Zeolite-Loaded Hydrogels as Wound pH-Modulating Dressings for Diabetic Wound Healing

Wound pH has emerged as a promising therapeutic target in diabetic foot ulcers (DFU). Here, we aimed to develop a microparticle-loaded hydrogel for pH modulation in wound fluid. In a screen of polymeric and inorganic microparticles, zeolites were identified as pH-modulating microparticles. Zeolites were encapsulated in a calcium cross-linked alginate hydrogel, a biocompatible matrix clinically used as a wound dressing. This hydrogel potently neutralized hydroxide ions in serum-containing simulated wound fluid. These findings encourage a further development of this pH-modulating device as a molecular therapeutic system for DFUs.

Does Media Choice Matter When Evaluating the Performance of Hydroxypropyl Methylcellulose Acetate Succinate-Based Amorphous Solid Dispersions?

Hydroxypropyl methylcellulose acetate succinate (HPMCAS) is a weakly acidic polymer that is widely used in the formulation of amorphous solid dispersions (ASDs). While the pH-dependent solubility of HPMCAS is widely recognized, the role of other solution properties, including buffer capacity, is less well understood in the context of ASD dissolution. The goal of this study was to elucidate the rate-limiting steps for drug and HPMCAS release from ASDs formulated with two poorly water soluble model drugs, indomethacin and indomethacin methyl ester. The surface area normalized release rate of the drug and/or polymer in a variety of media was determined. The HPMCAS gel layer apparent pH was determined by incorporating pH sensitive dyes into the polymer matrix. Water uptake extent and rate into the ASDs were measured gravimetrically. For neat HPMCAS, the rate-limiting step for polymer dissolution was observed to be the polymer solubility at the polymer-solution interface. This, in turn, was impacted by the gel layer pH which was found to be substantially lower than the bulk solution pH, varying with medium buffer capacity. For the ASDs, the HPMCAS release rate was found to control the drug release rate. However, both drugs reduced the polymer release rate with indomethacin methyl ester having a larger impact. In low buffer capacity media, the presence of the drug had less impact on release rates when compared to observations in higher strength buffers, suggesting changes in the rate-limiting steps for HPMCAS dissolution. The observations made in this study can contribute to the fundamental understanding of acidic polymer dissolution in the presence and absence of a molecularly dispersed lipophilic drug and will help aid in the design of more in vivo relevant release testing experiments.

Polysaccharide-Based Supramolecular Hydrogel Coatings with Corrosion Barrier Zone for Protection of Patina Bronze

Protective coatings for bronze relics should adhere to the basic principles of cultural relic preservation, such as not altering the color and appearance of the artifacts, and being moderately combined with the artifacts to resist erosion due to external environments (such as water and gas). This paper presents the development of a physically crosslinked supramolecular hydrogel produced from guanidinium-based chitosan (GC). The hydrogel exhibits the excellent adsorption protection of bronze, and the addition of clay enhances the water barrier properties of the chitosan film. The supramolecular interaction between sodium polyacrylate/GC/clay confers corrosion buffering capability to the hydrogel coating in corrosive environments, and the gel coating can be self-healing at room temperature for 24 h. The fabricated nanocomposites were comprehensively characterized using various methods (Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, etc.). The electrochemical properties of coated specimens were evaluated, and the impedance spectrum revealed a large impedance arc indicating high charge resistance, which has a corrosion resistance effect.

Performance analysis of two typical greenhouse lettuce production systems: commercial hydroponic production and traditional soil cultivation

Introduction

Due to the shortage of land and water resource, optimization of systems for production in commercial greenhouses is essential for sustainable vegetable supply. The performance of lettuce productivity and the economic benefit in greenhouses using a soil-based system (SBS) and a hydroponic production system (HPS) were compared in this study.

Methods

Experiments were conducted in two identical greenhouses over two growth cycles (G1 and G2). Three treatments of irrigation volumes (S1, S2, and S3) were evaluated for SBS while three treatments of nutrient solution concentration (H1, H2, and H3) were evaluated for HPS; the optimal levels from each system were then compared.

Results and discussion

HPS was more sensitive to the effects of environmental temperature than SBS because of higher soil buffer capacity. Compared with SBS, higher yield (more than 134%) and higher water productivity (more than 50%) were observed in HPS. We detected significant increases in ascorbic acid by 28.31% and 16.67% and in soluble sugar by 57.84% and 32.23% during G1 and G2, respectively, compared with SBS. However, nitrate accumulated in HPS-grown lettuce. When the nutrient solution was replaced with fresh water 3 days before harvest, the excess nitrate content of harvested lettuce in HPS was removed. The initial investment and total operating cost in HPS were 21.76 times and 47.09% higher than those in SBS, respectively. Consideration of agronomic, quality, and economic indicators showed an overall optimal performance of the H2 treatment. These findings indicated that, in spite of its higher initial investment and requirement of advanced technology and management, HPS was more profitable than SBS for commercial lettuce production.

Preparation of an amphiphilic peptide (P13) with proton sponge effect and analysis of its antitumor activity

In order to prevent drugs from being captured and degraded by the acidic environment of organelles, such as lysosomes, after entering cells, this study designed and synthesized a novel carrier amphiphilic polypeptide (DGRHHHLLLAAAA), designated P13, for use as a tumor-targeting drug delivery vehicle. The P13 peptide was synthesized by the solid phase synthesis method, and its self-assembly behavior and drug-loading capacity in aqueous solution were studied and characterizedin vitro. Doxorubicin (DOX) was loaded by dialysis method, and P13 and DOX were mixed at a mass ratio of 6:1 to form regular rounded globules. The acid-base buffering capacity of P13 was investigated determined by acid-base titration. The results revealed that P13 had excellent acid-base buffering capacity, a critical micelle concentration value of about 0.000 21 g l^-1, and the particle size of P13-Dox nanospheres was 167 nm. The drug encapsulation efficiency and drug loading capacity of micelles were 20.40 ± 1.21% and 21.25 ± 2.79%, respectively. At the concentration of 50μg ml^-1of P13-DOX , the inhibition rate was 73.35%. The results of thein vivoantitumor activity assay in mice showed that P13-DOX also exhibited excellent inhibitory effect on tumor growth, compared with the tumor weight of 1.1 g in the control group, the tumor weight in the P13-DOX-treated group was only 0.26 g. Additionally, the results of hematoxylin and eosin staining of the organs showed that P13-DOX had no damaging effect on normal tissues. The novel amphiphilic peptide P13 with proton sponge effect designed and prepared in this study is expected to be a promising tumor-targeting drug carrier with excellent application potential.

Oxygen Vacancy-Mediated CuCoFe/Tartrate-LDH Catalyst Directly Activates Oxygen to Produce Superoxide Radicals: Transformation of Active Species and Implication for Nitrobenzene Degradation

Oxygen vacancies play a vital role in the catalytic activity of layered double hydroxide (LDH) catalysts in wastewater treatment. However, the mechanism of oxygen vacancy-mediated LDH-activated oxygen to produce reactive oxygen species (ROS) still lacks a reasonable explanation. In this work, a tartrate-modified CuCoFe-LDH (CuCoFe/Tar-LDH) with abundant oxygen vacancies was designed, which can efficiently degrade nitrobenzene (NB) under room conditions. The technical energy consumption is 0.011 kW h L^-1. According to the characterization and calculation results, it is proposed that oxygen vacancies are formed because of the oxygen deficiency which is caused by the reduction of the energy between the metal ion and oxygen, and the metal ion transitions to a lower state. Compared with CuCoFe-LDH, the oxygen vacancy formation energy of CuCoFe/Tar-LDH decreased from 1.98 to 1.13 eV. The O₂ bond length adsorbed on the oxygen vacancy is 1.27 Å, close to the theoretical length of superoxide radicals (^•O₂^-) (1.26 Å). Radical trapping experiments and electron spin-resonance spectroscopy spectrum prove that ^•O₂^- is an important precursor of ^•OH. This work is dedicated to the in-depth exploration of the oxygen vacancy-mediated CuCoFe/Tar-LDH catalyst activation mechanism for molecular oxygen and the conversion relationship between ROS.

A Study of the Buffer Capacity of Polyelectrolyte Microcapsules Depending on Their Ionic Environment and Incubation Temperature

Polyelectrolyte microcapsules (PMCs) are used in the development of new forms of drugs, coatings and diagnostic systems. Their buffer capacity, depending on the conditions of the medium, has not been practically studied, although it can affect the structure of both the capsule itself and the encapsulated agents. In this connection, we studied the buffer capacity of polyelectrolyte microcapsules of the composition (polystyrene sulfonate/polyallylamine)₃ ((PSS/PAH)₃) depending on the concentration and the type of salt in solution, as well as the microcapsule incubation temperature. It was found that the buffer capacity of microcapsules in the presence of mono- and di-valent salts of the same ionic strength did not differ practically. Increasing the NaCl concentration to 1 M led to an increase of buffer capacity of PMCs at pH ≥ 5, and an increase in NaCl concentration above 1 M did not change buffer capacity. The study of the buffer capacity of pre-heated PMCs showed that buffer capacity decreased with increasing incubation temperature, which was possibly due to the compaction of the PMCs and an increase in the number of compensated PAH sites. The addition of 1 M sodium chloride to heated PMCs presumably reversed the process described above, since an increase in the ionic strength of the solution led to an increase of the buffer capacity of the PMCs. The effects described above confirm the hypothesis put forward that the buffer properties of microcapsules are determined by uncompensated PAH regions in their composition.

Acute effects of sodium bicarbonate ingestion on cycling time-trial performance: A systematic review and meta-analysis of randomized controlled trials

This study aimed to investigate the isolated effects of NaHCO₃ on cycling time-trial performance. Furthermore, we investigated whether the ingestion time of NaHCO₃, standardized or individualized based on time to peak, could be effective in improving cycling time-trial performance. A systematic review was carried out on randomized placebo-controlled studies. A random-effects meta-analysis assessed the standardized mean difference (SMD) between NaHCO₃ and placebo conditions. Eighteen studies were qualitatively (systematic review) and quantitatively (meta-analysis) analysed concerning mean power output (W_mean) (n = 182) and time performance (n = 201). The reviewed studies showed a low risk of bias and homogenous results for W_mean (I² = 0%) and performance time (I²= 0%). Overall, when compared to placebo, the NaHCO₃ ingestion improved the W_mean (SMD: 0.42; 95% CI: 0.21-0.63; P = 0.001) and performance time (SMD: 0.22; 95% CI: 0.02-0.43; P = 0.03). Similarly, the NaHCO₃ ingestion using a time-to-peak strategy improved the W_mean (SMD: 0.39; 95% CI: 0.03-0.75; P = 0.04; I²= 15%) and performance time (SMD: 0.34; 95% CI: 0.07-0.61, P = 0.01, I²= 0%). The present findings reveal that NaHCO₃ ingestion has the potential to increase the overall performance time and W_mean in cycling time trials. HighlightsNaHCO₃ is an effective strategy to increase cycling time-trial performance.The standardized protocol did not improve the cycling time-trial performance parameters.The individualized time-to-peak NaHCO₃ ingestion has a positive effect on time and W_mean during cycling time-trial performance.

The Discovery of the Buffer Capacity of Various Types of Polyelectrolyte Microcapsules

Polyelectrolyte microcapsules, which are obtained by the method of alternate adsorption of oppositely charged polyelectrolytes onto colloidal particles of micron size, are widely used in science and industry. Nevertheless, the properties of microcapsules are still poorly understood. In particular, there is no information in the literature on the buffer capacity. However, information on the presence of a buffer capacity and an understanding of its mechanisms can both simplify the use of microcapsules and expand the scope of their application. In this regard, the buffer capacity of various types of microcapsules was studied. It was found that polyelectrolyte microcapsules consisting of polyallylamine, and polystyrene sulfonate have a buffer capacity. In addition, in an acidic medium, the buffer capacity of microcapsules containing BSA is significantly greater than that of microcapsules without protein. This is due to the fact that BSA contributes to the buffering of microcapsules. Differences in the behaviour of the buffer capacity of microcapsules with the composition (PAH/PSS)3 and (PSS/PAH)3 were found. In addition, a hypothesis has been proposed that regions of unbound polyallylamine are responsible for the buffering properties of polyelectrolyte microcapsules. This hypothesis is confirmed by the fact that incubation of microcapsules in 0.5 M NaCl increases the amount of unbound polyallylamine, which leads to an increase in the buffer capacity of microcapsules at alkaline pH values higher than the buffer capacity of capsules in an aqueous solution.

Comparative Evaluation of Chair-Side Saliva Tests According to Current Dental Status in Adult Patient

Background: this cross-sectional study evaluated the correlation of commercial chair-side saliva tests with caries status in adults. Methods: teeth in 87 adults (20–40 years old) were clinically examined for carious lesions according to International Caries Detection and Assessment System (ICDAS) criteria. The Decayed-Missing-Filling-Tooth (DMFT) and Decayed-Missing-Filling-Surface (DMFS) indexes at D1 (lesions 1–6 according to ICDAS criteria) and D3 (lesions 4–6 according to ICDAS criteria threshold and the number of active lesions, according to the Lesion Activity Assessment (LAA)) criteria were measured. The saliva parameters measured by chair-side tests were stimulated and non-stimulated saliva flow rate, saliva consistency, saliva pH, saliva buffer capacity, and lactic acid production. The statistical analyses performed were Student t-test and Mann–Whitney U test at a = 0.05 significant level. Results: the low resting saliva pH was related to a high value of DMFT (D1) index (p = 0.007). Conclusions: among the saliva parameters measured, the values of low resting pH are associated with increased DMFT at threshold D1. None of the chair-side available saliva tests evaluated can accurately underline the tooth carious status.

Comparison of Some Salivary Characteristics in Iraqi Children with Early Childhood Caries (ECC) and Children without Early Childhood Caries

Background

Early Childhood Caries (ECC) is a unique form of caries that develops in temporary dentition. It has a multifactorial infectious disease. Saliva is one of the most important factors, which has an important protective effect against tooth decay when its multiple characteristics and functions are normal. The study aimed to compare some salivary characteristics in children with ECC and children without ECC.

Materials and Methods

Case-control, cross-sectional observational study. The 77 pre-schoolers aged 37 to 72 months (12 with ECC, 26 with ECC-S, and 39 without ECC) examined and we collected the stimulated saliva. The pH microelectrode was used to determine pH and buffer capacity; a formula that involves volume, collection time, and specific saliva weight was used to test the salivary flow rate. The potentiometric and phosphate methods were used to determine fluoride through spectrophotometric, colorimetric absorption techniques.

Results

The results got to show that there are no statistically significant differences in pH, buffer capacity, salivary flow rate, and levels of fluoride and phosphate, in children with ECC, ECC-S, and without ECC. The risk factors, such as mother's education, bottle use, brushing frequency, and previous dental care of the child are more important at the time of developing ECC than some salivary variables.

Conclusion

The risk factors, such as mother's education, bottle use, brushing frequency, and previous dental care of the child are more important at the time of developing ECC than some salivary variables such as pH, buffer capacity, salivary flow rate, and levels of fluoride and phosphate.

Salivary factors related to caries in pregnancy: A systematic review and meta-analysis

BACKGROUND

The authors of this meta-analysis aimed to assess saliva-related caries risk factors, including calcium and phosphate, hydrogen ion concentration, buffer capacity, Streptococcus mutans and Lactobacillus counts, flow rate, and decayed, missing and filled teeth index in each trimester during pregnancy.

TYPES OF STUDIES REVIEWED

The authors searched electronic databases up to July 1, 2019. Eligible observational studies were included. The authors assessed the quality of the included studies by using the Joanna Briggs Institute scale. To estimate the effects of pregnancy, standardized mean differences with 95% confidence intervals were pooled using the random-effects model. Subgroup analysis and meta-regression were used to explore heterogeneity. Publication bias was assessed using Begg and Egger tests.

RESULTS

Twenty-nine studies were included in the meta-analysis, representing 1,230 pregnant women in the case groups and 715 in the control groups (nonpregnant women). The results showed that salivary calcium concentration decreased in the third trimester, salivary phosphate decreased in the second and third trimesters, saliva hydrogen ion concentration decreased in the first and third trimesters, stimulated saliva flow rate increased in the third trimester, and salivary S mutans count increased in the second and third trimesters. In addition, the results showed that saliva calcium, phosphate, S mutans, and buffer capacity amounts had changed from the first trimester to the third.

CONCLUSIONS AND PRACTICAL IMPLICATIONS

In the third trimester, most salivary factors related to caries change and can increase the risk of developing caries in the future. Interventions and screening for caries prevention in pregnancy should start in the first or second trimesters.

The Proof-of-the Concept of Biochar Floating Cover Influence on Swine Manure pH: Implications for Mitigation of Gaseous Emissions From Area Sources

Mitigation of potentially hazardous and malodor compounds emitted from animal waste is needed to improve the sustainability of livestock agriculture. Bacteria control the generation of these compounds and also depend on the pH of manure. Influencing swine manure pH, especially on the liquid-air interface, may lead to a reduction of emission of odorous and hazardous compounds. The objective of this experiment was to test highly alkaline and porous (HAP) modified biochar with pH = 9.2 and red oak (RO) biochar with pH = 7.5 influence on swine manure pH acquired from the outdoor storage and deep pit storage under a barn. HAP and RO biochars were topically applied on the outdoor-stored (pH = 7.55), and pit (pH = 8.00) manures and spatial pH (every 1 mm of depth) were measured on days 0, 2, and 4. Results showed that HAP biochar increased outdoor-stored manure pH on day 4, particularly within the top 10 mm of depth, where pH ranged from 7.79 to 8.90, while in the case of RO pH ranged between 7.46 and 7.66, i.e., similar to control (7.57-7.64). Both biochars decreased pit-stored manure pH within the top 10 mm of depth (in comparison with the control pH of 8.36-8.47) to 8.19-8.30 (HAP), and 8.18-8.29 (RO) on day 4. However, differences were not considerable. The reason for the insignificant effect of biochars on pit manure was likely due to its higher buffer capacity in comparison with the outdoor-stored manure.

Utilization of Diluted Compendial Media as Dissolution Test Solutions with Low Buffer Capacity for the Investigation of Dissolution Rate of Highly Soluble Immediate Release Drug Products

Research from the past decade has shown that the buffer capacities of intestinal fluids are much lower than those in the media used for dissolution test of many solid formulations. The purpose of this study was to elucidate the effect of buffer capacity on the dissolution profiles of highly soluble drug products, using metoclopramide (a biopharmaceutics classification system [BCS] class III drug) tablets as a model. The dissolution profiles of three metoclopramide products were obtained in Japanese pharmacopeia dissolution medium (pH 1.2 and 6.8), diluted medium with low buffer capacity comparable to that of gastrointestinal fluid, and other biorelevant media. One product showed slower dissolution in the medium with lower buffer capacity (bio-relevant, diluted compendial solution), but substantially similar dissolution in the compendial test solutions. Disintegration difference was implied to be involved in the different dissolution profiles depending on the medium buffer capacity. This study indicated the importance of media buffer capacity as a factor inducing different dissolution between products of highly soluble active pharmaceutical ingredients. The diluted compendial media would be a useful alternative to biorelevant media for the detection of the different formulation performances depending on the buffer capacities.

Biphasic Dissolution as an Exploratory Method During Early Drug Product Development

Dissolution testing is a major tool used to assess a drug product's performance and as a quality control test for solid oral dosage forms. However, compendial equipment and methods may lack discriminatory power and the ability to simulate aspects of in vivo dissolution. Using low buffer capacity media combined with an absorptive phase (biphasic dissolution) increases the physiologic relevance of in vitro testing. The purpose of this study was to use non-compendial and compendial dissolution test conditions to evaluate the in vitro performance of different formulations. The United States Pharmacopeia (USP)-recommended dissolution method greatly lacked discriminatory power, whereas low buffer capacity media discriminated between manufacturing methods. The use of an absorptive phase in the biphasic dissolution test assisted in controlling the medium pH due to the drug removal from the aqueous medium. Hence, the applied non-compendial methods were more discriminative to drug formulation differences and manufacturing methods than conventional dissolution conditions. In this study, it was demonstrated how biphasic dissolution and a low buffer capacity can be used to assess in vitro drug product performance differences. This can be a valuable approach during the early stages of drug product development for investigating in vitro drug release with improved physiological relevance.

Polymorphism in the CAVI gene, salivary properties and dental caries

Objectives: Carbonic anhydrase (CA) VI is supposed to take part in pH or buffering capacity regulation, which can influence the caries risk of an individual. Its expression in the saliva can be modified by single nucleotide polymorphism (SNP). The aim was to investigate SNP in the CA VI gene in relation to active dental caries and physiochemical properties of saliva.Materials and methods: One hundred and thirty participants aged 11-16 years were involved. Clinical examinations were carried out using standardized WHO criteria, DMFT/DMFS and white spot lesions score was evaluated. Saliva samples were examined for salivary properties and CA VI concentration. DNA evaluated in the investigation was extracted from the buccal smear. Three SNP within CAVI gene (rs2274327; rs2274328; rs2274333) were selected and genotyping was performed.Results: In the active caries group, the mean CAVI concentration was significantly lower than in caries free group (p = .014). No association between increased or decreased risk of caries and analysed SNPs was found. There were some significant relations concerning SNPs and salivary buffer capacity and flow rate in rs2274327 and rs2274328.Conclusions: Polymorphism in the CAVI gene can affect salivary properties but there is no direct connection with dental caries.

Dynamics of Different Buffer Systems in Slurries Based on Time and Temperature of Storage and Their Visualization by a New Mathematical Tool

Simple Summary

Efficient slurry management is a key strategy to reduce the release of environmentally harmful gases produced by farm animals. Slurry treatments such as acidification and alkalization have proven to be promising solutions to reduce these emissions. In this context, it is crucial to understand how buffer capacities behave and may influence each other during storage under the influence of different temperatures. To realize this, we have developed and successfully verified a new mathematical tool. It allows an exact calculation and detailed visualization of the most important buffer systems found in the analyzed slurries. This knowledge can be used to optimize slurry treatments, as it allows faster, more precise and efficient timing of pH adjustment, thus, reducing the use of resources.

Abstract

Slurry treatments such as acidification and alkalization have proven to be promising solutions to reduce gaseous emission produced by farm animals. The optimization of these technologies requires detailed knowledge of how and to what extent the buffer capacities in slurries will change during storage under the influence of different temperatures, as this may save resources needed to adjust a targeted pH value. Fresh slurries from dairy cows, fattening pigs and sows were collected and stored for 12 weeks under either cold (4.7 ± 1.1 °C) or warm (23.6 ± 2.1 °C) conditions to perform titrations in acidic and alkaline milieu at regular intervals. Based on these results, we successfully verified a new mathematical tool that we have developed to be able to calculate and visualize the most important buffer systems found in the analyzed slurries. Our experimental results showed a strong correlation between the degradation of the volatile fatty acid (VFA) buffer and the emergence of the carbonate buffers, i.e., the HCO₃⁻ and the CO₃²⁻ buffer. Furthermore, a drop in the pH value caused by enhanced microbial production of VFAs can be mitigated by the presence of the NH₃ buffer. In conclusion, we demonstrated that the buffers cannot be considered individually but must be interpreted as a complex and interacting system.

Modeling the buffer capacity of ingredients in salad dressing products

The pH of most acid food products depends on undefined and complex buffering of ingredients but is critically important for regulatory purposes and food safety. Our objective was to define the buffer capacity (BC) of ingredients in salad dressing products. Ingredients of salad dressings were titrated individually and in combination using concentrations typical of dressing products. Titration curves from pH 2 to 12 were generated with sodium hydroxide and hydrochloric acid, which were then used to generate BC curves. A matrix of concentration and pK values for a series of monoprotic buffers approximated the pH of each ingredient. Some buffer series required anion or cation corrections for accurate pH prediction, possibly due to the presence of salts of acid or bases. Most buffers had BC values less than 10-fold the BC of acetic acid (0.25 β) typically in dressing formulations and had little influence on the final product pH of the dressings tested. Unexpectedly, we found that sugars in dressing formulations, including sucrose or corn syrup, exhibited buffering at pH values greater than 11 (0.035 β and 0.059 β, respectively), which was likely due to weakly acidic hydroxyl groups on the sugar molecules. However, the concentration and pK for buffers above pH 11 or below pH 2 were difficult to quantify due to the BC of water. The BC data may help to quantify the effects of salad dressing ingredients on the final product pH and benefit regulatory agencies and manufacturers in assessing product pH and safety. PRACTICAL APPLICATION: Buffer capacity data for salad dressing ingredients may help determine the influence ingredient addition will have on the final pH of a salad dressing product. The addition of low acid ingredients with little or no buffering may not significantly alter pH. The modeling method may be useful for regulatory purposes to estimate the effects of low acid ingredients on pH changes for food safety and may also be useful for product development of acid and acidified foods.

Modeling buffer capacity and pH in acid and acidified foods

Standard ionic equilibria equations may be used for calculating pH of weak acid and base solutions. These calculations are difficult or impossible to solve analytically for foods that include many unknown buffering components, making pH prediction in these systems impractical. We combined buffer capacity (BC) models with a pH prediction algorithm to allow pH prediction in complex food matrices from BC data. Numerical models were developed using Matlab software to estimate the pH and buffering components for mixtures of weak acid and base solutions. The pH model was validated with laboratory solutions of acetic or citric acids with ammonia, in combinations with varying salts using Latin hypercube designs. Linear regressions of observed versus predicted pH values based on the concentration and pK values of the solution components resulted in estimated slopes between 0.96 and 1.01 with and without added salts. BC models were generated from titration curves for 0.6 M acetic acid or 12.4 mM citric acid resulting in acid concentration and pK estimates. Predicted pH values from these estimates were within 0.11 pH units of the measured pH. Acetic acid concentration measurements based on the model were within 6% accuracy compared to high-performance liquid chromatography measurements for concentrations less than 400 mM, although they were underestimated above that. The models may have application for use in determining the BC of food ingredients with unknown buffering components. Predicting pH changes for food ingredients using these models may be useful for regulatory purposes with acid or acidified foods and for product development. PRACTICAL APPLICATION: Buffer capacity models may benefit regulatory agencies and manufacturers of acid and acidified foods to determine pH stability (below pH 4.6) and how low-acid food ingredients may affect the safety of these foods. Predicting pH for solutions with known or unknown buffering components was based on titration data and models that use only monoprotic weak acids and bases. These models may be useful for product development and food safety by estimating pH and buffering capacity.

Challenging the charge balance hypothesis: reconsidering buffer effect and reuptake of previously excreted organic acids by Penicillium ochrochloron

Penicillium ochrochloron was used in the past for the leaching of zinc from a zinc oxide containing filter dust via excreted organic acids. Organic acid excretion by P. ochrochloron was stimulated by the addition of an extracellular buffer (2-(N-Morpholino)ethanesulfonic acid, MES; or zinc oxide, ZnO: ZnO + 2 H⁺ → Zn²⁺ + H₂O). It was tested if the buffer stimulated excretion of organic acid anions is due to the necessity of an anion efflux across the plasma membrane to maintain electroneutrality by balancing the excretion of protons by the H⁺-ATPase. This charge balance hypothesis was previously postulated for P. ochrochloron. Two strains of P. ochrochloron were studied, which differed in growth parameters and amount of excreted organic acids. From the results, it was concluded that charge balance at the plasma membrane is not the main reason for organic acid excretion in these two strains of P. ochrochloron. Furthermore, the phenomenon of reuptake of excreted organic acids in the presence of about 100 mM of glucose is confirmed. It is suggested that the equilibrium between extracellular and intracellular organic acid anions may be maintained passively by a facilitated diffusion transporter.

Measuring pH and Buffer Capacity in Fluids Aspirated from the Fasted Upper Gastrointestinal Tract of Healthy Adults

PURPOSE

The design of biorelevant conditions for in vitro evaluation of orally administered drug products is contingent on obtaining accurate values for physiologically relevant parameters such as pH, buffer capacity and bile salt concentrations in upper gastrointestinal fluids.

METHODS

The impact of sample handling on the measurement of pH and buffer capacity of aspirates from the upper gastrointestinal tract was evaluated, with a focus on centrifugation and freeze-thaw cycling as factors that can influence results. Since bicarbonate is a key buffer system in the fasted state and is used to represent conditions in the upper intestine in vitro, variations on sample handling were also investigated for bicarbonate-based buffers prepared in the laboratory.

RESULTS

Centrifugation and freezing significantly increase pH and decrease buffer capacity in samples obtained by aspiration from the upper gastrointestinal tract in the fasted state and in bicarbonate buffers prepared in vitro. Comparison of data suggested that the buffer system in the small intestine does not derive exclusively from bicarbonates.

CONCLUSIONS

Measurement of both pH and buffer capacity immediately after aspiration are strongly recommended as "best practice" and should be adopted as the standard procedure for measuring pH and buffer capacity in aspirates from the gastrointestinal tract. Only data obtained in this way provide a valid basis for setting the physiological parameters in physiologically based pharmacokinetic models.

Distance and Color Change Based Hydrogel Sensor for Visual Quantitative Determination of Buffer Concentrations

We present here an innovative platform for the determination of pH buffer capacity based on FITC-dextran loaded hydrogels. Optical signals from the pH-sensitive hydrogels were analyzed by simple parameters including distance and color change. The methodology was validated on five different buffer systems and exhibited wide linearity (0.1 to 100 mM), good batch-to-batch reproducibility, high versatility, and resistance to background ionic strength changes. Experimental results also fit well with a theoretical model based on numerical simulation. Preliminary application in carbonate alkalinity determination of seawater proved very successful. This hydrogel buffer concentration sensor is fundamentally different from conventional acid-base titrations, brings minimum perturbation to samples, and shows great potential in real applications.

Mass Transport Analysis of the Enhanced Buffer Capacity of the Bicarbonate-CO2 Buffer in a Phase-Heterogenous System: Physiological and Pharmaceutical Significance

The bicarbonate buffer capacity is usually considered in a phase-homogeneous system, at equilibrium, with no CO₂ transfer between the liquid buffer phase and another phase. However, typically, an in vitro bicarbonate buffer-based system is a phase-heterogeneous system, as it entails continuously sparging (bubbling) the dissolution medium with CO₂ in a gas mixture, at constant ratio, to maintain a constant partial pressure of CO_2 (g) and CO_2(aq) molarity at a prescribed value, with CO₂ diffusing freely between the gas and the aqueous phases. The human gastrointestinal tract is also a phase-heterogeneous system, with CO₂ diffusing across the mucosal membrane into the mesenteric arterial blood, which serves as a sink for CO₂ from the intestinal lumen. In this report, a mass transport analysis of the apparent buffer capacity of a phase-heterogeneous bicarbonate-CO₂ system is developed. It is shown that, most significantly, a phase-heterogeneous bicarbonate-CO₂ system can have a much higher buffer capacity than a phase-homogeneous system such that the buffer capacity is dependent on the bicarbonate concentration. It is double that of a phase-homogeneous system at the pH = p K_a for a monoprotic buffer at the same concentration. This buffer capacity enhancement increases hyperbolically with pH above the p K_a, thus providing a much stronger buffering to keep the pH in the physiologically neutral range. The buffer capacity will be dependent on the bicarbonate molarity (which in vivo will depend on the bicarbonate secretion rate) and not the pH of the luminal fluid. Further, there is no conjugate acid accumulation as a result of bicarbonate neutralization, since the resulting carbonic acid (H₂CO₃) rapidly dehydrates producing CO₂ and H₂O. The mass transport analysis developed in this report is further supported by in vitro experimental results. This enhanced bicarbonate buffer capacity in a phase-heterogeneous system is of physiological significance as well as significant for the dissolution and absorption of ionizable drugs.

Low Buffer Capacity and Alternating Motility along the Human Gastrointestinal Tract: Implications for in Vivo Dissolution and Absorption of Ionizable Drugs

In this study, we determined the pH and buffer capacity of human gastrointestinal (GI) fluids (aspirated from the stomach, duodenum, proximal jejunum, and mid/distal jejunum) as a function of time, from 37 healthy subjects after oral administration of an 800 mg immediate-release tablet of ibuprofen (reference listed drug; RLD) under typical prescribed bioequivalence (BE) study protocol conditions in both fasted and fed states (simulated by ingestion of a liquid meal). Simultaneously, motility was continuously monitored using water-perfused manometry. The time to appearance of phase III contractions (i.e., housekeeper wave) was monitored following administration of the ibuprofen tablet. Our results clearly demonstrated the dynamic change in pH as a function of time and, most significantly, the extremely low buffer capacity along the GI tract. The buffer capacity on average was 2.26 μmol/mL/ΔpH in fasted state (range: 0.26 and 6.32 μmol/mL/ΔpH) and 2.66 μmol/mL/ΔpH in fed state (range: 0.78 and 5.98 μmol/mL/ΔpH) throughout the entire upper GI tract (stomach, duodenum, and proximal and mid/distal jejunum). The implication of this very low buffer capacity of the human GI tract is profound for the oral delivery of both acidic and basic active pharmaceutical ingredients (APIs). An in vivo predictive dissolution method would require not only a bicarbonate buffer but also, more significantly, a low buffer capacity of dissolution media to reflect in vivo dissolution conditions.

Immanent conditions determine imminent collapses: nutrient regimes define the resilience of macroalgal communities

Predicting where state-changing thresholds lie can be inherently complex in ecosystems characterized by nonlinear dynamics. Unpacking the mechanisms underlying these transitions can help considerably reduce this unpredictability. We used empirical observations, field and laboratory experiments, and mathematical models to examine how differences in nutrient regimes mediate the capacity of macrophyte communities to sustain sea urchin grazing. In relatively nutrient-rich conditions, macrophyte systems were more resilient to grazing, shifting to barrens beyond 1 800 g m-2 (urchin biomass), more than twice the threshold of nutrient-poor conditions. The mechanisms driving these differences are linked to how nutrients mediate urchin foraging and algal growth: controlled experiments showed that low-nutrient regimes trigger compensatory feeding and reduce plant growth, mechanisms supported by our consumer-resource model. These mechanisms act together to halve macrophyte community resilience. Our study demonstrates that by mediating the underlying drivers, inherent conditions can strongly influence the buffer capacity of nonlinear systems.

Metabolic consequences of β-alanine supplementation during exhaustive supramaximal cycling and 4000-m time-trial performance

The present study investigated the effects of β-alanine supplementation on the resultant blood acidosis, lactate accumulation, and energy provision during supramaximal-intensity cycling, as well as the aerobic and anaerobic contribution to power output during a 4000-m cycling time trial (TT). Seventeen trained cyclists (maximal oxygen uptake = 4.47 ± 0.55 L·min(-1)) were administered 6.4 g of β-alanine (n = 9) or placebo (n = 8) daily for 4 weeks. Participants performed a supramaximal cycling test to exhaustion (equivalent to 120% maximal oxygen uptake) before (PreExh) and after (PostExh) the 4-week supplementation period, as well as an additional postsupplementation supramaximal cycling test identical in duration and power output to PreExh (PostMatch). Anaerobic capacity was quantified and blood pH, lactate, and bicarbonate concentrations were measured pre-, immediately post-, and 5 min postexercise. Subjects also performed a 4000-m cycling TT before and after supplementation while the aerobic and anaerobic contributions to power output were quantified. β-Alanine supplementation increased time to exhaustion (+12.8 ± 8.2 s; P = 0.041) and anaerobic capacity (+1.1 ± 0.7 kJ; P = 0.048) in PostExh compared with PreExh. Performance time in the 4000-m TT was reduced following β-alanine supplementation (-6.3 ± 4.6 s; P = 0.034) and the mean anaerobic power output was likely to be greater (+6.2 ± 4.5 W; P = 0.035). β-Alanine supplementation increased time to exhaustion concomitant with an augmented anaerobic capacity during supramaximal intensity cycling, which was also mirrored by a meaningful increase in the anaerobic contribution to power output during a 4000-m cycling TT, resulting in an enhanced overall performance.

[Buffer capacity of infant formulas diluted with different types of water]

Artificial feeding of infants under 1 year old deserves a special attention. It is generally accepted that the infant formula is approximated to the human milk and adapted to the infantile digestive system. Important properties of breast milk are pH and acid-based buffer capacity. According to this fact, the results of the experimental determination of pH and buffer properties of fresh, fermented, and anti-reflux infant formulas, diluted with water of different pH, have been presented. It was found that reconstituted fermented infant formulas has one unit pH less than the antireflux and fresh mixtures. When restoring infant formula with waters of different alkalinity, pH value changed slightly. Thus, pH of fresh and antireflux mixtures varied in the range 6.67±0.76, of fermented milk mixtures - 5.75±0.55. The buffer capacity with respect to acid of infant formulas play an important role in the nutrition of the child. It depends on the proteins (having different amino acid composition) comprising the milk mixture, and on the type of water, which is used for restoring. Restored infant formulas having a greater buffer capacity for acid can reduce infant gastric acidity. Six of submitted infant formula reconstituted with children bottled water "Nutrilak AQUA", "HiPP" and "Arhyzik" observed the lowest values of the buffer capacity (9.00±3.00 mmol/l). The larger value of the buffer capacity by acid (>12.00 mmol/l)) was observed in formulas reconstituted with boiled tap water and children bottled water "Agusha" and "FrutoNyanya".

Rising atmospheric CO2 leads to large impact of biology on Southern Ocean CO2 uptake via changes of the Revelle factor

The Southern Ocean is a key region for global carbon uptake and is characterized by a strong seasonality with the annual CO₂ uptake being mediated by biological carbon drawdown in summer. Here we show that the contribution of biology to CO₂ uptake will become even more important until 2100. This is the case even if biological production remains unaltered and can be explained by the decreasing buffer capacity of the ocean as its carbon content increases. The same amount of biological carbon drawdown leads to a more than twice as large reduction in CO_2(aq) concentration and hence to a larger CO₂ gradient between ocean and atmosphere that drives the gas exchange. While the winter uptake south of 44°S changes little, the summer uptake increases largely and is responsible for the annual mean response. The combination of decreasing buffer capacity and strong seasonality of biological carbon drawdown introduces a strong and increasing seasonality in the anthropogenic carbon uptake.

KEY POINTS

Decrease of buffer capacity leads to stronger summer CO₂ uptake in the futureBiology will contribute more to future CO₂ uptake in Southern OceanSeasonality affects anthropogenic carbon uptake strongly.

Characterization of commercially available vaginal lubricants: a safety perspective

Vaginal lubricants are widely used by women to help solve intercourse difficulties or as enhancers, but recent reports raise questions about their safety. Twelve commercially available gel products were tested for pH value, pH buffering capacity, osmolality and cytotoxicity relevant to vaginal delivery. Obtained data were analyzed in light of the recent Advisory Note by the World Health Organization (WHO) for personal lubricants to be concomitantly used with condoms. Results showed that most products do not comply with pH and osmolality recommended standards, thus posing a potential hazard. Four products presented values of osmolality around three-times higher than the maximum acceptable limit of 1200 mOsm/kg. In vitro cell testing further identified substantial cytotoxicity even at 1:100 dilutions for three products, contrasting with no significant effect of up to at least a 1:5 dilution of a Universal Placebo gel. However, no direct correlation between these last results and pH or osmolality was found, thus suggesting that the individual toxicity of specific formulation components plays an important role in the outcome of a particular product. Although further assessment is required, these results highlight potential safety issues related to the formulation of commercially available vaginal lubricants.

Caffeine, but not bicarbonate, improves 6 min maximal performance in elite rowers

This study examined the ergogenic effects in a 6 min maximal performance test (PT) on 12 elite rowers: 6 open-weight (mean ± SD; 25 ± 1 years, and 92 ± 3 kg) and 6 light-weight (25 ± 3 years, and 73 ± 6 kg), following supplementation with caffeine (CAF), sodium bicarbonate (SB), and the combination of both, in a double-blind randomized placebo (PLA) controlled design. PT was executed on 4 occasions, on separate days within a week, and in a non-fasted state, with standardized training being performed the day before PT. Protocols were as follows: (i) CAF, 3 mg/kg, 45 min prior to PT + calcium as SB-PLA; (ii) SB, 0.3 g/kg, 75 min prior to PT + dextrose as CAF-PLA; (iii) CAF + SB; and (iv) PLA; CAF-PLA + SB-PLA. The total distance in the CAF (1878 ± 97 m) and CAF + SB (1877 ± 97 m) was longer than in the PLA (1865 ± 104 m; P < 0.05) and SB (1860 ± 96 m; P < 0.01). The mean power in CAF (400 ± 58 W) and CAF + SB (400 ± 58 W) was higher than the PLA (393 ± 61 W; P < 0.05) and SB (389 ± 57 W; P < 0.01). In CAF and CAF + SB, power was higher (P < 0.05) relative to PLA in the last half (4-6 min) of PT. Trials with CAF were more effective in light-weight rowers (1.0% ± 0.8% improvement in distance; P < 0.05) than in open-weight rowers (0.3% ± 0.8%; P > 0.05). No difference between interventions was observed for readiness and stomach comfort before PT and perceived exertion during PT. This study demonstrates that caffeine ingestion does improve performance in elite rowing. In contrast sodium bicarbonate does not appear to be ergogenic, but it does not abolish the ergogenic effect of caffeine.

Acid-induced changes of brain protein buffering

Excessive cellular acidosis is thought to enhance destruction of brain from ischemia. Protein denaturation may contribute to such injury although the behavior of brain proteins to acidosis is poorly defined. As a first approach to detect acid-induced changes in brain proteins and to characterize buffer content, homogenates were acidified for 20 min (as low as pH 3.1), returned to baseline pH (6.9), and then titrated. Titration curves show a significant (P less than 0.0001) and permanent increase in buffer content compared to controls when pH of acid exposure was 4.5-3.7 or less. Since acidity of pH 4.5 is rarely, if ever, achieved in vivo, protein denaturation from acidity alone is unlikely to account for necrosis of brain from ischemia.