Mild Acid Treatment Research Articles

A Facile Preparation of λ-MnO2 as Cathode Material for High-Performance Zinc-Manganese Redox Flow Battery

Aqueous-based rechargeable zinc-manganese redox flow batteries have displayed a great advantage in the field of large-scale energy storage due to low cost of zinc and manganese resources and environmentally-safe. Various types of MnO2, including α and δ have been proposed as cathode material, but low capacity and cycling life limited their large scale application. Herein, we report highly crystalline, spinel-type λ-MnO2 as cathode for zinc-manganese (Zn/λ-MnO2) redox flow battery system which derived from LiMn2O4 via mild acid treatment. This system exhibits diffusion controlled insertion mechanism of Li+ in λ-MnO2 spinel structure with little contribution of surface controlled process in 1 M Li2SO4 + 1 M ZnSO4 electrolyte. The obtained λ-MnO2 cathode delivers two high discharge voltage platforms of 1.97 and 1.81 V with specific capacity of 128 mAh g−1 at a current rate of 2 C under the operating potential window of 1.5–2.1 V. The assembled battery system exhibits excellent rate performance and cyclic stability with high capacity retention of 83% after 1,000 continuous cycles at a high current density of 10 C. This mechanism enables an outstanding energy efficiency of 98% and provides key insights for the development of high-performance, low-cost and reversible zinc-manganese redox flow batteries.

Mild generation of surface oxygen vacancies on CeO2 for improved CO2 photoreduction activity.

The vacancy defects of semiconductor photocatalysts play key roles in enhancing their photocatalytic CO2 reduction activity. In this work, CeO2 was chosen as a model catalyst and oxygen vacancies were introduced on its surface by a facile and mild oxalic acid treatment followed by moderate heating in N2. Such a treatment resulted in a much increased ratio of Ce3+/Ce4+ in CeO2, and the oxygen vacancy-enriched CeO2 showed remarkably enhanced photocatalytic activity in CO2 reduction, with CO being the dominant reduction product, whose yield was about 8 times that on the pristine CeO2. In situ FT-IR spectra showed that the abundant oxygen vacancies substantially improved the CO2 adsorption/activation on the surface of CeO2, which facilitated the subsequent reduction of CO2. However, the carbonates strongly adsorbed on the photocatalyst surface might be the main obstacle to maintaining the high CO2 reduction activity and stability of CeO2 with O vacancies.

Effects of the acid–base treatment of corn on rumen fermentation and microbiota, inflammatory response and growth performance in beef cattle fed high-concentrate diet

Beef cattle are often fed high-concentrate diet (HCD) to achieve high growth rate. However, HCD feeding is strongly associated with metabolic disorders. Mild acid treatment of grains in HCD with 1% hydrochloric acid (HA) followed by neutralization with sodium bicarbonate (SB) might modify rumen fermentation patterns and microbiota, thereby decreasing the negative effects of HCD. This study was thus aimed to investigate the effects of treatment of corn with 1% HA and subsequent neutralization with SB on rumen fermentation and microbiota, inflammatory response and growth performance in beef cattle fed HCD. Eighteen beef cattle were randomly allocated to three groups and each group was fed different diets: low-concentrate diet (LCD) (concentrate : forage = 40 : 60), HCD (concentrate : forage = 60 : 40) or HCD based on treated corn (HCDT) with the same concentrate to forage ratio as the HCD. The corn in the HCDT was steeped in 1% HA (wt/wt) for 48 h and neutralized with SB after HA treatment. The animal trial lasted for 42 days with an adaptation period of 7 days. At the end of the trial, rumen fluid samples were collected for measuring ruminal pH values, short-chain fatty acids, endotoxin (or lipopolysaccharide, LPS) and bacterial microbiota. Plasma samples were collected at the end of the trial to determine the concentrations of plasma LPS, proinflammatory cytokines and acute phase proteins (APPs). The results showed that compared with the LCD, feeding the HCD had better growth performance due to a shift in the ruminal fermentation pattern from acetate towards propionate, butyrate and valerate. However, the HCD decreased ruminal pH and increased ruminal LPS release and the concentrations of plasma proinflammatory cytokines and APPs. Furthermore, feeding the HCD reduced bacterial richness and diversity in the rumen. Treatment of corn increased resistant starch (RS) content. Compared with the HCD, feeding the HCDT reduced ruminal LPS and improved ruminal bacterial microbiota, resulting in decreased inflammation and improved growth performance. In conclusion, although the HCD had better growth performance than the LCD, feeding the HCD promoted the pH reduction and the LPS release in the rumen, disturbed the ruminal bacterial stability and increased inflammatory response. Treatment of corn with HA in combination with subsequent SB neutralization increased the RS content and helped counter the negative effects of feeding HCD to beef steers.

Allylic hydroxylation of triterpenoids by a plant cytochrome P450 triggers key chemical transformations that produce a variety of bitter compounds

Cucurbitacins are highly oxygenated triterpenoids characteristic of plants in the family Cucurbitaceae and responsible for the bitter taste of these plants. Fruits of bitter melon (Momordica charantia) contain various cucurbitacins possessing an unusual ether bridge between C5 and C19, not observed in other Cucurbitaceae members. Using a combination of next-generation sequencing and RNA-Seq analysis and gene-to-gene co-expression analysis with the ConfeitoGUIplus software, we identified three P450 genes, CYP81AQ19, CYP88L7, and CYP88L8, expected to be involved in cucurbitacin biosynthesis. CYP81AQ19 co-expression with cucurbitadienol synthase in yeast resulted in the production of cucurbita-5,24-diene-3β,23α-diol. A mild acid treatment of this compound resulted in an isomerization of the C23-OH group to C25-OH with the concomitant migration of a double bond, suggesting that a nonenzymatic transformation may account for the observed C25-OH in the majority of cucurbitacins found in plants. The functional expression of CYP88L7 resulted in the production of hydroxylated C19 as well as C5-C19 ether-bridged products. A plausible mechanism for the formation of the C5-C19 ether bridge involves C7 and C19 hydroxylations, indicating a multifunctional nature of this P450. On the other hand, functional CYP88L8 expression gave a single product, a triterpene diol, indicating a monofunctional P450 catalyzing the C7 hydroxylation. Our findings of the roles of several plant P450s in cucurbitacin biosynthesis reveal that an allylic hydroxylation is a key enzymatic transformation that triggers subsequent processes to produce structurally diverse products.

Gelling mechanism of RG-I enriched citrus pectin: Role of arabinose side-chains in cation- and acid-induced gelation

RG-I enriched pectin is present in fruit and vegetable containing products. However, it is removed by the hot acid treatment during commercial pectin production to improve gelling properties and to afford a more uniform pectin quality. Recently, an awareness of the health benefits of RG-I enriched pectin has caused technologists to rethink its utilization by the food industry, especially as a novel healthy gelling agent. Unique RG-I enriched pectin with abundant arabinan side-chains was extracted from citrus membrane by sequential mild acidic and alkaline treatment. Arabinose was then removed by enzymatic treatment to investigate the impact of arabinose side-chains on gelation. The properties of RG-I enriched pectin gels, prepared using cations or acid, showed it could form gels under conditions required for both low and high methoxyl pectin as a result of its highly branched structure. In cation-induced gelation, the HG region forms egg-box junction zones with divalent cations and the side-chains of the RG-I region stabilizes the network structure through entanglements. In acid-induced gelation, low pH promotes formation of hydrogen bonding and hydrophobic interactions within the HG region and the side-chains create a tighter conformation, eventually allowing for stronger interactions between the pectin chains.

Fe3O4@Pt Core-Shell Nanocatalyst Supported on N-Doped Functionalized Graphene As Novel Cathode Catalysts for Microbial Fuel Cells

Microbial Fuel Cells (MFCs) are bio-electrochemical systems that use bacteria to generate bioelectricity via the oxidation of organic matter contained in a substrate (such as wastewater). However, this new method of renewable energy recovery has several technical challenges. At the cathode, for example, the Oxygen Reduction Reaction (ORR) takes place. This reaction is kinetically slow, remaining one of the main drawbacks of MFCs. Even though Pt/C nanocatalysts are widely used to promote the ORR, their performance in MFC is low due to the complex operating conditions. Therefore, alternative cathode nanocatalysts must be developed. Regarding to this issue, core-shell nanocatalysts are a promising alternative for MFCs cathodes. In this study, Fe3O4@Pt core-shell nanoparticles have been supported on N-doped and functionalized graphene (N-Gf) to obtain the Fe3O4@Pt/N-Gf nanocatalyst. First, nitrogen-doped graphene (N-G) has been synthesized by a one-step ball milling process using graphite as carbon source and melamine as both exfoliating agent and nitrogen source. Then, N-G has been functionalized by a mild acid treatment and labeled as N-Gf. Separately, the Fe3O4 core has been obtained by co-precipitation reaction of Fe2+/Fe3+, using citric acid as surfactant. The Pt shell has been deposited on the core by the Bromide Anion Exchange (BAE) method, resulting in a Fe3O4@Pt nanostructure having a 1:1 Fe3O4:Pt molar ratio. The 20 wt.% Fe3O4@Pt/N-Gf core-shell nanocatalyst has been obtained also by the BAE method. Regarding N-Gf, its X-ray diffraction (XRD) pattern shows well-defined peaks at 2θ=26.5°, 44.39 and 54.4°, characteristic of graphitic structures. Moreover, its ID/IG intensity ratio calculated from Raman spectra is 1.40, which indicates a high degree of disorder in the carbon lattice, most likely due to the incorporation of N species into the structure. Additionally, an N content of 1.40 at. % has been determined by energy-dispersive X-ray spectroscopy (EDS). The XRD pattern of the magnetite phase shows reflections at 2θ= 30.44, 35.53, 43.46, 54.01, 57.79, 63.06 and 74.75°, attributed to the (220), (311), (400), (422), (511) (440) and (531) planes. The crystallite size of Fe3O4 has been calculated as 9.2 nm. In addition, its Raman spectrum shows signals corresponding to the A1g, Eg and T2g vibrational modes, characteristic of magnetite. Meanwhile, the catalytic activity of the Fe3O4@Pt/N-Gf nanocatalyst for the ORR has been evaluated by the Rotating Ring-Disk Electrode (RRDE) technique in 0.5 M H2SO4 and in H2SO4 having a pH=6.1. The latter is because of the pH of the pharmaceutical residual water used as substrate in the MFC. Electrochemical parameters such as hydrogen peroxide percentage, number of electrons transferred, and onset and half wave potentials has been determined. The results show that Fe3O4@Pt/N-Gf has a catalytic activity for the ORR in low and almost neutral pH comparable to that of a commercial Pt/C nanocatalyst. Therefore, these results suggest that Fe3O4@Pt/N-Gf is a promising cathode nanocatalyst for MFC applications. To the best of the authors knowledge, this is the first time that such nanostructures have been evaluated in MFCs.

Lanthanide ion processing from monazite based on magnetic nanohydrometallurgy

A systematic work has been performed for the separation of the lanthanide elements from monazite mineral using magnetic nanohydrometallurgy. The process was based on DTPA (diethylenetriaminepentaacetic acid) functionalized Fe3O4 superparamagnetic nanoparticles as the active species for carrying out the magnetic extraction of the lanthanide ions in aqueous solution, at pH 6. The process was monitored by means of X-ray fluorescence (EDXRF) techniques, and the corresponding Langmuir isotherms were carefully elaborated, allowing to evaluate the equilibrium (affinity) constants involved. The results obtained for La3+, Pr3+, Nd3+, Sm3+, Gd3+ and Dy3+ ions followed the trends dictated by the lanthanide ion contraction. In the process, the elements are reversibly captured and released from the magnetically confined nanoparticles after applying a mild acid treatment (pH 2). Their chemical separation based on their relative affinity constants, can be performed by applying successive magnetic extraction/releasing cycles in aqueous solution, at room temperature, using the same reactor, dispensing the use of organic solvents and more intensive chemical processing.

Multifunctional Fe(III)-Binding Polyethers from Hydroxamic Acid-Based Epoxide Monomers.

Multiple hydroxamic acids are introduced at poly(ethylene glycol) (PEG) via copolymerization of ethylene oxide with a novel epoxide monomer containing a 1,4,2-dioxazole-protected hydroxamic acid (HAAGE). AB- and ABA-type di- and triblock copolymers as well as statistical copolymers of HAAGE and ethylene oxide are prepared in a molecular weight range between 2600 and 12 000 g mol-1 with low dispersities (Ð < 1.2). Cleavage of the acetal protecting group after the polymerization is achieved by mild acidic treatment, releasing multiple free hydroxamic acids tethered to the polyether backbone. The chelation properties of different polymer architectures (statistical versus diblock and ABA triblock) are investigated and compared with regard to the number and position of hydroxamic acids. Separation of the hydroxamic acid units by at least 5 ethylene glycol monomer units is found to be essential for high Fe(III) binding efficiency, while block copolymers are observed to be the best-suited architecture for polymer network and hydrogel formation via Fe(III) chelation.

Isolation and characterisation of nanofibrillated cellulose from waste cotton: effects on thermo-mechanical properties of polylactic acid/MA-g-SEBS blends

In garment industry, cotton waste is the major threat for disposal or waste management due to environmental issues. Nanofibrillated cellulose (NFC) from waste cotton was isolated by steam explosion technique, an eco-friendly method in comparison with chemical methods. Nanocellulose was characterised by different analysis techniques like TEM, SEM and XRD. The crystallinity index of nanocellulose was found to be 66% based on Seigel’s empirical method. SEM micrographs showed highly entangled nanofibrils with diameters ranging from 67 to 70 nm. TEM results revealed reduction in the size of fiber from micro to nano upon mild acid treatment along with steam explosion. Bionanocomposites of maleated styrene ethylene butylene styrene (MA-g-SEBS) toughened polylactic acid (PLA) reinforced with nanocellulose were fabricated by twin screw extruder and tested for thermo-mechanical behaviour using injection molded specimen. Mechanical property evaluation showed that the composites containing nanocellulose exhibited higher modulus compared to virgin PLA and PLA binary blend system containing SEBS or MA-g-SEBS. The elongations of bionanocomposites were substantially increased, possibly due to good dispersion of nanocellulose and its plasticizing effect. Morphological studies were also carried out to investigate the effect of nanocellulose on toughened PLA. The impact strength was also found to be higher compared to virgin PLA by the incorporation of nanocellulose to SEBS toughened PLA. Differential scanning calorimetry measurements observed an increase in crystallization of PLA by heterogeneous nucleation effect of NFC.

Structural analyses and deposition of purified carbon nanotubes using electrophoretic deposition

This study was conducted to elucidate the analysis of purified carbon nanotubes (CNTs) in dimethylformamide (DMF) that allows good performance in electrophoretic deposition (EPD) process. In this attempt, the effect of mild acid treatment of nitric acid (HNO3) on CNTs of purification process was evaluated. The purified CNTs quality was observed using Thermal Gravimetric Analysis (TGA), Fourier Transformation Infrared Spectroscopy (FTIR), Transmission Electron microscopy (TEM), Scanning Electron Microscope (SEM) and Energy Dispersive x-ray (EDX). Meanwhile for the suspended purified CNTs, the conducted analyses were zeta potential and UV–vis spectroscopy in different solvents (DMF, distilled water, mixture of acetone/ethanol, NMP, and Texanol). The suspension stability was observed for three days prior to EPD process. It was found that the purity of CNTs increased where only 0.03 wt.% of catalyst were left from TGA analyses. Moreover, the TEM and SEM images showed that the catalyst was being removed after purification and functional groups are introduced as observed through FTIR analysis. The UV–vis results showed that the CNTs were suspended longer in DMF and formed more stable suspension as compared to other solvents where constant reading during observations were obtained while the zeta potential result was indicated to have sufficient particle charge (−35.87 mV) for EPD process. In addition, the mechanism of CNTs purifications was studied and it clearly justified the role of functional group as CNTs charge with good reading of zeta potential was obtained. The SEM image of EPD result shows the performance of CNTs suspension in DMF with optimum deposition thickness of 11.98 μm and 0.9 mg of deposition weight.

Characterization of the Salmonella Typhimurium core oligosaccharide and its reducing end 3-deoxy-d-manno-oct-2-ulosonic acid used for conjugate vaccine production

One of the strategies adopted for the development of a bivalent conjugate vaccine against invasive nontyphoidal Salmonella consists of linking the O-antigen component of S. Typhimurium and S. Entertidis lipopolysaccharides to the carrier protein CRM197, a non-toxic variant of diphtheria toxin. The conjugation reaction uses the reducing end residue 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) of the core to which the O-antigen chain is bound (OAg-core). OAg-core chains are cleaved from the lipid A directly in the fermentation broth by mild acid treatment. Kdo has been reported to undergo structural changes under these conditions and therefore the Kdo at the reducing end was thoroughly analysed to verify its structural integrity. For this purpose, low molecular mass OAg-core chains extracted from S. Typhimurium wild type bacteria and core oligosaccharides extracted from S. Typhimurium bacteria mutated not to produce O-antigen repeats were characterized by GLC-MS, MALDI-TOF-MS and NMR spectroscopy. Moreover, a combination of 1H–1H and 1H–13C experiments confirmed the linkage positions, sequence and structure of the octasaccharide core with 5-linked Kdo present at the reducing end in its native structure: α-GlcpNAc-(1→2)-α-Glcp-(1→2)-α-Galp-(1→3)-[α-Galp-(1→6)]-α-Glcp-(1→3)-[α-Hepp-(1→7)]-α-Hepp-(1→3)-α-Hepp-(1→5)-Kdo.

Enrichment of solution-processable single-walled carbon nanotubes for flexible nanoelectronics

Here we fabricate solution-processable single-walled carbon nanotubes that feature enhanced dispersion in solvents while still affording excellent structural integrity, which is examined by adopting both the microscopic (scanning electron microscopy) and spectroscopic (Raman spectroscopy) characterization techniques. The controlled functionalization is key to producing the electronic grade carbon nanotubes that exhibit the G-to-D peak ratio easily exceeding 10 when deposited as a thin-film by spin coating. A comparative study is conducted to further investigate the effect of the deposition method (spin coating versus drop casting), the chemical treatment (functionalization), and the substrate (rigid substrates such as SiO2 or glass, and flexible substrates such as polyimide) on the structural properties of carbon nanotubes. Additionally, a low-cost inkjet printing method enables us to study the current-voltage characteristics of carbon nanotube thin-films of varying channel lengths, and the measured electrical resistivity values approach those of moderately doped semiconducting materials (in the range of 10−3 Ωm). This study suggests that upon the mild acid treatment, the single-walled carbon nanotubes possess the potential to advance flexible nanoelectronics.

Highly conducting, durable and large area carbon nanotube thick films for stretchable and flexible electrodes

We demonstrated a straightforward strategy to fabricate highly conductive carbon nanotube (CNT) films by introducing polyacrylic acid (PAA) as a dispersant and a dopant. A dispersion process was developed to fabricate highly concentrated and viscous aqueous suspensions, which enabled an easy deposition of uniform micrometer-thick CNT films on a large scale. The CNT-PAA hybrid film exhibited a ten fold increase in the conductivity as compared with the nondoped film. Furthermore, a mild acid-treatment was utilized to modify the CNTs before dispersion, resulting in a high density of small-bundle CNTs without clear structural damage and a further two fold increase in the conductivity. The CNT-PAA hybrid film with a thickness of around 5.1 μm exhibited a sheet resistance of 0.1 Ω/sq with a surprisingly high electrical conductivity of 19 600 ± 4000 S/cm. The conductivity of the hybrid film remained almost constant after aging tests under the conditions of 85 °C and 85% relative humidity for more than 1000 h, suggesting its outstanding long-term stability. Furthermore, HNO3 doping increased the conductivity to 35 000 ± 5000 S/cm.

Easy fabrication of mussel inspired coated foam and its optimization for the facile removal of copper from aqueous solutions

Herein we present a straightforward approach for the use of polydopamine (PDA) in adsorption of heavy metals from aqueous solutions. This is achieved by fabricating a healthy and environmentally friendly polydimethylsiloxane (PDMS) foam with a mussel inspired PDA layer deposited on the surface. Critical adsorption parameters (pH, temperature and PDA thickness) are optimized by the application of experimental design methodology. Adsorption kinetics and isotherms are studied in detail evidencing a good fitting with Langmuir isotherm and pseudo-second-order kinetics thus suggesting the occurrence of a chemical sorption process with monolayer nature between metals and PDMS/PDA foam. Intraparticle diffusion model evidences good accessibility and high affinity of binding sites on PDA surface. Once adsorbed, metals are reduced to a lower toxic form and can be then removed by a mild acidic treatment thus being easily collected and stocked.

Sequential Enzymatic and Mild-Acid Hydrolysis of By-Product of Carrageenan Process from Kappaphycus alvarezii

Kappaphycus alvarezii is a red macroalgae widely used to produce carrageenan. The carrageenan processing produces a by-product rich in glucan which has been reported as easily hydrolyzed with enzymes, but the hydrolysate forms a gel at usual fermentation temperatures. The purpose of this study was to evaluate the enzymatic hydrolysis integrated with a mild-acid treatment of the by-product to obtain a hydrolysate rich in monomeric sugars. Using an enzyme load of 10 FPU g−1 of by-product, close to 100 and 14.7% of glucan and galactan conversion were reached, respectively. Increasing the enzyme load to 100 FPU g−1 raised the galactan conversion to 30%. The mild-acid treatment after enzymatic hydrolysis was satisfactory, increasing the glucose and galactose concentrations, without producing significant amounts of fermentation inhibitors and avoiding the formation of a gel structure. The statistical analysis showed that the main effects on the response were negative for the three independent variables, meaning that the selectivity (S) becomes lower when experimental conditions at the higher levels are used (longer time, higher temperature, and acid concentration). Therefore, the integrated enzymatic and acid hydrolysis of the by-product becomes a promising technological route to produce monomeric sugars for bioethanol or fine chemical production.

Treatment of corn with lactic acid or hydrochloric acid modulates the rumen and plasma metabolic profiles as well as inflammatory responses in beef steers

BackgroundHigh-grain diets that meet the energy requirements of high-producing ruminants are associated with a high risk of rumen disorders. Mild acid treatment with lactic acid (LA) has been used to modify the degradable characteristics of grains to improve the negative effects of high-grain diets. However, the related studies mainly focused on dairy cows and explored the effects on rumen fermentation, production performance, ruminal pH and so forth. And up to date, no studies have reported the hydrochloric acid (HA) treatment of grains for ruminant animals. Therefore, based on metabolomics analysis, the aim of this study was to evaluate the effects of treatment of corn by steeping in 1% LA or 1% HA for 48 h on the rumen and plasma metabolic profiles in beef steers fed a high corn (48.76%) diet with a 60:40 ratio of concentrate to roughage. The inflammatory responses of beef cattle fed LA- and HA-treated corn were also investigated.ResultsBased on ultra-high-performance liquid tandem chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-QTOF/MS) metabolomics and multivariate analyses, this study showed that steeping corn in 1% LA or 1% HA modulated the metabolic profiles of the rumen. Feeding beef steers corn steeped in 1% LA or 1% HA was associated with lower relative abundance of carbohydrate metabolites, amino acid metabolites, xanthine, uracil and DL-lactate in the rumen; with higher ruminal pH; with lower concentrations of acetate, iso-butyrate and iso-valerate; and with a tendency for lower ruminal lipopolysaccharide (LPS) concentrations. Moreover, the data showed lower concentrations of plasma C-reactive protein, serum amyloid A, haptoglobin, interleukin (IL)-1β and IL-8 in beef steers fed 1% LA- or HA-treated corn. The 1% LA treatment decreased the concentrations of plasma LPS, LPS-binding protein and tumour necrosis factor-alpha and the relative abundance of L-phenylalanine, DL-3-phenyllactic acid and tyramine in plasma. The 1% HA treatment decreased the relative abundance of urea in plasma and increased the relative abundance of all amino acids in the plasma.ConclusionsThese findings indicated that LA or HA treatment of corn modulated the degradation characteristics of starch, which contributed to improving the rumen and plasma metabolic profiles and to decreasing inflammatory responses in beef steers fed a high-concentrate diet.

Exploring the contributions of two glutamate decarboxylase isozymes in Lactobacillus brevis to acid resistance and \u03b3-aminobutyric acid production

BackgroundThe glutamate decarboxylase (GAD) system of Lactobacillus brevis involves two isoforms of GAD, GadA and GadB, which catalyze the conversion of L-glutamate to γ-aminobutyric acid (GABA) in a proton-consuming reaction contributing to intracellular pH homeostasis. However, direct experimental evidence for detailed contributions of gad genes to acid tolerance and GABA production is lacking.ResultsMolecular analysis revealed that gadB is cotranscribed in tandem with upstream gadC, and that expression of gadCB is greatly upregulated in response to low ambient pH when cells enter the late exponential growth phase. In contrast, gadA is located away from the other gad genes, and its expression was consistently lower and not induced by mild acid treatment. Analysis of deletion mutations in the gad genes of L. brevis demonstrated a decrease in the level of GAD activity and a concomitant decrease in acid resistance in the order of wild-type> ΔgadA> ΔgadB> ΔgadC> ΔgadAB, indicating that the GAD activity mainly endowed by GadB rather than GadA is an indispensable step in the GadCB mediated acid resistance of this organism. Moreover, engineered strains with higher GAD activities were constructed by overexpressing key GAD system genes. With the proposed two-stage pH and temperature control fed-batch fermentation strategy, GABA production by the engineered strain L. brevis 9530: pNZ8148-gadBC continuously increased reaching a high level of 104.38 ± 3.47 g/L at 72 h.ConclusionsThis is the first report of the detailed contribution of gad genes to acid tolerance and GABA production in L. brevis. Enhanced production of GABA by engineered L. brevis was achieved, and the resulting GABA level was one of the highest among lactic acid bacterial species grown in batch or fed-batch culture.

Use of Algae Biomass Obtained by Single-Step Mild Acid Hydrolysis in Hydrogen Production by the β-Glucosidase-Producing Clostridium beijerinckii Br21

Macroalgae biomass is a potential feedstock for fermentative H2 production: it has high carbohydrate concentration and is lignin-free. Here, we optimize a mild acid treatment of Kappaphycus alvarezii biomass by an experimental design 24. The optimal acid treatment conditions were 90 °C, HCl concentration of 55.9 mmol/L, 0.375 g of algae mass, and 8 h of treatment. Under these conditions, the hydrolysate presented mono-, but also di- and oligosaccharides. We used this hydrolysate as substrate for fermentative hydrogen (H2) production by the Clostridium beijerinckii Br21 grown in two different conditions: (1) in medium containing galactose and no β-glucosidase activity; (2) in medium with cellobiose to stimulate β-glucosidase activity, which was 0.33U/mL. The fermentative assay conducted in the presence of the C. beijerinckii Br21 with β-glucosidase activity provided higher H2 concentration and yield as compared to the assay accomplished in the presence of the inoculum with no β-glucosidase activity—171.76 ± 2.10 and 140.95 ± 10.92 mL of H2/L, and 70.3 ± 0.9 and 62.7 ± 4.9 mL of H2/g of dry algae, respectively. Therefore, a fermentative β-glucosidase-producing organism such as C. beijerinckii Br21 can potentially complete biomass saccharification for later renewable H2 production.

The effect of pH on surface activation of wood polymer composites (WPCs) with hydrogen peroxide for improved adhesion

Wood Polymer Composites (WPCs) have become widely acceptable for use in different products, including furniture. This range of applications could be increased by improvement in effective bonding and jointing techniques. However adhesion between WPC components is problematic because of their low surface energy and the hydrophobic nature of the polyolefin matrices which are commonly used. Surface activation pretreatments using hydrogen peroxide solutions have been investigated, and shown an improvement in lap-joint shear when bonding using epoxy adhesives. The effect on surface energy, roughness and chemical composition was studied. The improvement in adhesion appeared to be governed by the pH of the treatment solution, with clear differences being identified between treatments in acidic and alkaline media.The best results were achieved with a mild alkaline hydrogen peroxide treatment at a pH of 7.5 (37% improvement); however a mild acidic hydrogen peroxide treatment also showed a suitable level of adhesion improvement (29%, pH 6). In the alkaline medium it was found that the hydroperoxy anion was efficient in altering both the lignin and the hemicellulose component of the wood flour. It was necessary to limit the extent of wood particle degradation by the hydroperoxy anion, explaining the poor adhesion for treatments with pH 9 peroxide solution. This study indicates that mild (pH 7.5) alkaline treatment solution could be employed. In the acidic medium, the free radical based reaction processes dominated, and were likely to have altered the polypropylene matrix of the WPC material.

Isolation and Characterization of Nanocellulose Obtained from Industrial Crop Waste Resources by Using Mild Acid Hydrolysis

Cellulose, microcrystalline cellulose and nanocellulose were prepared from three agricultural waste resources: pineapple leaf (PALF), banana rachis (BR), and sugarcane bagasse (SCB). Each waste resource was first converted into microcrystalline cellulose which was subsequently converted into cellulose nanoparticles by using mild (30% w/v) and strong (60% w/v) sulfuric acid concentrations for extraction. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were used to characterize each waste resource and extracted cellulosic materials. Furthermore, nanocelluloses were studied by zeta potential, size analysis, and transmission electron microscopy (TEM). Cellulose nanowhiskers were successfully obtained and isolated with a 33% average yield by applying a mild acid treatment. Substrates BR and SCB proved to be more promising agricultural waste resources in terms of their crystalline cellulosic content and properties.