Acid Treatment pH Research Articles

The occurring of astringency during persimmon pulp drying and its correlation with tannin derivatives

Drying persimmon pulp causes an increase in astringency, which is a great concern for persimmon manufacturers. This research investigates the increment in astringency observed during three drying technologies, freeze, vacuum and hot air drying, respectively, and proposes two mitigation pretreatments. The phenols in persimmon samples were correlated with their astringent level measured by tannin content, mean degree of polymerization (mDP) and degree of galloylation (DG). The astringency of fresh persimmon pulp increased four times after freeze drying, which is the least compared to hot air and vacuum drying. However, pH adjustment and pectinase hydrolysis can effectively mitigate the astringent taste. The best pre-treatment was pectinase hydrolysis since it decreased the mDP to 4.7 and DG to 13 %, similar to the level of fresh pulp. The acidic pH treatment (pH=2) can also significantly decrease the astringent level, however, the taste perception also changed dramatically. An HPLC-MS-DAD analysis has identified and quantified the phenol profile of dried persimmon, and the concentration of small molecular weight phenols was negatively correlated to the tannin content, thus astringent level. A further multivariate analysis including tannin concentration, phenols quantification and taste simulation by e-tongue confirmed that pectinase pretreatment has the least increment in astringency and similar taste perception.

Lutein and Zeaxanthin Enhance, Whereas Oxidation, Fructosylation, and Low pH Damage High-Density Lipoprotein Biological Functionality.

High-density lipoproteins (HDLs) are key regulators of cellular cholesterol homeostasis but are functionally altered in many chronic diseases. The factors that cause HDL functional loss in chronic disease are not fully understood. It is also unknown what roles antioxidant carotenoids play in protecting HDL against functional loss. The aim of this study was to measure how various disease-associated chemical factors including exposure to (1) Cu2+ ions, (2) hypochlorous acid (HOCL), (3) hydrogen peroxide (H2O2), (4) sialidase, (5) glycosidase, (6) high glucose, (7) high fructose, and (8) acidic pH, and the carotenoid antioxidants (9) lutein and (10) zeaxanthin affect HDL functionality. We hypothesized that some of the modifications would have stronger impacts on HDL particle structure and function than others and that lutein and zeaxanthin would improve HDL function. HDL samples were isolated from generally healthy human plasma and incubated with the corresponding treatments listed above. Cholesterol efflux capacity (CEC), lecithin-cholesterol acyl transferase (LCAT) activity, and paraoxonase-1 (PON1) activity were measured in order to determine changes in HDL functionality. Median HDL particle diameter was increased by acidic pH treatment and reduced by HOCl, high glucose, high fructose, N-glycosidase, and lutein treatments. Acidic pH, oxidation, and fructosylation all reduced HDL CEC, whereas lutein, zeaxanthin, and sialidase treatment improved HDL CEC. LCAT activity was reduced by acidic pH, oxidation, high fructose treatments, and lutein. PON1 activity was reduced by sialidase, glycosidase, H2O2, and fructose and improved by zeaxanthin and lutein treatment. These results show that exposure to oxidizing agents, high fructose, and low pH directly impairs HDL functionality related to cholesterol efflux and particle maturation, whereas deglycosylation impairs HDL antioxidant capacity. On the other hand, the antioxidants lutein and zeaxanthin improve or preserve both HDL cholesterol efflux and antioxidant activity but have no effect on particle maturation.

Acidic pH or salt treatment can convert soluble antibody aggregates in culture harvest into monomers and improve Protein A chromatography step yield

While purifying a regular monospecific antibody, we found that the Protein A step yield was much lower than expected. Further studies revealed that the antibody formed large-size aggregates that did not bind to the Protein A resin, hence leading to dropped recovery. In an attempt to solve this low yield issue, we found that mildly acidic pH or ammonium sulfate treatment can partially convert the aggregates into monomers. In addition, when acidic pH treated culture harvest was processed by Protein A chromatography, the yield was restored to the normal range, suggesting that the monomers recovered from aggregates regained Protein A binding capability. Thus, low pH treatment of culture harvest can be potentially used as a general approach for improving Protein A step yield in cases where non-binding antibody aggregates are formed through noncovalent interactions.

Evaluating the viral clearance ability of continuous monoclonal antibody purification steps, in order to inactivate and/or remove four model viruses.

Viral clearance studies are an essential part of a manufacturer's plan to ensure the safety of an injectable biologic product. In this way, viral safety is a critical quality attribute for biologics such as monoclonal antibodies (Mabs). Evaluation of virus purification by downstream processes is a key component of risk mitigation. In this study, the capability of continuous monoclonal antibody purification steps was evaluated in the process of instant monoclonal antibody purification in different stages of purification, and the amount of reduction or inactivation of each step was determined. Four enveloped and non-enveloped viral models VSV, Reovirus, EMCV, and HSV1 were used for spiking in selected samples in the designated tests, to have a comprehensive examination of the ability to clear the virus such as the type of genetic material, chemical resistance, and particle size. A TCID50 and qPCR methods were used to measure viral reduction. Two cell lines, Vero (African green monkey kidney) and L929 (Mouse fibroblast) were used for 4 model viruses propagation. The steps that were evaluated included 4 steps monoclonal antibody purification; cation exchange chromatography, acidic pH treatment, affinity chromatography, and nanofiltration. The nano-filter stage showed the highest viral reduction and cation exchange chromatography showed the lowest reduction. The cumulative decrease using TCID50 is equal to 19.27 [log10] for all steps and for the qPCR method is equal to 12.47 [log10] in three steps of nano-filter, affinity chromatography, and ion exchange chromatography. The overall average reduction coefficient for all four model viruses is significantly high, which indicates the high capacity of the monoclonal antibody production process in inactivating and removing viruses leads to reducing the load of all four model viruses.

Coordination-driven robust antibacterial coatings using catechol-conjugated carboxymethyl chitosan

To prevent bacterial contamination on solid surfaces, a simple yet efficient antibacterial coating was developed in a substrate-independent manner by using the catechol-conjugated carboxymethyl chitosan (CMC-DOPA). The CMC-DOPA was firstly synthesized via an aza-Michael reaction with methyl acrylate and the subsequent acyl substitution with dopamine. The coating strategy consists of spin-coating-assisted deposition of CMC-DOPA on polydopamine-coated substrates and coordination-driven crosslinks between catechol groups and Fe3+ ions in sequence, producing the multilayered CMC-DOPA films. The film thickness was controllable depending on the concentration of CMC-DOPA. Compared to bare controls, the CMC-DOPA-coated substrates reduced the bacterial adhesion by up to 99.8 % and 96.2 % for E. coli and S. aureus, respectively. It is demonstrated that the CMC-DOPA coating can be a robust antibacterial coating across various pH environments, inhibiting bacterial adhesion by 78.7 %, 95.1 %, and 93.2 %, respectively, compared to the control, even after 7 days of acidic, physiological, and alkaline pH treatment. The current coating approach could be applied to various substrates including silicon dioxide, titanium dioxide, and polyurethane. Given its simple and versatile coating capability, we think that the coordination-driven CMC-DOPA coating could be useful for various medical devices and implants.

The Relationship between Antibiotic Susceptibility and pH in the Case of Uropathogenic Bacteria.

Urinary tract infections (UTIs) are common bacterial infections caused mainly by enteric bacteria. Numerous virulence factors assist bacteria in the colonization of the bladder. Bacterial efflux pumps also contribute to bacterial communication and to biofilm formation. In this study, the phenotypic and genetic antibiotic resistance of clinical UTI pathogens such as Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis were determined by disk diffusion method and polymerase chain reaction (PCR). Following this, different classes of antibiotics were evaluated for their antibacterial activity at pH 5, 6, 7 and 8 by a microdilution method. Gentamicin (GEN) was the most potent antibacterial agent against E. coli strains. The effect of GEN on the relative expression of marR and sdiA genes was evaluated by quantitative PCR. The slightly acidic pH (pH 6) and GEN treatment induced the upregulation of marR antibiotic resistance and sdiA QS activator genes in both E. coli strains. Consequently, bacteria had become more susceptible to GEN. It can be concluded that antibiotic activity is pH dependent and so the artificial manipulation of urinary pH can contribute to a more effective therapy of multidrug resistant bacterial infections.

Microbial and physicochemical properties of spray dried kefir microcapsules during storage

To preserve the probiotic and functional potential of kefir and increase its stability, this study aimed to characterize and evaluate the effect of microencapsulation on the viability and stability of kefir microparticles storage and simulated gastrointestinal conditions. Kefir microencapsulation was performed using the spray drying with different encapsulating matrices and without a coating material at 140 °C. Seven organic acids were identified and quantified, with lactic acid found in the highest amounts. Different wall material influenced the hygroscopicity, dispersibility and solubility stability. Fresh kefir had 9.64 and 7.60 log CFU·g−1 lactic acid bacteria (LAB) and yeast counts, respectively. After the spray drying at 140 °C, all samples at 4 °C had lower LAB counts. The use of MD (p = 0.7819) or CAP (p = 0.0507) affected positively the stability of LAB, regardless of storage temperature over 77 days. Yeast counting has higher at 4 °C in microparticles with or without wall encapsulant. Lactobacillus lactis and Lactococcus mesenteroides survived the acid pH and bile salt treatment. Kefir beverage had a high overall acceptance by non-trained judges compared to fresh kefir. In conclusion, kefir encapsulation by spray-dryer allowed developing a fermented food product preserved, stable and source of bioactive compounds.

Xanthan-based polysaccharide/protein nanoparticles: Preparation, characterization, encapsulation and stabilization of curcumin

This work presents the use of xanthan gum (XG) to prepare protein-containing nanoparticles (NPs). A biocompatible methodology of electrostatic complexation at acidic pH and subsequent thermal treatment is applied using the protein bovine serum albumin (BSA). The NPs have well-defined size and molar mass and are stable upon increase of pH. The secondary conformation of BSA appears irreversibly changed upon thermal treatment within the complexes with XG. The NPs inherit the properties of BSA as they are found to have hydrophobic domains and pH-dependent surface charge. XG-BSA NPs are able to bind the nutraceutical substance curcumin (CUR) and protect its structure against degradation at neutral pH. This investigation introduces the employment of XG for the formulation of protein NPs as nanocarriers of bioactive compounds.

Enhancing the efficiency of some agricultural wastes as low-cost absorbents to remove textile dyes from their contaminated solutions

Four agricultural wastes, i.e., sugarcane bagasse, rice straw, cotton stalk, and corn stalk were experienced as low-cost lignocellulosic materials for their ability to adsorb reactive red dye from its contaminated solutions. Batch adsorption technology was carried out in order to analyze sorption behavior of dye-adsorbent systems at different wastes, initial dye concentration, and solution pH value. The acid pH treatment was detected to significantly enhance the adsorption efficiency of used lignocellulosic wastes to maximum removal efficiency (96%). Bioreactor technology was applied as up-scaling experiments using sugarcane bagasse (SCB) waste (the best adsorbent under batch experiments) with different adsorbent dosage and flow rates. The maximum removal efficiency (89.65%) was recorded by 448 g of SCB waste, hydraulic retention time of 24 h and 12.6 l/h flow rate. The SEM characterization illustrated accumulation of dye molecules onto lignocellulosic structure. Also, elemental analyses by EDAX instrument confirmed absorption technology. Thus, the sugarcane bagasse wastes can be applied as low-cost and environmental safe absorbent for RR dye removal from its contaminated wastewater and introducing non-traditional water resource.

Acid treatment enhances phosphorus release and recovery from waste activated sludge: Performances and related mechanisms

Waste activated sludge (WAS) has attracted considerable attention as an excellent material for P recovery from sewage. This study took concentrated phosphorus removal sludge as objective, and aimed at providing an effective route to promote the transformation of polyphosphate in sludge pellets to dissolved phosphate. After acid pH adjustment, total dissolved phosphate at pH 3.0 was 37.3-fold higher than that at natural pH. The P distribution results illustrated that acid pH accelerated the degradation of short chain polyphosphate into orthophosphate. Furthermore, cell staining results confirmed that the polyphosphate was sourced from the leakage of intracellular matters. Low field NMR and rheology properties analysis were adopted to illustrate that acid pH treatment further improved WAS dewatering performances. Accompanied with the reduction of heavy metals in WAS pellets, the acid pH treatment was also beneficial for WAS subsequent treatment or final disposal. Lastly, Fe3+ addition was proposed as favorable P recovery method, and spherical nanometric materials of FePO4 crystal was obtained accordingly.

Effect of washing, soaking and pH in combination with ultrasound on enzymatic rancidity, phytic acid, heavy metals and coliforms of rice bran

Simultaneous reduction in activity of fat destabilizing enzymes (lipase and lipoxygenase), contaminants heavy metals (As, Cd, Pb, and Hg), antinutrient phytic acid and hazardous coliforms in rice bran was investigated. Application of washing, soaking the washed sample at different pH values (2, 6 and 9) alone or in combination with ultrasonication were examined. While washing was beneficial, its low efficiency acquired further treatment, which was prevailed by application of acidic pH and ultrasound (28 kHz) treatments. Free fatty acids and peroxide value, as indicators of enzymes activity, implied the effectiveness of treatments with adverse impact of sonication on peroxide value. Remarkably, reduction of dominant heavy metals (As, Pb and Zn) and phytic acid were synergistically facilitated by sonication. Coliforms growth was inhibited at pH 2 even at the absence of ultrasonic treatment. Evidently, combination of acidic pH and ultrasound is a practical approach to improve rice bran stability and safety.

Susceptibility of Tick-Borne Encephalitis Virus to Inactivation by Heat, Acidic pH, Chemical, or UV Treatment.

Tick-borne encephalitis virus (TBEV) is a single-stranded, positive-sense RNA virus in the family Flaviviridae that is endemic in parts of Europe and Asia and can cause meningitis or encephalitis. Due to the disease severity, TBEV requires handling under heightened biosafety measures. The establishment and validation of inactivation procedures is a prerequisite for downstream analyses and management of occupational exposure. Therefore, different procedures for TBEV inactivation were tested. Our results suggest that TBEV is susceptible to inactivation by heat, acidic pH, different concentrations of alcohol, formaldehyde, or detergents, and exposure to UV irradiation, which may depend on sample size and composition.

Surface morphologies and wetting properties of layer-by-layer assembled films of polyelectrolytes with bimodal molecular weight distribution

Layer-by-layer (LbL) assembly has been rigorously applied to the construction of superhydrophobic surfaces. Typically, this involves generating a hierarchical porous structure which is then coated with a low surface energy compound. In this study, a porous LbL film was constructed from poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) using a PAA solution with a bimodal molecular weight distribution. This solution was prepared by mixing two PAA solutions with different average molecular weights (100,000 and 15,000 g/mol). The mixing ratio was adjusted for fine control of the porous structure, which was induced by acid treatment at pH 2.0–2.4. Generally, surface pore structure was weakened as the 15,000 g/mol PAA ratio increased. However, the surface roughness decreased or increased as the 15,000 g/mol PAA ratio increased depending on the acid treatment pH and time. The porous LbL films were coated with fluorinated silane to make them hydrophobic. When the acid condition was pH 2.4 for 5 min, the water contact angle decreased significantly from 132° to minimum of 105° as the amount of 15,000 g/mol PAA increased. However, at pH 2.0 for 5 min, the water contact angle decreased smaller from 148° to 139° as the amount of 15,000 g/mol PAA increased.

Boosting nanotoxicity to combat multidrug-resistant bacteria in pathophysiological environments.

Nanomaterials are promising novel antibiotics, but often ineffective. We found that nanomaterial–bacteria complex formation occurred with various nanomaterials. The bactericidal activity of NMs strongly depends on their physical binding to (multidrug-resistant) bacteria. Nanomaterials' binding and antibiotic effect was reduced by various pathophysiological biomolecule coronas strongly inhibiting their antibiotic effects. We show from analytical to in vitro to in vivo that nanomaterial-based killing could be restored by acidic pH treatments. Here, complex formation of negatively-charged, plasma corona-covered, nanomaterials with bacteria was electrostatically enhanced by reducing bacteria's negative surface charge. Employing in vivo skin infection models, acidic pH-induced complex formation was critical to counteract Staphylococcus aureus infections by silver nanomaterials. We explain why nano-antibiotics show reduced activity and provide a clinically practical solution.

Unfolding and Inhibition of Polyphenoloxidase Induced by Acidic pH and Mild Thermal Treatment

The activity of polyphenoloxidase (PPO) treated by acidic pH and mild thermal processing was found to be closely related to the conformational changes. Weakly acidic environment (pH 4.0–6.0) resulted in reversible inhibition of activity and slight changes in the conformation, and refolding of PPO was observed after readjusting pH to 6.8. At pH lower than 4.0, PPO activity was strongly inhibited with great unfolding in conformation and all changes were irreversible. Acidic environment increased the susceptibility of PPO to thermal treatment, and greater changes in activity and conformation of PPO were observed under the combined treatment of acidic pH and mild thermal treatment. Besides, the inactivation of PPO induced by thermal treatment followed a biphasic kinetic model, and acidic pH increased the inactivation rate of labile and stable PPO. The combination of acidic pH and mild thermal processing expected to avoid the nutritional loss and sensory damage in fruits and vegetables caused by severe acid or temperature.

Modeling transport of arsenic through modified granular natural siderite filters for arsenic removal

Groundwater arsenic (As) contamination is a hot issue, which is severe health concern worldwide. Recently, many Fe-based adsorbents have been used for As removal from solutions. Modified granular natural siderite (MGNS), a special hybrid Fe(II)/Fe(III) system, had higher adsorption capacity for As(III) than As(V), but the feasibility of its application in treating high-As groundwater is still unclear. In combination with transport modeling, laboratory column studies and field pilot tests were performed to reveal both mechanisms and factors controlling As removal by MGNS-filled filters. Results show that weakly acid pH and discontinuous treatment enhanced As(III) removal, with a throughput of 8700 bed volumes (BV) of 1.0 mg/L As(III) water at breakthrough of 10 μg/L As at pH 6. Influent HCO3− inhibited As removal by the filters. Iron mineral species, SEM and XRD patterns of As-loading MGNS show that the important process contributing to high As(III) removal was the mineral transformation from siderite to goethite in the filter. The homogeneous surface diffusion modeling (HSDM) shows that competition between As(III) and HCO3− with adsorption sites on MGNS was negligible. The inhibition of HCO3− on As(III) removal was connected to inhibition of siderite dissolution and mineral transformation. Arsenic loadings were lower in field pilot tests than those in the laboratory experiments, showing that high concentrations of coexisting anions (especially HCO3− and SiO44−), high pH, low EBCT, and low groundwater temperature decreased As removal. It was suggested that acidification and aeration of high-As groundwater and discontinuous treatment would improve the MGNS filter performance of As removal from real high-As groundwater.

Effect of pH shifting on conformation and gelation properties of myosin from skeletal muscle of blue round scads(Decapterus maruadsi)

To clarify the gel formation mechanism of isolated proteins recovered from blue round scads by isoelectric solubilization/precipitation, the physiochemical, conformational and gelation properties of the major protein myosin treated by acidic-(AM) or alkaline-(KM) pH-shifting were investigated and compared with native myosin (NM). The solubility in all myosin samples dropped significantly at 40 °C, with remarkable increases of particle size, turbidity and surface hydrophobicity. Among the samples, AM exhibited the lowest solubility and highest turbidity than NM and KM as the temperature was higher than 40 °C, indicating that AM is easily to be denatured and aggregated. Circular dichroism (CD) analysis showed that both acidic and alkaline pH treatments led to conformational changes of myosin, together with α-helix content variations. When pH was readjusted to neutral, KM recovered its structure similar to NM, while AM failed to refold to its native state. NM exhibited the highest storage modulus (G′) at 90 °C, while AM revealed the lowest G′ value. Furthermore, AM did not change obviously during heating, especially at the gelling temperature range (60–90 °C). These results strongly suggested that acidic treatment led to an irreversible conformational change in myosin, consequently induced a fierce denaturation and aggregation at the initial stage of heating, and eventually led to a complete loss of gel-forming ability. Alkaline pH-shifting, on the other hand is thus more feasible for protein recovery from blue round scads.

Cryo-EM structure of the SARS coronavirus spike glycoprotein in complex with its host cell receptor ACE2.

The trimeric SARS coronavirus (SARS-CoV) surface spike (S) glycoprotein consisting of three S1-S2 heterodimers binds the cellular receptor angiotensin-converting enzyme 2 (ACE2) and mediates fusion of the viral and cellular membranes through a pre- to postfusion conformation transition. Here, we report the structure of the SARS-CoV S glycoprotein in complex with its host cell receptor ACE2 revealed by cryo-electron microscopy (cryo-EM). The complex structure shows that only one receptor-binding domain of the trimeric S glycoprotein binds ACE2 and adopts a protruding “up” conformation. In addition, we studied the structures of the SARS-CoV S glycoprotein and its complexes with ACE2 in different in vitro conditions, which may mimic different conformational states of the S glycoprotein during virus entry. Disassociation of the S1-ACE2 complex from some of the prefusion spikes was observed and characterized. We also characterized the rosette-like structures of the clustered SARS-CoV S2 trimers in the postfusion state observed on electron micrographs. Structural comparisons suggested that the SARS-CoV S glycoprotein retains a prefusion architecture after trypsin cleavage into the S1 and S2 subunits and acidic pH treatment. However, binding to the receptor opens up the receptor-binding domain of S1, which could promote the release of the S1-ACE2 complex and S1 monomers from the prefusion spike and trigger the pre- to postfusion conformational transition.

PH and Heat Resistance of the Major Celery Allergen Apig1.

The major celery allergen Apig1 is a member of the pathogenesis-related 10 class protein family. This study aims to investigate the impact of heat and pH on the native protein conformation required for Immunoglobulin E (IgE) recognition. Spectroscopic methods, MS and IgE-binding analyses are used to study the effects of pH and thermal treatment on Apig1.0101. Heat processing results in a loss of the native protein fold via denaturation, oligomerization, and precipitation along with a subsequent reduction of IgE recognition. The induced effects and timescales are strongly pH dependent. While Apig1 refolds partially into an IgE-binding conformation at physiological pH, acidic pH treatment leads to the formation of structurally heat-resistant, IgE-reactive oligomers. Thermal processing in the presence of a celery matrix or at pH conditions close to the isoelectric point (pI = 4.63) of Apig1.0101 results in almost instant precipitation. This study demonstrates that Apig1.0101 is not intrinsically susceptible to heat treatment in vitro. However, the pH and the celery matrix strongly influence the stability of Apig1.0101 and might be the main reasons for the observed temperature lability of this important food allergen.

Effect of Acid Modification of Soy Glycinin on Its Interfacial and Emulsifying Properties

AbstractSoybean glycinin [11S] was modified by an acidic pH treatment to improve its emulsifying properties. Glycinin was obtained by isoelectric precipitation (11Sn) and then treated with acid (11St). The oil–water interfacial tension and rheology were measured. The rate constants of adsorption (ka) and rearrangement (kr) of proteins at the interface and the dilational (E), elastic (Ed), and viscous modulus (Ev) of the protein interfacial film were determined. Particle size distribution (PSD), interfacial protein concentration (Γ), and the creaming destabilization rate constants ks (for the smaller droplets) and kl (for the larger droplets) were analyzed in oil‐in‐water emulsions (25% v/v of oil and 75% v/v of 1 mg/mL protein solution in 10 mM sodium phosphate buffers, pH 7.0 and 2.5, respectively).Compared to the native protein, the acid treatment caused irreversible denaturation of 11S and significantly increased Г, ka, E, Ed, and Ev (P ≤ 0.05), resulting in a greater rate of protein adsorption to the interface and a stronger interfacial film. PSD showed a bimodal distribution with peaks above and below 4 μm. Smaller droplets moved toward smaller diameters for 11St. It also showed lower values of creaming destabilization constants ks (d ≤ 4 μm) and kl (d ≥ 4 μm) than 11Sn. In conclusion, acid treatment of 11S enhances the creaming stability of its emulsions by improving the interfacial properties and reducing the droplet size.