Comparative study on composition and functional properties of brewer's spent grain proteins precipitated by citric acid and hydrochloric acid

Brewer's spent grain (BSG) is an abundant agro-industrial residue and a sustainable low-cost source for extracting proteins. The composition and functionality of BSG protein concentrates are affected by extraction conditions. This study examined the use of citric acid (CA) and HCl to precipitate BSG proteins. The resultant protein concentrates were compared in terms of their composition and functional properties. The BSG protein concentrate precipitated by CA had 10% lower protein content, 5.8% higher carbohydrate, and 5.4% higher lipid content than the sample precipitated by HCl. Hydrophilic/hydrophobic protein and saturated/unsaturated fatty acid ratios increased by 16.9% and 26.5% respectively, in the sample precipitated by CA. The formation of CA-cross-linkages was verified using shotgun proteomics and Fourier transform infrared spectroscopy. Precipitation by CA adversely affected protein solubility and emulsifying properties, while improving foaming properties. This study provides insights into the role of precipitants in modulating the properties of protein concentrates.

Effect of exogenous organic acids on chemical compositions and sensory attributes of fortified sweet wines from dehydrated grapes

In this study, acidity was regulated with the addition of exogenous tartaric acid and citric acid before bottling. The effect of exogenous organic acids on chemical compositions and sensory attributes of fortified sweet wines from dehydrated grapes were investigated. The results indicated that exogenous organic acids promoted the conversion of monomeric anthocyanins to copigmented anthocyanins in wines. Specifically, the combination of malvidin-3-O-glucoside and flavanols (catechin and epicatechin) was facilitated to form copigmented anthocyanins. Sensory analysis suggested that exogenous organic acids improved the balance of sugar and acidity and benefited the harmony in wines on the taste. Wines with a residual sugar and titratable acidity ratio of about 11:1 exhibited the more harmonious taste. In addition, it was also observed changes in the aroma profile related to volatile compounds, namely, more intense fruity aroma in wines with the addition of organic acids.

Application of sodium alginate-based edible coating with citric acid to improve the safety and quality of fresh-cut melon (Cucumis melo L.) during cold storage

The safety and quality of fresh-cut melons is reduced by a series of decay processes by enzymatic browning and microbial contamination. This study aimed to assess the impact of a 2% sodium alginate-based edible coating (ALC) combined with different concentrations of citric acid (CA; 0.5%, 1%, 2%, and 3%) on the microbial safety and physical quality of fresh-cut melons during a 7-day storage period at 10 °C. The findings revealed that the combination of ALC and 3% CA was successful in preventing the growth of pathogenic bacteria (Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, and Staphylococcus aureus) and natural microflora on fresh-cut melons during storage. In addition, treating fresh-cut melons with ALC containing 3% CA improved their quality by reducing browning and softening during storage at 10 °C. Based on these findings, it can be concluded that using ALC with 3% CA is an effective method to improve the safety and quality of fresh-cut melons.

Citric acid crosslinked soluble soybean polysaccharide films for active food packaging applications

In this work, a nontoxic crosslinking agent, citric acid (CA), was used to crosslink glycerol-plasticized SSPS films via a heat activated reaction. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results confirmed the occurrence of esterification reaction between CA and SSPS. Microstructure of the CA-crosslinked SSPS films were characterized by scanning electron microscopy, atomic force microscopy and X-ray diffraction. The water resistance, mechanical, UV-barrier, water vapor barrier, antioxidant and thermal properties of SSPS films were enhanced by CA crosslinking. The SSPS film crosslinked with 5 % CA exhibited a maximum tensile strength of 6.5 MPa and a minimum water solubility of 34.3 %. The CA-crosslinked SSPS film also presented superior antibacterial properties against Gram-positive and Gram-negative bacteria. Application test results showed that the CA-crosslinked SSPS film can effectively delay the oxidative deterioration of lard during storage, suggesting that the developed CA-crosslinked SSPS film could be a promising candidate for active food packaging.

Aspergillus niger as an eco-friendly agent for potassium release from K- bearing minerals: Isolation, screening and culture medium optimization using Plackett-Burman design and response surface methodology

The potential of Aspergillus niger, to enhance non-exchangeable potassium (K+) release from mineral structures were investigated as a cost-effective and environmentally friendly alternative to traditional chemical fertilizers. Optimizing the culture medium for maximum K+ release, alongside identifying potential mechanisms of action of the A. niger including the production of various organic acids and pH reduction in the minerals feldspar and phlogopite, were among the primary objectives of the present study. K+ dissolution from feldspar and phlogopite in the presence of Aspergillus niger were examined through a two-step experiment; impact of different carbon sources (glucose, sucrose, and fructose) on K+ release using the Plackett-Burman design (PBD) with 12 experimental runs and effect of other independent variables including pH (ranging from 5 to 10), carbon concentration (3-12.3 g l-1), and incubation time (5-18 days) on K+ release using the central composite design (CCD). Our results indicated that the PBD demonstrated a strong predictive capacity (RMSE = 0.012-0.018 g l-1 and R2 = 0.85-0.89) for K+ release. According to the CCD model, pH exerted a significant positive influence on increasing soluble K+ release (P < 0.001). The highest levels of K+ release (157.8 and 175.3 mg l-1 in feldspar and phlogopite, respectively) were observed at the central levels (0) of time and carbon source, and at the +α level (+1.68) of pH. Furthermore, based on the CCD model, the optimal conditions for achieving high K+ release from feldspar and phlogopite in a medium were pHs of 10.36 and 10.31, sucrose concentrations of 11.23 and 11.32 g l-1, and incubation times of 15 and 18 days, respectively. The determination coefficients of the CCD model indicated that 89.5% and 92.6% of the changes in soluble K+ for feldspar and phlogopite, could be explained by this model, respectively. In the current study, the production of organic acids and the resulting pH reduction, along with the reduction in mineral particle size in feldspar and phlogopite, were identified as potential mechanisms influencing the enhancement of potassium solubility. The predominant acids in both feldspar and phlogopite were lactic acid (70.9 and 69.15 mg l-1) and citric acid (40.48 and 22.93 mg l-1), although the production levels of organic acids differed in the two minerals. Overall, our findings highlight the potential of A. niger to proficiently release non-exchangeable potassium from mineral matrices, indicating its promising potential in agricultural applications.

Sustainable remediation of Cr(VI)-contaminated soil by soil washing and subsequent recovery of washing agents using biochar supported nanoscale zero-valent iron

Soil contamination by Cr(VI) has attracted widespread attention globally in recent years, but it remains a significant challenge in developing an environmentally friendly and eco-sustainable technique for the disposal of Cr(VI)-contaminated soil. Herein, a sustainable cyclic soil washing system for Cr(VI)-polluted soil remediation and the recovery of washing agents using biochar supported nanoscale zero-valent iron (nZVI-BC) was established. Citric acid (CA) was initially screened to desorb Cr(VI) from contaminated soil, mobilizing Cr from the highly bioaccessible fractions. The nZVI-BC exhibited superior properties for Cr(VI) and Cr(total) removal from spent effluent, allowing effective recovery of the washing agents. The elimination mechanism of Cr(total) by nZVI-BC involved the coordinated actions of electrostatic adsorption, reduction, and co-precipitation. The contributions to Cr(VI) reduction by Fe0, surface-bound Fe(II), and soluble Fe(II) were 0.6 %, 39.8 %, and 59.6 %, respectively. Meanwhile, CA favored the activity of surface-bound Fe(II) and Fe0 in nZVI-BC, enhancing the production of soluble Fe(II) to strengthen Cr(VI) removal. Finally, the recovered washing agent was proven to be reused three times. This study showcases that the combined soil washing using biodegradable chelant CA and effluent treatment by nZVI-BC could be a sustainable and promising strategy for Cr(VI)-contaminated soil remediation.

Ammonia hydroxide and citric acid modified wheat straw-biochars: Preparation, characterization, and environmental applications

This study presents an assessment of inorganic and organic modification of biochar on physicochemical properties, dissolved organic carbon (DOC) release, sorption efficiency towards enrofloxacin (E) and silver nanoparticles (Ag-NPs), as well as an evaluation of addition of prepared materials on hydro-physical properties and adsorption capacity of montmorillonite (M). The biochar was derived from wheat straw at 650 °C. An inorganic modification was performed using ammonia hydroxide, whereas an organic modification, using citric acid. The ammonia hydroxide and citric acid changed the biochar nature and surface chemistry by introducing amino and ester groups. The lowest DOC release was from ammonia-biochar (BCN) and the highest, from citric acid-biochar (BCC). The adsorption data were better described by pseudo-II order equation and Marczewski-Jaroniec isotherm. Results showed that BCN exhibited the highest efficiency in adsorption of E and Ag-NPs. It also improved the adsorptive abilities and saturated hydraulic conductivity of M. This provides the chemically modified biochars have an excellent potential to improve pollution removal from aqueous media and hydro-physical/sorption properties of soil sorption complex. They can be used with advantageous in environmental applications.

Citric acid crosslinked carboxymethyl cellulose edible films: A case study on preserving freshness in bananas

The study involves the preparation and characterization of crosslinked-carboxymethyl cellulose (CMC) films using varying amounts of citric acid (CA) within the range 5 %-20 %, w/w, relative to the dry weight of CMC. Through techniques such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, carbonyl content analysis, and gel fraction measurements, the successful crosslinking between CMC and CA is confirmed. The investigation includes an analysis of chemical structure, physical and optical characteristics, swelling behavior, water vapor transmission rate, moisture content, and surface morphologies. The water resistance of the cross-linked CMC films exhibited a significant improvement when compared to the non-crosslinked CMC film. The findings indicated that films crosslinked with 10 % CA demonstrated favorable properties for application as edible coatings. These transparent films, ideal for packaging, prove effective in preserving the quality and sensory attributes of fresh bananas, including color retention, minimized weight loss, slowed ripening through inhibiting amyloplast degradation, and enhanced firmness during storage.

Effect of experimental dentin etchants on dentin bond strength, metalloproteinase inhibition, and antibiofilm activity

OBJECTIVE

this study evaluated dentin microtensile bond strength (µTBS) and failure modes (at 24 h and one year), bonding interface regarding hybridization, surface morphology regarding demineralization, in situ metalloproteinase (MMP) activity, and antibacterial effect of three dentin etchants compared to 35% phosphoric acid (PA).

MATERIALS AND METHODS

The Adper Single Bond 2 adhesive (3 M Oral Care) was applied on moist dentin etched with PA (control) or on air-dried dentin etched with 3% aluminum nitrate + 2% oxalic acid (AN), 6.8% ferric oxalate + 10% citric acid (FO), or 10% citric acid (CA). The µTBS test used 40 human teeth (n = 10). Failure modes and surface morphology were analyzed by scanning electron microscopy (n = 3), while bonding interface morphology and MMP activity were evaluated by laser scanning confocal microscopy (n = 3). Antibacterial activity was evaluated against S. Mutans biofilm by means of viable cells count (CFU/mL).

RESULTS

PA presented the highest bond strengths regardless of aging time. PA, AN, and CA showed stable bond strengths after one year of storage. Adhesive and mixed failures were predominant in all groups. Thin hybrid layers with short resin tags were observed for the experimental etchants. The AN-based etchant was able to inhibit MMP activity. All tested etchants presented antibacterial activity against S. Mutans biofilm.

SIGNIFICANCE

This study suggests different dentin etchants capable of inhibiting MMP activity while also acting as cavity disinfectants.

Preparation and application of curcumin loaded with citric acid crosslinked chitosan-gelatin hydrogels

While oral administration offers safety benefits, its therapeutic efficacy is hindered by various physiological factors within the body. In this study, a novel approach was explored using a matrix consisting of 2 % chitosan and 2 % gelatin, with citric acid (CA) serving as a green cross-linking agent (ranging from 0.4 % to 1.0 %), and curcumin (Cur) as the model drug to formulate hydrogel carriers. The results showed that a 0.4 % CA concentration, the hydrogel (CGA0.4) reached swelling equilibrium in deionized water within 40 min, exhibiting a maximum swelling index was 539 g/g. The addition of Cur to the CGA hydrogel (CGACur) notably enhanced release efficiency, particularly in simulated intestinal fluid, where Cur release rates exceeded 40 % within 100 min compared to below 8 % in other solutions. Among these hydrogels, CGA0.4Cur exhibited the fastest degradation rate in the combined solution, reaching >90 % degradation after 7 days. Additionally, Cur and CA demonstrated positive effects on the tensile strength, antioxidant activity and antibacterial activity of hydrogels. Compare to the bioaccessibility of CGC (27 %), those of CGACur had increased to over 34 %. These findings offer provide theoretical support for CA-crosslinked chitosan/gelatin gels in delivering hydrophobic bioactive molecules and their application in intestinal drug delivery system.

Anaphylaxis secondary to citric acid allergy in End Stage Renal Disease patient

Dialysis reactions are not uncommon in End Stage Renal Disease (ESRD) patients who are undergoing in-center hemodialysis. Here we report the first case of anaphylaxis related to citric acid solutions used for dialysis machine disinfection and descaling. The patient developed repeated episodes of anaphylactic reactions during hemodialysis only in the inpatient setting leading to respiratory failure needing intubation and anaphylactic shock. This had failed to resolve despite using various combinations of different dialysis machines and dialyzer membranes and only resolved after the elimination of citric acid from the dialysis circuit. This case highlights the importance of different allergens in dialysis circuits and emphasizes the importance of looking for alternative reasons for dialyzer reactions.

Citric acid/chitosan adhesive with viscosity-controlled for wood bonding through supramolecular self-assembly

Developing bio-based sustainable wood adhesives is significant as a substitute for petroleum-derived adhesives. However, the existing bio-based adhesives have disadvantages of complex fabrication, uncontrollable viscosity, and poor water resistance. Herein, we developed a citric acid/chitosan adhesive with viscosity-controlled and water-resistant features by one-step dissolution at room temperature based on the supramolecular self-assembly strategy. Different wood products (plywood, laminated veneer lumber and particleboard) with superior performance were prepared by applying that adhesive on veneer and wood particles (fine and rough particles). The plywood test results showed that the citric acid/chitosan adhesive had dry and wet shear strengths outperforming the China National Standard (GB/T 9846-2015, ≥0.7 MPa), reaching 2.1 and 1.1 MPa, respectively. The adhesion mechanism was mechanical interlocks and cross-linking of citric acid/chitosan in adhesives with those in the cell wall. This work provides high promise for alternatives to traditional unsustainable wood adhesives (urea-formaldehyde, melamine-urea-formaldehyde and phenolic resins) for fabricating different wood products.

Synthesis and characterization of citric acid-modified chitosan Schiff base with enhanced antibacterial properties for the elimination of Bismarck Brown R and Rhodamine B dyes from wastewater

In this study, a new chitosan Schiff base with surface modification using citric acid was synthesized for efficient removal of pernicious dyes, namely Bismarck Brown R (BBR) and Rhodamine B (RhB), from wastewater. The physicochemical properties of the modified chitosan Schiff base were comprehensively investigated. Adsorption studies demonstrated that BBR adsorption occurred through monolayer formation, while RhB adsorption proceeded via multilayer formation on the heterogeneous surface. The synthesized adsorbent exhibited exceptional dye removal efficiency, with a Langmuir saturation capacity of 348 ± 11.0 mg.g-1 for BBR and 145 ± 18.44 mg.g-1 for RhB. Isotherm data fitting revealed consistency with the Langmuir isotherm model for BBR and the Freundlich isotherm model for RhB. Notably, the modified chitosan Schiff base showcased enhanced antibacterial properties, effectively inhibiting both gram-positive and gram-negative bacteria. The study's findings underscore the potential of this novel chitosan-based Schiff base as an efficient adsorbent for the removal of various dyes from wastewater, emphasizing its versatility and practical applicability in water treatment processes.

Synergistic impact of natural gums and crosslinkers on the properties of oilseed meals based biopolymeric films

The waste material utilization from available agricultural resources can be beneficial in the field of economic, social, and environmental well-being. One of the main industrial crops used to manufacture oil from oilseeds worldwide is agricultural waste, such as the cake made from oilseeds. In this study, de-oiled cakes are used to create biopolymeric films. Three widely accessible oilseed meals viz. flaxseed, soybean, and mustard were gathered, ground, and sieved. A film forming suspension of defatted meals along with natural gums (acacia and xanthan gum) and crosslinkers (citric acid and glutaraldehyde) were formed. The suspension was cast into petri dishes and dried to produce smooth and even films. The physical, functional, color, thermal and morphological properties of the oilseed meals-gums crosslinked biopolymeric film were evaluated and statistical analysis was performed. The solubility was found to be decreased and tensile strength was increased with the addition of citric acid and increase in tensile strength. There was significant difference observed in the values of elongation at break after addition of citric acid as crosslinker. The research shows how oilseed meals enriched with natural gum and crosslinkers may be converted into biopolymeric films, which can then be used in food packaging to lessen reliance on petroleum-based, non-biodegradable plastics.

Influence of citric acid concentrations on the porosity and performance of cellulose acetate-based porous membranes: A comprehensive study

This study investigates the influence of citric acid concentration on the fabrication of porous cellulose acetate (CA) membranes using the Non-Solvent Induced Phase Separation (NIPS) method. A notable aspect is the precise control over membrane properties, particularly pore size and porosity, achieved solely through the adjustment of citric acid concentration, serving as the additive. Higher concentrations of citric acid increase pore size by rendering polymer chains more pliable, whereas lower concentrations lead to smaller, denser pores due to improved dispersion in the CA matrix and altered water interactions during phase separation. A decrease in porosity and Gurley values with reducing citric acid concentrations (from 5 × 10-2 to 1 × 10-3 M ratios) indicates less plasticization of CA chains. However, at very low concentrations (1 × 10-4 and 1 × 10-5), porosity increases, despite the presence of smaller pores, and Gurley values approach those of pure CA in terms of gas permeability. Fourier Transform Infrared (FT-IR) spectroscopy confirms the presence of citric acid and its interaction with carbonyl groups, consistent with the pore size observations from Scanning Electron Microscopy (SEM). Spectral data deconvolution reveals weakened carbonyl bonds due to the reduced presence of citric acid, correlating with the smaller pores observed in SEM. Thermal Gravimetric Analysis (TGA) demonstrates that composite membranes are more thermally stable than pure CA, attributed to the citric acid-induced crosslinking within the polymer chains. Stability increases with decreasing citric acid concentration, with some anomalies at the lowest levels. In conclusion, this study highlights the capability of adjusting citric acid concentration to tailor membrane properties, offering valuable insights for the creation of porous materials across diverse industrial applications.

Enhancement of norfloxacin degradation by citrate in S-nZVI@Ps system: Chelation and FeS layer

The degradation of organic pollution by sulfur-modified nano zero-valent iron(S-nZVI) combined with advanced oxidation systems has been extensively studied. However, the low utilization of nZVI and low reactive oxygen species (ROS) yield in the system have limited its wide application. Herein, a natural organic acid commonly found in citrus fruits, citric acid (CA), was combined with the conventional S-nZVI@Ps system to enhance the degradation of norfloxacin (NOR). The addition of CA increased the NOR removal by about 31% compared with the conventional S-nZVI@Ps system under the same experimental conditions. Among them, the enhanced effect of CA is mainly reflected in its ability to promote the release of Fe2+ and accelerate the cycling of Fe2+ and Fe3+ to further improve the utilization of nZVI and the generation of ROS; it also promotes the dissolution of the active substance (FeS) on the surface of S-nZVI to further improve the degradation rate of NOR. More importantly, the chelate of CA and Fe2+ (CA-Fe2+) had higher reactivity than alone Fe2+. Free radical quenching and electron spin resonance (ESR) experiments indicated that the main ROS for the degradation of NOR in the CA/S-nZVI@Ps system were SO4•- and OH•. CA-bound sulfur-modifying effects on NOR degradation was systematically investigated, and the degradation mechanism of NOR in CA/S-nZVI@Ps system was explored by various techniques. Additionally, the effect of common anions in water matrix on the degradation of NOR in CA/S-nZVI@Ps system and its degradation of various pollutants were also studied. This study provides a new perspective to enhance the degradation of pollutants by S-nZVI combined with advanced oxidation system, which can help to solve the application boundary problem of S-nZVI.

Unravelling the removal mechanisms of trivalent arsenic by sulfidated nanoscale zero-valent iron: The crucial role of reactive oxygen species and the multiple effects of citric acid

The remediation of arsenic-contaminated groundwater by sulfidated nanoscale zero-valent iron (S-nZVI) has raised considerable attention. However, the role of trivalent arsenic (As(III)) oxidation by S-nZVI in oxic conditions (S-nZVI/O2) remains controversial, and the comprehensive effect of citric acid (CA) prevalent in groundwater on As(III) removal by S-nZVI remains unclear. Herein, the mechanisms of reactive oxygen species (ROS) generation and multiple effects of CA on As(III) removal by S-nZVI/O2 were systematically explored. Results indicated that the removal efficiency of As(III) by S-nZVI/O2 (97.81 %) was prominently higher than that by S-nZVI (66.71 %), resulting from the significant production of ROS (mainly H2O2 and OH) under oxic conditions, which played a crucial role in promoting the As(III) oxidation. Additionally, CA had multiple effects on As(III) removal by S-nZVI/O2 system: (i) CA impeded the diffusion of As(III) towards S-nZVI and increased the secondary risk of immobilized As(III) re-releasing into the environment due to the Fe dissolution from S-nZVI; (ii) CA could significantly enhance the yields of OH from 25.29 to 133.00 μM via accelerating the redox cycle of Fe(II)/Fe(III) and increasing the oriented conversion rate of H2O2 to OH; (iii) CA could also enrich the types of ROS (such as O2- and 1O2) in favor of further As(III) oxidation. This study contributed novel findings regarding the control of As(III) contaminated groundwater using S-nZVI technologies.

Closed-loop recycling of lithium iron phosphate cathodic powders via citric acid leaching

Lithium recovery from Lithium-ion batteries requires hydrometallurgy but up-to-date technologies aren't economically viable for Lithium-Iron-Phosphate (LFP) batteries. Selective leaching (specifically targeting Lithium and based on mild organic acids and low temperatures) is attracting attention because of decreased environmental impacts compared to conventional hydrometallurgy. This study analysed the technical and economic performances of selective leaching with 6%vv. H2O2 and citric acid (0.25-1 M, 25 °C, 1 h, 70 g/l) compared with conventional leaching with an inorganic acid (H2SO4 1 M, 40 °C, 2 h, 50 g/l) and an organic acid (citric acid 1 M, 25 °C, 1 h, 70 g/l) to recycle end of life LFP cathodes. After conventional leaching, chemical precipitation allowed to recover in multiple steps Li, Fe and P salts, while selective leaching allowed to recover Fe and P, in the leaching residues and required chemical precipitation only for lithium recovery. Conventional leaching with 1 M acids achieved leaching efficiencies equal to 95 ± 2% for Li, 98 ± 8% for Fe, 96 ± 3% for P with sulfuric acid and 83 ± 0.8% for Li, 8 ± 1% for Fe, 12 ± 5% for P with citric acid. Decreasing citric acid's concentration from 1 to 0.25 M didn't substantially change leaching efficiency. Selective leaching with citric acid has higher recovery efficiency (82 ± 6% for Fe, 74 ± 8% for P, 29 ± 5% for Li) than conventional leaching with sulfuric acid (69 ± 15% for Fe, 70 ± 18% for P, and 21 ± 2% for Li). Also, impurities' amounts were lower with citric acid (335 ± 19 335 ± 19 of S mg/kg of S) than with sulfuric acid (8104 ± 2403 mg/kg of S). In overall, the operative costs associated to 0.25 M citric acid route (3.17€/kg) were lower compared to 1 M sulfuric acid (3.52€/kg). In conclusion, citric acid could be a viable option to lower LFP batteries' recycling costs, and it should be further explored prioritizing Lithium recovery and purity of recovered materials.

Resistance mechanisms of Saccharomyces cerevisiae against silver nanoparticles with different sizes and coatings

To investigate the underlying resistance mechanisms of Saccharomyces cerevisiae against Ag-NPs with different particle sizes and coatings, transcriptome sequencing (RNA-seq) technology was used to characterize the transcriptomes from S. cerevisiae exposed to 20-PVP-Ag, 100-PVP-Ag, 20-CIT-Ag and 100-CIT-Ag, respectively. The steroid biosynthesis was found as a general pathway for Ag-NPs stress responding, in which ERG6 and ERG3 were inhibited and ERG11, ERG25 and ERG5 were significantly up-regulated to resist the stress by supporting the later mutation and resistance and modulate drug efflux indirectly. The resistance mechanism of S. cerevisiae to 20-PVP-Ag seems different from that of 100-PVP-Ag, 20-CIT-Ag and 100-CIT-Ag. Under the 20-PVP-Ag, transmembrane transporter activity, transition metal ion homeostasis and oxidative phosphorylation pathway were main resistance pathways to enhance cell transport processes. While 100-PVP-Ag, 20-CIT-Ag and 100-CIT-Ag mainly impacted RNA binding, structural constituent of ribosome and ribosome pathway which can provide more energy to maintain the number and function of protein in cells. This study reveals the differences in resistance mechanisms of S. cerevisiae to Ag-NPs with different particle sizes and coatings, and explains several main regulatory mechanisms used to respond to silver stress. It will provide theoretical basis for the study of chemical risk assessment.

Study on cellulose nanofibrils/copolymacrolactone based nano-composites with hydrophobic behaviour, self-healing ability and antioxidant activity

The multiple uses of cellulose nanofibrils (CNFs) originate from their availability from renewable resources, and are due to their physico-chemical properties, biodegradability and biocompatibility. At the same time, reducing sensitivity to humidity, increasing interfacial adhesion and hydrophobic modification of the CNF surface to diversify applications and improve operation, are current targets pursued. This study focuses on the preparation of a novel gel structure using cellulose nanofibrils (CNFs) and poly(ethylene brassylate-co-squaric acid) (PEBSA50/50), a bio-based copolymacrolactone. The primary goal is to achieve the gel with reduced sensitivity to humidity and enhanced hydrophobic behaviour. The new system was characterized in comparison to its constituent components using various techniques, such as Fourier transform infrared spectroscopy, thermal analysis, X-ray diffraction, and NIR - chemical imaging. Rheological tests demonstrated the formation of the CNF_PEBSA50/50 gel as a result of physical interactions between the two polymeric partners and revealed self-healing abilities for the prepared gels. Determination of the contact angle, surface free energy, as well as dynamic measurements of the vapour sorption of the CNF_PEBSA50/50 system, confirmed the achievement of the study's aim. Furthermore, the CNF_PEBSA50/50 network was utilized to encapsulate citric acid, resulting in the creation of a new bioactive composite with both antioxidant and antimicrobial activity.

Development of films based on chitosan, gelatin and collagen extracted from bocachico scales (Prochilodus magdalenae)

Biodegradable biopolymers from species of the animal kingdom or their byproducts are sustainable as ecological materials due to their abundant supply and compatibility with the environment. The research aims to obtain a biodegradable active material from chitosan, gelatin, and collagen from bocachico scales (Prochilodus magdalenae). Regarding the methodology, films were developed from gelatin, chitosan, and collagen from bocachico scales (Prochilodus magdalenae) at different concentrations using glycerol as a plasticizer and citric acid as a cross-linker. The films were obtained with the hydrated mass processed by compression molding and characterized according to humidity, water solubility, contact angle, mechanical properties, and structural properties. The results of the films showed a hydrophobic characteristic. First, the chitosan-collagen (CS/CO) films showed a yellowish color, while the gelatin-collagen (Gel/CO) films were transparent and less soluble than the gelatin-collagen (Gel/CO) films. Concerning mechanical properties, gelatin films showed higher stiffness and tensile strength than chitosan films. Furthermore, in the morphological analysis, more homogeneous chitosan films were obtained by increasing the concentration of citric acid. In general, chitosan, gelatin, and collagen extracted from the scales of the bocachico (Prochilodus magdalenae) are an alternative in the application of films in the food industry.

A bioinspired and sustainable route for the preparation of Ag-crosslinked alginate fibers decorated with silver nanoparticles

Functional materials obtained through green and sustainable routes are attracting particular attention due to the need to reduce the environmental impact of the chemical industry. In this work we propose a bioinspired approach for the preparation of alginate fibers containing silver nanoparticles (AgNPs), to be used for antimicrobial purposes. We demonstrate that filiform polymeric structures with length of a few meters can be easily obtained by extruding an alginate solution in an aqueous Ag+-containing bath (i.e. wet spinning) and that treating the fibers with freshly-squeezed lemon juice leads to the formation of AgNPs homogeneously distributed within the polymeric network. Using mixtures of ascorbic and citric acid to mimic lemon juice composition we highlight the influence of the aforementioned molecules on the nanoparticles formation process as well as on the properties of the fibers. Varying the amount of citric and ascorbic acid used for the treatment allows to finely tune the thermal, morphological and water absorption properties of the fibers. This evidence, along with the possibility to easily monitor the preparation through FT-IR spectroscopy, endows the fibers with a high application potential in several fields such as wound healing, water/air purification and agriculture.

Progress on green crosslinking of polysaccharide hydrogels for drug delivery and tissue engineering applications

Natural polysaccharides are being studied for their biocompatibility, biodegradability, low toxicity, and low cost in the fabrication of various hydrogel devices. However, due to their insufficient physicochemical and mechanical qualities, polysaccharide hydrogels alone are not acceptable for biological applications. Various synthetic crosslinkers have been tested to overcome the drawbacks of standalone polysaccharide hydrogels; however, the presence of toxic residual crosslinkers, the generation of toxic by-products following biodegradation, and the requirement of toxic organic solvents for processing pose challenges in achieving the desired non-toxic biomaterials. Natural crosslinkers such as citric acid, tannic acid, vanillin, gallic acid, ferulic acid, proanthocyanidins, phytic acid, squaric acid, and epigallocatechin have been used to generate polysaccharide-based hydrogels in recent years. Various polysaccharides, including cellulose, alginate, pectin, hyaluronic acid, and chitosan, have been hydrogelized and investigated for their potential in drug delivery and tissue engineering applications using natural crosslinkers. We attempted to provide an overview of the synthesis of polysaccharide-based hydrogel systems (films, complex nanoparticles, microspheres, and porous scaffolds) based on green crosslinkers, as well as a description of the mechanism of crosslinking and properties with a special emphasis on drug delivery, and tissue engineering applications.

Marine cyanobacterial biomass is an efficient feedstock for fungal bioprocesses

BACKGROUND

Marine cyanobacteria offer many sustainability advantages, such as the ability to fix atmospheric CO2, very fast growth and no dependence on freshwater for culture. Cyanobacterial biomass is a rich source of sugars and proteins, two essential nutrients for culturing any heterotroph. However, no previous study has evaluated their application as a feedstock for fungal bioprocesses.

RESULTS

In this work, we cultured the marine cyanobacterium Synechococcus sp. PCC 7002 in a 3-L externally illuminated bioreactor with working volume of 2 L with a biomass productivity of ~ 0.8 g L-1 day-1. Hydrolysis of the biomass with acids released proteins and hydrolyzed glycogen while hydrolysis of the biomass with base released only proteins but did not hydrolyze glycogen. Among the different acids tested, treatment with HNO3 led to the highest release of proteins and glucose. Cyanobacterial biomass hydrolysate (CBH) prepared in HNO3 was used as a medium to produce cellulase enzyme by the Penicillium funiculosum OAO3 strain while CBH prepared in HCl and treated with charcoal was used as a medium for citric acid by Aspergillus tubingensis. Approximately 50% higher titers of both products were obtained compared to traditional media.

CONCLUSIONS

These results show that the hydrolysate of marine cyanobacteria is an effective source of nutrients/proteins for fungal bioprocesses.

Effects of citric acid on arsenic transformation and microbial communities in different paddy soils

Root exudate is a major source of soil organic matter and can significantly affect arsenic (As) migration and transformation in paddy soils. Citric acid is the main component of rice root exudate, however, the impacts and rules of citric acid on As bioavailability and rhizobacteria in different soils remains unclear. This study investigated the effects of citric acid on As transformation and microbial community in ten different paddy soils by flooded soil culture experiments. The results showed that citric acid addition increased total As and arsenate (As(V)) in the soil porewater by up to 41-fold and 65-fold, respectively, after 2-h incubation. As(V) was the main As species in soil porewater within 10 days with the addition of citric acid. Non-specifically sorbed As of soils, total Fe and total As were the main environmental factors affecting the soil microbial communities. High-throughput sequencing analysis demonstrated that citric acid addition significantly altered the soil microbial community structure, shifting the Proteobacteria-related reducing bacteria to Firmicutes-related reducing bacteria in different paddy soils. The relative abundance of Firmicutes was promoted by 174-196%. Clostridium-related bacteria belonging to Firmicutes became the dominant genera, which is believed to regulate As release through the reductive dissolution of iron oxides or the direct reduction of As(V) to arsenite (As(III)). However, citric acid addition significantly decreased the relative abundance of Geobacter and Anaeromyxobacter, which are also typical active As(V)- and ferric-reducing bacteria. Real-time quantitative polymerase chain reaction (qPCR) also revealed that the addition of citric acid significantly decreased the relative abundances of Geobacter in the different soils by 8-28 times while the relative abundances of Clostridium increased by 2-5 times. These results provide significant insight on As transformation in different types of rice rhizospheric soils and guidance for the application of rice varieties with low citric acid exuding to restrict As accumulation.

Citric Acid Conditioning as an Alternative to EDTA for Growth Factors Release and Stem Cell Response in Regenerative Endodontics: A Systematic Review of In Vitro Studies

INTRODUCTION

Citric acid (CA) conditioning may be a promising alternative to ethylenediaminetetraacetic acid (EDTA) in regenerative endodontic procedures, as reported to improve growth factors' release from dentin. This review systematically investigated the effect of CA conditioning on the growth factors release from dentin and cell behavior compared to EDTA conditioning.

METHODS

Searches were conducted (PubMed/MEDLINE, Scopus, Web of Science, Embase, SciELO, Cochrane Library, and grey literature) until May-2023. Only in vitro studies that evaluated the effects of CA on growth factors' release from dentin and cell behavior outcomes compared to EDTA were included. The studies were critically appraised using a modified Joanna Briggs Institute's checklist. Meta-analysis was unfeasible.

RESULTS

Out of the 335 articles screened, nine were included. Among these, three studies used dentin discs/roots from permanent human teeth; the rest combined them with stem cells. 10% CA for 5 or 10 minute was the most used protocol. Meanwhile, EDTA concentrations ranged from 10% to 17%. In eight studies examining the release of growth factors, five reported a significant release of transforming growth factor-β after dentin conditioning with 10% CA compared to 17% EDTA. Regarding cell behavior (6 studies), three studies assessed cell viability. The findings revealed that 10% CA conditioning showed cell viability similar to those of 17% EDTA. Additionally, in two out of three studies, it was observed that 10% CA conditioning did not affect cell morphology. The studies had a low risk of bias.

CONCLUSIONS

The use of 10% CA to condition dentin for 5-10 minutes resulted in a notable transforming growth factor -β1 release, but its cell responses were similar to those of EDTA.

Study on the mechanism of sodium ion inhibiting citric acid fermentation in Aspergillus niger

Excessive sodium significantly inhibits citric acid fermentation by Aspergillus niger during the recycling of citric acid wastewater. This study aimed to elucidate the inhibition mechanism at the interface of physiology and transcriptomics. The results showed that excessive sodium caused a 22.3 % increase in oxalic acid secretion and a 147.6 % increase in H+-ATPase activity at the 4 h fermentation compared to the control. Meanwhile, a 13.1 % reduction in energy charge level and a 15.2 % decline in NADH content were found, which implied the effects on carbon metabolism and redox balance. In addition, transcriptomic analysis revealed that excessive sodium altered the gene expression profiles related to ATPase, hydrolase, and oxidoreductase, as well as pathways like glyoxylate metabolism, and transmembrane transport. These findings gained insights into the metabolic regulation of A. niger response to environmental stress and provided theoretical guidance for the construction of sodium-tolerant A. niger for industrial application.

Different crosslinking as a strategy to improve films produced from external mesocarp of pequi (Caryocar brasiliense)

The pequi (Caryocar brasiliense) external mesocarp is rich in phenolic compounds and pectin and demonstrates the potential to produce active and biodegradable films. Thus, the present study aimed to produce films with pequi mesocarp as a polymer matrix and evaluate the influence of crosslinking agents (calcium chloride and citric acid) on the film's properties. The films obtained from pequi mesocarp (MF), showed in general, complete biodegradation in 33 days, good antioxidant capacity, and inhibition against S. aureus (24.7 mm) and E. coli (23.0 mm). The crosslinking agents reduced solubility by up to 35% and increased the elongation of the films by up to 3.5-fold. Calcium chloride promoted a higher reduction in solubility, and both agents increase the antioxidant and antimicrobial activities, compared to MF. Citric acid proved to be the best agent to modify the properties of pequi mesocarp films. In addition to the crosslinking action, it presented plasticizing effect.

Effect of ethanol, phytic acid and citric acid treatment on the physicochemical and heavy metal adsorption properties of corn starch

Corn starch dispersions were heated with ethanol (E) and reacted with phytic acid (E-PA), citric acid (E-CA), and a mixture of phytic and citric acid (E-PACA) under dry-heating to prepare heavy metal adsorbents. Microscopy images indicated that ethanol treatment induced the formation of porous structures on the surface; furthermore, treatment with phytic and citric acid induced indentations, pores, and irregular structures in E-PA, E-CA, and E-PACA starches. Phytic and citric acid were retained in the starch molecules through ester bonds with the phosphate and carboxyl groups, respectively. Starch esterification by phytic and citric acid induced a loss of crystallinity, high water absorption capacity, and low solubility. E-PACA starch exhibited more efficient Cu2+ adsorption (38.13 mg/g) than native, E, E-PA, and E-CA starches (0.11, 0.49, 2.05, and 36.23 mg/g, respectively). Thus, modification with ethanol, phytic acid and citric acid can be applied to prepare natural starch-based heavy metal adsorbents.

Enhanced porous membrane fabrication using cellulose acetate and citric acid: Improved structural integrity, thermal stability, and gas permeability

In this study, our primary objective was to enhance the properties of porous membranes by addressing the limitations associated with phase separation. We employed a non-solvent induced phase separation (NIPS) method, utilizing cellulose acetate (CA) in conjunction with citric acid to fabricate these membranes. Citric acid played a dual role: ensuring a uniform pore structure and cross-linking the CA polymer, thereby enhancing its mechanical strength. This approach resulted in the development of a more robust membrane with superior structural integrity. Thermogravimetric analysis (TGA) confirmed enhanced thermal stability, particularly up to 150 °C, as a result of citric acid's cross-linking effect. Beyond 150 °C, the decomposition temperatures of the CA/citric acid membrane were found to be comparable to those of pure CA. Remarkably, a CA/citric acid ratio of 1:0.05 exhibited the slowest decomposition rate as the temperature increased. Scanning electron microscopy (SEM) examination unveiled a sponge-like membrane structure with numerous evenly distributed fine pores. Through the use of citric acid as a plasticizer, we were able to effectively control the penetration of water molecules, preventing the formation of macrovoids and promoting the creation of fine pores. This resulted in the fabrication of a high-porosity membrane, boasting an impressive porosity measurement of 84.9 %. Furthermore, measurements of the Gurley value confirmed efficient gas permeation, a critical characteristic for applications requiring effective gas transport. Fourier transform infrared (FT-IR) spectroscopy attested to the presence of citric acid in the membrane post-phase separation, indicating its successful integration. Our work presents a novel approach to enhance porous membranes, providing improvements in mechanical strength, thermal stability, and gas permeability. These findings offer valuable insights for the development of advanced materials with diverse applications in various fields.

Preparation of crosslinked starches with enhanced and tunable gel properties by the cooperative crosslinking-extrusion combined modification

Due to its safety and palatability, the citric acid crosslinking modification is an excellent way to modify the properties of starch gels. However, the application of this method is restricted by the low degree of crosslinking of gels produced by this method in the hydrogel system. To produce citric acid-crosslinked starch with improved strength and tunable gel characteristics, a novel ion-esterification cooperative crosslinking-extrusion combined (CCEC) modification approach is presented in this study. The linear and nonlinear rheological characteristics of the samples were measured to evaluate the effectiveness of CCEC modification. Findings disclosed that at 0.1 % strain, the elastic modulus of the CCEC-modified starch (SC-0.5Zn2+, G' = 1522.29 ± 36.31) exhibited a significant rise of 387.27 % as compared to the elastic modulus of citric acid-crosslinked starch (SC, G' = 318.29 ± 11.62). Furthermore, changing the cation concentration allowed for efficient control of the gel's rheological characteristics. The samples were characterized by SEM, FTIR, XRD, and XPS. The CCEC-modified gels had a smaller pore size distribution and a denser honeycomb porous structure. The CCEC modification reaction involves ester bonds and electrostatic attraction. This research is essential to elucidate how coupled physicochemical modification techniques affect the manipulation of starch gel characteristics.

pH-dependent virucidal effects of weak acids against pathogenic viruses

BACKGROUND

Weak acids, such as acetic acid, show virucidal effects against viruses, and disinfectants are considered effective virucidal agents possibly because of their low pH, depending on the proton concentration. This study aimed to evaluate the efficacy of different weak acids (acetic, oxalic, and citric acids) and eligible vinegars under different pH conditions by comparing their inactivation efficacies against enveloped and non-enveloped viruses.

METHODS

Acetic, oxalic, and citric acids were adjusted to pH values of 2, 4 and 6, respectively. They were also diluted from 1 M to 0.001 M with distilled water. Enveloped influenza A virus (FulV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and non-enveloped feline calicivirus (FCV) were treated with adjusted weak acids for up to 30 min. These viruses were also reacted with white distilled vinegar (WDV) and grain-flavored distilled vinegar (GV) for up to 30 min. Infectious viral titers after the reactions were expressed as plaque-forming units per mL.

RESULTS

Acetic acid showed virucidal effects against FulV at pH 4, whereas citric and oxalic acids did not. Acetic and citric acids inactivated SARS-CoV-2 at pH 2, whereas oxalic acid did not. All acids showed virucidal effects against FVC at pH 2; however, not at pH 4. The virucidal effects of the serially diluted weak acids were also reflected in the pH-dependent results. WDV and GV significantly reduced FulV titers after 1 min. SARS-CoV-2 was also susceptible to the virucidal effects of WDV and GV; however, the incubation period was extended to 30 min. In contrast, WDV and GV did not significantly inactivate FCV.

CONCLUSIONS

The inactivation efficacy of weak acids is different even under the same pH conditions, suggesting that the virucidal effect of weak acids is not simply determined by pH, but that additional factors may also influence these effects. Moreover, eligible vinegars, the main component of which is acetic acid, may be potential sanitizers for some enveloped viruses, such as FulV, in the domestic environment.

Integrating metal-organic framework ZIF-8 with green modifier empowered bacteria with improved bioremediation

Suspended microorganisms often experience diminished efficacy in the bioremediation of polycyclic aromatic hydrocarbons (PAHs). In this study, the potential of zeolite imidazolate framework-8 (ZIF-8) and the eco-friendly modifier citric acid (CA) was harnessed to generate a biomimetic mineralized protective shell on the surface of Bacillus subtilis ZL09-26, resulting in an enhanced capability for PAH degradation. This investigation encompassed the integrated responses of B. subtilis ZL09-26 to ZIF-8 and ZIF-8-CA at both cellular and proteomic levels. The amalgamation of ZIF-8 and CA not only stimulated the growth and bolstered the cell viability of B. subtilis ZL09-26, but also counteracted the toxic effects of phenanthrene (PHE) stress. Remarkably, the bioremediation prowess of B. subtilis ZL09-26@ZIF-8-CA surpassed that of ZL09-26@ZIF-8 and ZL09-26, achieving a PHE removal rate of 94.14 % within 6 days. After undergoing five cycles, ZL09-26@ZIF-8-CA demonstrated an enduring PHE removal rate exceeding 83.31 %. A complex interplay of various metabolic pathways orchestrated cellular responses, enhancing PHE transport and degradation. These pathways encompassed direct PHE biodegradation, central carbon metabolism, oxidative phosphorylation, purine metabolism, and aminoacyl-tRNA biosynthesis. This study not only extends the potential applications of biomineralized organisms but also offers alternative strategies for effective contaminant management.

Promotion of phosphate release from humic acid-iron hydroxide coprecipitates in the presence of citric acid

Phosphate (P) resources are expected to be depleted within a century. Therefore, promoting balanced phosphorus fertilizer use and understanding phosphorus dynamics in soils containing iron (III), organic acids, and iron (III)-organic molecule particulates is crucial. This study investigated the sorption of citric acid onto humic acid-iron hydr(o)xide coprecipitate (HAFHCP) and the reciprocal effects of citric acid and P sorption on HAFHCP with different C/Fe ratios. The results showed that the maximum sorption capacity (MSC) of citric acid on HAFHCP decreased with increasing C/Fe ratios in the HAFHCP. The P sorption on HAFHCP pre-sorbed with citric acids (denoted as C-P) decreased by 50% compared with that of the MSC on FH. However, citric acids could only reduce P sorption by 20% when P was pre-sorbed on HAFHCP (denoted as P-C). The results suggested that upon the formation of HAFHCP, citric acids might increase P availability, especially in the C-P system. Although citric acids initially inhibited P sorption on HAFHCP in the P-C system, P sorption increased with prolonged reaction time. The exposures of new sorption sites upon dissolution of Fe from HAFHCP by citric acids or/and the formations of Fe bridge between P and organic domains of HAFHCP might contribute to these results. Additionally, a number of large HAFHCP aggregates became smaller while sorbing P due to the increasing electric repulsion on the surfaces of FH, enabling the subsequent dissolutions of more Fe by citric acids from HAFHCP in the P-C system. By integrating these innovative and sustainable strategies, the recycling and reuse of P can be optimized, thereby minimizing the reliance on synthetic fertilizers and mitigating environmental impacts. This approach fosters the efficient utilization of phosphorus resources, improves soil fertility, and enhances the overall resilience of agricultural systems and ecosystems.

Citric acid cross-linked β-cyclodextrins: A review of preparation and environmental/biomedical application

The β-cyclodextrins (β-CD) are biocompatible macrocyclic candidates for the preparation of various composites with enhanced functions. While nontoxic and biodegradable citric acid (CA) is the favorite crosslinking agent for fabricating hierarchical advanced structures. The carboxyl and hydroxyl groups on CA can serve as "structural bridges" and enhance the solubility of β-CD. Leading to the construction of CA cross-linked β-CD with marvelous complicated structures and targeted functions. Here, we directly categorized the grafted composite materials into two main types such as organic and inorganic materials. Particularly, some representative composite materials are listed and analyzed in detail according to their preparation, advantages of unique characteristics, as well as the possible applications in environmental and biomedical fields such as adsorption of pollutants, sensors, and biomedical applications.

Cadmium, lead, and zinc immobilization in the soil using a phosphate compound with citric acid present

Low molecular weight organic acids (LMWOAs) are common in rhizospheric soil and may impede the interaction between phosphate and metals. Thus, studying how phosphate compounds impact metal immobilization in rhizospheric soil using LMWOAs is crucial. An incubation experiment examined the effects of NaH2PO4 (a P compound) (3%), various concentrations of citric acid (CA), and combinations of P and CA, on soil cadmium (Cd), lead (Pb), and zinc (Zn) immobilization using the European Community Bureau of Reference (BCR) sequential extraction method, CaCl2 extraction method, zeta potential, fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The P, low CA (2 mmol kg-1 soil) (CA2), and P-CA2 treatments reduced acid-soluble and CaCl2-extractable Cd, Pb, and Zn, indicating metal immobilization, with the P-CA2 treatment being the most effective. High CA (>5-20 mmol kg-1 soil) or a P with high CA reversed prior patterns, suggesting metal mobilization. The zeta potential study indicated that when pH increased, treatments became more negative, notably P-CA2 followed by P, suggesting that electrostatic adsorption was the predominant metal immobilization mechanism, especially in P-CA2. XRD tests, however, showed that the P treatment alone produced Cd phosphate, pyromorphite, and hopeite, indicating that sorption and precipitation were the main metal immobilization processes in the P treatment alone. In conclusion, P-CA2 was found to be the most efficient metal immobilization and redistribution treatment for contaminated soils. Rhizospheric CA may alter Cd, Pb, and Zn mineral stability. Therefore, when treating Cd, Pb, and Zn-contaminated soils with a P compound, CA should be addressed.

Enhancement of phycocyanin productivity and thermostability from Arthrospira platensis using organic acids

Intracellular hyperaccumulation of phycocyanin (PC) and its high susceptibility to degradation at higher temperatures are major challenging problems associated with its production from cyanobacteria. The present study evaluated different concentrations of organic acids (1, 2, and 3 mM) (citric acid, acetic acid, succinic acid, fumaric acid, and oxalic acid) under fed-batch mode on the biomass and phycobiliproteins' production from Arthrospira platensis. Besides they were evaluated at 2.5-7.5 mM as preservative to stabilize PC at high temperatures. The incorporation of 3 mM of succinic acid into the cultivation medium enhanced the biomass and PC productivity to 164.05 and 26.70 mg L-1 day-1, which was ~ 2- and threefold higher than control, respectively. The produced PC in this treatment was food-grade with a 2.2 purity ratio. The use of organic acids also enhanced the thermal stability of PC. Citric acid (7.5 mM) markedly promoted the half-life values of PC to 189.44 min compared to 71.84 min in the control. The thermodynamic analysis confirmed higher thermostability of PC in the presence of organic acids and indicated the endothermic and non-spontaneity of the thermal denaturation process. The findings of the present study confirmed that organic acids could be utilized as cost effective and sustainable compounds for promoting not only phycobiliproteins' production but also the thermostability of PC for potential application in food industry.

Metabolomics analysis of the metabolic effects of citric acid on Issatchenkia terricola WJL-G4

In current research, yeast species Issatchenkia terricola WJL-G4 was shown to be capable of degrading citric acid, especially in the processing of fruit juice and wine. I. terricola WJL-G4 was able to use citric acid as a carbon source, but the metabolic effects of citric acid on yeast remained unclear. In this study, the metabolic effects of citric acid on I. terricola WJL-G4 were studied using liquid chromatography-mass spectrometry metabolomics technology, with glucose treatment as the control. Results showed that organic acid contents related to the extracellular tricarboxylic acid cycle (TCA) varied greatly. The metabolomics results indicated that I. terricola WJL-G4 might metabolize citric acid through the TCA pathway, and the glycolysis pathway might be inhibited; however, gluconeogenesis proceeded normally during citric acid treatment. Some fatty acids and phospholipids, along with the metabolic pathways of amino acids, vitamins, purines and nicotinamide in I. terricola WJL-G4 were also affected by the citric acid treatment. This work provided a theoretical basis for further study of the mechanism of yeast metabolism of citric acid.

24-h urine collection in patients with urolithiasis: perspective on renal function

A prospective observational study involving consecutive patients diagnosed with symptomatic urolithiasis was conducted to evaluate the serial change of urinary protein and 24-h urine chemistry with time after surgical procedures for urolithiasis. A consecutive 24-h urine samples, including calcium, uric acid and citrate were collected before surgical treatments, 4 ~ 8 weeks after surgery and 6 months after surgery. The urinary protein to creatinine ratio was also repeated at each timepoint. Forty-seven patients completed the study. The quantity of 24-h urine chemistry, including calcium, uric acid and citrate, changed over time and tended to increase (p = 0.013, 0.076 and 0.004, respectively), but the changes were not prominent during short-term follow-up. In contrast, the urinary protein to creatinine ratio decreased (p < 0.001) after surgical treatment for symptomatic renal stones, and the change was reflected in short-term follow-up. However, the serial changes in the urinary protein to creatinine ratio were significantly related to the serial changes in the 24-h urinary chemistry (p < 0.001). Surgical decompression for symptomatic urolithiasis could decrease the urinary protein to creatinine ratio, indicating improvement from renal damage, which may be reflected in the increase in 24-h urinary chemistry, including calcium, uric acid and citrate. These results strengthen the previous guidelines for the timing of 24-h urine collection and provide new insight into the optimal timing from the perspective of renal function.

The self-regulating on cohesion properties of calcium phosphate/ calcium sulfate bone cement improved by citric acid/sodium alginate

Calcium phosphate cement (CPC) has attracted extensive interest from surgeons and materials scientists. However, the collapsibility of calcium phosphate cement limits its clinical application. In this work, a gel network of SA-CA formed by the reaction of citric acid (CA) and sodium alginate (SA) was introduced into the α-TCP/α-CSH composite. Furthermore, a high proportion of α-CSH provided more calcium sources for the system to combine with SA forming a gel network to improve the cohesion property of the composite, which also played a regulating role in the conversion of materials to HA. The morphology, physicochemical properties, and cell compatibility of the composites were studied with SA-CA as curing solution. The results show that SA-CA plays an important role in the compressive strength and collapse resistance of bone cement, and its properties can be regulated by changing the content of CA. When CA is 10 wt%, the mechanical strength is the highest, reaching 12.49 ± 2.03 MPa, which is 265.80% higher than water as the solidifying liquid. In addition, the cell experiments showed that the samples were not toxic to MC3T3 cells. The results of ALP showed that when SA-CA were used as curing solution, the activity of ALP was higher than that of blank sample, indicating that the composite bone cement could be conducive to the differentiation of osteoblasts. In this work, the α-CSH/α-TCP based composite regulated by gel network of SA-CA can provide a promising strategy to improve the cohesion of bone cement.

Regulation of cell differentiation to promote pullulan synthesis in Aureobasidium pullulans NG

Pullulan is a polymer produced by Aureobasidium spp. The yield of pullulan production can be impacted by the cellular differentiation of Aureobasidium spp., which changes with alterations in the growth environment. To improve pullulan yield, identifying key factors that regulate cellular differentiation is crucial. In this study, the main form of pullulan synthesis in Aureobasidium pullulans NG was through swollen cells (SC). The results showed that citric acid (CA) can regulate the cellular differentiation of Aureobasidium pullulans NG by accumulating higher levels of CA in the cells to maintain growth in SC form and increase pullulan production. The addition of 1.0% CA to Aureobasidium pullulans NG for 96 h resulted in a significant increase in pullulan production, producing 18.32 g/l compared to the control group which produced 10.23 g/l. Our findings suggest that controlling cellular differentiation using CA is a promising approach for enhancing pullulan production in Aureobasidium pullulans. KEY POINTS: • The regulation of cell differentiation in Aureobasidium pullulans NG is demonstrated to be influenced by citric acid. • Intracellular citric acid levels in Aureobasidium pullulans NG have been shown to support the growth of swollen cells. • Citric acid has been found to increase pullulan production in Aureobasidium pullulans NG.

Bioindustrial applications of thermostable Endoglucanase purified from Trichoderma viride towards the conversion of agrowastes to value-added products

Importance of biocatalytic reactions and biotransformations mediated by fungal enzymes has increased tremendously in various industries. Endoglucanase obtained from Trichoderma viride has been utilized for bioconversion of agrowastes; wheat straw (WS) and corn stover (CS) as biomass into citric acid and single cell protein (SCP) as value-added products. The enzyme was purified to apparent homogeneity with Mr:44.67 kDa; purification-fold, yield, specific activity to be 19.5-, 29.2%, and 150.4 Units.mg-1, respectively, with thermostability up to 70 °C. The enzyme showed a novel N-terminal peptide and its computational analysis revealed a conserved 'SG' amino acid sequence alike microbial cellulases. The experimental results have shown the potential of endoglucanase for the conversion of agrowastes; wheat straw (WS) and corn stover (CS) into citric acid, maximum yield (KgM-3) found in submerged (WS:50;CS:45) fermentation process. Single-cell protein (SCP) production in WS (68 KgM-3) hydrolysate was superior to both CS hydrolysate (60 KgM-3) and YEPD (standard medium) (58 KgM-3).

Proteome insights of citric acid-mediated cadmium toxicity tolerance in Brassica napus L

Cadmium (Cd) is a toxic substance that is uptake by plants from soils, Cd easily transfers into the food chain. Considering global food security, eco-friendly, cost-effective, and metal detoxification strategies are highly demandable for sustainable food crop production. The purpose of this study was to investigate how citric acid (CA) alleviates or tolerates Cd toxicity in Brassica using a proteome approach. In this study, the global proteome level was significantly altered under Cd toxicity with or without CA supplementation in Brassica. A total of 4947 proteins were identified using the gel-free proteome approach. Out of these, 476 proteins showed differential abundance between the treatment groups, wherein 316 were upregulated and 160 were downregulated. The gene ontology analysis reveals that differentially abundant proteins were involved in different biological processes including energy and carbohydrate metabolism, CO2 assimilation and photosynthesis, signal transduction and protein metabolism, antioxidant defense, heavy metal detoxification, plant development, and cytoskeleton and cell wall structure in Brassica leaves. Interestingly, several candidate proteins such as superoxide dismutase (A0A078GZ68) L-ascorbate peroxidase 3 (A0A078HSG4), glutamine synthetase (A0A078HLB2), glutathione S-transferase DHAR1 (A0A078HPN8), glutamine synthetase (A0A078HLB2), cysteine synthase (A0A078GAD3), S-adenosylmethionine synthase 2 (A0A078JDL6), and thiosulfate/3-mercaptopyruvate sulfur transferase 2 (A0A078H905) were involved in antioxidant defense system and sulfur assimilation-involving Cd-detoxification process in Brassica. These findings provide new proteome insights into CA-mediated Cd-toxicity alleviation in Brassica, which might be useful to oilseed crop breeders for enhancing heavy metal tolerance in Brassica using the breeding program, with sustainable and smart Brassica production in a metal-toxic environment.

Characterization and in vivo evaluation of a fabricated absorbable poly(vinyl alcohol)-based hernia mesh

The most widely taken medical approach toward hernia repair involves the implementation of a prosthetic mesh to cover the herniated site and reinforce the weakened area of the abdominal wall. Biodegradable meshes can serve as biocompatible grafts with a low risk of infection. However, their major complication is associated with a high rate of degradation and hernia recurrence. We proposed a facile and cost-effective method to fabricate a poly(vinyl alcohol)-based mesh, using the solution casting technique. The inclusion of zinc oxide nanoparticles, citric acid, and three cycles of freeze-thaw were intended to ameliorate the mechanical properties of poly(vinyl alcohol). Several characterization, cell culture, and animal studies were conducted. Swelling and water contact angle measurements confirmed good water uptake capacity and wetting behavior of the final mesh sample. The synthesized mesh acquired a high mechanical strength of 52.8 MPa, and its weight loss was decreased to 39 %. No cytotoxicity was found in all samples. In vivo experiments revealed that less adhesion and granuloma formation, greater tissue integration, and notably higher neovascularization rate were resulted from implanting this fabricated hernia mesh, compared to commercial Prolene® mesh. Furthermore, the amount of collagen deposition and influential growth factors were enhanced when rats were treated with the proposed mesh instead of Prolene®.

Citric acid and hydrogen sulfide cooperate to mitigate chromium stress in tomato plants by modulating the ascorbate-glutathione cycle, chromium sequestration, and subcellular allocation of chromium

The study aimed to investigate the role of hydrogen sulfide (H2S) in regulating chromium stress (Cr-S) tolerance of tomato plants treated with citric acid (CA). Prior to the Cr treatment, tomato plants were foliar-fed with CA (100 μM) daily for 3 days. Subsequently, the plants were grown for another ten days in a hydroponic system in a 50 μM Cr (VI) solution. Chromium treatment reduced photosynthetic pigments and plant biomass, but boosted the levels of hydrogen peroxide (H2O2) malondialdehyde (MDA), H2S, phytochelatins (PCs), and glutathione (GSH), electrolyte leakage (EL), and antioxidant enzyme activity in tomato plants. However, the foliar spray of CA mitigated the levels of H2O2, MDA, and EL, promoted plant growth and chlorophyll content, enhanced antioxidant enzymes' activities, and increased H2S production in Cr-S-tomato plants. CA also increased the levels of GSH and PCs, potentially reducing the toxicity of Cr through regulated sequestration. Additionally, the application of sodium hydrogen sulfide (NaHS), a donor of H2S, improved CA-induced Cr stress tolerance. The addition of CA promoted Cr accumulation in root cell wall and leaf vacuoles to suppress its toxicity. To assess the involvement of H2S in CA-mediated Cr-S tolerance, 0.1 mM hypotaurine (HT), an H2S scavenger, was provided to the control and Cr-S-plants along with CA and CA + NaHS. HT reduced the beneficial effects of CA by decreasing H2S production in tomato plants. However, the NaHS addition with CA + HT inverted the adverse impacts of HT, indicating that H2S is required for CA-induced Cr-S tolerance in tomato plants.

Cation-exchange performance of a citric-acid esterified cellulose nanofibrous membrane for highly-selective proteins' permeability and adsorption capacity

The usage of low-cost, readily available, or even disposable, single-use membranes in macromolecules' purification and separation is still in the development phase. In this research, highly porous (>95 %), water- and compression stable cation-exchange membranes were prepared by freeze-casting using cellulose nanofibrils (CNF) and citric acid (CA) acting as a crosslinker and source of weak anionic (carboxylic) surface groups arising from the mono-esterified CA. The membranes were characterized by different analytical techniques, and evaluated for the ionic adsorption efficacy of different proteins in dead-end filtration mode using a Tri-buffer of pH 8. The membrane's internal microstructure (porosity and density) with the available (quantity and access) carboxylic groups was confirmed, to determine not only the proteins' specific (related to the net charged and molecular weight) adsorption dynamic (>52 % of positive Lysozyme/Cytochrome, <8 % of negative BSA/Myoglobin; ≤0.5 g/L) at extremely high flow rates (>3.000 hL/h*MPa*m2), but also their desorption (>97 %) and re-equilibration (using NaCl) with flux recovery (>80 %). Such efficiency was achieved with up to 5 consecutive filtering cycles. The high permeability (>87 %) of the spherical and negatively surface charged microparticles (used as models) also suggests the likelihood of removing larger microbial species, which, while retaining relatively smaller and positively charged proteins, further increases their potential in biopharma applications.

The release of Cd, Cu, Fe, Mn, Ni, Pb, and Zn from clay loam and sandy loam soils under the influence of various organic amendments and low-molecular-weight organic acids

Low-molecular-weight organic acids (LMWOAs) interact with potentially toxic elements (PTEs) and affect their mobility; however, the effect of different amendments on PTEs release from soils when added along with LMWOAs is still unclear. In this study, two soils (a clay loam and a sandy loam) amended with sugar beet bagasse ash (SBBA), poultry manure (PM), sewage sludge (SS) from Kermanshah city (SSK), and SS from Toyserkan city (SST) at a rate of 5 %. In these treatments we studied release of Cd, Cu, Fe, Mn, Ni, Pb, and Zn with citric, oxalic, and malic acids added at 10 different rates each, i.e., 0.1, 1, 2.5, 5, 10, 30, 40, 50, 70, and 100 mmol L-1. We found that the percentage of PTEs release was higher for citric, followed by oxalic and malic acids. The highest amount of PTEs released in both soils decreased in the following order: SST > SBBA > SSK > PM. The percentage of PTEs complexed with LMWOAs and the log activity of PTEs species mostly increased with decreasing pH. It could be concluded that the application of PM is more environmentally friendly than that of the other amendments. Since Cd had the highest percentage of release in all treated soils and LMWOAs, more consideration should be given to Cd to prevent environmental pollution.

Citric acid-modified pH-sensitive bone-targeted delivery of estrogen for the treatment of postmenopausal osteoporosis

Bone targeted delivery of estrogen offers great promise for the clinical application of estrogen in the treatment of postmenopausal osteoporosis (PMOP). However, the current bone-targeted drug delivery system still has several issues that need to be solved, such as the side effects of bone-targeted modifier molecules and the failure of the delivery system to release rapidly in the bone tissue. It is important to aggressively search for new bone-targeted modifier molecules and bone microenvironment-responsive delivery vehicles. Inspired by the distribution of citric acid (CA) mainly in bone tissue and the acidic bone resorption microenvironment, we constructed a CA-modified diblock copolymer poly(2-ethyl-2-oxazoline)-poly(ε-caprolactone) (CA-PEOz) drug delivery system. In our study, we found that the CA modification significantly increased the bone targeting of this drug delivery system, and the delivery system was able to achieve rapid drug release under bone acidic conditions. The delivery system significantly reduced bone loss in postmenopausal osteoporotic mice with a significant reduction in estrogenic side effects on the uterus. In summary, our study shows that CA can act as an effective bone targeting modifier molecule and provides a new option for bone targeting modifications. Our study also provides a new approach for bone-targeted delivery of estrogen for the treatment of PMOP.

Synergistic enhancing effect of xanthan gum, carboxymethyl cellulose and citric acid on the stability of betacyanins in fermented red dragon fruit (Hylocereus polyrhizus) drink during storage

Nowadays, the demand for using healthy natural pigments (betacyanins) in the food industry is increasing. The present study aimed to overcome the circumstances that render the betacyanins instability in the red dragon fruit drink using mild approaches. These included optimised fermentation, incorporation of anionic polysaccharide mixture solution [xanthan gum (XG, 0.30-0.40 %, w/v) and carboxymethyl cellulose (CMC, 0.50-0.90 %, w/v)] and also addition of citric acid (CA, 0.05-0.20 %, w/v). The results of this study showed that the hydrocolloid mixture solution of XG and CMC significantly increased the samples' viscosity, pH and °Brix but reduced the aw, while betacyanins concentration had no significant change. The incorporation of CA at increasing concentration only reduced the samples' pH significantly without affecting the viscosity, aw and °Brix. Among all fermented samples, Formulation 3E (0.40 % XG + 0.50 % CMC + 0.20 % CA) had achieved the desired commercial reference viscosity while also successfully minimised betacyanins degradation from 60.18 % to 14.72 %, had the best pH stability and no significant change in viscosity, aw and °Brix values after 4-week storage at 25 °C. The fermented red dragon fruit drink with betacyanins stabilised by Formulation 3E can be produced and served as an independent functional drink product and as a stable, functional ingredient (natural colourant) for the food industry.

Effects of a commercial whitening toothpaste containing hydrogen peroxide and citric acid on dentin abrasion and erosion

BACKGROUND

Hydrogen peroxide (HP) and citric acid (CA), key contributors to toothpaste acidity, can lead to dental loss. This study aimed to compare the amount of abrasion or loss of dentin based on pH, buffering, and concentration of HP and CA in commercial and experimental toothpastes after toothbrushing or immersion.

METHODS

Bovine dentin specimens were randomly assigned to nine solutions. The prepared solutions included two commercial toothpastes (whitening toothpaste [WT] with HP and CA; conventional toothpaste [CT] without HP and CA), reference slurry (RS), two CA solutions (1.92%, CAS1; 0.001%, CAS2), basic solution (7.16% sodium phosphate dibasic [SPDS]), CA phosphate buffer solution (3.58% SPDS and 0.96% CA [CAPB]), HP solution (4%, HPS), and distilled water (DW). Dentin specimens were performed in two treatments: one with only abrasion (10,000 brushings) and one with only immersion (1 h). After treatments, the amount of dentin loss and surface images were measured and observed using noncontact profilometry. Data were analyzed using an one-way analysis of variance and the Tukey test as a post hoc analysis (p < 0.05).

RESULTS

WT with pH 5.0 had lower dentin abrasion than CT and RS after brushing but had higher dentin loss than both after immersion. The dentin surfaces of CAS1, CAPB, and WT were damaged after immersion, whereas HPS, CAS2, CT, SPDS, RS, and DW remained intact after soaking. CAS2 and HPS, which had a pH of 5.0 like WT, did not significantly differ from those of DW after brushing.

CONCLUSIONS

WT containing HP and CA did not cause significant dentin abrasion but may cause additional dentin loss even without brushing. After brushing or immersion, the CA concentration may affect the dentin surface more than the HP concentration included in WT. The amount of abrasion or loss of dentin after brushing or soaking can vary based on the composition, concentration, and buffer in the solution, even if the pH of the solution is similar to pH 5.0.