Acidic pH Range Research Articles

PH-induced structural changes of tyrosinase fromAgaricus bisporususing fluorescence andin silicomethods

Tyrosinases are involved in enzymatic browning reactions in damaged fruits during post-harvest handling and processing. The overall structure of tyrosinase from Agaricus bisporus mushrooms at different pH values was monitored using fluorescence spectroscopy and molecular dynamics simulations. When the pH value was increased from 6.0 to 9.0, the protein passed through several structural intermediates, including the tetramer, trimer and dimer stages. Changes in the secondary and tertiary structure of tyrosinase at neutral pH were outlined after running molecular dynamics simulations. A detailed check at the single-molecule level by means of molecular modeling tools suggested that the most important contribution to the fluorescence intensity is given by the H subunits with seven Trp and nine Tyr residues exposed to the solvent, whereas the lectin-like folded L subunits have only six Trp and three Tyr residues, of which only Trp(15) , Trp(59) and Trp(93) are partially exposed to the solvent. The results indicated that the enzyme was sensitive to pH. The experimental results revealed the unfolding of the native tetrameric enzyme in acidic pH range, causing exposure of the hydrophobic residues.

Production and in vitro evaluation of xylooligosaccharides generated from corncobs using immobilized Penicillium occitanis xylanase

Abstract Penicillium occitanis xylanase 3 expressed in Pichia pastoris , termed PoXyn3, was immobilized on chitosan with glutaraldehyde by covalent coupling reaction. The immobilization yield and the xylanase activity recovery were 98.8 ± 2.5% and 94.45 ± 3.5%, respectively. The optimum pH was not affected by immobilization, but the immobilized PoXyn3 exhibited more acidic and large optimum pH range (pH 2.0–4.0) than that of the free PoXyn2 (pH 3.0). The free PoXyn3 had an optimum temperature of 50 °C, whereas that of the immobilized enzyme was shifted to 65 °C. Immobilization increased both pH stability and thermostability when compared with the free enzyme. It also exhibited high storage stability and retained 70% of its initial activity after 120 days. The main hydrolysis products yielded from corncob extracted xylan were xylobiose and xylotriose. The resulting xylooligosaccharides (XOS) could be used as a special nutrient for lactic bacteria. Therefore, prebiotic effect of XOS was evaluated by in vitro fermentation using known probiotic strains viz . Bifidobacterium adolescentis and Lactobacillus acidophilus . The results of this study revealed better growth of Bifidobacterium spp on XOS as a carbon source than Lactobacillus spp.

Arsenic(III) removal from aqueous solution by raw and zinc-loaded pine cone biochar: equilibrium, kinetics, and thermodynamics studies

The potential of raw pine cone (PC) biochar and its modified form (Zn-loaded biochar) was evaluated for the removal of trivalent arsenic [As(III)] from the aqueous solution. The influence of treatment of PC biochar with Zn(NO3)2 on the physico-chemical properties of biochar was examined using elemental analyzer, surface area analyzer, thermo-gravimetric analyzer, Fourier transform infrared spectroscopy, and scanning electron microscopy. Experimental results revealed that the removal of As(III) was almost consistent (66.08 ± 3.94 and 87.62 ± 3.88 % on raw and Zn-loaded biochar, respectively) over an acidic pH range of 2–4 as a consequence of high affinity between the positively charged biochar surface and the predominant arsenic species (H3AsO3 and H2AsO4 −), followed by a decrease with increase in pH in the range of 4–12. Langmuir isotherm model was well fitted to the experimental equilibrium data (R 2 = 0.93) rendering the maximum adsorption capacity of 5.7 and 7.0 μg g−1 on raw and Zn-loaded PC biochar, respectively. The adsorption of As(III) was well represented by pseudo-second order with reaction rate constant (k 2) of 0.040 and 0.282 mg g−1 min on raw and zinc-loaded PC biochar, respectively, and was mainly controlled by boundary layer diffusion followed by some extent of intra-particle diffusion. The adsorption process was spontaneous with Gibb’s free energy (ΔG°, −4.42 ± 0.72 and −11.86 ± 1.78 kJ mol−1) and exothermic in nature with enthalpy (ΔH°, 13.25 and 31.10 kJ mol−1) and entropy (ΔS°, 0.058 and 0.141 kJ mol−1 K−1) for raw and zinc-loaded adsorbent, respectively.

Histidinylated poly-L-lysine-based vectors for cancer-specific gene expression via enhancing the endosomal escape

In this work, we synthesized a series of poly-L-lysine (PLL)-based polymers for gene delivery, by modifying the PLL with both cationic peptide and histidine. The peptide moieties serve as cationic centers for polyplex formation, and also as substrates for protein kinase Cα (PKCα), which is specifically activated in many types of cancer cells, to achieve cancer-specific gene expression. The histidine groups serve as buffering moieties to increase the ability of the plasmid DNA (pDNA)-polymer complex (polyplex) to escape the endosome and thus to promote expression of the pDNA in the transfected cells. The facile synthesis of the polymers proceeded by modifying the PLL with side-group-protected peptide and protected histidine, followed by deprotection of the functional groups. The synthesized polymers showed significant buffering capacity over the neutral to acidic pH range and showed less cytotoxicity in vitro compared with histidine-unmodified polymers. The polyplexes successfully showed PKCα-responsive gene expression immediately after their introduction into cancer cells and the gene expression continued for at least 24 h. These PLL-based carriers thus show promise for cancer-targeted gene therapy.

Bisphenol A sorption by organo-montmorillonite: Implications for the removal of organic contaminants from water

Remediation of bisphenol A (BPA) from aqueous solutions by adsorption using organoclays synthesized from montmorillonite (MMT) with different types of organic surfactant molecules was demonstrated. High adsorption capacities of the organoclays for the uptake of BPA were observed and these demonstrated their potential application as strong adsorbents for noxious organic water contaminants. The adsorption of BPA was significantly influenced by pH, with increased adsorption of BPA in acidic pH range. However, the organoclays intercalated with highly loaded surfactants and/or large surfactant molecules were less influenced by the pH of the environment and this was thought to be due to the shielding the negative charge from surfactant molecules and the development of more positive charge on the clay surface, which leads to the attraction of anionic BPA even at alkaline pH. The hydrophobic phase created by loaded surfactant molecules contributed to a partitioning phase, interacting with BPA molecules strongly through hydrophobic interaction. Pseudo-second order kinetic model and Langmuir isotherm provided the best fit for the adsorption of BPA onto the organoclays. In addition, the adsorption process was spontaneous and exothermic with lower temperature facilitating the adsorption of BPA onto the organoclays. The described process provides a potential pathway for the removal of BPA from contaminated waters.

Degradation of Dyestuff Pollutant Sudan I Using Advanced Oxidation Process

Due to an increasing environmental pollution, a search for the cost effective treatment and disposal of the dyes from the textile effluents is getting more and more importance. Oxidation and reduction processes play important roles in the degradation treatments of the azo dyes. The latter process is more effective and in consequence its mechanism is also better understood. The mechanism of the oxidation processes, the intermediates involved in these reactions and their role in the effectiveness of the oxidative degradation of the azo dyes, viz, phenyl azo b-naphthol (PAN), Sudan I. On exposure to sunlight at 2 1/2 hours for various samples in different concentrations of PAN mixed with Fenton reagent, when the reactive intermediate reacted with the colour, the pH vs. absorbance generally showed significant degradation in between pH 5 and 6. The results were compared with the same samples on exposure to uv-light of 254 nm and irradiated at 20 minutes. The degradation occurred in samples of relatively high concentrations, viz, 10-3 and 5 × 10-4 mol· dm-3 at near neutral pH 6 whereas. Low concentration samples such as 10-4 and 5 × 10-5 mol·dm-3 showed degradation towards more acidic range of pH 2 to 4. In advanced oxidation process (AOP), generally reactive, strongly oxidizing ·OH radicals play a main role in destruction of the dye molecules. The proposed mechanisms and the rate coefficients for the reactions of ·OH intermediates with the dye molecules and with model compounds are summarized.

Comparison of Alkali-Tolerant Fungus Myrothecium Sp. IMER1 and White-Rot Fungi for Decolorization of Textile Dyes and Dye Effluents

A new isolated nonligninolytic fungus, strain Myrotheciumsp. IMER1, was found to decolorize five different synthetic dyes when grown on dye-containing agar plates. The capability of Myrothecium sp. IMER1 for decolorization of Remazol Brilliant Blue R (RBBR) and dye effluents was compared with that of five white-rot fungi. More than 65% RBBR removal by Myrotheciumsp. IMER1was observed at various pHs (5-10). About 60-95% of decolorization was observed with these white-rot fungi in the acidic pH range of 5.0-6.0, whereas color removal rate was less than 30% in the basic pH range of 8.0-10.0. Myrothecium sp. IMER1 had a more efficient decolorization of the dye in a broad pH range than white-rot fungi tested. In comparison with color removal performance, Myrotheciumsp. IMER1 was approximately 2-5-fold better than white-rot fungi tested in the basic pH range. Additionally, the visual observation and Ultraviolet-Visible (UV-VIS) spectral analysis demonstrated that decolorization of dye by Myrothecium sp. IMER1 was due to biodegradation and biosorption. Biomass production was not affected by changes in the pH range of 7-10, indicated that Myrothecium sp. IMER1 is alkali-tolerant fungus. Decolorization of dye effluents by Myrothecium sp. IMER1 at pH 7 and 9 was 73 and 70%, respectively, while less than 25% of decolorization was observed in the case of white-rot fungi tested. Our results showed that Myrothecium sp. IMER1 exhibited efficient decolorization of dye effluents comparedtowhite-rot fungi, indicatingthat the alkali-tolerant strain Myrothecium sp. IMER1 will be potential candidates for wastewater treatment of dye effluents, especially alkaline dye effluents.

Synthesis of radiation crosslinked poly(acrylic acid) in the presence of phenyltriethoxysilane

Acrylic acid based superabsorbent hydrogel was prepared using phenyltriethoxysilane (PTES) as polyfunctional monomer. Different amounts of PTES were incorporated in acrylic acid and irradiated at different doses upto maximum of 30kGy. The crosslinked acrylic acid showed hydrogel properties and its swelling kinetics, gel fraction and equilibrium degree of swelling (EDS) were studied. It was found that the increased PTES concentration decreased the EDS of the hydrogels. Infrared spectroscopy confirmed the crosslinking reaction between the feed components and the existence of siloxane bond. Thermogravimetric analysis showed an increase in the stability of the hydrogels having high PTES content. The swelling of the hydrogel was affected by pH, ionic strength and temperature. These hydrogels showed low swelling in acidic and basic pH range and high swelling around neutral pH. This switchable pH response of these hydrogels can be exploited in environmental and biomedical applications.

A SERS-based pH sensor utilizing 3-amino-5-mercapto-1,2,4-triazole functionalized Ag nanoparticles

We report the first use of 3-amino-5-mercapto-1,2,4-triazole (AMT) to construct a surface-enhanced Raman scattering (SERS) based pH nano- and microsensor, utilizing silver nanoparticles. We optimize the procedure of homogenous attachment of colloidal silver to micrometer-sized silica beads via an aminosilane linker. Such micro-carriers are potential optically trappable SERS microprobes. It is demonstrated that the SERS spectrum of AMT is strongly dependent on the pH of the surroundings, as the transformation between two different adsorption modes, upright (A form) and lying flat (B form) orientation, is provoked by pH variation. The possibility of tuning the nanosensor working range by changing the concentration of AMT in the surrounding solution is demonstrated. A strong correlation between the pH response of the nanosensor and the AMT concentration in solution is found to be controlled by the interactions between the surface and solution molecules. In the absence of the AMT monomer, the performance of both the nano- and microsensor is shifted substantially to the strongly acidic pH range, from 1.5 to 2.5 and from 1.0 to 2.0, respectively, which is quite unique even for SERS-based sensors.

Photocatalytic removal of selenite and selenate species: effect of EDTA and other process variables

TiO2-assisted photocatalysis was employed for the removal of aqueous phase selenite and selenate species in conjunction with EDTA as a hole (h+) scavenger. Findings from the binary selenite/EDTA and selenate/EDTA systems showed high selenite and selenate removal at pH 4 and pH 6, with faster removal kinetics noted for the selenite species compared with the selenate species that showed a gradual change over the reaction course. The noted removal of selenite and selenate was attributed to their reduction by the conduction band electrons (e−). The effect of pH studies indicated high selenite, selenate, and EDTA removal in the acidic pH range, with the following specific trend: pH 4>pH 6>pH 12. Different from the EDTA studies, the use of thiocyanate alone did not initiate reduction of selenium oxyanions, and hence, its role as a hole scavenger in the present systems was not evident. However, the addition of EDTA to respective selenite/selenate/thiocyanate system at pH 4 did yield near complete removal of selenite and selenate species. The marginal role of thiocyanate as a hole scavenger was attributed to its negligible adsorption onto TiO2 surface. Furthermore, at pH 4 and within 3 h reaction time, enhanced selenate removal was noted with an increase in its initial concentration from 20 to 100 ppm, with near complete selenate removal noted for both cases. In general, findings from the present work indicate that both selenite and selenate can be successfully removed from the aqueous phase employing the TiO2-mediated photocatalysis and h+-scavenging agent EDTA.

Hydroxypyridinecarboxylic acid derivatives influencing metal ion levels in the brain: Equilibrium complexation studies with Cu(II) and Zn(II)

The metal ion chelators 4-hydroxy-5-methyl-3-pyridinecarboxylic acid (DQ5) and 1,5-dimethyl-4-hydroxy-3-pyridinecarboxylic acid (DQ715) and Cu(II) and Zn(II) were investigated with the aim to restore the homeostasis of the brain Cu(II) and Zn(II) in neurodegenerative diseases. The proton dissociation constants of the ligands, the stability constants, and the coordination modes of the metal complexes formed were determined by pH-potentiometric, and spectral (UV–Vis and EPR or 1H NMR) methods. The results show that in slightly acidic and neutral pH range mono and bis complexes are formed through bidentate coordination of the ligands. The biological MTT-test reveals that the DQ715 ligand is able to lower the cytotoxic effect of Cu(II) in human embryonic kidney HEK-293 cells. Our studies revealed, however, that none of the chelators were efficient enough to withdraw these metal ions from the amyloid aggregates.

Adsorption behaviour of sodium hexametaphosphate on pyrochlore and calcite

FTIR, XPS and zeta potential measurements were performed on pyrochlore and calcite to study the adsorption mechanisms of sodium hexametaphosphate (NaHMP). While no hexametaphosphate could be detected on the FTIR spectra of NaHMP treated pyrochlore or calcite, the observed chemical shifts of the binding energies of Ca 2p5/2 (0·25 eV) and P 2p (0·20 eV) electrons indicated that the hexametaphosphate groups formed a complex with calcium on calcite. The complex seemed soluble in water leaving a low concentration of its residue on calcite surface after water washing, thus undetectable by FTIR. The binding energy shifts of Nb 3d5/2 (0·13 eV) and Ca 2p5/2 (0·10 eV) electrons on NaHMP-treated pyrochlore were within instrumental resolution, therefore, NaHMP was not strongly bound to pyrochlore. The zeta potentials of pyrochlore and calcite were both lowered in the presence of NaHMP. However, for pyrochlore, the zeta potential drop occurred mainly in the acidic pH range, while the drop for calcite was independent of pH, indicating possible chemisorption of NaHMP on calcite. The work explained the selective depressive function of NaHMP in the hydroxamic acid flotation of carbonatite niobium ores.On a effectué des mesures de FTIR, de XPS et de potentiel zêta du pyrochlore et de la calcite afin d’étudier les mécanismes d’adsorption de l’hexamétahosphate de sodium (NaHMP). Bien qu’on ne puisse pas détecter d’hexamétaphosphate dans les spectres de FTIR du pyrochlore ou de la calcite traités au NaHMP, les décalages chimiques observés des énergies de liaison des électrons de Ca 2p5/2 (0·25 eV) et de P 2p (0·20 eV) indiquaient que les groupes d’hexamétaphosphate formaient un complexe avec le calcium sur la calcite. Le complexe semblait soluble dans l’eau, laissant une faible concentration de son résidu à la surface de la calcite après lavage à l’eau, donc indétectable par FTIR. Les décalages de l’énergie de liaison des électrons du Nb 3d5/2 (0·13 eV) et du Ca 2p5/2 (0·10 eV) du pyrochlore traité au NaHMP se situaient dans les limites de résolution de l’instrument. Donc, le NaHMP n’était pas fortement lié au pyrochlore. Les potentiels zêta du pyrochlore et de la calcite s’abaissaient tous deux en présence de NaHMP. Cependant, la chute de potentiel zêta du pyrochlore se produisait principalement dans la gamme de pH acide, alors que la chute pour la calcite était indépendante du pH, indiquant la possibilité d’une chemisorption du NaHMP sur la calcite. Ce travail explique la fonction sélective et dépressive du NaHMP lors de la flottation à l’acide hydroxamique des minerais de carbonite de niobium.

Effect of temperature on the solubility and solid phase stability of zirconium hydroxide

Summary The solubility and solid phase stability of zirconium hydroxide was investigated in the acidic pH range after heating the aqueous samples at 50, 70 and 90 ◦C. The solubility measured at room temperature after exposing the batch samples to elevated temperatures for a given period of time significantly decreased with increasing heating periods. The Zr concentrations at given pH after heating at 90 ◦C for 3 weeks are about 5 orders of magnitude lower than the solubility of amorphous zirconium hydroxide (Zr(OH)4(am)) kept at room temperature. Size distributions of the Zr colloidal species after heating were investigated by sequential filtration using different pore-sized membranes, and the contribution of the colloidal species to the solubility was assessed. The TEM images and XRD spectra of the solid phases after heating indicated the agglomeration and crystallization of the initial amorphous hydroxide solid phase. The solid phase was identified as crystalline oxide after heating at 90◦C. The solubility product determined from the solubility data excluding contributions of colloidal species is correlated to the particle size of the solid phase.

Visible light induced photocatalytic reduction of metals (Cr, Cu, Ni, and Zn) and its synergism with different pH, TiO2, and H2O2 doses in simulated wastewater

An attempt has been made to treat the wastewater containing a combination of inorganic contaminants to take the advantage of solar photocatalytic redox reactions. Synthetic wastewater is prepared containing substantial heavy metals to obtain a simultaneous reduction of both the wastewater components. The reaction is also attempted at different pH values to optimize the same. The metals in the waste combination are Cr, Ni, Zn, and Cu. Dark adsorption reactions are also performed along with the sunlight irradiation, in order to understand the process in detail. Results show that significant chromium and copper are the metals which are significantly reduced as compared to the other two metals studied. Chromium showed maximum reduced in the acidic pH range whereas the other metals were reduced in the alkaline and neutral pH ranges. The results provide a cost-effective method to remove organic and inorganic pollutants simultaneously in the simulated wastewater through photocatalytic.

Site directed mutagenesis of StSUT1 reveals target amino acids of regulation and stability

Plant sucrose transporters (SUTs) are functional as sucrose-proton-cotransporters with an optimal transport activity in the acidic pH range. Recently, the pH optimum of the Solanum tuberosum sucrose transporter StSUT1 was experimentally determined to range at an unexpectedly low pH of 3 or even below. Various research groups have confirmed these surprising findings independently and in different organisms. Here we provide further experimental evidence for a pH optimum at physiological extrema. Site directed mutagenesis provides information about functional amino acids, which are highly conserved and responsible for this extraordinary increase in transport capacity under extreme pH conditions. Redox-dependent dimerization of the StSUT1 protein was described earlier. Here the ability of StSUT1 to form homodimers was demonstrated by heterologous expression in Lactococcus lactis and Xenopus leavis using Western blots, and in plants by bimolecular fluorescence complementation. Mutagenesis of highly conserved cysteine residues revealed their importance in protein stability. The accessibility of regulatory amino acid residues in the light of StSUT1's compartmentalization in membrane microdomains is discussed.

Investigation of carbazole degradation by the sono-Fenton process

The present report aimed to describe the roles of ultrasonic power and reaction time in the Fenton reagent-based degradation of carbazole in wastewater, and to analyze the effects of the Fe2SO4 and H2O2 concentrations and the initial pH on the reaction kinetics. Application of 40 or 80 W of ultrasound at a frequency of 40 KHz substantially improved the effectiveness of carbazole degradation, whereas application of 20 W of ultrasound had little effect. The optimal concentration of the Fe2SO4·7H2O catalyst was lower for extended operating times. Increased degradation was observed with increasing H2O2 concentrations below 1.8 mg L(-1), whereas decreased degradation was observed at concentrations above this value. The best performance was obtained at a neutral or slightly alkaline pH range (pH 7-9) rather than at the commonly used acidic pH range (pH 2-4). Under optimal conditions, the extent of carbazole degradation was 98% after 180 min. The degradation process followed second-order kinetics.

Two cold-induced family 19 glycosyl hydrolases from cherimoya (Annona cherimola) fruit: An antifungal chitinase and a cold-adapted chitinase

Two cold-induced chitinases were isolated and purified from the mesocarp cherimoyas (Annona cherimola Mill.) and they were characterised as acidic endochitinases with a Mr of 24.79 and 47.77kDa (AChi24 and AChi48, respectively), both family 19 glycosyl hydrolases. These purified chitinases differed significantly in their biochemical and biophysical properties. While both enzymes had similar optimal acidic pH values, AChi24 was enzymatically active and stable at alkaline pH values, as well as displaying an optimal temperature of 45°C and moderate thermostability. Kinetic studies revealed a great catalytic efficiency of AChi24 for oligomeric and polymeric substrates. Conversely, AChi48 hydrolysis showed positive co-operativity that was associated to a mixture of different functional oligomeric states through weak transient protein interactions. The rise in the AChi48 kcat at increasing enzyme concentrations provided evidence of its oligomerisation. AChi48 chitinase was active and stable in a broad acidic pH range, and while it was relatively labile as temperatures increased, with an optimal temperature of 35°C, it retained about 50% of its maximal activity from 5 to 50°C. Thermodynamic characterisation reflected the high kcat of AChi48 and the remarkably lower ΔH(‡), ΔS(‡) and ΔG(‡) values at 5°C compared to AChi24, indicating that the hydrolytic activity of AChi48 was less thermodependent. In vitro functional studies revealed that AChi24 had a strong antifungal defence potential against Botrytis cinerea, whereas they displayed no cryoprotective or antifreeze activity. Hence, based on biochemical, thermodynamic and functional data, this study demonstrates that two acidic endochitinases are induced at low temperatures in a subtropical fruit, and that one of them acts in an oligomeric cold-adapted manner.

Characterization of Acid-Soluble Collagen From Bone of Pacific Cod (Gadus macrocephalus)

Acid-soluble collagen (ASC) was isolated from Pacific cod (Gadus macrocephalus) bone. The ASC was rich in glycine. The amount of imino acid was lower than that of calf skin collagen, as was the transition temperature (48.6°C). Electrophoresis revealed two different α chains (α1 and α2), β-component, and γ-component. Fourier transform infrared spectroscopy measurement showed that ASC was in triple-helix structure. ASC had a solubility greater than 90% in a very acidic pH range (pH 1–4), and the solubility decreased with increasing NaCl concentrations up to 3%. Lyophilized ASC had a network ultrastructure with lace-like fibers, similar to calf skin collagen sponge.

Fusion of a Flavin-Based Fluorescent Protein to Hydroxynitrile Lyase from Arabidopsis thaliana Improves Enzyme Stability

Hydroxynitrile lyase from Arabidopsis thaliana (AtHNL) was fused to different fluorescent reporter proteins. Whereas all fusion constructs retained enzymatic activity and fluorescence in vivo and in vitro, significant differences in activity and pH stability were observed. In particular, flavin-based fluorescent reporter (FbFP) fusions showed almost 2 orders of magnitude-increased half-lives in the weakly acidic pH range compared to findings for the wild-type enzyme. Analysis of the quaternary structure of the respective FbFP-AtHNL fusion proteins suggested that this increased stability is apparently caused by oligomerization mediated via the FbFP tag. Moreover, the increased stability of the fusion proteins enabled the efficient synthesis of (R)-mandelonitrile in an aqueous-organic two-phase system at a pH of <5. Remarkably, (R)-mandelonitrile synthesis is not possible using wild-type AtHNL under the same conditions due to the inherent instability of this enzyme below pH 5. The fusion strategy presented here reveals a surprising means for the stabilization of enzymes and stresses the importance of a thorough in vitro characterization of in vivo-employed fluorescent fusion proteins.

Characteristics of Aspergillus niger xylanases produced on rice husk and wheat bran in submerged culture and solid‐state fermentation for an applicability proposal

SummaryXylanolytic rich filtrates were obtained by A. niger sp in both submerged and solid‐state culture using rice husk or wheat bran as the only carbon source. Filtrates obtained on rice husk showed the highest activities (~6500 and 5200 U g−1, respectively). Independent of carbon source, these filtrates were very stable in an acidic pH range (4–7) and mild temperatures, with high half‐life time values (more than 7 h at 50 °C) in the corresponding inactivation kinetic models. Also the effect of different metallic ions and denaturing substances was verified finding that these enzymes are not metaloproteins, and metals as Hg2+ and Pb2+ caused the greatest loss of xylanolytic activity (not higher than 30%). Xylanases produced by this A. niger strain showed important features that make them potential candidates for applications on human and livestock food industries.