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.

Simultaneous reuse and treatment of sugar-sweetened beverage wastes for citric acid production

This study aimed to evaluate the feasibility of using sugar-sweetened beverages (SSB) for citric acid (CA) production and its impact on chemical oxygen demand (COD) of SSB. Five types of SSB were used as a carbon source for CA production by A. niger, and the COD of each SSB was measured before and after the bioprocess. Results showed that all tested SSB were suitable for CA production, with maximum yields ranging from 13.01 to 56.62 g L- 1. The COD was reduced from 53 to 75.64%, indicating that the bioprocess effectively treated SSB wastes. The use of SSB as a substrate for CA production provides an alternative to traditional feedstocks, such as sugarcane and beet molasses. The low-cost and high availability of SSB makes it an attractive option for CA production. Moreover, the study demonstrated the potential of the bioprocess to simultaneously treat and reuse SSB wastes, reducing the environmental impact of the beverage industry.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05761-9.

Effective and eco-friendly safe self-antimildew strategy to simultaneously improve the water resistance and bonding strength of starch-based adhesive

Starch adhesive, as a sustainable biomass-based adhesive, could be used to solve environmental problems from petroleum-derived adhesive. But its application is hindered by poor water resistance, mildew resistance, and storage stability. Here, a fully bio-based citric acid-starch adhesive (CASt) with high properties was successfully introduced by a simple method. Liquid chromatography/mass spectrometry (LC-MS), and Fourier Transform Infrared spectroscopy (FT-IR) determined that esterification of citric acid (CA) and starch (St) occurred to form a stable three-dimensional crosslinking structure, which strengthened water resistance and bonding strength of the starch adhesive. Compared with native starch (100 %), the soluble content of cured CASt was 1-16 %. CASt adhesive has well storage stability and high mildew resistance. Even after being stored for 5 months, the CASt-1 adhesive (mass ratio of CA/St = 1:1, and reaction time = 1 h) still have good liquidity. And its hot water strength (1.05 ± 0.22 MPa) also satisfied the standard requirements (≥0.7 MPa). The exhibited CASt adhesive is eco-friendly with components from plant resources, which performed as a bright alternative that can substitute petroleum-based adhesives in the artificial board industry.

Use of citric acid-activated chlorine dioxide to control Ulva prolifera

Since 2007, green tides have occurred almost every year in the Yellow Sea, and a method to prevent them and to control levels of attached Ulva prolifera is urgently needed. In this study, we measured the effects of different concentrations of citric acid-activated chlorine dioxide solution (0, 50, 100, 150, 200, and 250 mg/L of chlorine dioxide) on the morphology (macrostructure and microstructure), chlorophyll a content, chlorophyll b content, carotenoid content, and chlorophyll fluorescence parameters (Fv/Fm, Y (II), NPQ, and ETRmax) of U. prolifera. Micropropagules in the treatment filtrate were cultured to determine whether the solution reduced the number of micropropagules released during the treatment process. The results showed that citric acid-activated chlorine dioxide at the appropriate concentration can be applied to remove U. prolifera from Neopyropia cultivation rafts. Because U. prolifera and its micropropagules died in the 250 mg/L chlorine dioxide group, we recommend that the appropriate concentration of chlorine dioxide for removing green macroalgae is ≥250 mg/L. Our results provide a scientific basis for convenient collection of accurate data for the U. prolifera prevention trial organized by the Ministry of Natural Resources of the People's Republic of China.

Co-application of citric acid and Nocardiopsis sp. strain RA07 enhances phytoremediation potentiality of Sorghum bicolor L

This study investigated the combined effects of citric acid (CA) and Nocardiopsis sp. RA07 on the phytoremediation potential of lead (Pb)- and copper (Cu)-contaminated soils by Sorghum bicolor L. The strain RA07 was able to tolerate Pb and Cu, and exhibited plant growth-promoting features like siderophore production, indole-3-acetic acid (IAA) synthesis, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity and phosphate solubilization. The combined application of CA and strain RA07 significantly increased S. bicolor growth, chlorophyll content and antioxidant enzymatic activity, and decreased oxidative stress (hydrogen peroxide and malondialdehyde content) under Pb and Cu stress circumstances as compared to individual treatments (i.e., CA and strain RA07). Furthermore, the combined application of CA and RA07 significantly enhanced S. bicolor ability to accumulate Pb and Cu by 64.41% and 60.71% in the root and 188.39% and 125.56% in the shoot, respectively, as compared to the corresponding uninoculated plants. Our results indicate that inoculation of Nocardiopsis sp. together with CA could be a useful practical approach to mitigate Pb and Cu stress on plant growth and increase the effectiveness of phytoremediation in Pb- and Cu-polluted soils.

Structural characteristics of resistant starch-enriched rice during digestion and its effects on gut barrier function in high-fat induced obese mice

Dietary supplementation with indigestible carbohydrates is known to improve the gut environment and prevent obesity and inflammatory diseases by modulating the gut microbiota. In previous work, we established a method for the production of resistant starch (RS)-enriched high-amylose rice (R-HAR) using citric acid. The present study aimed to evaluate changes in structural characteristics during digestion of R-HAR and its effects on the gut health. A three-step in vitro digestion and fermentation model was used, then, RS content, scanning electron microscopy, and branch chain length distribution were analyzed during in vitro digestion. During the digestion of R-HAR, the RS content increased, and the structure was predicted to have a greater impact on the gut microbiota and gut environment. To study the intestinal health effects of R-HAR, its anti-inflammatory and gut barrier integrity activities were assayed in HFD-induced mice. Intake of R-HAR suppressed colonic shortening and inflammatory responses induced by HFD. Furthermore, R-HAR exhibited gut barrier protective activity with an increase in tight junction protein levels. We determined that R-HAR may be a potentially beneficial intestinal environment improver, which may have various implications in the food industry as rice.

Inactivation of Foodborne Pathogen Biofilm Cells Using a Combination Treatment with Gaseous Chlorine Dioxide and Aerosolized Sanitizers

A biofilm is a three-dimensional microbial community, which is difficult to completely control with a typical sanitizer owing to its complex structure. The aim of this study was to establish a system for the combined treatment of biofilms with 10 ppmv gaseous chlorine dioxide (ClO2) and antimicrobial agents (2% citric acid, 2% hydrogen peroxide [H2O2], and 100 ppm peracetic acid [PAA]), and to investigate the synergistic microbicidal efficacy of the combination treatments to inactivate Listeria monocytogenes, Salmonella Typhimurium, and Escherichia coli O157:H7 in biofilms. The antimicrobial agents were aerosolized using a humidifier on top of a chamber to achieve a relative humidity of 90% (within a range of ±2%). While biofilm treatment with the aerosolized antimicrobial agents for 20 min inactivated approximately 1 log CFU/cm2 (0.72-1.26 log CFU/cm2) of the pathogens and the gaseous ClO2 gas treatment for 20 min inactivated <3 log CFU/cm2 (2.19-2.77 log CFU/cm2), combination treatment with citric acid, H2O2, and PAA for 20 min achieved microbial reductions of 2.71-3.79, 4.56-5.12, and 4.45-4.67 log CFU/cm2, respectively. Our study demonstrates that foodborne pathogens in biofilms can be inactivated by combining gaseous ClO2 treatment with aerosolized antimicrobial agents. The results of this study provide baseline data for the food industry to help control foodborne pathogens in biofilms on inaccessible surfaces.

Preparation and characterization of a novel absorbent pad based on polyvinyl alcohol/gellan gum/citric acid with incorporated Perilla leaf oil nanoemulsion for chilled chicken packaging

A novel absorbent pad based on polyvinyl alcohol (PVA)/gellan gum/citric acid (CA) composite with incorporated Perilla leaf oil (PO) nanoemulsion was prepared and characterized. The esterification between PVA and CA and strong hydrogen bonds were detected. The PVA improved the tensile strength and elongation at break by 110% and 73%, respectively, whereas PO concentration ≤ 1.5 % (w/v) had little effect on the material properties. The CA and PO nanoemulsion loaded in the pads showed good antioxidant activity, and the pads with PO concentration ≥ 1.5 % (w/v) had effective antimicrobial activity against Escherichia coli and Staphylococcus aureus. The results of chilled chicken storage experiments indicated that the pad with 1.5% (w/v) PO nanoemulsion extended the shelf life of chicken to at least 9 days, demonstrating that the developed absorbent pads are potential materials for chilled chicken storage packing.

Thermoplastic starch/polyvinyl alcohol blends modification by citric acid-glycerol polyesters

Thermoplastic starch/polyvinyl alcohol (TPS/PVA) films have limitations for being used in long-term applications due to starch retrogradation. This leads to plasticizer migration, especially when low molecular weight plasticizers such as glycerol, are used. In this work, we employed mixtures of oligomers based on glycerol citrates with higher molecular weight than glycerol as plasticizers for potato-based TPS/PVA blends obtained by melt-mixing. This constitutes an alternative to reduce plasticizer migration while keeping high swelling degree, and to provide high mechanical performance. The novelty lies in the usage of these oligomers by melt-mixing technique, aspect not deeply explored previously and that represents the first step towards industrial scalability. Prior to the blending process, oligomers mixtures were prepared with different molar ratios of citric acid (0-40 mol%) and added them. This minimizes the undesirable hydrolysis effect of free carboxylic groups on starch chains. The results demonstrated that the migration of plasticizers in TPS/PVA blends decreased by up to 70 % when the citric acid content increased. This reduction was attributed to the higher molecular weight (the majority in the range 764-2060 Da) and the 3D structure of the oligomers compared to using raw glycerol. Furthermore, the films exhibited a 150 % increase in Young's modulus and tensile strength without a reduction in elongation at break, while maintaining a high gel content, due to a moderate crosslinking.

Sequential extraction of labile and recalcitrant fractions of soil organic matter: A case study focusing on antimony (Sb) in humic acids, fulvic acids and humin fractions of long-term aged contaminated soils

Soil organic matter (SOM) plays a key role in environmental chemistry of macro and micro nutrients as well as heavy metal (loids). In this research, a modified sequential extraction scheme was used to isolate labile and recalcitrant SOM from organic rich soils after 18 months of ageing with antimony. Humic substances were extracted with a mixture of 0.5 M sodium hydroxide +0.1 M sodium pyrophosphate solution from soils. Then soils deprived of humic substances were sequentially subjected to extraction with glycerol, citric acid, pre-treated with acid and extracted with boiling alkali mixture. The humic acids (HA) and fulvic acids (FA) of isolated SOM fractions were separated and HAs been characterized using FTIR, 1H NMR, and UV-VIS. Acid-alkali treatment of the most recalcitrant SOM fraction (A1-ROM) led to the extraction of sparingly soluble, highly aromatic compound with considerable amounts of N (44% of the extractable N), possibly due to the breakdown of bounds between aromatic rings and amine functional groups. Nevertheless, the highest content of C and TOC was associated with the glycerol extractable SOM. Substantial amounts of Fe and Al were extracted with glycerol, resulting in a dramatic rise of Sb in SOM extracts. The largest increase (60%) in Sb concentrations was observed after the removal of Fe with citric acid. The humic substances (HS) were responsible for 63% of extractable Sb, whereas even after exhaustive alkali extractions 22% of the total Sb remained in the residual humin fraction. Within the HS fraction, 95% of antimony was associated with the low molecular weight FAs. Antimony concentrations in organic fractions correlated significantly with TOC and N contents, possibly due to the role of amine functional groups in Sb complexation. The results of this research highlight the importance of Fe-Al-SOM bridging and humin fraction in sequestration of Sb in recalcitrant SOM pools.

Evolution of the free volume during water desorption in thermoplastic starch/citric acid films: In situ positron annihilation studies

The effect of citric acid (CA) concentration and water content on the free hole volume of thermoplastic cassava starch films (TPS) was studied. To this aim, continuous in situ positron annihilation lifetime spectroscopy measurements were performed at fixed moisture content and during water desorption. The results show that the increase in CA concentration leads to wider free hole volume distributions with lower mean values. During water desorption, the mean values and width of such distributions systematically decrease with the exposure time, and the evolution of the hole volumes was well-described using the Kohlrausch-Williams-Watts function. The water vapour permeability was significantly higher in films incorporating 5 % (w/w) of CA, in line with the more open network of this material that was revealed in the hole volumes distribution. The Young's modulus of all the developed films increased significantly after partial water desorption, which was attributed to the plasticizer loss reflected in a decrease in the mean hole volume value (between 4 % and 13 %). This work evidences that the control and report of the relative humidity are essential when testing TPS-based films, as their nanostructures are strongly dependent on external conditions.

Assessment of natural low molecular weight organic acids in facilitating cadmium phytoextraction by Lepidium didymus (Brassicaceae)

The present study examined the ability of three naturally occurring low molecular weight organic acids (tartaric, TA; citric, CA; and oxalic, OA) to improve the efficiency of cadmium (Cd) phytoextraction in Lepidium didymus L. (Brassicaceae). The plants were grown in soil containing three different concentrations, i.e., 35, 105, and 175 mg kg^-1, of total Cd and 10 mM of TA, CA, and OA. After 6 weeks, plant height, dry biomass, photosynthetic traits, and metal accumulation were determined. All three organic chelants significantly increased the Cd accumulation in L. didymus plants; however, the greatest accumulation was seen with TA (TA > OA > CA). In general, Cd accumulation was the highest in the roots, followed by the stems, and the leaves. Highest BCF_Stem was observed upon the addition of TA (7.02) and CA (5.90) at Cd₃₅, compared to Cd-alone (3.52) treatment. The BCF was the highest in the stem (7.02) and leaves (3.97) under Cd₃₅ treatment supplemented with TA. The BCF_Root in the plants under different chelant treatments were in the following order: Cd₃₅ + TA (~ 100) > Cd₃₅ + OA (~ 84) > Cd₃₅ + TA (~ 83). The stress tolerance index and translocation factor (root-stem) were maximal at Cd₁₇₅ with TA and OA supplementation, respectively. The study concludes that L. didymus could be a viable option for Cd-remediation projects, and the addition of TA improved its phytoextraction efficiency.

Effect of organic acids and soil particle size on heavy metal removal from bulk soil with washing

To evaluate the effect of soil particle size on heavy metals removal by washing, two soil samples were collected around a lead-zinc mining area (SM) and lead-zinc smelter (SS). The total content of Cd, Pb and Zn in SM and SS were determined. And the effect of soil particle size on Cd removal by low molecular organic acids was studied. The results showed that Cd was the main pollutant and the total content of Cd in SS can reach to 24.8 mg Kg^-1. 68.4% of the total Cd in SM existed in the form of residual state, while 54.7% of the total Cd in SS was in weak acid extractable state. About 50.0% of the Cd distributed in < 2 μm soil size fraction. The washing results indicated that citric acid was a highly efficient eluent among the five low molecular weight organic acids (citric acid, malic acid, tartaric acid, oxalic acid and acetic acid). After washing, 40% and 69.6% of the total Cd in SS and SM can be removed by citric acid, respectively. While only 18.7-40.2% and 32.6-68.7% of Cd was removed from different size fractions of SM and SS, respectively. The species of Cd in soil size fractions affected the removal effect of citric acid. The citric acid can easily remove the weak acid extractable and reducible form of Cd in soil. After eluted by citric acid, the bioavailability of Cd in soil decreased markedly, and the highest decreasing rate reached 93%.

Chemical-microbial effects of acetic acid, oxalic acid and citric acid on arsenic transformation and migration in the rhizosphere of paddy soil

Low-molecular-weight organic acids (LMWOAs) are essential components of rice roots exudates and an important source of soil organic carbon. The chemical-microbial pathway by which LMWOA affects arsenic (As) cycling in the rhizosphere of paddy soils is still unclear. In this study, three typical LMWOAs (acetic acid (AA), oxalic acid (OA), and citric acid (CA)) in rice root exudates were added to As-contaminated soil at a concentration of 10 mM, mimicking the rhizosphere environment. The results showed that the addition of AA and OA inhibited the mobilization of As in the rhizosphere soil. After 14 days of incubation, the content of As in the porewater of AA and OA decreased by 40% and 22%, respectively, compared with the control. AA hindered the mobilization of As in soil via promoting the formation of secondary minerals. The addition of OA inhibits the mobilization of As via increasing the proportion of As (V) in porewater and promoting the formation of secondary minerals in soil. In addition, OA addition not only significantly increased the aioA gene abundance but also notably enriched the microorganisms containing As (III) methylation functional genes (arsM). The addition of CA greatly expedited the release of As from the soil solid phase through the solubilization of Fe/Mn minerals via the effects of both soil chemistry and microbial action. Furthermore, linear discriminant analysis effect size (LEfSe) revealed the possibility that bacteria such as Burkholderia, Magnetospirillum, and Mycobacterium were involved in the reduction or methylation of As in the rhizosphere of paddy soil. This study revealed the internal causes of LMWOAs regulating As transformation and mobilization in flooded paddy soil and provided theoretical support for reducing As accumulation in rice by breeding rice varieties with high AA and OA secretions.

A mechanically robust biodegradable bioplastic of citric acid modified plasticized yam starch with anthocyanin as a fish spoilage auto-detecting smart film

The current scenario of environmental pollution caused by non-biodegradable plastic and depleting non-renewable resources has called upon the need for biodegradable bioplastic production from renewable resources. Starch bioplastics production from underutilized sources is a viable option for packaging materials that are non-toxic, environmentally benign, and easily biodegradable under disposed conditions. Pristine bioplastic production results in some undesirable qualities and hence requires further modification in order to elevate its potential applicability in real-world scenarios. In this work, yam starch was extracted from a local variety of yams through an eco-friendly and energy-efficient process which was further utilized for bioplastic production. The produced virgin bioplastic was subjected to physical modification through the introduction of plasticizers such as glycerol, while citric acid (CA) was employed as modifier in order to produce the desired starch bioplastic film. The different compositions of starch bioplastics were analyzed for their mechanical properties and maximum tensile strength of 24.60 MPa was observed as the best possible experimental result. The biodegradability feature was further highlighted through soil burial test. Apart from their general function of preservation and protection, the produced bioplastic can be employed for pH-sensitive food spoilage detection through the minute introduction of plant-derived anthocyanin extract into it. The produced pH-sensitive bioplastic film showed distinct changes in color upon an extreme change in the pH value and hence has potential to be used as a smart food packaging material.

Bioleaching of valuable metals from spent LIBs followed by selective recovery of manganese using the precipitation method: Metabolite maximization and process optimization

Despite the increased demand for resource recovery from spent lithium-ion batteries (LIBs), low Mn leaching efficiencies have hindered the development of this technology. A novel process was devised to enhance the dissolution of metals by producing citric acid using a molasses medium by Penicillium citrinum. This investigation used response surface methodology to investigate the influence of molasses concentration and media components on citric acid production, which demonstrated that molasses (18.5% w/w), KH₂PO₄ (3.8 g/L), MgSO₄.7H₂O (0.11 g/L), and methanol (1.2% (v/v)) were the optimum values leading to the production of 31.50 g/L citric acid. Afterward, optimum inhibitor concentrations (iodoacetic acid: 0.05 mM) were added to accumulate citric acid, resulting in maximum bio-production (40.12 g/L) of citric acid. The pulp density and leaching time effect on metals dissolution was investigated in enriched-citric acid spent medium. The suitable conditions were a pulp density of 70 g/L and a leaching duration of 6 days, which led to the highest dissolution of Mn (79%) and Li (90%). Based on the results of the TCLP tests, the bioleaching residue is non-hazardous, suitable for safe disposal, and does not pose an environmental threat. Moreover, nearly 98% of Mn was extracted from the bioleaching solution with oxalic acid at 1.2 M. XRD, and FE-SEM analyses were utilized for further bioleaching and precipitation mechanism analysis.

UPLC-Q-TOF/MS-based metabolomic analysis reveals the effects of asomate on the citrus fruit

The regulation of the sugar-acid ratio is of great significance to the improvement of citrus fruit quality. The citric acid level in fruit is influenced by many factors. Among them, cultivar selection and production practices are the most important strategies under the grower's control. In recent years, an arsenic-containing preparation called "Tianmisu", with the main ingredient of asomate, has occasionally been reported to be used in citrus cultivation to improve the sweetness of fruits. In order to reveal the effects of the pesticide on citrus fruits, 'Harumi' tangor was treated with "Tianmisu", and the impact of this pesticide on fruit quality and metabolites was investigated through UPLC-Q-TOF/MS-based metabolomic analysis. Compared with the control, the concentration of titratable acidity, in particular citric acid, in the pulp of 'Harumi' tangor treated with the pesticide, was significantly reduced by 60.5%. The differences in metabolites between the pesticide-treated samples and the control were illustrated by Principal Component Analysis (PCA) and Partial Least Squares Discriminant Analysis (PLS-DA). The PLS-DA analysis demonstrated a clear discrimination, with R²Y and Q² values of 0.982 and 0.933 in the positive mode and 0.984 and 0.900 in the negative mode, respectively. A total of 155 compounds were identified, and 63 characteristic components were screened out from the pesticide-treated samples compared to the control. Aside from the upregulation observed for a few metabolites, the majority of the compounds, including citric acid and various lipids, were down-regulated in the treated citrus fruits compared to the control. This study can serve as a basis for understanding the regulatory mechanism of organic acids in citrus and will be helpful in developing different strategies to improve citrus quality.

Sensitive detection of butyrylcholinesterase activity based on a stimuli-responsive fluorescence reaction

A fluorogenic reaction between the chelate of Mn(II)-citric acid and terephthalic acid (PTA) was discovered, which was carried out through heating the aqueous mixture of Mn²⁺, citric acid and PTA. Detailed investigations indicated the reaction products were 2-hydroxyterephthalic acid (PTA-OH), which was attributed to the reaction between PTA and OH, formed by the triggering of Mn(II)-citric acid in the presence of dissolved O₂. PTA-OH showed a strong blue fluorescence, peaked at 420 nm, and the fluorescence intensity presented a sensitive response to pH of the reaction system. Based on these mechanisms, the fluorogenic reaction was used for the detection of butyrylcholinesterase activity, achieving a detection limit of 0.15 U/L. The detection strategy was successfully applied in human serum samples, and it was also extended for the detection of organophosphorus pesticides and radical scavengers. Such a facile fluorogenic reaction and its stimuli-responsive properties offered an effective tool for designing detection pathways in the fields of clinical diagnosis, environmental monitoring and bioimaging.

Influence of silylated nano cellulose reinforcement on the mechanical, water resistance, thermal, morphological and antibacterial properties of soy protein isolate (SPI)-based composite films

The aim of this research work is to improve the mechanical and water-resistance properties of soy protein isolate (SPI) biofilm. In this work, 3-aminopropyltriethoxysilane (APTES) coupling agent modified nanocellulose was introduced into the SPI matrix in the presence of citric acid cross-linker. The presence of amino groups in APTES facilitated to form cross-linked structures with soy protein. The incorporation of a citric acid cross-linker made the cross-linking process more productive, and the surface smoothness of the film was confirmed by a Scanning Electron Microscope (FE-SEM). From the study of the mechanical and thermal properties and water resistance of the film, it was confirmed that the results were highly satisfactory for the modified nanocellulose incorporated film compared to the non-modified one. Additionally, coating of citral essential oil onto SPI nanocomposite film displayed antimicrobial properties due to the presence of various phenolic groups in the citral oil. The Tensile Strength and Young's Modulus of silane-modified nanocellulose containing film were enhanced by ~119 % and ~ 112 %, respectively on incorporation of 1 % APTES-modified nanocellulose. Consequently, this work is expected to offer an effective way for silylated nano-cellulose reinforcing soy protein isolate (SPI) based bio nanocomposite films for packaging applications. As an example, we have demonstrated one of the application as wrapping films for packing black grapes.

Synthesis of glutamine-based green emitting carbon quantum dots as a fluorescent nanoprobe for the determination of iron (Fe3+) in Solanum tuberrosum (potato)

Herein, we reported the use of N-doped green-emitting carbon quantum dots (N-CQDs) as a fluorescent probe for determining of Fe³⁺ ions in Solanum tuberosum for the first time. The N-CQDs were synthesised through an efficient, one-step, and safe hydrothermal technique using citric acid as the carbon source and glutamine as a novel nitrogen source. The temporal evolution of the optical properties was investigated by varying the synthetic conditions with respect to temperature (160 °C, 180 °C, 200 °C, 220 °C and 240 °C) and citric acid: glutamine precursor ratio (1:1, 1:1.5, l.2,1:3 and 1:4). The N-CQDs was characterised using Fourier-Transform Infra-red Spectroscopy (FTIR) High-resolution transmission electron microscope (HRTEM), ultraviolet-visible spectroscopy (UV-vis) and X-Ray diffraction analysis (XRD) while its stability was evaluated in different media; NaCl, Roswell Park Memorial Institute (RPMI) and Phosphate Buffered Saline (PBS), and at different pHs. The N-CQDs displayed green (525 nm) emission and were spherical with an average particle diameter of 3.41 ± 0.76 nm. The FTIR indicated carboxylic, amino, and hydroxyl functional groups. The as-synthesised N-CQDs were stable in NaCl (up to 1 M), RPMI, and PBS without any significant change in its fluorescent intensity. The pH evaluation showed pHs 6 and 7 as the optimum pHs, while the fluorometric analysis showed selectivity towards Fe ³⁺ in the presence and absence of interfering ions. The detection limit of 1.05 μM was calculated, and the photoluminescence mechanism revealed static quenching. The as-synthesised N-CQDs was used as a fluorescent nanoprobe to determine the amount of Fe³⁺ in Solanum tuberosum (Potatoes) tubers. The result showed a high level of accuracy (92.13-96.20%) when compared with an established standard analytical procedure with excellent recoveries of 99.23-103.9%. We believe the as-synthesised N-CQDs can be utilised as a reliable and fast fluorescence nanoprobe for the determining of Fe³⁺ ions.

Metabolite fingerprinting of cassava (Manihot esculenta Crantz) landraces assessed for post-harvest physiological deterioration (PPD)

Cassava landraces are impacted by post-harvest physiological deterioration (PPD). 34 primary/secondary metabolites (carotenes, flavonols, indols, phenolic, hydroxycinnamic, and organic acids) were analysed using HPLC/GC-MS in 72 landraces harvested 8 months after planting (MAP) to clarify whether these compounds may play a role in PPD tolerance. Cluster analysis differentiated a first group with high organic acids contents, citric acid being dominant, a second group with landraces high in tryptophan, a third group including landraces with high phenolic and hydroxycinnamic acids content, and a fourth group characterised by 8 carotenoids. PPD tolerant and susceptible landraces were present in each group. To determine if PPD is related to age of harvest, 174 landraces were harvested at 6, 8, 10 and 12 MAP. Scopoletin, sucrose and glucose were analysed. PPD was positively correlated with DMC and negatively correlated with scopoletin at all ages of harvest. Scopoletin is a useful biomarker to characterize landraces.

Performance and mechanisms of citric acid improving biotransformation of waste activated sludge into short-chain fatty acids

Numerous effective chemical strategies have been explored for short-chain fatty acids (SCFAs) production from waste activated sludge (WAS), but many technologies have been questioned due to the chemical residues. This study proposed a citric acid (CA) treatment strategy for improving SCFAs production from WAS. The optimum SCFAs yield reached 384.4 mg COD/g VSS with 0.08 g CA/g TSS addition. Meanwhile, CA biodegradation occurred and its contribution to the yield of total SCFAs, especially acetic acid, cannot be ignored. Intensive exploration indicated the sludge decomposition, the biodegradability of fermentation substrates, as well as the abundance of fermenting microorganisms were definitely enhanced in the existence of CA. The optimization of SCFAs production techniques based on this study deserved further study. This study comprehensively revealed the performance and mechanisms of CA enhancing biotransformation of WAS into SCFAs and the findings promotes the research of carbon resource recovery from sludge.

GABA shunt pathway is stimulated in response to early defoliation-induced carbohydrate limitation in Mandarin fruits

The regulation of sugar and organic acid metabolism during fruit development has a major effect on high-quality fruit production. The reduction of leaf area is a common feature in plant growth, induced by abiotic and biotic stresses and disturbing source/sink ratio, thus impacting fruit quality. Here, we induced carbohydrate limitation by partial leaf defoliation at the beginning of the second stage of mandarin development (before the citrate peak). Resulting changes were monitored in the short-term (48 h and 1 week) and long-term (7 weeks) after the defoliation. Short-term response to early defoliation implied metabolic settings to re-feed TCA for sustaining respiration rate. These features involved (i) vacuolar sucrose degradation (high acid invertase activity and mRNA expression level) and enhanced glycolytic flux (high ATP-phosphofructokinase activity), (ii) malic and citric acid utilization (increased phosphoenolpyruvate kinase and NADP-Isocitrate dehydrogenase) associated with vacuolar citric acid release (high mRNA expression of the transporter CsCit1) and (iii) stimulation of GABA shunt pathway (low GABA content and increased mRNA expression of succinate semialdehyde dehydrogenase). A steady-state proline level was found in ED fruits although an increase in P5CS mRNA expression level. These results contribute to a better knowledge of the molecular basis of the relationship between defoliation and sugar and organic acid metabolism in mandarin fruit.

Shape memory and antibacterial chitosan-based cryogel with hemostasis and skin wound repair

Massive damage to the skin can lead to heavy bleeding and potential wound infection. Therefore, the preparation of low-cost wound dressings that meet these requirements by simple methods has a good application prospect. In the study, a shape memory cryogel prepared at low temperatures by mixing chitosan (CS) and citric acid (CA). Silver nanoparticles (Ag NPs) introduced into the cryogel through the reduction of Ag⁺ with tannic acid (TA) as a reducing agent. The CS/CA/Ag cryogel has good mechanical properties and interconnected macroporous structures. The results of hemostasis tests show that CS/CA/Ag cryogel can absorb a large amount of blood and promote blood cell adhesion compared with commercial gelatin sponges and gauze. Meanwhile, CS/CA/Ag cryogel has a good antibacterial ability against S. aureus and E. coli. Furthermore, CS/CA/Ag cryogel significantly promotes wound healing in the full-thickness wound model infected with S. aureus. In conclusion, the cryogel prepared by the simple method has great advantages in rapid hemostasis and promoting wound healing.

A method of diamorphine (heroin) administration for harm reduction

As societal attitudes toward narcotics have changed, harm reduction strategies have emerged which make it safer to inject intravenous drugs. Diamorphine (heroin) is commonly sold as its free base-better known as brown-which has extremely poor aqueous solubility. As such, it needs to be chemically modified (cooked) to enable administration. Needle exchange programmes commonly supply citric or ascorbic acids which facilitate intravenous administration by increasing heroin solubility. If heroin users mistakenly add too much acid, the low solution pH can cause damage to their veins and, after repeated injury, could result in the loss of that injection site. Currently, advice cards supplied with these exchange kits suggest that the acid should be measured in pinches, which could result in considerable error. This work employs Henderson-Hasselbalch models to analyse the risk of venous damage by placing solution pH within the context of the buffer capacity of the blood. These models also highlight the significant risk of heroin supersaturation and precipitation within the vein, an event that has the potential to cause further harm to the user. This perspective closes with a modified administration method which could be included as part of a wider harm reduction package.

Effect of branched polyethyleneimine and citric acid on the structural, physical and antibacterial properties of corn starch/chitosan films

To improve the antibacterial and physical properties of corn starch/chitosan films effectively, starch/chitosan/polyethyleneimine (PEI) blend films crosslinked by citric acid (labeled SCPC) with different contents (2.5 %, 5.0 %, 7.5 % and 10.0 %) were prepared by the solution casting method. The films were characterized in detail. The results showed that the addition of 3.75 % PEI improved the tensile strength and elongation at break of the starch/chitosan film simultaneously, but the thermal stability decreased. After CA was incorporated, the tensile strength and thermal stability of the films were enhanced significantly. FTIR, XRD, and ¹H NMR analyses revealed strong interactions among CA, PEI and starch-chitosan. All films showed smooth and homogenous fragile cross-sections. The water vapor permeability of the film decreased overall after PEI and CA addition. Moisture uptake (MU) accelerated after PEI addition, but the balanced MU was reduced by CA cross-linking. All films showed an inhibitory effect on E. coli and S. aureus, and CA incorporation significantly improved the inhibition ability of the film. The SCPC film with 3.75 % PEI and 5.0 % CA addition has the best comprehensive properties, which endowed its application in the bioactive packaging field.

Experimental study on the redistribution law of heavy metals in sludge disintegration

Aiming at the problems of large output of excess sludge, difficulty in treatment and disposal, and the potential toxicity of heavy metals restricting its resource utilization, this paper studies the redistribution law of heavy metals in the process of sludge disintegration. The dissertation investigates the distribution law of typical heavy metals such as Cu, Pb, Cd, Zn in the process of microwave and citric acid-microwave cracking sludge under different specific energy and fixed specific energy conditions. The Tessier five-step continuous extraction method was used to extract heavy metals, and the changes in their content and chemical forms were analyzed, which provided certain technical support for the subsequent harmless treatment and resource utilization of excess sludge. The main findings of this paper are as follows: The dissolution rate of heavy metals Cu, Pb, Cd, and Zn increased rapidly during the citric acid-microwave cracking process in the TS specific energy range of 0-45000 kJ/kg, and then gradually tended to be gradual. The maximum dissolution rates of Cu, Pb, Cd, Zn were 8.06%, 16.58%, 14.69%, and 24.11%, respectively. The concentrations of Cu, Pb, Cd, and Zn in the sludge were mainly F4; F3, F4; F2, F3. The proportions of stable states of Cu, Pb, Cd, and Zn in sludge increased to 88.6%, 55.91%, 35.7%, and 31.35%, respectively. When the specific energy was 45000 kJ/kg TS, the concentrations of Pb, Zn, and Cd in the solid phase of the sludge appeared to increase under microwave cracking alone and decrease under the combined action of citric acid and microwave. The concentration of Cu in the solid phase of the sludge increased slightly. The dissolution rates of Pb, Cd, and Zn by microwave alone and citric acid-microwave method were 14.23% and 16.58%, 10.34% and 14.69%, 17.53%, and 24.11%, respectively. The dissolution rates of Cu by both methods were lower. The steady state ratios of Pb and Zn in the citric acid-microwave method increased to 55.91% and 31.25%, respectively; the steady state ratio of Cd in the microwave alone method increased to 39.51%; both methods had no significant effect on the stability of Cu.

Physicochemical and functional properties of RG-I enriched pectin extracted from thinned-young apples

The demand for obtaining pectin from new sources has been continuously increasing. The abundant but underutilized thinned-young apple is a potential source of pectin. In this study, an organic acid (i.e., citric acid) and two inorganic acids (i.e., hydrochloric acid and nitric acid) commonly used in commercial pectin production were applied to extract pectin from three varieties of thinned-young apples. The physicochemical and functional properties of the thinned-young apple pectin were comprehensively characterized. The highest pectin yield (8.88 %) was obtained from Fuji apple using citric acid extraction. All pectin was high methoxy pectin (HMP) and rich in RG-I regions (>56 %). The citric acid extracted pectin had the highest molecular weight (Mw) and lowest degree of esterification (DE) values, and exhibited great thermal stability and shear-thinning property. Furthermore, Fuji-apple pectin possessed significantly better emulsifying properties compared to pectin obtained from the other two varieties of apples. Thus, pectin extracted with citric acid from Fuji thinned-young apples has great potential to be applied in the food industry as a natural thickener and emulsifier.

Synthesis and characterization of citric acid crosslinked carboxymethyl tamarind gum-polyvinyl alcohol hydrogel films

The aim of present work was to synthesize and characterize carboxymethyl tamarind gum-polyvinyl alcohol (CMTG-PVA) hydrogel films using citric acid (CA) as a crosslinker. Hydrogel films were prepared by solvent casting technique. The films were evaluated for total carboxyl content (TCC), tensile strength, protein adsorption, permeability properties, hemocompatibility, swellability, moxifloxacin (MFX) loading and release, in-vivo wound healing activity and characterized using instrumental techniques. An optimal increase in amount of PVA and CA increased the TCC and tensile strength of the hydrogel films. Hydrogel films exhibited low protein adsorption and microbial permeation, good permeability to water vapour and oxygen, and sufficient hemocompatibility. The films prepared using high concentration of PVA and low concentration of CA showed good swellability in phosphate buffer and simulated wound fluids. MFX loading in the hydrogel films was found in the range of 384-440 mg/g. The hydrogel films sustained the release of MFX up to 24 h. The release followed Non-Fickian mechanism. ATR-FTIR, solid state ¹³C NMR and TGA analysis indicated formation of ester crosslinks. In-vivo study revealed good wound healing activity for hydrogel films. From the overall study, it can be concluded that the citric acid crosslinked CMTG-PVA hydrogel films can be effectively used for wound treatment.

Effects of citric acid crosslinking on the structure and properties of ovotransferrin and chitosan composite films

In this study, ovotransferrin/chitosan (OVT/CS) composite films cross-linked by citric acid (CA) were prepared and the effects of CA cross-linking on the structure and physicochemical properties of the composite films were investigated. The cross-linking degree measured by 2,4,6-trinitrobenzenesulfonic acid (TNBS) method confirmed that CA was cross-linked with the matrix, and Fourier transform infrared spectroscopy confirmed that more hydrogen bonds and electrostatic interactions were formed between CA and the matrix. Differential scanning calorimetry, X-ray diffraction and Scanning electron microscope images revealed the compatibility between substances. The synergistic inhibition between the matrix results in a significantly higher antibacterial activity of the composite film than the pure film. Compared with uncross-linked films, the mechanical properties, barrier properties and water resistance of the cross-linked films were significantly improved. When the concentration of CA was 5 wt% (W/W, on a dry basis of the weight of OVT and CS), the most significant improvement in film performance was obtained. The tensile strength of the film increased from 32.05 MPa without cross-linking to 61.99 MPa and the swelling degree decreased from 51.5 % to 24.23 %. The observed phenomena suggest that cross-linking OVT and CS with CA can obtain functional edible films with improved properties.

Assessment of tea saponin and citric acid-assisted phytoextraction of Pb-contaminated soil by Salvia virgata Jacq

The present study, investigated the influence of the natural tea saponin (TS) obtained by microwave-assisted extraction and citric acid (CA) by commercially enhancing lead ion (Pb(II)) uptake by Salvia virgata Jacq. The Pb(II) tolerance was compared, and the growth of plants and Pb(II) accumulation characteristics of S. virgata with chemical agents TS and CA were studied for their phytoextraction potential of Pb(II) from artificially contaminated soil of 0-100 mg kg^-1 different concentrations under pot conditions. The different morphophysiological parameters of S. virgata such as growth, biomass, chlorophylls, and carotenoids were significantly changed under different Pb(II) stress and TS and CA concentrations. To evaluate the removal efficiency of the studied plant, the bioconcentration factor (BCF) or enrichment coefficient (EC), translocation factor (TF), and tolerance index (TI) values were also calculated and compared with the control. Phytotoxic effects were observed at 100 mg kg^-1; added Pb(II) treatments caused significant decreases of 33.05% in the biomass of S. virgata compared to the control. All the obtained results showed that the concentrations of Pb(II) being compared revealed a highest uptake (286 ± 5.2 mg kg^-1) of 100 mg kg^-1. The concentration of available Pb(II)-assisted TS and CA increased by 9.1-28.4% compared to the control. Based on these findings, S. virgata might be cultivated and used as a hyperaccumulator in the removal of Pb(II) from the contaminated soils, and appropriate application of TS and CA can enhance phytoremediation of Pb(II)-contaminated soil by other hyperaccumulator plants.

Facile synthesis of carbon dots via pyrolysis and their application in photocatalytic degradation of rhodamine B (RhB)

Carbon Quantum dot (CQDs) is one of the newest materials in carbon-based nanomaterials. It is pertinent to study the synthesis and the application of these carbon dots. Here we have studied the effect of precursor on the optical, morphological, and photocatalytic properties of CQDs. We have synthesized CQDs using pyrolysis method using the precursors citric acid, urea, polyethyleneimine. We have synthesized two samples: CQD-S1; synthesized using urea and polyethyleneimine, and CQD-S2; synthesized using citric acid and polyethyleneimine. In optical properties study two distinct peaks have been obtained at 243 nm and 345 nm for CQD-S1, and at 265 nm and 335 nm for CQD-S2. In fluorescence study, the maximum emission was found at excitation wavelength of 340 nm for CQD-S1 and at excitation wavelength of 350 nm for CQD-S2. In morphological studies, Transmission Electron Microscope (TEM) revealed particle size of sample CQD-S1 and CQD-S2 were 1.91 nm and 1.61 nm, respectively. EDX confirmed the elemental composition in both samples. The rhodamine B (RhB) dye degradation percentages in dark and under visible and UV light were found to 6, 13, and 98.4% respectively for CQD-S1. Similarly, dye degradation for CQD-S2 were 7, 11, and 99.63%, respectively. Effective degradation of photocatalysis performed under UV-light within 100 min using mineralization process.

Cordierite and citric acid regulate crystal structure of manganese oxide for effective selective catalytic reduction of nitrogen oxide

Catalyst is the key to effective selective catalytic reduction of nitrogen oxide, and developing catalyst is always one of the hottest topics in both field of industry and academy. In order to realize an industrial application, one catalyst must grow on a specific support. However, seldom work compared the difference of catalyst growth with or without support. In this work, Mn²⁺ growth on cordierite (a typical commercial catalyst support) was investigated. The formed active species were detailedly characterized. As a result, orthorhombic cordierite guided Mn²⁺ to form orthorhombic oxide (γ-MnO₂). In comparison, Mn²⁺ preferred to form tetragonal β-MnO₂ without the guide of cordierite. During the synthesis, cordierite and citric acid promoted γ-MnO₂ dispersion, increased growth of exposed (301) facet, and created lattice distortion between (301) and (101) planes. β-MnO₂ mainly exposed (101) facet. The best catalyst was γ-MnO₂, which was mostly dominated by (301) facet and had an obvious lattice distortion from 75° to 78° between (301) and (101) planes. In comparison, 0.1 g of the γ-MnO₂ reached a catalytic conversion rate 1.6 times bigger than 1.0 g of β-MnO₂ at 250 °C. This work helps to understand guiding effect of support on formed catalytic species, which is in favor of developing effective commercial catalysts for environmental pollutants.

Improvement of transformation efficiency in hypermucoviscous Klebsiella pneumoniae using citric acid

Transformation efficiency is very low in hypermucoviscous Kllebsiella pneumoniae owing to high amount of capsular polysaccharide. Here, we propose a method to improve the transformation in hypermucoviscous K. pneumoniae using citric acid. An increased number of recovered transformants was observed in the strains cultured in the presence of citric acid.

Remediation of Cr(VI)-contaminated soil by sulfidated zero-valent iron: The effect of citric acid as eluant and modifying agent

Leaching and chemical reduction are two commonly used methods for Cr(VI)-contaminated soil remediation. Leaching focuses more on leaching Cr(VI) out of the soil. Chemical reduction has the disadvantages of poor fluidity of reductant. Combining these two remediation methods, this study investigated the performance of Cr(VI)-contaminated soil when H₂O and citric acid were used as eluant separately and sulfidated zero-valent iron (SZVI) as reductant. And based on the properties of Cr(VI) chelated with -COOH to form a complex and the characteristics of -OH anchored to FeS_x, citric acid modified SZVI (Cit-SZVI) was prepared. The prepared Cit-SZVI was characterized by SEM-EDS, XPS, XRD to study its surface properties. The transformation of Cr species in soil was explored by BCR sequential extraction. The results indicated Cr(VI) removal by SZVI was significantly promoted when citric acid as eluant compared with H₂O. With SZVI dosage of 2.0 wt%, 23.1 mg/L Cr(VI) was basically removed within 60 min when citric acid as eluant, while only 60% Cr(VI) was removed when H₂O as eluant even after 3 h. The k_obs of Cit-SZVI was 1.4 times that of SZVI when H₂O as eluant. The characterization of Cit-SZVI showed that more FeS_x was formed on the surface of the Cit-SZVI, and more -OH of citric acid was anchored to FeS_x, leaving -COOH available to chelate Cr(VI). Compared with H₂O as eluant and SZVI/Cit-SZVI as reducing agent, the removal effect of Cr(VI) was the best when citric acid as eluant and SZVI as reducing agent. BCR sequential extraction showed that Cr(VI) was effectually fixed, weak acid extractable Cr proportion decreased significantly and residual Cr proportion increased in the treated soil. The combination of leaching and chemical reduction proposed in this study can greatly enhance the Cr(VI) removal effect in soil, which is important for the remediation of Cr(VI)-contaminated soil.

Phosphorylation and citration of normal corn starch by dry heating with phytic acid and citric acid

Normal corn starch was subjected to dry heating in the presence of phytic acid (PA, 2 %, starch basis) and citric acid (CA, 5 % and 10 %) for modification. Dual treatment with PA and CA induced structural and physicochemical changes in normal corn starch. Phosphorus concentration, degree of substitution, FTIR, and ³¹P NMR analyses confirmed esterification of starch by dry heating with PA and CA. Both phosphorylation and citration by esterification with PA and CA were observed in PA + 5CA starch, but high CA concentration inhibited covalent interaction between PA and starch in PA + 10CA starch. The degree of phosphorylation and citration resulted in different physicochemical properties in starch treated with PA and CA. The treatment with only PA did not change the crystalline regions of PA starch, but CA treatment induced the disruption of the crystalline structure of PA + 5CA and PA + 10CA starch. PA starch showed high solubility (46.41 %) and transmittance (90.51 %), but dual treatment of PA and CA induced significant decrease in solubility (3.23 %) and transmittance (2.18 %) of PA + 10CA starch. CA treatment increased the fraction of resistant starch in non-cooked (72.44 %) and cooked PA + 10CA starch (42.76 %). Therefore, dual treatment with PA and CA had potential to control physicochemical and functional properties of starch by phosphorylation and citration of starch.

Facile post-gelation soaking strategy toward low-alkaline konjac glucomannan gels

A facile post-gelation soaking strategy for producing low-alkaline konjac glucomannan (KGM) gels was investigated in this work. The dealkalization kinetics of soaking alkali-induced gels in citric acid (CA) solutions was determined. A comparison of sensory, textural, and water holding properties was made between untreated and post-soaking gels. Post-gelation exposure to acid took less time for lowering the gel pH at higher CA concentrations, eliminated the unattractive flavor of KGM gels and endowed them a higher hardness and breaking force. Comparatively, the whiteness of post-soaking gels was increased by 3.8%-13.1% with volume being decreased by 4.9%-8.6%, while the discrepancies were less apparent after a long-term storage. Low-alkaline gels treated by 4 g/L CA shared similar textural features with conventional KGM gels. Despite the difference in water distribution and water holding capacity of KGM gels, the syneresis of resultant low-alkaline KGM gels was not significantly affected.

Growth studies in commercial broiler birds offered citric acid in formulated feed with low mineral density

Study of 35 days was conducted to evaluate citric acid (CA) as an additive in poultry broiler feed with lower mineral content of calcium (Ca) and total phosphorus (TP) in commercial broiler poultry birds for its effect on growth, nutrient utilization, carcass characteristics, and economics. Vancobb-400 strain day old broiler chicks were divided into four main treatment groups T_0, T₁, T₂, and T_3. Treatment groups were further divided into eight replicates with ten chicks in each. T₀ served as control, given standard corn-soy flakes-based ration (Pre-starter %: Crude protein (CP)-23, Ca-1.00, TP-0.70; Starter %: CP-22, Ca-1.10, TP-0.72, and Finisher %: CP-20, Ca-0.99, TP-0.70). Treatment T₁ served as positive control with added 0.5% CA (Pre-starter %: CP-23, Ca-1.00, TP-0.70; Starter %: CP-22, Ca-1.10, TP-0.72 and Finisher %: CP-20, Ca-0.99, TP-0.70). Treatment T₂ was given feed containing 0.5% CA with low Ca and TP content (Pre-starter %: CP-23, Ca-0.90, TP-0.66; Starter %: CP-22, Ca-0.99, TP-0.71 and Finisher %: CP-20, Ca-0.90, TP-0.69), whereas treatment T₃ was given feed containing 0.5% CA with moderately low Ca and TP content (Pre-starter %: CP-23, Ca-0.80, TP-0.65; Starter %: CP-22, Ca-0.88, TP-0.70 and Finisher %: CP-20, Ca-0.79, TP-0.68). Birds offered moderately low Ca and TP with 0.5% CA addition, exhibited higher growth rate (P < 0.05), better nutrient utilization with positive influence on dressing percentage and forequarters weight. Economics of broiler feeding revealed that 0.5% CA supplementation fetched highest gross return above feed cost in broiler birds offered feed with moderately low Ca and TP content whereas lowest profit was recorded in feed with low content of Ca and TP. In conclusion, supplementation of 0.5% CA in feed with low and moderately low Ca and TP content positively influenced overall growth, and carcass characteristics. Economics of broiler feeding with moderately low Ca and TP content revealed highest profit with CA (0.5%) supplementation.

Citric Acid and Poly-glutamic Acid Promote the Phytoextraction of Cadmium and Lead in Solanum nigrum L. Grown in Compound Cd-Pb Contaminated Soils

Phytoextraction is an efficient strategy for remediating heavy metal-contaminated soil. Chelators can improve the bioavailability of heavy metals and increase phytoextraction efficiency. However, traditional chelators have gradually been replaced due to secondary pollution. In this study, a typical organic acid (citric acid, CA) and a novel biodegradable chelator (poly-glutamic acid, PGA), were investigated using pot experiments to compare the phytoextraction efficiency of Solanum nigrum L. (a Cd (hyper)accumulator) for cadmium (Cd) and lead (Pb) in contaminated soil. The results showed CA and PGA significantly improved plant growth, and total Cd and Pb amounts of S. nigrum, both CA and PGA significantly increased the shoot Cd and Pb concentrations. However, only PGA significantly increased the root Pb concentration. CA and PGA application promoted the bioavailability of Cd and Pb in rhizosphere soils and their translocations from roots to shoots in S. nigrum. Both CA and PGA increased the phytoextraction efficiency of Cd and Pb in S. nigrum plants, and the PGA for Cd and Pb phytoextraction was more effective than CA. Our findings demonstrate that the biodegradable chelator PGA has great potential for enhancing phytoextraction from compound Cd-Pb contaminated soils, suggesting that biodegradable chelator-assisted phytoextraction with (hyper)accumulator is strongly recommended in severely contaminated sites.

Leaching and characterization studies of heavy metals in contaminated soil using sequenced reagents of oxalic acid, citric acid, and a copolymer of maleic and acrylic acid instead of ethylenediaminetetraacetic acid

In this work, the removal performance of three environmentally friendly reagents, oxalic acid (OA), citric acid (CA), and a copolymer of maleic and acrylic acid (PMAA), on heavy metals in polluted soil was studied at the optimum conditions and compared their sequenced performance. The results showed that the consecutive washing with the individual acids significantly improved the removal percentage of heavy metals in the soil compared to that of EDTA (10.2%, 71.3%, 29.8%, 61.6%, and 52.4% removal for As, Cd, Cu, Pb, and Zn, respectively). The removal of As, Cd, Cu, Pb, and Zn in the sequence of CA-OA was 65.6%, 79%, 59.1%, 64.6%, and 63.5%, respectively. In addition, the organic acids had little influence on the soil physicochemical properties after washing with slight reductions of acidity (pH) and soil organic matter (SOM), which are the major determinants of the usability of washed soils for plant growth. The germination rate of Sorghum bicolor in CA-OA-washed soils reached over 70% on the 7th day. CA-OA-washed soils collectively stand out in using washed soils for plant growth with the following advantages: simultaneous removal of cationic and anionic metals, less harmful impact on soil properties, and successful support for the germination of crops. Based on the findings, we recommend the CA-OA sequence as the best alternative to EDTA with higher metal removal efficiency and germination success.

Mechanically strong and biodegradable holocellulose films prepared from Camellia oleifera shells

Bioplastic derived from renewable lignocellulosic biomass is an attractive alternative to petroleum-based plastics. Herein, Callmellia oleifera shells (COS), a unique byproduct from tea oil industry, were delignified and converted into high-performance bio-based films via a green citric acid treatment (15 %, 100 °C and 24 h), taking advantage of their high hemicellulose content. The structure-property relations of COS holocellulose (COSH) films were systematically analyzed considering different treatment conditions. The surface reactivity of COSH was improved via a partial hydrolysis route and strong hydrogen bonding formed between the holocellulose micro/nanofibrils. COSH films exhibited high mechanical strength, high optical transmittance, improved thermal stability, and biodegradability. A mechanical blending pretreatment of COSH, which disintegrated the COSH fibers before the citric acid reaction, further enhanced the tensile strength and Young's modulus of the films up to 123.48 and 5265.41 MPa, respectively. The films decomposed completely in soil, demonstrating an excellent balance between degradability and durability.

Update on citric acid use in endodontic treatment: a systematic review

This systematic review aims to analyse the available evidence concerning the use of citric acid (CA) in endodontics treatment and to assess its results in terms of different considerations: effect on smear layer removal, influence on sealer bond strength, activation effect by means of sonic or ultrasonic devices, effects on dentine surface, antibacterial activity, and effectiveness boost for regenerative procedures, releasing growth factors from dentin. To evaluate the results of CA as a final irrigant and compare them to other chelating agents. This review followed the PRISMA checklist. An electronic search was conducted in MEDLINE (OVID), Scopus (Elsevier) and the Web of Science (Thomson Reuters) databases. Risk of bias of included studies was evaluated using the modified CONSORT checklist and the PRIRATE checklist 2020 guidelines. 39 studies fulfilled the eligibility criteria to be included in this review: 27 in vitro studies using extracted human teeth, 10 in vitro studies using human dentin disks, and 2 RCT. Citric acid has proven to be effective in smear layer removal, showing better results in coronal and middle root thirds, improving its effect when combined with manual dynamic activation. There is no agreement regarding citric acid effect on sealer adhesion and adaptation to root canal walls due to heterogeneity within studies. Citric acid irrigation can decrease dentine microhardness and cause decalcification and erosion, especially when used before NaOCl. Citric acid has proven to be beneficial in regenerative endodontic procedures due to higher TGF-β1 release.Trial registration: Prospero database CRD42021267055.

Citric acid secretion from rice roots contributes to reduction and immobilization of Cr(VI) by driving microbial sulfur and iron cycle in paddy soil

Root exudates released by plants can promote microbial growth and activity, thereby affecting the transformation and availability of soil pollutants. However, the effects of the root exudates of rice plants on chromium (Cr) transformation in paddy soils and the underlying mechanisms are yet to be elucidated properly. The present study investigated how rice root exudates interact with rhizosphere microorganisms to influence the transformation of Cr and explored the key components in root exudates that affect Cr(VI) reduction. The results showed that the addition of root exudate and citric acid markedly decreased soil pH and increased dissolved organic carbon content that created favorable conditions and provided sufficient electron donors for Cr(VI) reduction, thereby greatly facilitating the reduction of Cr(VI) and the transformation of HOAc-extractable Cr into more stable oxidizable and residual Cr. Additionally, Desulfovibrio-related sulfate-reducing bacteria, Thiobacillus-related sulfide-oxidizing bacteria, and Geobacter-related Fe(III)-reducing bacteria were enriched with the addition of root exudate and citric acid. Among them, sulfate would be reduced by Desulfovibrio to sulfide, which would be further utilized by Thiobacillus to reduce Cr(VI), thereby enabling the continuous reduction of Cr(VI); simultaneously, Geobacter would sustain the reduction of Cr(VI) by reducing Fe(III) to Fe(II). Furthermore, based on the high-level secretion of citric acid in response to Cr(VI) exposure and the similar effects of root exudates and citric acid on Cr(VI) reduction, it is proposed that citric acid is the key component in rice root exudates that affects Cr(VI) reduction. These results suggest that root exudates (citric acid as the key component) contribute to the reduction and immobilization of Cr(VI) by driving microbial S and Fe cycles, with Desulfovibrio, Thiobacillus, and Geobacter being the keystone genera. The study provides a novel insight into the Fe/S/Cr co-transformation processes with microbial involvement, and the artificial root exudate mixtures designed to reduce Cr(VI).

Citric acid-based deep eutectic solvent (CA-DES) as a new soil detergent for the removal of cadmium from coking sites

In order to solve the problem of soil pollution caused by excess heavy metals, cadmium (Cd), a novel soil-washing agent organic chelating acid-based deep eutectic solvent (OCA-DES), was investigated for the removal of Cd from the contaminated soil of coking plant. Four kinds of OCA-DES were prepared by mixing choline chloride (Ch-Cl) with four organic chelating acids (citric acid, oxalic acid, tartaric acid, and malic acid), respectively, to compare their washing efficiency of Cd from soil. The effects of washing operation conditions on the Cd removal efficiency were investigated. Side effects of citric acid-based deep eutectic solvent (CA-DES) on soil were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). The results showed that CA-DES had the best Cd removal efficiency and could reach as high as 93.75%, under ideal conditions. CA-DES mainly washed extractable and reducible Cd. The CA-DES washing process has less side effects on soil and hardly eroded the soil or changed the mineral structure of the soil. The main roles of CA-DES washing Cd include (1) hydrogen bonds capturing Cd; (2) the carboxyl group(-COOH) forming soluble chelate with Cd; and (3) releasing H⁺ ions in exchange for Cd. This study demonstrates that CA-DES, a novel soil-washing agent, has excellent removal of cadmium from soil and is environment-friendly.

Screening of new adsorbents to remove algal organic matter from aqueous solutions: kinetic analyses and reduction of disinfection by-products formation

The algal organic matter (AOM) is a problem in water treatment. Although the adsorption process is extensively applied to drinking water treatment, little information is known about the potential of new adsorbents to remove AOM. Herein, this work evaluated the removal of AOM and its main compounds (dissolved organic carbon (DOC), carbohydrate, and protein) by new adsorbents-mesoporous silica (SBA-16), graphene oxide material from citric acid (CA), and sugar (SU), and a composite of CA immobilized on sand (GSC). In general, the removal efficiencies followed the order of SBA-16 > CA > SU or GSC for DOC, carbohydrate, and protein. At environmental condition (5 mg DOC·L^-1 and pH 8), high removals were reported for SBA-16 (88.8% DOC, 80.0% carbohydrate, and 99.6% protein) and CA (70.0% DOC, 66.7% carbohydrate, and 89.7% protein), while moderate removals were found for SU (60.5% DOC, 47.9% carbohydrate, and 66.5% protein) and GSC (67.4% DOC, 60.8% carbohydrate, and 57.4% protein). Based on these results, further analyses were done with SBA-16 and CA. Both adsorbents' efficiencies decayed with the pH increment of the test water. Disinfection by-products reductions found using SBA-16 - trihalomethanes (58.2 to 94.7%) and chloral hydrate (48.7 to 78.8%) - were higher than the ones using CA-trihalomethanes (45.2 to 82.4%) and chloral hydrate (40.1 to 70.8%). This study showed the potential of applying these adsorbents for AOM removal, and further investigations are suggested to increase the adsorption capacity of these adsorbents.

To compare the efficacy of various organic solvents on retrievability of Biodentine and their effect on microhardness of Biodentine and radicular dentin: An in vitro study

Background

Rotary and ultrasonic instruments are not appreciable in the complete removal of Biodentine from root canals. Therefore, organic solvents can be used as an adjunct for its retrieval.

Aim

The aim of this study was to compare the efficacy of 10% citric acid, 2% acetic acid, and 20% tartaric acid on the microhardness of Biodentine and radicular dentin.

Materials and Methods

Forty single-rooted extracted teeth were decoronated at the cementoenamel junction and root canals were prepared with peeso reamers. Two-millimeter sections were obtained and restored with Biodentine. All samples were subjected to Vicker's microhardness test to record the microhardness of Biodentine and radicular dentin. Samples were randomly divided into four experimental groups and treated with (n = 20) - distilled water, 10% citric acid, 2% acetic acid, and 20% tartaric acid groups for 10 min, after which specimens were again subjected to the same microhardness test.

Statistical Analysis

The data were subjected to Kruskal-Wallis ANOVA test, followed by Wilcoxon signed-rank test with a level of significance set at P ≤ 0.05.

Results

10% citric acid followed by 2% acetic acid exhibited the lowest mean microhardness values after immersing in respective solutions, whereas 20% tartaric acid exhibited the highest mean microhardness values on Biodentine and radicular dentin.

Conclusion

10% citric acid can be used for retrieving Biodentine from root canals for a limited time without adversely affecting the physical and chemical composition of radicular dentin.

Recent advances and perspectives on production of value-added organic acids through metabolic engineering

Organic acids are important consumable materials with a wide range of applications in the food, biopolymer and chemical industries. The global consumer organic acids market is estimated to increase to $36.86 billion by 2026. Conventionally, organic acids are produced from the chemical catalysis process with petrochemicals as raw materials, which posts severe environmental concerns and conflicts with our sustainable development goals. Most of the commonly used organic acids can be produced from various organisms. As a state-of-the-art technology, large-scale fermentative production of important organic acids with genetically-modified microbes has become an alternative to the chemical route to meet the market demand. Despite the fact that bio-based organic acid production from renewable cheap feedstock provides a viable solution, low productivity has impeded their industrial-scale application. With our deeper understanding of strain genetics, physiology and the availability of strain engineering tools, new technologies including synthetic biology, various metabolic engineering strategies, omics-based system biology tools, and high throughput screening methods are gradually established to bridge our knowledge gap. And they were further applied to modify the cellular reaction networks of potential microbial hosts and improve the strain performance, which facilitated the commercialization of consumable organic acids. Here we present the recent advances of metabolic engineering strategies to improve the production of important organic acids including fumaric acid, citric acid, itaconic acid, adipic acid, muconic acid, and we also discuss the current challenges and future perspectives on how we can develop a cost-efficient, green and sustainable process to produce these important chemicals from low-cost feedstocks.