, G2) and over 3 different orifices' capping materials - Dycal (G3), Endo Sequence root repair material (ESRRM, G4), and mineral trioxide aggregate (MTA) Angelus (G5). Another 10 sound premolars served as the Reference group (G1). The restored teeth were incubated at 37±1°C in sealed containers filled with deionized water to assess Ca⁺⁺ and OH⁻ ions release after 24 h and at 1, 4, and 8 weeks. Two-way ANOVA and Tukey's comparisons at alpha=0.05 were used to statistically analyze the collected data. RESULTS Two-way ANOVA revealed significant differences in Ca⁺⁺ ions between test groups at different testing time intervals (P<0.05). Despite the constant (Tukey's, P<0.05) pH levels (OH⁻ release), Group 5 specimens exhibited higher Ca⁺⁺ ion release in comparison to Groups 4 and 3 at different testing timepoints (Tukey's, P<0.05). CONCLUSIONS Although all the assessed pulp dressing materials had equivalent and stable pH levels, ESRRM and MTA-Angelus had the highest Ca⁺⁺ ion release at the assessment intervals.

Bipolar Membranes for Photoelectrochemical CO2 Conversion

CO2 capture and conversion represent one of the most critical challenges of our society. One sustainable approach to tackle it is the development of electrochemical processes coupling a solar-driven carbon dioxide reduction to CO/water oxidation to O2 with reactions leading tohigh-value products. In such photoelectrochemical reactors, (photo)electrocatalysts and membranes play a crucial role to achieve high CO2 conversion with minimum energy.The aim of this study is developing polymer membranes with high stability, mechanical resistance and ion conductivity, that can work in the broad pH operation range of CO2/H2O co-electrolysis cells. Consistently with the use of KOH at the anode, the used membrane is often an anion exchange membrane (AEM). However, carbonate crossover through AEM occurs during CO2 electrolysis via diffusion and migration. [1] The use of a bipolar membrane (BPM) allows to mitigate this issue, bringing novel challenges of stability and performance.The BPM consists in a cation exchange layer (CEL) and an anion exchange layer (AEL), with a bipolar junction formed at their interface. Such membrane must guarantee a constant pH level generating H+ and OH- by water dissociation at the junction, avoid product crossover, and optimize mass transfer and reactivity of coupled anodic and cathodic reactions. A crucial point is the control of the electrochemical behavior at the CEL/AEL interface. With this aim, a 3D-structure made of a network of fibers was developed [2, 3] providing a great interfacial area and mechanical interlocking of the anion and cation exchange ionomers preventing delamination and facilitating the exchange of ions and matter at the interface. Furthermore, such fiber webs allow the controlled deposition of inorganic or organic catalysts to enhance the water dissociation rate at the bipolar junction.The bipolar membrane was prepared interposing a web of electrospun fibers bearing water dissociation nanocatalysts at the interface between anion and cation exchange polymer layers. The prepared BPMs were characterized for their morphology, composition, ion conductivity, and performance.This work has been performed with the financial support of the European Union’s Horizon 2020 Research and Innovation Action Program under the project SunCoChem (Grant agreement No 862192).

Quantifying Variability in Zebrafish Larvae Locomotor Behavior across Experimental Conditions: A Learning-Based Tracker

This study investigated the effects of environmental changes on zebrafish larval behavior, using single-factor and orthogonal experiments to assess locomotion during temperature and pH changes. In single-factor experiments, zebrafish larvae were exposed to variations in temperature (22 to 30 °C) and pH levels (6.0, 7.0, 9.0). The simultaneous temperature and pH changes were investigated by orthogonal tests. In both experiments, each zebrafish larva was recorded in three 5 min videos at different stages (before exposure, during short-term exposure (10 min), and after long-term exposure (60 min)). You Look Only Once (YOLOv5) and Deep Simple Online Real Time Tracking (DeepSORT) models were adopted to develop a zebrafish larva tracking system, and YOLOv5 was improved in two aspects of anchor clustering and network structure. The tracking accuracy of the tracking system for small targets effectively improved, reaching more than 98% MOTA (Multiple Object Tracking Accuracy). Principal Component Analysis (PCA) was employed to extract three behavioral features from 13 motion parameters, namely motion activity, edge behavior, and motion direction preference. Our findings reveal that lower temperatures and acidic conditions both led to a decrease in motion behavioral activity, and the former also increased edge behavior. Conversely, elevated temperatures and alkaline conditions had a muted impact on these behaviors. Interestingly, concurrent changes in temperature and pH significantly altered directional preference. Additionally, we observed that lower temperatures elicited distinct temporal behavioral patterns at a constant pH level. In summary, we recommend the precise control and explicit reporting of ambient temperature and pH in both breeding devices and experimental wells to minimize the environmental impact on zebrafish behavior and enhance experiment repeatability and reliability.

A novel approach for the lifetime prediction and structural health monitoring of concrete sewer systems exposed to biogenic sulphide corrosion

A novel, combined experimental-modelling approach is presented for the estimation of the corrosion depth, load bearing capacity and lifetime of unreinforced concrete sewer pipes exposed to prolonged biogenic sulphide corrosion. The biogenic sulphide corrosion process is mimicked through two types of representative chemical experiments, namely: (i) long-term experiments performed under moderately controlled pH conditions, where dry-cast concrete cube samples are exposed to monthly refreshed sulphuric acid solutions with initial pH values of 3, 2 and 1 for a period of 12 months, and (ii) short-term experiments carried out under highly controlled pH conditions, in which dry-cast concrete disk samples are subjected to sulphuric acid solutions with almost constant pH values of 2, 1 and 0.5 for a period of two months. By applying X-ray diffraction, optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy analyses, insight into the micro-scale morphology and elemental composition of the corrosion profile is obtained. In addition, the corrosion front and depth characteristics are measured by conducting phenolphthalein tests and analyses of surface colour and texture of macro-scale samples. From the experimental results, the time course of the corrosion depth is calibrated with a model for sulphate attack under a constant pH level. The model formulation is combined with detailed finite element method results from the literature to predict the long-term load bearing capacity of a concrete sewer pipe. The model is subsequently generalised for sulphate corrosion under a varying pH level. When combined with the installation of pH measuring devices on the inside of sewer pipes, the current engineering model may serve as an excellent practical tool for continuously monitoring the structural health and predicting the lifetime of in-situ sewer systems subject to sulphate attack under random acidity fluctuations.

Methane Production Characteristics of an Anaerobic Co-Digestion of Pig Manure and Fermented Liquid Feed.

Methane production characteristics of anaerobic co-digestion of pig manure (PM) and fermented liquid feed (FLF) were investigated in a continuous digester under mesophilic conditions. The experiment followed three phases. PM alone was digested in phase I. In phases II and III, PM and FLF were mixed in a ratio of 95:5 and 90:10 (% v/v), respectively. The specific methane yields (SMYs) during phases I, II, and III were 238, 278, and 326.8 mLCH4·gVS−1-added, respectively. It was due to the effect of balancing the feedstock carbon-to-nitrogen ratio by adding FLF. This improvement can also be attributed to the readily biodegradable compounds in the FLF. The higher SMY obtained in this study showed a positive synergistic effect in the anaerobic co-digestion of PM and FLF. The results also indicate that adding the FLF positively affected and maintained a constant pH level, avoiding volatile fatty acid accumulation and ammonia inhibition in the anaerobic digestion (AD). Thus, this study provides valuable information regarding the usage of unused or wasted FLF as a co-substrate for the practical AD of PM. The production of fermented liquid additives such as FLF to improve the methane production from the AD of PM is a potential novel alternative to food waste recycling in Japan, besides compost and animal feeding.

The influence of environmental factors on seed germination of Xanthium strumarium L.: Implications for management.

Xanthium strumarium L. (Common cocklebur) is a noxious weed prevailing in different ecosystems around the world. It incurs significant yield and economic losses in different cropping systems globally. Successful management of any weed species depends on sound knowledge of seed germination biology. However, detailed knowledge on seed germination biology of the species is missing. Therefore, we investigated the impact of different environmental factors on seed germination and seed burial depths on seedling emergence of two X. strumarium populations. The impact of different sorghum mulch doses (0–10 t ha-1) on seedling emergence of the tested populations was also explored. Seed germination was evaluated under different photoperiods (0, 12 and 24), constant temperatures (0–50°C with 5°C stepwise rise), and different levels of pH (3–12), salinity (0–600 mM) and osmotic potential (0 to -1.6 MPa). Seedling emergence was observed for seeds buried at different depths (0–15 cm). Seeds of both populations proved non-photoblastic; however, higher germination was recorded under 12-hour photoperiod. The seeds germinated under a wide range of constant temperatures (10–45°C), pH (4–10), osmotic potentials (0 to -0.8 MPa) and salinity levels (0–400 mM NaCl). However, the highest germination was observed under 30–31°C temperature and neutral pH (7.51–7.52). Seeds were able to withstand 400 mM salinity and -1.00 MPa osmotic potential. Seedling emergence was initially improved with increasing burial depth and then a sharp decline was noted for the seeds buried >3 cm depth. Most of the seeds of both populations did not emerge from >8 cm depth. Different sorghum mulch doses linearly suppressed seedling emergence of tested populations, and 5.83–5.89 t ha-1 mulch application suppressed 50% of seedling emergence. Seedling emergence was completely retarded with 8 t ha-1 sorghum mulch. The tested populations germinated under diverse environmental circumstances indicating that the species can become troublesome in marginal habitats and cropped lands. Deep burial of seeds and application of sorghum mulches suppressed seedling emergence. Thus, deep burial followed by shallow tillage and application of sorghum mulches could be used as a successful strategy to manage the species in agricultural fields. Nonetheless, management strategies must be developed to control the species in other habitats.

Application of sodium hydrocarbonate solution on purpose of correction acid-base state in patient with comorbid pathology – COPD and community-acquired pneumonia

Background. Community-acquired pneumonia is a frequent complication of chronic obstructive pulmonary disease (COPD), especially in patients with small weight. Respiratory acidosis is a natural manifestation of COPD, which clinically is characterized by dominated obstructive pulmonary ventilation. Respiratory acidosis is a form of acid-base deviation which associated with insufficient excretion of carbon dioxide by the lungs. But in patients with comorbid pathology (COPD and community-acquired pneumonia) in addition to respiratory acidosis also can be evolved a metabolic acidosis (MA) conditioned by tissue hypoxia, intense systemic inflammation with next disturbances in correlation between pro-inflammatory and anti-inflammatory mediators, accelerating catabolic processes. The severity of acid-base deviation in patients with the possibility of developing decompensated acidosis depends not only on the degree of obstructive ventilation disorders, but also increasingly to the gravity of community-acquired pneumonia which causes severe acidotic metabolic changes.&#x0D; Objective. To evaluate the expediency of application 4.2 % buffered sodium bicarbonate solution (Soda-buffer) in the case of mixed acidosis in patients with comorbid pathology: COPD which is compounded by community-acquired pneumonia.&#x0D; Materials and methods. To all patients with comorbid pathology aged from 18 to 75 were prescribed the drug Soda-buffer manufactured by “Yuria-Pharm” (Ukraine), which contains 42 mg of sodium bicarbonate intravenously at a rate of 1.5 mmol/kg per hour (4.2 % Soda-buffer – 3 ml/kg per hour) under control of blood pH, acid-base and water-electrolyte (water-salt) balance of the body.&#x0D; Results and discussion. Qualified treatment of patients with comorbid pathology (COPD and community-acquired pneumonia) should be comprehensive and directed towards the struggle against the manifestations of obstructive ventilation disorders and hypoxemia, lower respiratory tract infection, intense inflammatory process in the lung parenchyma and bronchial tree. The complex treatment includes not only modern antibacterial drugs in combination with systemic glucocorticoids, but also methods of correction of metabolic, hemodynamic and coagulation disorders. With the aim of acidosis correction the most effective way is using infusion solutions which contain sodium bicarbonate. Due to dissociation of sodium bicarbonate has released a bicarbonate anion that binds hydrogen ions to form of carbonic acid, which then decomposes into water and carbon dioxide. In case of severe respiratory insufficiency oxidation of sodium hydrocarbonate can contribute increasing of hypercapnia by the connection with the accumulated CO2. It was found that 4.2 % buffered sodium bicarbonate solution in the comprehensive therapy of patients with comorbid pathology of COPD and community-acquired pneumonia helps to restore acid-base balance, reduce metabolic disorders and improve the clinical condition of patients. In the matter of normalization of the function of external respiration and reduction of the manifestations of respiratory insufficiency, usually substantially reduces not only respiratory, but also MA. Therefore, during correction of concomitant MA by Soda-buffer we should compensate the deficiency of bases not more than half percentage. In situation with rapid balancing of acidosis, particularly in the case of impaired pulmonary ventilation, the rapid release of CO2 may exacerbate cerebral acidosis. It’s a well known fact that small uses of Soda-buffer together with other infusion solutions with an acidic pH are provided a neutralizing agent and prevent the appearance of post-infusion phlebitis after administration of widely used infusion solutions (glucose fluids of different concentrations, chloride solution, ciprofloxacin and some other fluoroquinolones).&#x0D; Conclusions. Soda-buffer (4.2 % sodium bicarbonate buffered solution) is an effective infusion agent for the correction of MA in patients with comorbid pathology (COPD and community-acquired pneumonia) in condition of provided effective gas exchange. This solution is a physiological bicarbonate buffer that maintains a constant pH level, prevents abrupt alkalization of the blood and provides a smooth correction of acidosis at the same time with increasing alkaline blood reserves. The drug also increases the excretion of sodium and chlorine ions, osmotic diuresis, alkalizes urine.

Ultra-low noise system to detect membrane capacitive currents of C6 Glioma cells

Event Abstract Back to Event Ultra-low noise system to detect membrane capacitive currents of C6 Glioma cells Paulo R. Rocha1* and Dago De Leeuw2 1 University of Bath, Department of Electronic & Electrical Engineering, United Kingdom 2 Delft University of Technology, Netherlands Recording minuscule electrical activity of cell populations is currently a major technical challenge to electrophysiology. For this purpose we built an extremely low-noise measuring system. The sensing system comprises a bidirectional transducer based on a metal/Si/SiO2/interdigitated gold electrode. The highly doped Si substrate can be used as a common gate to stimulate the cells. In order to reduce external interferences the transducer was located inside an incubator and all the instrumentation shielded by a faraday’s cage. The background noise level with only cell culture medium was less than 100 fA. [1-3] Bioelectric activity is recorded by measuring the capacitive current using zero bias at the electrodes. To validate the extreme sensitivity of the measuring system, we investigated the electrical activity of large populations of two cell lines known to be electrically quiescent. The cell lines studied were the human cervix carcinoma cell line, HeLa, and C6 glioma cells. HeLa cells are supposed to be electrically quit as they don’t originate from the brain or any other electrically excitable tissue. However, due to the high sensitivity of our measurement system, even the HeLa cells demonstrate fluctuations of their basal current level, which is much higher in amplitude than the background acquisition noise. The low frequency analysis of the HeLa cells reveals clear current fluctuations of about 3 pA. [3] Non-neuronal cell types such as glia and their transformed counterparts, glioma cells, exhibit distinctive single-cell oscillations in membrane potential, which are highly functional and coordinated. However, measurement of their subtle electrical activity is typically hampered by the high background noise. Here we demonstrate that we can detect the electrical behavior of entire large cell populations of C6 glioma cells without any physical disruption or interference into their physiology. Malfunctioning glioma cells can develop to brain tumors. Glioma patients often suffer from epileptic seizures due to the tumors impact on brain electrophysiology. Here we show that seizure-like events in glioma cells spontaneously appear and evolve from a few pA to more than 100 pA on a time scale of hours. A direct correlation between electrical bursting and extracellular pH reduction was accomplished. Furthermore, at constant pH levels, a current noise analysis could determine that the glioma cell activity is primarily caused by the opening of voltage-gated Na+ and K+ ion channels and can be efficiently abolished using specific pharmacological inhibitors. We argue that our measuring system is unique to study electrophysiological properties of large cancer cell populations as an in vitro reference for tumor bulks in vivo.

The use of oxidising agents for control of electrochemical potential in flotation

Relating flotation performance to the electrochemical characteristics of a pulp remains a complex issue both in fundamental research and in practice. For example, in the case of thiol collectors different Eh values can result in the formation of the dimer or the metal thiolate which may or may not enhance the hydrophobicity of the mineral. Reducing or oxidising conditions in a flotation system, viz. changing the Eh value, are usually manipulated to achieve an optimum flotation response by the control of pH and dissolved oxygen levels in the system. It is also possible to vary the potential by the addition of modifiers such as sodium hydrosulphide (NaHS), sodium hypochlorite (NaClO) and hydrogen peroxide (H2O2). The objective of the present study was to investigate the effect of the addition of the oxidising agents, NaClO and H2O2, on valuable mineral recoveries and grades in the flotation of sulphides from a PGM bearing Merensky ore. Batch flotation tests were conducted at pH 9.2, the natural pH of the system, in the absence and presence of a xanthate collector and Eh modifiers, viz. NaClO or H2O2. Most importantly in this way it was possible to vary Eh at constant pH and DO levels. The results indicate that in the absence or presence of xanthate the addition of H2O2 reduced both the recovery and grade of copper and nickel. In the absence of xanthate, the addition of NaClO improved the recovery of copper slightly and both the recovery and grade of nickel significantly, but in the presence of xanthate NaClO addition resulted in unchanged copper recovery and grade, but those of nickel were reduced. Based on anecdotal evidence that the addition of trace amounts of a potential modifier could improve flotation performance further tests were conducted the results of which suggest improved flotation performance.

Effect of FeO/MgO Ratio on Dissolution and Leaching of Magnesiowüstite

If slag is to be used as construction material, the leaching of some elements, such as chromium must be limited. The leaching of slag depends on the leaching properties of the minerals in the slag. However, the leaching/dissolution properties of individual slag minerals are usually not studied. One common slag mineral that can contribute to the leaching of chromium is magnesiowüstite. The object of this study is to determine whether magnesiowüstite can be modified to avoid chromium leaching. Magnesiowüstite samples with different FeO/MgO ratios with and without chromium content are manufactured. The dissolution is evaluated at pH 7 and 10 using the magnesiowüstite samples without chromium, at size fraction 20–38 μm, by measuring the acid consumption required to maintain constant pH level. The magnesiowüstite samples with chromium content are leached at pH 10; the leachate is analyzed for chromium. The results are unanimous, with increasing FeO content the dissolution of magnesiowüstite and leaching of chromium decrease. At pH 10 the magnesiowüstite, with ≥60 wt% FeO show no sign of dissolution and no chromium leaching could be detected with ≥70 wt% FeO. The results prove that the FeO content can stabilize magnesiowüstite and, thereby, prevent chromium leaching.

XANES Demonstrates the Release of Calcium Phosphates from Alkaline Vertisols to Moderately Acidified Solution.

Calcium phosphate (CaP) minerals may comprise the main phosphorus (P) reserve in alkaline soils, with solubility dependent on pH and the concentration of Ca and/or P in solution. Combining several techniques in a novel way, we studied these phenomena by progressively depleting P from suspensions of two soils (low P) using an anion-exchange membrane (AEM) and from a third soil (high P) with AEM together with a cation-exchange membrane. Depletions commenced on untreated soil, then continued as pH was manipulated and maintained at three constant pH levels: the initial pH (pHi) and pH 6.5 and 5.5. Bulk P K-edge X-ray absorption near-edge structure (XANES) spectroscopy revealed that the main forms of inorganic P in each soil were apatite, a second more soluble CaP mineral, and smectite-sorbed P. With moderate depletion of P at pHi or pH 6.5, CaP minerals became more prominent in the spectra compared to sorbed species. The more soluble CaP minerals were depleted at pH 6.5, and all CaP minerals were exhausted at pH 5.5, showing that the CaP species present in these alkaline soils are soluble with decreases of pH in the range achievable by rhizosphere acidification.

Modeling and predicting the biofilm formation of Salmonella Virchow with respect to temperature and pH.

Biofilm formation of Salmonella Virchow was monitored with respect to time at three different temperature (20, 25 and 27.5 °C) and pH (5.2, 5.9 and 6.6) values. As the temperature increased at a constant pH level, biofilm formation decreased while as the pH level increased at a constant temperature, biofilm formation increased. Modified Gompertz equation with high adjusted determination coefficient (Radj(2)) and low mean square error (MSE) values produced reasonable fits for the biofilm formation under all conditions. Parameters of the modified Gompertz equation could be described in terms of temperature and pH by use of a second order polynomial function. In general, as temperature increased maximum biofilm quantity, maximum biofilm formation rate and time of acceleration of biofilm formation decreased; whereas, as pH increased; maximum biofilm quantity, maximum biofilm formation rate and time of acceleration of biofilm formation increased. Two temperature (23 and 26 °C) and pH (5.3 and 6.3) values were used up to 24 h to predict the biofilm formation of S. Virchow. Although the predictions did not perfectly match with the data, reasonable estimates were obtained. In principle, modeling and predicting the biofilm formation of different microorganisms on different surfaces under various conditions could be possible.

Development of an Extracorporeal Perfusion Device for Small Animal Free Flaps.

BackgroundExtracorporeal perfusion (ECP) might prolong the vital storage capabilities of composite free flaps, potentially opening a wide range of clinical applications. Aim of the study was the development a validated low-cost extracorporeal perfusion model for further research in small animal free flaps.MethodsAfter establishing optimal perfusion settings, a specially designed extracorporeal perfusion system was evaluated during 8-hour perfusion of rat epigastric flaps followed by microvascular free flap transfer. Controls comprised sham-operation, ischemia and in vivo perfusion. Flaps and perfusate (diluted blood) were closely monitored by blood gas analysis, combined laser Doppler flowmetry and remission spectroscopy and Indocyanine-Green angiography. Evaluations were complemented by assessment of necrotic area and light microscopy at day 7.ResultsECP was established and maintained for 8 hours with constant potassium and pH levels. Subsequent flap transfer was successful. Notably, the rate of necrosis of extracorporeally perfused flaps (27%) was even lower than after in vivo perfusion (49%), although not statistically significant (P = 0,083). After sham-operation, only 6% of the total flap area became necrotic, while 8-hour ischemia led to total flap loss (98%). Angiographic and histological findings confirmed these observations.ConclusionsVital storage capabilities of microvascular flaps can be prolonged by temporary ECP. Our study provides important insights on the pathophysiological processes during extracorporeal tissue perfusion and provides a validated small animal perfusion model for further studies.

A biologically inspired variable-pH strategy for enhancing short-chain fatty acids (SCFAs) accumulation in maize straw fermentation

This study investigates the feasibility of varying the pH to enhance the accumulation of short-chain fatty acids (SCFAs) in the in vitro fermentation of maize straw. The corresponding hydrolysis rate and the net SCFA yield increased as inoculum ratio (VSinoculum/VSsubstrate) increased from 0.09 to 0.79. The pH were maintained at 5.3, 5.8, 6.3, 6.8, 7.3, and 7.8, respectively. A neutral pH of approximately 6.8 was optimal for hydrolysis. The net SCFA yield decreased by 34.9% for a pH of less than 5.8, but remained constant at approximately 721±5mg/gvs for a pH between 5.8 and 7.8. In addition, results were obtained for variable and constant pH levels at initial substrate concentrations of 10, 30 and 50g/L. A variable pH increased the net SCFA yield by 23.6%, 29.0%, and 36.6% for concentrations of 10, 30 and 50g/L. Therefore, a variable pH enhanced SCFA accumulation in maize straw fermentation.

A mathematical model of the effect of pH and food matrix composition on fluid transport into foods: An application in gastric digestion and cheese brining

The question of bioaccessibility of nutrients within a food matrix has become of increasing interest in the fields of nutrition and food science as bioaccessibility is the precursor to bioavailability. By analyzing the propagation of the wetting front of acidic water in raw carrot core and Edam cheese as model systems, we show that the diffusion of the acidic water is dependent on the pH of the gastric fluid and the food matrix. In addition, we demonstrate that the diffusion of NaCl during cheese brining is also dependent upon the concentration of the NaCl. This demonstrates that Fickian diffusion, along with a concentration dependent diffusion coefficient, is a valid model for describing concentration profiles in multiple food systems.Utilizing the diffusion rates found at various pH levels (1.50, 2.00, 3.50, 4.30, 5.25 and 7.00), we developed a model to describe the measured non-linear rate of soluble solid loss during digestion at various constant pH levels. Additionally, we have developed a model to predict the likely rate of soluble solid loss during digestion in the stomach where pH decreases with time. This model can be used to help understand and optimize the relationship between food structure/composition and food degradation in the human stomach, which may help in the development of novel foods with desired functionality.

Seasonal dynamics in water quality and vegetation cover in temporary pools with variable hydroperiods in Kiskunság (Hungary)

The seasonal dynamics in habitat characteristics of temporary freshwater pools were studied in relation to hydroperiod and geographical location for a set of 36 pristine pools in and around the Kiskunsag National Park (Hungary). The pools were geographically distributed over three clusters and their hydroperiod varied from seven to more than 18 weeks. Biweekly to monthly monitoring started two weeks after inundation (March) and lasted until most pools were dry again (July). Throughout the season, nutrient concentrations and conductivity increased in all study pools. Algal biomass increased after short hydroperiod pools were already dry, resulting in an increase in the amount of suspended solids and turbidity in pools with a relatively long hydroperiod. Both the longer inundation period and conditions later in the season may have contributed to the stronger algal growth in these pools. Oxygen was not depleted towards the end of the season, potentially due to growing algae and vegetation. The high buffering capacity of the water may have contributed to the near constant pH levels through time. Pools in one of the clusters were typically more turbid, less vegetated, and had higher amounts of suspended matter when compared to pools in the two other clusters. Temporary pool characteristics were related to local environmental conditions and seasonal dynamics differed according to the duration of inundation.

Dark fermentative [formula omitted] production from xylose and lactose—Effects of on-line pH control

Although xylose and lactose, two major carbohydrates existing in lignocellulosic and dairy wastes, are produced in huge amounts every year, their potentials in dark fermentative H 2 production were not investigated sufficiently and the optimum fermentation pH is still unclear particularly at thermophilic temperatures. Therefore, in this study, the influence of pH on fermentative H 2 production from xylose and lactose was investigated using a mixed culture compost inoculum. Completely mixed thermophilic ( 55 ∘ C ) bioreactors were operated in sequential batch mode at constant pH levels between 4.7 and 6.5. The highest H 2 yield in fermentation of xylose was achieved as 1.70 mol/mol at pH 5.0. The H 2 yield was strongly affected by the level of pH and butyrate fermentation. The unsatisfactory yields were associated with lactate fermentation at pH 4.7 and without pH control and with ethanol formation at pH 6.0. The optimal pH for stable H 2 yield from lactose was suggested to be 5.3 considering the molar yields increased to a maximum of 3.45 mol H 2 / mol hexose sugar . Another indication of efficient H 2 production at pH 5.3 was the metabolic shift from ethanol to butyrate fermentation. Acetate fermentation yielding H 2 below stoichiometric ratios especially in low H 2 yielding runs revealed that some portion of the H 2 was consumed by acetogenic bacteria.

Acetate-mediated pH-stat fed-batch cultivation of transconjugant Enterobacter sp. BL-2S over-expressing glmS gene for excretive production of microbial polyglucosamine PGB-1

A unique cationic polyglucosamine biopolymer PGB-1 comprising more than 95% D-glucosamine was excretively produced from a new bacterial strain Enterobacter sp. BL-2 under acetate-mediated culture conditions. Since the biopolymer PGB-1 could be synthesized from the UDP-N-acetylglucosamine monomer derived from the hexosamine pathway, three glmS, glmM, and glmU genes in the hexosamine pathway were cloned from Enterobacter sp. BL-2, and their molecular structures were elucidated. The cloned glmS, glmM, and glmU genes were reintroduced into the parent strain Enterobacter sp. BL-2 through a conjugative transformation for the overproduction of the biopolymer PGB-1. The biopolymer production increased 1.5-fold in the transconjugant Enterobacter sp. BL-2S over-expressing the first-step glmS gene encoding glucosamine-6-phosphate synthase. The transconjugant Enterobacter sp. BL-2S was cultivated pH-stat fed-batch widely, while intermittently feeding an acetate solution to maintain a constant pH level of 8.0 for 72 h, resulting in 1.15 g/L of the extracellular polyglucosamine biopolymer PGB-1.

Erosive effects of different acids on bovine enamel: release of calcium and phosphate in vitro

The present study intended to investigate minimal erosive effects of different acids on enamel during short time incubation via determination of calcium and phosphate dissolution. Bovine enamel specimens were eroded for 1-5 min with eight different acids of pH 2, 2.3 and 3 (citric (CA), maleic (MA), lactic (LA), tartaric (TA), phosphoric (PA), oxalic (OA), acetic (AA) and hydrochloric acid (HCl)). Calcium (Ca) and phosphate (P) release were determined photometrically using arsenazo III (calcium) and malachite green (phosphate) as substrates. Each subgroup contained eight enamel specimens. Amount of titratable acid was determined for all acidic solutions. MA, LA, TA, AA and HCl caused linear release of Ca and P, PA of Ca, CA of P. For CA, MA, LA, TA, AA, PA and HCl mineral loss was shown to be pH-dependent. Ca dissolution varied between 28.6+/-4.4 (LA, pH 2) and 2.4+/-0.7 nmol mm(-2)min(-1) (HCl, pH 3), P dissolution ranged between 17.2+/-2.6 (LA, pH 2) and 1.4+/-0.4 nmol mm(-2)min(-1) (HCl, pH 3). LA was one of the most erosive acids. AA was very erosive at pH 3. HCl and MA were shown to have the lowest erosive effects. There was only a weak correlation (r=0.28) between P and Ca release and the amount of titratable acid. The method of the present study allows investigation of minimal erosive effects via direct determination of P and Ca dissolution. During short time exposition at constant pH level, erosive effects mainly depend on pH and type of acid but not on amount of titratable acid.

Changes in oxygen content and acid-base balance in arterial and portal blood in response to the dietary electrolyte balance in pigs during a 9-h period after a meal.

The effect of two dietary electrolyte balance (dEB, Na+ + K+ - Cl-) levels on arterial and portal blood oxygen content, blood pH, and acid-base status in pigs was studied during a 9-h period after a meal, using a crossover experimental design. The dEB levels were established by changing the Cl- level in the diets. Four pigs with a mean weight of 45 kg were surgically fitted with catheters in the carotid artery and portal vein. Two dEB levels (-100 and 200 mEq/kg) were evaluated in two periods of 1 wk each. Feed was given at 2.6 times the maintenance requirement for energy in two meals per day. Water was freely available. Blood samples were taken at 0, 0.5, 1, 1.5, 2, 3, 4, 6, and 9 h after feeding. Blood hemoglobin; O2 pressure; O2 saturation; O2 content; pH; PCO2; HCO3-; base excess; and Na+, K+, and Cl- contents were measured. Oxygen contents in arterial and portal blood were lower (P < 0.008) in the -100 mEq/kg group (5.78 and 4.82 mmol/L respectively) compared to the 200 mEq/kg group (6.18 and 4.99 mmol/L respectively). This was related to the lower hemoglobin content in the blood of animals in the -100 mEq/kg group. Arterial and portal blood pH were lower (P < 0.003) at -100 mEq/kg (7.46 and 7.37) than at 200 mEq/kg (7.49 and 7.43). The difference in blood pH between the two groups was sustained throughout the sampling period. The average values of arterial and portal blood for base excess and HCO3- content were higher (P < 0.001) at high dEB (6.96 and 31.0 mmol/L, respectively, for -100 mEq/kg and 12.54 and 35.9 mmol/ L, respectively, for 200 mEq/kg). The Na+ concentration in the blood was increased and K+ and Cl- concentrations were decreased (P < 0.02) by increasing dEB from -100 mEq/kg to 200 mEq/kg. Blood electrolyte balance level was higher (P < 0.001) in the 200 mEq/kg dEB group than in the -100 mEq/kg dEB group. In conclusion, dEB changed blood oxygen content and pH, and influenced the acid-base buffer system in pigs. Also, within each group, pigs maintained a relatively constant blood pH level during the 9-h period after feeding.