Citric Acid Residue Research Articles

Preparation and Performance of Carbon-Based Ce-Mn Catalysts for Efficient Degradation of Acetone at Low Temperatures.

Based on the porous carbon material from citric acid residue, catalysts of different Ce-Mn ratios were prepared with incipient-wetness impregnation (IWI) to delve into their acetone-degrading performance and relevant mechanisms. When the Ce-Mn molar ratio is 0.8, the prepared catalyst Ce0.8-Mn/AC shows abundant and uniformly dispersed Mn and Ce particles on the surface. The content of Mn and Ce on the Ce0.8-Mn/AC surface reaches 5.64% and 0.75%, respectively. At the acetone concentration of 238 mg/m3 (100 ppm), the laws of acetone degradation in different catalysts at different catalyzing temperatures and with various oxygen concentrations were studied, and we found that the rate of acetone degradation by Ce0.8-Mn/AC can exceed 90% at 250 °C. Cerium oxide and manganese oxide are synergistic in the catalytic degradation of acetone. Adding cerium to manganese-based catalysts can increase the oxygen migration rate in the catalysts and thus raise the reduction rate of lattice oxygen in manganese oxide. The results offer new ideas and approaches for the efficient and comprehensive utilization of bio-fermentation by-products, and for the development of cheap and high degradation performance catalysts for acetone.

Assessment of organic acid salts on fermentation quality, aerobic stability, and in vitro rumen digestibility of total mixed ration silage.

The work aimed to investigate the effects of four organic acid salts on fermentation quality, aerobic stability, and in vitro rumen digestibility of total mixed ration (TMR) silage prepared with citric acid residue, wet brewers' grains, and Napier grass. The TMR was ensiled with the following: (1) no additives (control), (2) 0.1% sodium benzoate (SB), (3) 0.1% potassium sorbate (PS), (4) 0.5% sodium diacetate (SDA), (5) 0.5% calcium propionate (CAP) on a fresh weight basis. All silos (10 L) were opened after 60days of ensiling to determine fermentation profiles and in vitro rumen digestibility, and then were subjected to a 9-day aerobic stability test. Four organic acid salts significantly (p < 0.05) increased dry matter contents, lactic acid bacteria count, and decreased ethanol content and yeast count compared with the control. The SDA and CAP significantly (p < 0.05) increased water-soluble carbohydrates, lactic acid, and crude protein contents, and decreased pH, ammonia nitrogen, neutral detergent fiber, and hemicellulose contents compared with other TMR silages after 60days of ensiling. Organic acid salts significantly (p < 0.05) prolonged the hours of aerobic stability and significantly (p < 0.05) increased cumulative gas production and potential gas production compared with the control. The treatments of SDA and CAP significantly (p < 0.05) improved aerobic stability as indicated by higher (p < 0.05) lactic acid and water-soluble carbohydrates contents, and lower (p < 0.05) pH, ammonia nitrogen, ethanol contents, and yeast count compared with the control. The treatments of SDA and CAP significantly (p < 0.05) increased in vitro rumen parameters, as indicated by higher (p < 0.05) in vitro digestibility of dry matter, crude protein, and neutral detergent fiber after 60days of ensiling. Overall, these results indicated that the addition of SDA and CAP could ensure the good fermentation quality and improve aerobic stability of TMR silages. By comprehensive consideration, CAP was recommended for improving fermentation quality, aerobic stability, and in vitro rumen digestibility of TMR silages prepared with wet brewers' grains, citric acid residue, and Napier grass.

Effect of citric acid residue and short-chain fatty acids on fermentation quality and aerobic stability of lucerne ensiled with lactic acid bacteria inoculants.

The experiment aimed to compare the effects of citric acid residue (CAR) to that of three commonly used short-chain fatty acids on the fermentation quality, aerobic stability and structural carbohydrate degradation of lucerne ensiled with lactic acid bacteria (LAB) inoculants. Fresh lucerne was ensiled with distilled water (control), LAB inoculant (L), CAR+LAB inoculant (CL), formic acid+LAB inoculant (FL), acetic acid+LAB inoculant (AL) and propanoic acid+LAB inoculant (PL) for 50days. Chemical composition and microbial populations were determined after ensiling. The residual silages ensiled for 50days were evaluated for aerobic stability. Compared with control, CL, FL, AL and PL treatments significantly (p<0.05) decreased pH, ammonia nitrogen (NH3 -N) and butyric acid contents and increased lactic acid, acetic acid and propionic acid contents. Among them, CL silages had the lowest pH, dry matter and water-soluble carbohydrate (WSC) content, whereas the population of LAB and the lactic acid contents were highest. Besides, CL outperformed in enhancing fibre degradation, CL silages significantly decreased (p<0.05) neutral detergent fibre, acid detergent fibre, hemicellulose and cellulose contents compared with control and had the highest Flieg's point. All treated-silages improved the aerobic stability compared with control, of which L improved 32h, whereas CL, FL, AL and PL improved 46, 20, 46, >64h, respectively. Applying a combination of CAR and LAB inoculant improved the fermentation quality and structural carbohydrate degradation of lucerne silage and had a similar effect on aerobic stability compared with other three short-chain fatty acids. The CAR had a comparable effect on enhancing the fermentation quality compared with three short-chain fatty acids. Thus, the combination of CAR and LAB inoculant might be used as an ideal additive for lucerne silage making with low WSC and high moisture content.

Hemin Covalently Functionalized Carbon Nanobranch with Enzyme‐Like and Photocatalytic Activities for Synergistic Dye Degradation and Antibacterial Therapy

AbstractThe development of artificial enzymes with excellent enzyme‐like activities and unique features is highly desirable for their practical applications. Herein, a one‐pot facile method to synthesize hemin covalently functionalized carbon nanobranch (CN‐hemin) via direct pyrolysis of citric acid and covalent coupling of hemin to the formed carbon skeleton, is reported. This strategy is reasonably straightforward, cheap, and environmentally friendly, without any extraneous oxidant, reductant, and harmful additives during the preparation process. Furthermore, the obtained dendritic hybrids possess good water‐solubility, intrinsic peroxidase‐like activity, and satisfactory photocatalytic performance in visible light. These extraordinary properties are mainly due to the structure of CN‐hemin which contains iron porphyrin, aromatic carbon, and citric acid residues. Most importantly, under visible light irradiation, the as‐prepared hemin‐incorporated nanohybrid can act as robust agents for synergistic dye degradation and antibacterial therapy toward Staphylococcus aureus and methicillin‐resistant S. aureus. It is expected that this study can shed valuable light on developing advanced multifunctional nanozymes with combined favorable properties for highly efficient elimination of environmental pollutants and antibacterial treatment.

Antioxidant activity of polyphenolic compounds obtained from Euphorbia antisyphilitica by-products

In this study, an alternative extraction technique, ultrasound-assisted extraction, was used to extract the polyphenolic fraction from two different residues of the candelilla plant (Euphorbia antisyphilitica). These metabolites were further analyzed to evaluate their bioactivity as antioxidants. In addition, their functional groups were identified by Fourier transform infrared (FTIR) spectroscopy. The antioxidant assays showed statistically significant differences between the phenolic extracts, with citric acid residues (CAR) exhibiting a higher oxidant effect than sulfuric acid residues (SAR). The CAR from San Jerónimo (SJ) cultivar showed decreased IC50 values (179.441 ± 7.92 μL mL−1, DPPH•), and its polyphenolic fraction was able to inhibit lipid oxidation (70.31 ± 2.50%). FTIR analysis subsequently revealed the presence of functional groups related to polyphenolic compounds, such as hydroxy, carbonyl, carbon double bond, and amine groups. In addition, FTIR spectra showed slight differences in phenolic compounds, due to the strong acid treatment involved in the extraction of wax. The present study demonstrated that candelilla by-products from citric acid-wax extraction have a polyphenolic fraction with strong antioxidant activity, which may be useful in food and pharmaceutical products.

Fermentation quality and aerobic stability of Napier grass ensiled with citric acid residue and lactic acid bacteria

This study was conducted to investigate the effects of adding citric acid residue (CAR) with or without lactic acid bacteria (LAB) to Napier grass (Cenchrus purpureus; syn. Pennisetum purpureum) cv. Sumu No. 2 at ensiling on the fermentation quality and aerobic stability of the resulting silage. Treatments included: Control (Napier grass forage without additives); and Napier grass inoculated with lactic acid bacteria (Lactobacillus plantarum and L. buchneri) at 1 × 106 cfu/gfresh weight (FW) forage (LAB) or 36 g citric acid residue/kg FW forage (CAR) or a mixture of CAR and LAB (CL). Forty-five days after ensiling the silages were tested for chemical and microbial composition and an aerobic stability test was conducted. The addition of CAR with or without LAB increased the DM and lactic acid concentrations in silage and decreased pH plus acetic acid, ammonia nitrogen (NH3-N), neutral detergent fiber and cellulose concentrations relative to Control. The pH in LAB silage was lower than in Control, while lactic acid concentration was higher. During the first 2 days of aerobic exposure, all additives increased the water-soluble carbohydrate (WSC) and lactic acid concentrations and decreased pH plus NH3-N and acetic acid concentrations. Moreover, CL silages had the highest WSC and the lowest NH3-N and acetic acid concentrations during aerobic exposure. However, all additives failed to improve the aerobic stability of the silage. While CAR with or without LAB inoculant improved the fermentation quality of silage made from Napier grass, more studies are warranted to identify additives which can improve aerobic stability of the silage after opening.

Effect of ensiling alfalfa with citric acid residue on fermentation quality and aerobic stability

This experiment was conducted to investigate the effects of citric acid residue (CAR) on the fermentation quality and aerobic stability of alfalfa silage and to define the optimal application level of CAR in silage making. Alfalfa was ensiled without additives (CON) or with 1.2 % CAR (C1), 3.6 % CAR (C2) and 6.0 % CAR (C3) on a fresh weight (FW) basis for 3, 6, 9, 15, 30 and 45 days. Chemical and microbial compositions were determined after ensiling. The residual silages ensiled for 45 days were evaluated for aerobic stability. The addition of CAR to alfalfa silages increased (P<0.05) dry matter (DM) and water-soluble carbohydrate (WSC) contents and decreased (P<0.05) acetic acid, ethanol, ammonia nitrogen (NH3-N) and neutral detergent fibre (NDF) contents compared with those of the control. The values of pH and the contents of DM, lactic acid, acetic acid, ethanol, WSC, NH3-N, hemicellulose and cellulose showed a linear relationship with the increasing application level of CAR (P<0.05). The C3 silages showed the optimal fermentation quality. The C1 and C2 silages showed lower aerobic stability than that of the control (P<0.05). The results indicated that addition of CAR effectively improved the fermentation quality and enhanced fibre degradation, but had no obvious positive effects on aerobic stability. By comprehensive consideration, 6.0 % CAR was recommended for alfalfa silage making.

Fermentation and aerobic stability of Napier grass silage treated with different levels of citric acid residue

AbstractThe experiment was conducted to investigate the effects of different levels of citric acid residue (CAR) on the fermentation quality and aerobic stability of Napier grass. Napier grass was ensiled with no additives control (CON), 1.2% CAR (C1), 3.6% CAR (C2) and 6.0% CAR (C3) on a fresh weight basis in laboratory silos for 3, 6, 9, 15 and 45 days. After opening the silos, the silages were subjected to analyzing the chemical and microbial compositions, and the residual silages ensiled for 45 days were evaluated for aerobic stability. Addition of CAR increased lactic acid/acetic acid, dry matter, lactic acid and water‐soluble carbohydrate contents, and decreased pH, acetic acid, ammonia nitrogen (NH3‐N), neutral detergent fiber, acid detergent fiber and cellulose contents as compared to the control. At the day 45 of ensiling, the C2 and C3 silages showed higher lactic acid contents and lactic acid/acetic acid, and lower NH3‐N and acetic acid contents than these of C1 silages. There was no significant difference in the aerobic stability between CAR‐treated silages and the control. Application of CAR effectively improved the fermentation quality of Napier grass, but had no obvious effects on the improvement of aerobic stability. In conclusion, application of CAR at the level of 3.6% or 6.0% is recommended for Napier grass silage making.

Effects of citric acid residue and lactic acid bacteria on fermentation quality and aerobic stability of alfalfa silage

An experiment was conducted to investigate the effects of citric acid residue (CAR) and lactic acid bacteria (LAB) on fermentation quality and aerobic stability of alfalfa silage. Alfalfa was treated as follows: (1) control without additive (CON); (2) LAB (L); (3) 12 g/kg CAR (C); (4) 12 g/kg CAR + LAB (CL) and fermented for 3, 6, 9, 15, 30 and 45 days. The residual silages ensiled for 45 days were evaluated for aerobic stability. The results showed that addition of CAR with or without LAB inoculant decreased pH, acetic acid, ammonia nitrogen , neutral detergent fibre, hemicellulose contents and Enterobacteriaceae counts (p < .05) and increased dry matter and lactic acid contents (p < .05) after 45 days of ensiling. Whereas, the lower lactic acid and higher acetic acid contents were observed in L silages (p < .05) after 45 days of ensiling. During aerobic exposure, L and CL silages remained stable in pH, lactic and acetic acid contents, while the control and C silages showed higher pH, yeast and mould counts and lower lactic and acetic acid contents. Compared with the control, L and CL improved aerobic stability, whereas the poorer aerobic stability was shown in C silages (p < .05). In conclusion, applying a combination of CAR and LAB inoculant improved both fermentation quality and aerobic stability of alfalfa silage. Highlights Citric acid residue (CAR) was compared with a lactic acid bacteria (LAB) inoculant in ensiling alfalfa. The CAR improved fermentation quality compared to control and LAB treated silages. Aerobic stability improved when CAR was used in combination with LAB but not when used alone.

Adsorption behavior of multicomponent volatile organic compounds on a citric acid residue waste-based activated carbon: Experiment and molecular simulation

A considerable amount of volatile organic compounds (VOCs) is emitted, and a vast amount of citric acid residue (CAR) waste is simultaneously produced during citric acid production. Thus, a suitable method realizing the clean production of citric acid must be developed. This study investigated the adsorption of the multicomponent VOCs in a homemade CAR waste-based activated carbon (CAR-AC). A fixed-bed experimental setup was used to explore the adsorption and desorption of single- and multi-component VOCs. Surface adsorption and diffusion molecular models with different defects were built to study the underlying adsorption and diffusion mechanisms of multicomponent VOCs on CAR-AC. The adsorption amount of ethyl acetate in CAR-AC from multicomponent VOCs was 3.04 and 5.91 times higher than those of acetone and acetaldehyde, respectively, and the interaction energy between ethyl acetate and C surfaces was low at −13.41 kcal/mol. During desorption, the most weakly adsorbed acetaldehyde desorbed from the surface of CAR-AC first, followed by acetone and ethyl acetate. The regeneration efficiencies of acetaldehyde, acetone, and ethyl acetate reached 88.77, 85.55, and 91.46 %, respectively, after four adsorption/desorption cycles. We aimed to provide a new strategy to realize the recycle use of CAR and the clean production of citric acid.

Synthesis of Activated Carbon from Citric Acid Residue by Phosphoric Acid Activation for the Removal of Chemical Oxygen Demand from Sugar-Containing Wastewater

Over 2 million tons of citric acid residue (CAR) are generated from citric acid production in China each year. Thus, it is of great significance to find a suitable method for recycling the waste products of citric acid fermentation. Herein, activated carbon (AC) samples were prepared from CAR with phosphoric acid activation. Effects of impregnation ratio, activation time, and activation temperature on pore structure and surface functional group formation were evaluated. AC prepared by 1.5 h of pyrolysis in nitrogen at 550°C from CAR and phosphoric acid at an impregnation ratio of 2.0 (CAR-AC-2.0) had the largest specific surface area (786 m2/g) and total pore volume (0.71 mL/g). The surface morphologies and chemical properties of AC samples were characterized by scanning electron microscopy, thermogravimetric analysis, elemental analysis, and Fourier transform infrared spectroscopy (FTIR), and their adsorption capacities for methylene blue (MB) and iodine were tested. There were rare functional groups on the surfaces of CAR-AC-2.0, and the adsorption amounts of CAR-AC-2.0 for iodine and MB reached up to 729 and 121 mg/g, respectively. CAR-AC-2.0 was an ideal adsorbent for removing organic matters from solutions and wastewater. Adsorption efficiency of CAR-AC-2.0 for chemical oxygen demand (COD) from sugar-containing wastewater was 291.6 mg/g, and the removal efficiency was 80.9% when the dosage was 15 g/L. This study provided a new strategy for removing COD from fermentation wastewater with high efficiency and low cost.

Photoluminescence and Scintillation Modulation Upon UV/X‐ray‐Induced Photochromism in Europium Tungstate Phosphors

AbstractRare earth (RE) tungstates with general formula REW2O6(OH)3 (RE = YIII or EuIII) were synthesized by hydrothermal method by using different citric acid contents. The prepared samples exhibit both UV and X‐ray‐induced photochromism at room temperature, as well as photomodulated luminescence. The presence of citric acid residues improves the photochromism when the samples are UV‐irradiated, but has a secondary effect when the material is exposed to X‐ray, evidencing particular mechanisms of action in each case. The emission profiles, in its turn, are similar independently of irradiation source. The continuous irradiation leads to color changes of samples concomitantly to the suppression of EuIII emission, without variations in the point symmetry of EuIII, but showing differences in the quenching behaviour according the excitation energy. The observed photochromic effect is stable and persists for several hours, which can be reversed by heating the irradiated material in air for a few minutes, when the restitution of emission intensity takes place. The observed properties make these materials promising for ionizing radiation detection and optical data storage.

The Legionella pneumophila Siderophore Legiobactin Is a Polycarboxylate That Is Identical in Structure to Rhizoferrin.

Legionella pneumophila, the agent of Legionnaires' disease, secretes a siderophore (legiobactin) that promotes bacterial infection of the lung. In past work, we determined that cytoplasmic LbtA (from Legiobactin gene A) promotes synthesis of legiobactin, inner membrane LbtB aids in export of the siderophore, and outer membrane LbtU and inner membrane LbtC help mediate ferrilegiobactin uptake and assimilation. However, the past studies examined legiobactin contained within bacterial culture supernatants. By utilizing high-pressure liquid chromatography that incorporates hydrophilic interaction-based chemistry, we have now purified legiobactin from supernatants of virulent strain 130b that is suitable for detailed chemical analysis. High-resolution mass spectrometry (MS) revealed that the molecular mass of (protonated) legiobactin is 437.140 Da. On the basis of the results obtained from both MS analysis and various forms of nuclear magnetic resonance, we found that legiobactin is composed of two citric acid residues linked by a putrescine bridge and thus is identical in structure to rhizoferrin, a polycarboxylate-type siderophore made by many fungi and several unrelated bacteria. Both purified legiobactin and rhizoferrin obtained from the fungus Cunninghamella elegans were able to promote Fe(3+) uptake by wild-type L. pneumophila as well as enhance growth of iron-starved bacteria. These results did not occur with 130b mutants lacking lbtU or lbtC, indicating that both endogenously made legiobactin and exogenously derived rhizoferrin are assimilated by L. pneumophila in an LbtU- and LbtC-dependent manner.

The configuration of the chiral carbon atoms in staphyloferrin A and analysis of the transport properties in Staphylococcus aureus

Staphyloferrin A, the iron-transporting siderophore of Staphylococci, contains two citric acid residues linked to a D-ornithine backbone, having thus three chiral centers. While the chirality of the backbone can be determined after hydrolysis, the chirality of the two citryl residues can only be determined from the intact staphyloferrin A molecule by circular dichroism spectra. The chirality of the quarternary carbon atoms of citryl residues in fungal rhizoferrin and bacterial enantio-rhizoferrin have been determined previously to be R,R and S,S respectively. The present investigation shows that of the three chiral centers in staphyloferrin A, the citryl residues can be assigned an S,S-configuration by comparison with synthetic analogs, confirming a common chirality among the bacterial enantio-rhizoferrin and staphyloferrin A. This suggests that the bacterial carboxylates originate from a common biosynthetic pathway leading to an S,S-configuration, while the fungal rhizoferrin possessing an R,R-configuration must have a different biosynthetic origin. Growth promotion tests with staphylococci revealed that the S,S-configuration of staphyloferrin A and enantio-rhizoferrin enabled iron uptake, while the fungal rhizoferrin with R,R-configuration was not utilized.

Synthesis of novel citrate-based siderophores and siderophore-.beta.-lactam conjugates. Iron transport-mediated drug delivery systems

The synthesis of analogs of arthrobactin (5), a microbial iron chelator, and its imide 8 are described. The differentially protected citric acid residue 31 served as the key intermediate in making conjugates having a generalized structure 14 with two representative carbacephalosporin units, 15 and 16. Both conjugates, 49 and 51, showed antibiotic activity, while conjugate 51 obtained from β-lactam 16 bearing a phenylglycyl side chain was shown to be more effective

Stereochemical characterization of rhizoferrin and identification of its dehydration products

The polycarboxylate siderophore, rhizoferrin, and its dehydration products were separated by preparative HPLC and characterized by13C-NMR,1H-NMR, UV, circular dichroism (CD) and IR spectroscopy, and also by capillary electrophoresis. Assginment of all carbon atoms and protons by NMR spectra confirmed the structure of rhizoferrin and gave evidence for the presence of the cyclized dehydration byproducts, imidorhizoferrin and bis-imidorhizoferrin. The imido forms were also characterized by their mobility during capillary electrophoresis. UV spectra revealed a 1∶1 iron:ligand ratio above pH 3. Based on the absorption maximum of the metal ligand charge transfer hand at 335 nm a molar extinction coefficient of 2300m−1 cm−1 was calculated for ferric rhizoferrin. CD measurements revealed that the quarternary carbon atoms of the two citric acid residues possess anR,R configuration and that the iron complex of rhizoferrin adopts a A configuration around the metal center.

Rhizoferrin ? a novel siderophore from the fungusRhizopus microsporus var.rhizopodiformis

From a strain ofRhizopus microsporus var.rhizopodiformis a novel siderophore, named rhizoferrin, was isolated by ion-exchange column chromatography, gel filtration and preparative HPLC. Hydrolysis with 6 M HCl and subsequent gas chromatography/mass spectrometry (GUMS) of the esterified/trifluoroacetylated derivatives indicated that citric acid and diaminobutane were the only constituents. From positive fastatom-bombardment (FAB) and ion-spray tandem mass spectrometry, a molecular mass of 436 Da and the assignment of several daughter ion fragments could be obtained, which indicated the presence of two citric acid residues and one diaminobutane residue. NMR studies finally confirmedN 1,N 4-bis(1-oxo-3-hydroxy-3,4-dicarboxybutyl)-diaminobutane as the structure of rhizoferrin. The iron-binding property was demonstrated on chromeazurol S plates and its siderophore activity was confirmed by iron transport measurements in young mycelia ofR. microsporus. While rhizoferrin and also ferrioxamines B and E proved to be effective siderophores, coprogen was a poor siderophore in this fungus.

Staphyloferrin A: a structurally new siderophore from staphylococci

Two ferric ion-binding compounds, designated staphyloferrin A and B, were detected in the culture filtrates of staphylococci grown under iron-deficient conditions. Staphyloferrin A was isolated from cultures of Staphylococcus hyicus DSM 20459. The structural elucidation of this highly hydrophilic, acid-labile compound revealed a novel siderophore, N2,N5-di-(1-oxo-3-hydroxy-3,4-dicarboxybutyl)-D-ornithine, which consists of one ornithine and two citric acid residues linked by two amide bonds. The two citric acid components of staphyloferrin A provide two tridentate pendant ligands, comprising of a beta-hydroxy, beta-carboxy-substituted carboxylic acid derivative, for octahedral metal chelation. The CD spectrum of the staphyloferrin A ferric complex indicates a predominant A configuration about the ferric ion center. The uptake of ferric staphyloferrin A by S. hyicus obeys Michaelis-Menten kinetics (Km = 0.246 microM; vmax = 82 pmol.mg-1.min-1), indicating active transport of this siderophore. The staphyloferrin A transport system is different from that of the ferrioxamines as shown by an antagonism test. Production of staphyloferrin A is strongly iron-dependent and is stimulated by supplementation of the medium with either D- or L-ornithine. DL-[5-14C]ornithine was incorporated into staphyloferrin A, demonstrating that ornithine is an intermediate in staphyloferrin A biosynthesis.