Genome of Wild Mandarin and Domestication History of Mandarin

Mandarin (Citrus reticulata) is one of the most important citrus crops worldwide. Its domestication is believed to have occurred in South China, which has been one of the centers of mandarin cultivation for four millennia. We collected natural wild populations of mandarin around the Nanling region and cultivated landraces in the vicinity. We found that the citric acid level was dramatically reduced in cultivated mandarins. To understand genetic basis of mandarin domestication, we de novo assembled a draft genome of wild mandarin and analyzed a set of 104 citrus genomes. We found that the Mangshan mandarin is a primitive type and that two independent domestication events have occurred, resulting in two groups of cultivated mandarins (MD1 and MD2) in the North and South Nanling Mountains, respectively. Two bottlenecks and two expansions of effective population size were identified for the MD1 group of cultivated mandarins. However, in the MD2 group there was a long and continuous decrease in the population size. MD1 and MD2 mandarins showed different patterns of interspecific introgression from cultivated pummelo species. We identified a region of high divergence in an aconitate hydratase (ACO) gene involved in the regulation of citrate content, which was possibly under selection during the domestication of mandarin. This study provides concrete genetic evidence for the geographical origin of extant wild mandarin populations and sheds light on the domestication and evolutionary history of mandarin.

Effect of multi-wall carbon nanotubes on Cr(VI) reduction by citric acid: Implications for their use in soil remediation

The potential application of carbon nanotubes (CNTs) in waste water treatment and their effect on the fate of heavy metals in the environments have attracted wide attention. However, the influence of CNTs on the reduction of Cr(VI) to Cr(III) in soils remains unknown. In this study, Cr(VI) adsorption by carboxylated or hydroxylated multi-walled carbon nanotubes (MWCNT-COOH or MWCNT-OH) was investigated together with their catalytic effect on Cr(VI) reduction by citric acid. Across the initial concentration range examined (5-60 mg/L), the adsorption capacity of Cr(VI) by MWCNT-COOH and MWCNT-OH (pH 5.0) could reach to 8.09 and 7.85 mg/g, respectively. With the decrease in pH, the Cr(VI) adsorption by both MWCNTs increased, while their difference in adsorption capacity became more pronounced, evidenced by that the percentage of Cr(VI) adsorbed by MWCNT-COOH can be 1.3-fold higher than that of MWCNT-OH at a pH of 3.2. The Cr(VI) adsorption kinetics could be well described by pseudo-second-order (R² > 0.95) and intra-particle diffusion models (R² > 0.98). MWCNT-OH or MWCNT-COOH could accelerate the reduction of 0.1 mM Cr(VI) by 1.0 mM citric acid, with the first-order rate constant of 0.0325 and 0.0147 h^-1, respectively. This finding was explained as that the reactivity of citric acid might be enhanced with its adsorption on the MWCNT surfaces. The catalysis of the functionalized CNTs on the Cr(VI) reduction was inhibited as the pH increased. The addition of MWCNTs to an oxisol can enhance the Cr(VI) reduction because the final concentration of aqueous Cr(III), compared with that without addition of MWCNTs, increased from 20.7 to 32.6 μM. Meanwhile, re-adsorption of aqueous Cr(III) onto the solid surfaces was also observed. The results above are important for understanding on the effect of CNTs on the fate of Cr(VI) and how they can be used to remediate Cr(VI)-polluted soils.

Effect of adsorbent and acidulants on enzymatic browning of sugarcane juice

Enzymatic browning is a major factor affecting the quality of sugarcane juice, mainly due to the activities of polyphenol oxidase (PPO) and peroxidase (POD). Effect of bentonite (0-1%, w/v) on the activities of these enzymes, when employed alone and also in combination with acidulants, was determined. Bentonite alone could reduce the activities of PPO and POD enzymes to 160 and 24.2 u/mL, respectively. The PPO and POD activity was completely inhibited below pH 4.1 when ascorbic acid was used alone or in combination with bentonite. However, PPO and POD activity was inhibited to 60 and 51 u/mL, respectively, at pH 3.7 when citric acid was used individually and to 112 and 15.36 u/mL, respectively, when employed along with bentonite. In addition, color changes at 4 and 10 °C were measured during the storage of sugarcane juice.

Thermo-chemical modification of a natural biomembrane to induce mucoadhesion, pH sensitivity and anisotropic mechanical properties

In the present study due to the distinctive mechanochemical/biological characteristics of natural biomembranes, we state the preparation, characterization and cytocompatibility of modified eggshell membrane (ESM) by citric acid (CA) for biomedical and pharmaceutical applications. FTIR spectroscopy and CHNS analysis demonstrated the successful reaction of ESM with CA. Also, successful modification of the ESM was observed by the change in thermogravimetric analysis. SEM micrographs of neat ESM and ESM-CA gave further insight into membranes morphology and revealed that aligned oriented fibrous frameworks were prepared using thermo-chemical process. The ESM-CA displayed dense and orderly shapes with tailorable architectures to mimic the intended tissue. Moreover, mechanical analyzes for ESM-CA indicated anisotropic mechanical properties and proved that the ESM-CA could induce enhanced mucoadhesion, because of the existence of an enormous amounts of functional groups. It was found that by modification of ESM the swelling behavior was significantly changed. Indomethacin release from the ESM-CA showed enhanced pH sensitivity. The modified membranes have clearly presented adequate mucoadhesion, pH sensitivity and cell viability which can be tailored for potential use in controlled lipophilic drug delivery systems and tissue engineering.

Effect of EDTA and citric acid on absorption of heavy metals and growth of Moso bamboo

The effect of EDTA and citric acid on accumulation, toxicity of heavy metals (Cu, Zn, Cd, and Pb), and growth of Moso bamboo was investigated in current experiment. The availability of heavy metals in soil and its uptake by plants has indicated toxicity. The results revealed that EDTA and citric acid has reduced biomass of Moso bamboo but non-significant difference in biomass was observed compared with control. Application of EDTA (10 mmol kg^-1) has significantly improved copper (Cu) by 56.5 and 84.9% in roots and above ground parts of plants. Application of EDTA (10 mmol kg^-1) has significantly enhanced lead (Pb) by 51.8 and 210.8% in roots and above ground parts of Moso bamboo. Furthermore, treatment of EDTA has significantly improved activities of water-soluble Cd, Cu, and Pb in soil by 98.9, 70.1, and 73.1 times compared with control. In case of contents of diethylenetriaminepentaacetic acid (DTPA)-extractable metals, the treatment of EDTA (10 mmol kg^-1) has produced maximum increase of 244.5 mg kg^-1 Zn and 157.9 mg kg^-1 Pb, respectively. It is concluded that effect of EDTA was superior compared with citric acid for improvement of phytoremediation potential of Moso bamboo.

Quantification of sugars and organic acids in tomato fruits

Sugar and organic acid contents are major factors for tomato fruit flavour and are important breeding traits. Here we provide an improved protocol for accurate quantification of the main sugars, glucose and fructose, and the organic acids, citric acid and malic acid, present in tomato. The tomato extract is spiked with lactose and tricarballylic acid as internal standards and loaded onto a NH2 solid phase extraction (SPE) column. The sugars appear in the flow-through and are subsequently analysed by HPLC using a Nucleodur NH2 column and a refractive index detector. The organic acids bind to the SPE column and are eluted with 400 mM phosphoric acid. For analysis, the organic acids are separated by HPLC using a Nucleodur C18ec column and detected by UV absorption at 210 nm. The method shows excellent inter-day and intra-day reproducibility for glucose, fructose and citric acid with standard deviations of 1–5%. Quantification of citric acid by HPLC and GC–MS showed perfect agreement with a deviation of less than 3%.

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Simple method for quantification of glucose, fructose, citric acid and malic acid in tomato.

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Efficient removal of interfering compounds by solid phase extraction.

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High intra and inter-day reproducibility.

How a fungus shapes biotechnology: 100 years of Aspergillus niger research

In 1917, a food chemist named James Currie made a promising discovery: any strain of the filamentous mould Aspergillus niger would produce high concentrations of citric acid when grown in sugar medium. This tricarboxylic acid, which we now know is an intermediate of the Krebs cycle, had previously been extracted from citrus fruits for applications in food and beverage production. Two years after Currie’s discovery, industrial-level production using A. niger began, the biochemical fermentation industry started to flourish, and industrial biotechnology was born. A century later, citric acid production using this mould is a multi-billion dollar industry, with A. niger additionally producing a diverse range of proteins, enzymes and secondary metabolites. In this review, we assess main developments in the field of A. niger biology over the last 100 years and highlight scientific breakthroughs and discoveries which were influential for both basic and applied fungal research in and outside the A. niger community. We give special focus to two developments of the last decade: systems biology and genome editing. We also summarize the current international A. niger research community, and end by speculating on the future of fundamental research on this fascinating fungus and its exploitation in industrial biotechnology.

Impacts of supplementing growing rabbit diets with whey powder and citric acid on growth performance, nutrient digestibility, meat and bone analysis, and gut health

The present study evaluated the impact of supplementing the rabbit diet with graded levels of whey powder and citric acid. The dietary treatments were as follows: T1, control diet (basal diet); T2, basal diet + 10 g/kg citric acid; T3, T2 + whey powder (7.5 g/kg); T4, T2 + whey powder (15 g/kg); and T5, T2 + whey powder (22.5 g/kg). Results, the T5 diet resulted in the best (P < 0.05) final body weight, body weight gain, feed conversion ratio, protein efficiency, relative growth rate, and dressed weight. The best (P < 0.05) digestion coefficients were associated with the T4 and T5 diets. Rabbits fed diets supplemented with citric acid alone or with addition of graded levels of whey powder showed significantly lower (P < 0.05) intestinal pH than those fed the T1 diet. The T4 and T5 diets resulted in greater CP and ash in the thigh muscle compared with the T1 and T2 diets. Calcium content in the femur bone was higher (P < 0.05) in the T5 group followed by T4 and T3. The wall of different parts of the small intestine improved in the T4 and T5 groups, showing the greatest increase in the small intestinal villi, intestinal glands, and amount of goblet cells. In conclusion, addition of whey powder (1.5, and 2.25%) increased the growth performance, nutrient digestibility and crude protein content of the thigh muscle, and improved the gut health of growing rabbits and the best level was 2.25% whey powder. Citric acid addition had no positive effect on growth performance, nutrient digestibility, crude protein content of the thigh muscle, and the gut health.

Implementing Cough Reflex Testing in a Clinical Pathway for Acute Stroke: A Pragmatic Randomised Controlled Trial

Silent aspiration is common after stroke and can lead to subsequent pneumonia. While standard bedside dysphagia assessments are ineffective at predicting silent aspiration, cough reflex testing (CRT) has shown promise for identifying patients at risk of silent aspiration. We investigated the impact of CRT on patient and service outcomes when embedded into a clinical pathway. 488 acute stoke patients were randomly allocated to receive either CRT or standard care (i.e. bedside assessment). Primary outcomes included confirmed pneumonia within 3 months post stroke and length of acute inpatient stay. Secondary outcomes related to the feasibility of implementing a CRT pathway and clinician and patient satisfaction. There was a non-significant reduction in pneumonia rates by 2.2% points in the CRT group (OR 0.32, 95% CI 0.06-1.62). There was a non-significant difference of 0.7 days (95% CI - 0.29 to 1.71 days) in length of stay between the standard care group and the CRT group. The CRT took on average 3 min longer to complete (p < 0.01) and resulted in a significant 6.7% increase in videofluoroscopic referrals (p = 0.02); however, these results are clinically insignificant. High patient and clinician satisfaction with CRT was found, with clinicians reporting additional knowledge and confidence in decision making for dysphagia management. Post hoc subgroup analyses according to stroke types were conducted and revealed no significant differences in pneumonia rates after adjustment for multiple comparisons. In conclusion, it was possible to implement a CRT pathway with minimal increases in clinician resources. While clinicians perceived CRT as beneficial in clinical decision making, the efficacy of CRT for reducing pneumonia rates in acute stroke remains to be established.Clinical Trial Registration-URL: http://www.anzctr.org.au . Unique identifier: ACTRN12616000724471.

Anaerobic co-digestion of waste yeast biomass from citric acid production and waste frying fat

The application of spent yeast for biogas production has been studied only in the context of breweries so far. This study is focused on the anaerobic digestion of concentrated yeast biomass (CYB), being a by-product of citric acid biosynthesis. Two experimental set-ups were used in order to test CYB as a mono-substrate and co-substrate for closing the loop in accordance with the 'bioeconomy' approach. The results show that CYB allows for obtaining a high biogas yield, with a maximum of 1.45 m³ _N/kg_VS produced when CYB was used as a mono-substrate. The average methane concentration was 66 ± 4%. However, anaerobic digestion of CYB alone was difficult to perform because of a tendency for over-acidification, meaning that the maximum possible organic loading rate was 1 kg/(m³*d). Repeated clogging of tubes with coagulated biomass also disturbed continuous feeding. In contrast, the co-digestion of CYB with waste frying fat at a ratio of 1:20 showed stable operation during a 70-day fermentation period. The biogas yield using the substrate mixture was 1.42 m³/kg_VS at an organic loading rate of 2 kg/(m³*d). The methane concentration reached 67 ± 4% and the acetate concentration did not exceed 30 mg/L during the entire fermentation.

Citrate chemistry and biology for biomaterials design

Leveraging the multifunctional nature of citrate in chemistry and inspired by its important role in biological tissues, a class of highly versatile and functional citrate-based materials (CBBs) has been developed via facile and cost-effective polycondensation. CBBs exhibiting tunable mechanical properties and degradation rates, together with excellent biocompatibility and processability, have been successfully applied in vitro and in vivo for applications ranging from soft to hard tissue regeneration, as well as for nanomedicine designs. We summarize in the review, chemistry considerations for CBBs design to tune polymer properties and to introduce functionality with a focus on the most recent advances, biological functions of citrate in native tissues with the new notion of degradation products as cell modulator highlighted, and the applications of CBBs in wound healing, nanomedicine, orthopedic, cardiovascular, nerve and bladder tissue engineering. Given the expansive evidence for citrate's potential in biology and biomaterial science outlined in this review, it is expected that citrate based materials will continue to play an important role in regenerative engineering.

High monomeric sugar yields from enzymatic hydrolysis of soybean meal and effects of mild heat pretreatments with chelators

Defatted soybean meal has 30-35% oligo-/polymeric carbohydrates and approximately 50% proteins. Enzymatic carbohydrate monomerization enables easy separation to enrich protein content, reduces indigestibility concerns, and facilitates use of carbohydrate as fermentation feedstock. Among soybean carbohydrates, pectin and glucan are more recalcitrant to hydrolyze. To destabilize Ca2+-bridged junctures in pectin, effects of 3 chelators ethylenediaminetetraacetic acid (EDTA), sodium hexametaphosphate (HMP) and citric acid under 2-h 90 °C pretreatments were investigated here. Citric acid was the most effective while EDTA decreased enzymatic hydrolysis. In a 3-factor 2-level factorial study, heat (90 °C, 2 h) and citric acid (10 g/L) pretreatments and cellulase supplementation (10 FPU/g) were found to increase yields of all monosaccharides, to 86.8 ± 5.2% glucose, 98.1 ± 1.6% xylose, 87.5 ± 5.2% galactose, 83.6 ± 1.6% arabinose, and 91.4 ± 3.1% fructose + mannose. The largest percentage improvements were for arabinose (382%), mannose (113%) and glucose (51%). Achieving high monosaccharide yields greatly increases value of soybean carbohydrate as fermentation feedstock.

Mitochondria dysfunctions under Fe and S deficiency: is citric acid involved in the regulation of adaptive responses?

Within the last years, extensive information has been accumulated on the reciprocal influence between S and Fe nutrition at both physiological and molecular level in several plant species, but the mechanisms regulating S and Fe sensing and signaling are not fully understood. Fe and S interact for the building of Fe-S clusters, and mitochondria is one of the cellular compartments where Fe-S cluster assembly takes place. Therefore, it would be expected that mitochondria might play a central role in the regulation of Fe and S interaction. The Fe deficiency-induced alteration in the synthesis of mitochondria-derived carboxylic acids, such as citric acid, and the evidence that such molecules have already been identified as important players of metabolite signaling in several organisms, further support this hypothesis. Tomato plants were grown under single or combined Fe and S deficiency with the aim of verifying whether mitochondria activities played a role in Fe/S interaction. Both Fe and S deficiencies determined similar alteration of respiratory chain activity: a general decrease of Fe-S containing complexes as well as an increase of alternative NAD(P)H activities was observed in both Fe and S deficient-plants. However, the content of Krebs cycle-related organic acids in roots was substantially different in response to treatments, being the accumulation of citric acid always increased, while the others (i.e. succinic, malic, fumaric acids) always decreased. Interestingly, citric acid levels significantly correlated with the expression of some Fe and S deficiency induced genes. Our results contribute to existing knowledge on the complexity of the S/Fe interaction, suggesting a model in which endogenous alteration of citric acid content in plant tissues might act as signal molecule for the regulation of some nuclear-encoded and nutrient-responsive genes and also provide a basis for further study of the mechanism underlying S and Fe sensing and signalling.

Effect of organic amendments on cadmium stress to pea: A multivariate comparison of germinating vs young seedlings and younger vs older leaves

Despite significant recent advancement in research, biogeochemical behavior of heavy metals with respect to their applied form is still topical. Moreover, metal toxicity to plants may vary with their stage of development/maturity. Therefore, this study for the first time evaluated the influence of ethylenediaminetetraacetic acid (EDTA) and citric acid (CA) on cadmium (Cd) accumulation and toxicity to germinating and young pea seedlings as well as in younger and older leaves. The experimental setup of current study consisted of two separate studies. The first study was performed on germinating seedlings grown in a Cd-contaminated sand media. Pea seeds were treated with two levels of Cd (Cd-25 and Cd-100) alone and combined with different levels of EDTA and CA. The second study was carried out in hydroponic solution. The influence of organic amendments on Cd accumulation and toxicity to pea plants was evaluated by determining Cd contents in pea seedlings, H2O2 contents, chlorophyll contents and lipid peroxidation in younger and older leaves. Cadmium stress caused overproduction of H2O2 in roots and leaves of pea seedlings. Cadmium-induced overproduction of H2O2 caused a decrease in the pigment contents and increased lipid peroxidation. Application of EDTA at higher levels (81 and 200µM) increased Cd accumulation by pea plants. However, CA did not affect Cd accumulation by pea. Both EDTA and CA increased Cd-induced H2O2 production and lipid peroxidation. Younger pea leaves showed more sensitivity to Cd stress compared to older leaves. Similarly, Cd toxicity was more pronounced in germinating seedlings than young seedlings. Moreover, Pearson correlation and principal component analysis (PCA) showed very interesting correlations between treatments and stress responses of germination and young seedlings as well as younger and older leaves. Based on multivariate analysis, it is proposed that the Cd toxicity to pea plants greatly vary with its growth stage and the maturity of organs (younger or older leaves).

Simultaneous saccharification and aerobic fermentation of high titer cellulosic citric acid by filamentous fungus Aspergillus niger

Simultaneous saccharification and fermentation (SSF) is the most efficient operation in biorefining conversion, but aerobic SSF under high solids loading significantly faces the serious oxygen transfer limitation. This study took the first insight into an aerobic SSF by high oxygen demanding filamentous fungi in highly viscous lignocellulose hydrolysate. The results show that oxygen requirement in the aerobic SSF by Aspergillus niger was well satisfied for production of cellulosic citric acid. The record high citric acid titer of 136.3 g/L and the overall conversion yield of 74.9% of cellulose were obtained by the aerobic SSF. The advantage of SSF to the separate hydrolysis and fermentation (SHF) on citric acid fermentation was compared based on the rigorous Aspen Plus modeling. The techno-economic analysis indicates that the minimum citric acid selling price (MCSP) of $0.603 per kilogram by SSF was highly competitive with the commercial citric acid from starch feedstock.

Environmental Life Cycle Assessment of marine sediment decontamination by citric acid enhanced-microwave heating

The potential ability of microwave heating (MWH) for the remediation of marine sediments affected by severe hydrocarbon (HC) contamination was investigated. Decontamination effectiveness and environmental sustainability through a comparative Life Cycle Assessment (LCA) were addressed. Main results revealed that the application of a 650-W MWH treatment resulted in a rapid (15min) HC removal. A citric acid (CA) dose of 0.1M led to enhanced-HC removals of 76.9, 96.5 and 99.7% after 5, 10 and 15min of MW irradiation, respectively. The increase in CA dose to 0.2M resulted in a shorter successful remediation time of 10min. The exponential kinetic model adopted showed a good correlation with the experimental data with R² values in the 0.913-0.987 range. The nature of the MW treatment was shown to differently influence the HC fraction concentration after the irradiation process. Achieved HC removals in such a short remediation time are hardly possible by other clean-up techniques, making the studied treatment a potential excellent choice. Removal mechanisms, which allowed the enhanced-MWH to operate as a highly effective multi-step technique (pure thermal desorption+chemical washing), undoubtedly represent a key factor in the whole remediation process. The LCA highlighted that the MW technology is the most environmentally sustainable alternative for sediment decontamination applications, with a total damage, which was 75.74% lower than that associated with the EK (0.0503pt).

PAMAM-modified citric acid-coated magnetic nanoparticles as pH sensitive biocompatible carrier against human breast cancer cells

Denderimer-modified magnetic nanoparticles are a promising drug delivery nanosystem which can improve the therapeutic efficacy of chemotherapy drugs and can also be beneficial as magnetic resonance (MR) images contrast agent. The present study introduces the preparation and characterization of the potential therapeutic efficiency of curcumin (CUR)-loaded denderimer-modified citric acid coated Fe₃O₄ NPs. Polyamidoamine (PAMAM, generation G₅) was used to encapsulate citric acid coated Fe₃O₄ nanoparticles. The successful preparation of CUR-loaded nanocarriers were confirmed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), and transmission electron microscopy (TEM) techniques. The loading capacity and encapsulation efficiency of CUR molecules were 12 ± 0.03% and 45.58 ± 0.41%, respectively. The anticancer effect of void CUR and CUR-loaded nanocarriers were compared to each other by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay on treated MCF-7 cell line. It can be concluded that application of nanoparticles can be more effective strategy for controlled and slow release of CUR in human breast cancer treatment.

Supplement comprising of laccase and citric acid as an alternative for antibiotics: In vitro triggers of melanin production

An indiscriminate use of antibiotics in humans and animals has led to the widespread selection of antibiotic-resistance, thus constricting the use of antibiotics. A possible solution to counter this problem could be to develop alternatives that can boost the host immunity, thus reducing the quantity and frequency of antibiotic use. In this work, for the first time, citric acid and laccase were used as extracellular inducers of melanin production in yeast cells and human cell lines. It is proposed that the formulation of laccase and citric acid together could further promote melatonin-stimulated, melanocyte-derived melanin production. Melanization as a probe of immunity described in this study, is an easy and a rapid test compared to other immunity tests and it allows performing statistical analyses. The results showed the synergistic effect of citric acid and laccase on melanin production by yeast cells, with significant statistical differences compared to all other tested conditions (p: 0.0005-0.005). Laccase and citric acid together boosted melanin production after 8 days of incubation. An increase in melanin production by two human colon cells lines (Cacao-2/15 and HT-29) was observed on supplementation with both laccase and citric acid in the cell growth medium. Produced melanin showed antimicrobial properties similar to antibiotics. Therefore, a formulation with citric acid and laccase may prove to be an excellent alternative to reduce the antibiotic use in human and animal subjects.

Effects of osmotic pressure and pH on citric acid and erythritol production from waste cooking oil by Yarrowia lipolytica

Erythritol and citric acid could be produced from waste cooking oil (WCO) by Yarrowia lipolytica under different medium conditions, and osmotic pressure together with pH were considered to be the critical factors in this process. High osmotic pressure (2.76 osmol/L) combined with low pH (pH 3.0) promoted the highest yield of erythritol (21.8 g/L) accompanied by low-producing citric acid (2.5 g/L). By contrast, the highest citric acid biosynthesis (12.6 g/L) was detected under a pH of 6.0 and an osmotic pressure of 0.75 osmol/L, when only 4.0 g/L of erythritol was yielded. Moreover, lipase activities in these two media were also detected, and pH 3.0-OP 2.76 was supposed to be more beneficial to lipase activity. Biochemical pathways involved in the biosynthesis of erythritol and citric acid were subsequently investigated, and the products yielded from WCO were assumed to be correlated with the activities of transketolase, erythrose reductase, citrate synthase, and glycerol kinase. However, RT-PCR analysis revealed that mRNA levels of these enzymes did not significantly differ, confirming that metabolic flux regulations of erythritol and citric acid mostly took place at the post-transcriptional level.

Comparative leaching of six toxic metals from raw and chemically stabilized MSWI fly ash using citric acid

The leaching behavior of six typical toxic metals (Pb, Zn, Cr, Cd, Cu and Ni) from raw and chemically stabilized (phosphate and chelating agent) municipal solid waste incineration (MSWI) fly ash were investigated using citric acid. Leaching tests indicated that phosphate stabilization can effectively decrease the leaching of Zn, Cd and Cr; whereas chelating agent stabilization shows a strong ability to lower the release of Pb, Cd and Cu, but instead increases the solubility of Zn and Cr at low pH conditions. Sequential extraction results suggested that the leaching of Pb, Zn and Cd in both the stabilized MSWI fly ash samples led to the decrease in Fe/Mn oxide fraction and the increase in exchangeable and carbonate fractions. The leaching of Cr was due to the decrease in exchangeable, carbonate and Fe/Mn oxide fractions in phosphate-stabilized and chelating agent-stabilized MSWI fly ash. The leaching of Cu in both stabilized MSWI fly ash was greatly ascribed to the decrease in Fe/Mn oxide and oxidisable fractions. Moreover, predicted curves by geochemical model indicated that both stabilized MSWI fly ash have the risk of releasing toxic metals under strong acid environment.

Carboxyl groups of citric acid in the process of complex formation with bivalent and trivalent metal ions in biological systems

Binary complexes of citric acid (H₃L - protonated form, H₂L and HL - partly protonated forms, L - fully deprotonated) with d- and f-electron metal ions were investigated. The studies have been performed in aqueous solution using the potentiometric method with computer analysis of the data, electron paramagnetic resonance, infrared, visible as well as luminescence spectroscopies. The overall stability constants of the complexes were determined. Analysis of the equilibrium constants of the reactions and spectroscopic data has allowed determination of the type of coordination and effectiveness of the carboxyl groups in the process of complex formation. On the basis of potentiometric titration for d-electron were found dimeric and monomeric type of complexes and for f-electron four type of complexes: MHL, ML, ML(OH) and ML(OH)₂.

Quantitative GC-MS assay of citric acid from humans and db/db mice blood serum to assist the diagnosis of diabetic nephropathy

The early diagnosis of diabetic nephropathy (DN) is rather challenging. Our previous study suggested that citric acid is a potential marker for the early diagnosis of diabetic nephropathy in db/db mice. For the first time, in this study, a surrogate analyte of ¹³C₆-citric acid was employed to generate calibration curves for the quantitative measurement of the endogenous citric acid in the sera of db/db mice and diabetic nephropathy patients by GC/MS after the analytes were extracted, methoximated and trimethylsilylated. The constant response factor of ¹³C₆-citric acid versus citric acid over the linear range indicated the identical ionization efficiency of these two compounds. The full validation assessments suggested that the method is sensitive, specific, reliable, reproducible and has acceptable parameters. Statistical analysis revealed cut-off citric acid concentrations of 29.24 μg/mL with a 95% confidence interval between 32.75 and 39.16 μg/mL in the diabetic nephropathy patients and 16.74 and 22.57 μg/mL in the normal controls. The areas under the receiver operating characteristic curves indicated accuracies of over 90% for the diagnoses of early diabetic nephropathy in both humans and db/db mice, which suggests that the serum citric acid level is potentially a biomarker that could assist in the diagnosis of diabetic nephropathy.

Effect of carboxylic acids on the properties of zerovalent iron toward adsorption and degradation of trichloroethylene

Zerovalent iron (ZVI) based technology has been applied to remediate contaminated groundwater and has been paid great attention as an economic alternative. But it is still remains highly challenging to remove chlorinated pollutants such as trichloroethylene (TCE) with ZVI. Low molecular weight carboxylic ligands (formic acid (FA), oxalic acid (OA), and citric acid (CA)) were chosen to study the influence on the performance of ZVI in groundwater, including the morphology of Fe surface and the Fe dissolution. The removal rate of TCE with ZVI in the presence of 30 mM carboxylic groups followed an order of FA > OA > pure water ≅ CA. FA provides protons to promote the surface corrosion and generated more magnetite on the ZVI surface, which was further responsible for a high adsorption of TCE. With the strong complexing ability of OA and CA, passive layers could form dissoluble complexes via a ligand-promoted dissolution process. However, high concentration of OA resulted in Fe oxalate reprecipitated back onto the ZVI surface then inhibited the reactivity of ZVI. The Fe-ligand complexes also have ability to transform TCE depending on their redox properties. It is expected that effectiveness of carboxylic ligands on the ZVI: those low molecular weight carboxylic ligands in groundwater and soil may enhance the reaction efficiency of ZVI by altering the surface characteristics of ZVI. Therefore, the carboxylic ligands could increase the reactivity and the longevity of ZVI.

Sonochemical assisted synthesis and characterization of magnetic PET/Fe3O4, CA, AS nanocomposites: Morphology and physiochemical properties

Ultrasonic-assisted synthesized iron oxide (Fe₃O₄) nanoparticles (NP)s were modified with biodegradable citric acid (CA) and ascorbic acid (AS) [vitamin C] as capping agents. The ultrasonication (US) was applied for the synthesis and modification process as an easy, safe and fast method. Dissolution/reprecipitation procedure was offered to recycle poly(ethylene terephthalate) (PET) bottles and then, it has been focused on the preparation of PET nanocomposites (NC)s based on solution method via sonication agitation to disperse the Fe₃O₄, CA, AS NPs in the organic polymeric surrounding substance. Magnetic PET NCs with modified Fe₃O₄ NPs loading (1, 3, and 5wt%) were fully characterized and the effect of NPs was examined by focusing on four aspects: Fourier transform infrared spectroscopy, X-ray diffraction, thermal stability studies, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. Also, flame retardant behaviors of the NCs were investigated. Achieved morphology pictures displayed the presence of well dispersed magnetic NPs in the polymer matrix at nano-scale. In this work after recycling of PET waste bottles, it was aim to have magnetic PET due to its various potential applications such as wastewater treatment, catalysts, biomedicine and drug delivery system and electromagnetic devises. It was also intention to show easy, time saving and safe way (US method) to have magnetic PET which was achieved. From the results it can be concluded that one can readily have good dispersion of magnetic NPs in the PET matrix.

Remediation of electronic waste polluted soil using a combination of persulfate oxidation and chemical washing

Laboratory experiments were conducted to investigate the efficiency of a simultaneous chemical extraction and oxidation for removing persistent organic pollutants (POPs) and toxic metals from an actual soil polluted by the recycling activity of electronic waste. Various chemicals, including hydroxypropyl-β-cyclodextrin (HPCD), citric acid (CA) and sodium persulfate (SP) were applied synchronously with Fe²⁺ activated oxidation to enhance the co-removal of both types of pollutants. It is found that the addition of HPCD can enhance POPs removal through solubilization of POPs and iron chelation; while the CA-chelated Fe²⁺ activation process is effective for extracting metals and degrading residual POPs. Under the optimized reagent conditions, 69.4% Cu, 78.1% Pb, 74.6% Ni, 97.1% polychlorinated biphenyls, 93.8% polycyclic aromatic hydrocarbons, and 96.4% polybrominated diphenylethers were removed after the sequential application of SP-HPCD-Fe²⁺ and SP-CA-Fe²⁺ processes with a duration of 180 and 240 min, respectively. A high dehalogenation efficiency (84.8% bromine and 86.2% chlorine) is observed, suggesting the low accumulation of halogen-containing organic intermediates. The remediated soil can satisfy the national soil quality standard of China. Collectively, co-contaminated soil can be remediated with reasonable time and capital costs through simultaneous application of persulfate oxidation and chemical extraction.

[Quantitative measurement of citric acid in urine using tandem liquid chromatography mass spectrometry]

Objective: To find a suitable method for the determination of citric acid in the urine of patients with stones, in order to provide a new method and basis for the prevention and treatment of stone. Methods: Liquid chromatography tandem mass spectrometry was used to analyze the citric acid in urine directly. And the accuracy, stability, repeatability and other indicators of the results were detected. Results: The results showed a good linear relationship with the concentration of citric acid in urine. y=50.31x+ 0.002 6 (R(2)=0.994 21). The results were stable, reproducible [intra-day (Coefficient of Variance) CV ≈1% and inter-day CV<10%], and the accuracy of which was comparable with that of the enzyme method (n=20, R=0.97). Conclusion: Using the method of this study to detect the content of citric acid in urine has the advantages of simple operation, good repeatability, accurate results, and low price. So it is worth to be popularized and applied in clinical practice.

FTIR spectroscopy as a unified method for simultaneous analysis of intra- and extracellular metabolites in high-throughput screening of microbial bioprocesses

BACKGROUND

Analyses of substrate and metabolites are often bottleneck activities in high-throughput screening of microbial bioprocesses. We have assessed Fourier transform infrared spectroscopy (FTIR), in combination with high throughput micro-bioreactors and multivariate statistical analyses, for analysis of metabolites in high-throughput screening of microbial bioprocesses. In our previous study, we have demonstrated that high-throughput (HTS) FTIR can be used for estimating content and composition of intracellular metabolites, namely triglyceride accumulation in oleaginous filamentous fungi. As a continuation of that research, in the present study HTS FTIR was evaluated as a unified method for simultaneous quantification of intra- and extracellular metabolites and substrate consumption. As a proof of concept, a high-throughput microcultivation of oleaginous filamentous fungi was conducted in order to monitor production of citric acid (extracellular metabolite) and triglyceride lipids (intracellular metabolites), as well as consumption of glucose in the cultivation medium.

RESULTS

HTS FTIR analyses of supernatant samples was compared with an attenuated total reflection (ATR) FTIR, which is an established method for bioprocess monitoring. Glucose and citric acid content of growth media was quantified by high performance liquid chromatography (HPLC). Partial least square regression (PLSR) between HPLC glucose and citric acid data and the corresponding FTIR spectral data was used to set up calibration models. PLSR results for HTS measurements were very similar to the results obtained with ATR methodology, with high coefficients of determination (0.91-0.98) and low error values (4.9-8.6%) for both glucose and citric acid estimates.

CONCLUSIONS

The study has demonstrated that intra- and extracellular metabolites, as well as nutrients in the cultivation medium, can be monitored by a unified approach by HTS FTIR. The proof-of-concept study has validated that HTS FTIR, in combination with Duetz microtiter plate system and chemometrics, can be used for high throughput screening of microbial bioprocesses. It can be anticipated that the approach, demonstrated here on single-cell oil production by filamentous fungi, can find general application in screening studies of microbial bioprocesses, such as production of single-cell proteins, biopolymers, polysaccharides, carboxylic acids, and other type of metabolites.

Utilization of biodiesel derived-glycerol for 1,3-PD and citric acid production

Today, biofuels represent a hot topic in the context of petroleum and adjacent products decrease. As biofuels production increase, so does the production of their major byproduct, namely crude glycerol. The efficient usage of raw glycerol will concur to the biodiesel viability. As an inevitable waste of biodiesel manufacturing, glycerol is potentially an attractive substrate for the production of value-added products by fermentation processes, due to its large amounts, low cost and high degree of reduction. One of the most important usages of glycerol is its bioconversion through microbial fermentation to value-added materials like 1,3-propanediol and citric acid. There is a considerable industrial interest in 1,3-propanediol and citric acid production based on microbial fermentations, as it seems to be in competition with traditional technologies utilized for these products. In the present work, yields and concentrations of 1,3-propanediol and citric acid registered for different isolated strains are also described. Microbial bioconversion of glycerol represents a remarkable choice to add value to the biofuel production chain, allowing the biofuel industry to be more competitive. The current review presents certain ways for the bioconversion of crude glycerol into citric acid and 1,3-propanediol with high yields and concentrations achieved by using isolated microorganisms.

Differential effects of citric acid on cadmium uptake and accumulation between tall fescue and Kentucky bluegrass

Organic acids play an important role in cadmium availability, uptake, translocation, and detoxification. A sand culture experiment was designed to investigate the effects of citric acid on Cd uptake, translocation, and accumulation in tall fescue and Kentucky bluegrass. The results showed that two grass species presented different Cd chemical forms, organic acid components and amount in roots. The dormant Cd accumulated in roots of tall fescue was the pectate- and protein- integrated form, which contributed by 84.85%. However, in Kentucky bluegrass, the pectate- and protein- integrated Cd was only contributed by 35.78%, and the higher proportion of Cd form was the water soluble Cd-organic acid complexes. In tall fescue, citric acid dramatically enhanced 2.8 fold of Cd uptake, 3 fold of root Cd accumulation, and 2.3 fold of shoot Cd accumulation. In Kentucky bluegrass, citric acid promoted Cd accumulation in roots, but significantly decreased Cd accumulation in shoots. These results suggested that the enhancements of citric acid on Cd uptake, translocation, and accumulation in tall fescue was associated with its promotion of organic acids and the water soluble Cd-organic acid complexes in roots.

Enhanced effect of HAH on citric acid-chelated Fe(II)-catalyzed percarbonate for trichloroethene degradation

This work demonstrates the impact of hydroxylamine hydrochloride (HAH) addition on enhancing the degradation of trichloroethene (TCE) by the citric acid (CA)-chelated Fe(II)-catalyzed percarbonate (SPC) system. The results of a series of batch-reactor experiments show that TCE removal with HAH addition was increased from approximately 57 to 79% for a CA concentration of 0.1 mM and from 89 to 99.6% for a 0.5 mM concentration. Free-radical probe tests elucidated the existence of hydroxyl radical (HO^•) and superoxide anion radical (O₂^•-) in both CA/Fe(II)/SPC and HAH/CA/Fe(II)/SPC systems. However, higher removal rates of radical probe compounds were observed in the HAH/CA/Fe(II)/SPC system, indicating that HAH addition enhanced the generation of both free radicals. In addition, increased contribution of O₂^•- in the HAH/CA/Fe(II)/SPC system compared to the CA/Fe(II)/SPC system was verified by free-radical scavengers tests. Complete TCE dechlorination was confirmed based on the total mass balance of the released Cl^- species. Lower concentrations of formic acid were produced in the later stages of the reaction for the HAH/CA/Fe(II)/SPC system, suggesting that HAH addition favors complete TCE mineralization. Studies of the impact of selected groundwater matrix constituents indicate that TCE removal in the HAH/CA/Fe(II)/SPC system is slightly affected by initial solution pH, with higher removal rates under acidic and near neutral conditions. Although HCO₃^- was observed to have an adverse impact on TCE removal for the HAH/CA/Fe(II)/SPC system, the addition of HAH reduced its inhibitory effect compared to the CA/Fe(II)/SPC system. Finally, TCE removal in actual groundwater was much significant with the addition of HAH to the CA/Fe(II)/SPC system. The study results indicate that HAH amendment has potential to enhance effective remediation of TCE-contaminated groundwater.

Microwave irradiation and citric acid assisted seed germination and phytoextraction of nickel (Ni) by Brassica napus L.: morpho-physiological and biochemical alterations under Ni stress

The complex bio-geochemistry of soil allows pollutant to persist for a longer period of time which further decreased the fertility and natural composition of land. Nickel, an inorganic pollutant, coming from a wide range of industrial and manufacturing units possesses serious threat to soil degradation and crop productivity around the world. The present study was carried to evaluate the combined role of microwave irradiation (MR) and citric acid (CA) on the phytoextraction potential of Brassica napus L. under Ni stress. An initial seed germination test was conducted to select effective time scale of MR exposure. Highest seed germination was observed at exposure of 2.45 GHz frequency for 30 s. Healthy seeds of B. napus L. genotype Faisal Canola (RBN-03060) treated with MR at 2.45 GHz for 30 s were sown in plastic pots filled with 5 kg of soil. Nickel and CA applied exogenously in solution form with different combinations to both MR-treated and untreated B. napus plants. The MR-treated plants showed higher growth, biomass, photosynthetic pigments (Chl a, b, total, and carotenoids) and activities of antioxidant enzymes (SOD, POD, APX, CAT) as compared to untreated plants who showed higher reactive oxygen species (MDA, H₂O₂) and electrolyte leakage. Increasing Ni concentration significantly decreased the physiological and biochemical attributes of B. napus both in MR-treated and untreated plants. The addition of CA alleviated Ni-induced toxic effects in both MR-treated and untreated plants by improving antioxidant defense system. The degree of Ni stress mitigation was higher in MR-treated plants. The Ni concentration was higher in root, stem, and leaves of MR-treated plants under CA application as compared to untreated plants. The present study concluded that seeds treated with MR before sowing showed higher accumulation and concentration of Ni from soil, and this phenomenon boosted with the application of CA.

Development, evaluation and optimization of superparamagnetite nanoparticles prepared by co-precipitation method

Magnetic nanoparticles (MNPs) are of high interest due to their application in medical fields, in particular for theranostics. Specific properties required for such particles include high magnetization, appropriate size and stability. Biocompatible magnetically soft magnetite particles (Fe₃O₄) have been investigated for biological purposes. The intrinsic instability of these nanoparticles and their susceptibility to the oxidization in air, are limitations for their applications. Various methods have been described for synthesis of these nanoparticles among which co-precipitation method is widely experimented. In order to illustrate the synthesis of MNPs elaborately, the effect of different factors on particle formation were studied. The particles morphology, stability, paramagnetic effect, chemical structure and cytotoxicity were evaluated. Particles of 58 and 60 nm obtained by oleic acid coated (OMNPs) and citric acid coated (CMNPs) magnetite nanoparticles respectively. Transmission electron microscopy images exhibited the real sizes are 15 and 13 nm. Magnetic saturations of these nanoparticles were 72 and 68 emu/g which is suitable for medical applications. Both OMNPs and CMNPs were non-toxic to the SK-Br-3 and MCF-7 cells in the concentrations of <2.5 μg/mL. Since these particles exhibit relatively high magnetic saturation, low dose of such material would be required; therefore, these NPs seem to be suitable for theranostics.

Application of methanol and sweet potato vine hydrolysate as enhancers of citric acid production by Aspergillus niger

Background

Agricultural waste is as an alternative low-cost carbon source or beneficial additives which catch most people’s eyes. In addition, methanol and sweet potato vine hydrolysate (SVH) have been reported as the efficient enhancers of fermentation according to some reports. The objective of the present study was to confirm SVH as an efficient additive in CA production and explore the synergistic effects of methanol and SVH in fermentation reactions.

Results

The optimal fermentation conditions resulted in a maximum citric acid concentration of 3.729 g/L. The final citric acid concentration under the optimized conditions was increased by 3.6-fold over the original conditions, 0.49-fold over the optimized conditions without methanol, and 1.8-fold over the optimized conditions in the absence of SVH. Kinetic analysis showed that Q_p, Y_p/s, and Y_x/s in the optimized systems were significantly improved compared with those obtained in the absence of methanol or SVH. Further, scanning electron microscopy (SEM) revealed that methanol stress promoted the formation of conidiophores, while SVH could neutralize the effect and prolong Aspergillus niger vegetative growth. Cell viability analysis also showed that SVH might eliminate the harmful effects of methanol and enhance cell membrane integrity.

Conclusions

SVH was a superior additive for organic acid fermentation, and the combination of methanol and SVH displayed a significant synergistic effect. The research provides a preliminary theoretical basis for SVH practical application in the fermentation industry.

Evaluation of synergistic effect of Chlorella vulgaris and citric acid on oxidative stability of virgin olive oil

Green microalga Chlorella (Chlorella vulgaris) powder was employed as a natural antioxidant in virgin olive oil and its antioxidant activity was compared with those of β-carotene and α-tocopherol during 16 days of accelerated storage. Furthermore, the synergistic effects of Chlorella and citric acid were investigated. The primary, secondary, and total oxidation products of Chlorella samples (with and without citric acid) were lower than those of the control samples. Induction period of Chlorella samples were significantly higher than those of the control, β-carotene, and α-tocopherol samples. Furthermore, carotenoid and chlorophyll contents of Chlorella samples were significantly higher than those of the control samples. These pigments can delay the oxidation process. Using Chlorella and citric acid in combination with each other showed no synergistic effect against the oxidation of virgin olive oil. In conclusion, Chlorella can be affirmed as a natural antioxidant, which extends the shelf life of virgin olive oil.

Citric acid enhanced the antioxidant defense system and chromium uptake by Lemna minor L. grown in hydroponics under Cr stress

Phytoextraction is a cost-effective and eco-friendly technique for the removal of pollutants, mainly heavy metal(loids) especially from polluted water and metal-contaminated soils. The phytoextraction of heavy metals is, in general, limited due to the low availability of heavy metals in the growth medium. Organic chelators can help to improve the phytoextraction by increasing metal mobility and solubility in the growth medium. The present research was carried out to examine the possibility of citric acid (CA) in improving chromium (Cr) phytoextraction by Lemna minor (duckweed). For this purpose, healthy plants were collected from nearby marsh and grown in hydroponics under controlled conditions. Initial metal contents of both marsh water and plant were measured along with physico-chemical properties of the marsh water. Different concentrations of Cr and CA were applied in the hydroponics in different combinations after defined intervals. Continuous aeration was supplied and pH maintained at 6.5 ± 0.1. Results showed that increasing concentration of Cr significantly decreased the plant biomass, photosynthetic pigments, leaf area, and antioxidant enzyme activities (like catalase, ascorbate peroxidase, superoxide dismutase, peroxidase). Furthermore, Cr stress increased the Cr concentrations, electrolyte leakage, hydrogen peroxide, and malondialdehyde contents in plants. The addition of CA alleviated the Cr-induced toxicity in plants and further enhanced the Cr uptake and its accumulation in L. minor. The addition of CA enhanced the Cr concentration in L. minor by 6.10, 26.5, 20.5, and 20.2% at 0, 10, 100, and 200 μM Cr treatments, respectively, compared to the respective Cr treatments without CA. Overall, the results of the present study showed that CA addition may enhance the Cr accumulation and tolerance in L. minor by enhancing the plant growth and activities of antioxidant enzymes.

Effect of crosslinking on the physical and chemical properties of β-lactoglobulin (Blg) microgels

HYPOTHESIS

Microgels assembled from the protein β-lactoglobulin are colloidal structures with potential applications in food materials. Modifying the internal crosslinking within these microgels using enzymatic or chemical treatments should affect dissolution, swelling, and viscous attributes under strongly solvating conditions.

EXPERIMENTS

Microgels were treated with citric acid, glutaraldehyde and transglutaminase to induce cross-linking or with tris(2-carboxyethyl)phosphine to reduce disulfide linkages. Change in hydrodynamic particle size due to acidic pH, alkaline pH, ionic strength, osmolyte concentration, ethanol, urea, sodium dodecyl sulfate, and reducing agents was evaluated by light scattering measurements. Changes in microgel nanomechanical properties were evaluated via force spectroscopic measurements in water.

FINDINGS

Average microgel size increased ∼20% in alkaline pH and with ethanol contents above 10%, and decreased ∼20% with sucrose contents above 10%. Cross-linking by glutaraldehyde and transglutaminase prevented size increases in alkaline pH. Microgel plasticity and elastic modulus were unaffected by treatments. Microgels treated with glutaraldehyde were found to have much greater stability to urea, sodium dodecyl sulfate, and reducing agents when compared to other samples. Even without cross-linking, microgels remained stable against precipitation and dissolution over a wide range conditions, indicating their broad utility as colloidal stabilizers, texture modifiers or controlled release agents in food or other applications.

Comparative Analyses of Smear Layer Removal Using Four Different Irrigant Solutions in the Primary Root Canals - A Scanning Electron Microscopic Study

INTRODUCTION

A clinician's path to success is a clean root canal system with three dimensional seal. Mechanical instrumentation of root canals alone leaves behind a smear layer covering the dentinal walls. Instrumentation must always be supported by use of irrigants which are considered as an essential prerequisite for root canal debridement.

AIM

The aim of this in vitro study was to compare the efficacy of four irrigating solutions in removing the smear layer in primary root canals after hand instrumentation.

MATERIALS AND METHODS

A total number of 40 human primary incisors were decoronated and split longitudinally. The specimens were divided randomly into four groups (n=10): Group I: 5.25% Sodium Hypochloride (NaOCl), Group II: 6% citric acid solution, Group III: smear clear and Group IV: 0.2% chitosan. Scanning electron microscopic analysis was performed to assess the presence or absence of smear layer at the coronal, middle and the apical portion of each canal. The data was analysed using Stastical Package For Social Sciences (SPSS) version 19.0 Armonk, NY IBM Corp soft ware.

RESULTS

The pictures from the scanning electron microscopy showed that Group II exhibited better efficacy in removing smear layer without altering the normal dentinal structures with lowest mean scores (p<0.001) followed by Group III, Group IV and Group I. The presence of debris was more evident in the apical third rather than in the middle and the coronal part of the root canal.

CONCLUSION

A 6% citric acid removed the smear layer more efficiently than other test irrigants in primary root canals.

Substrates and oxygen dependent citric acid production by Yarrowia lipolytica: insights through transcriptome and fluxome analyses

BACKGROUND

Unlike the well-studied backer yeast where catabolite repression represents a burden for mixed substrate fermentation, Yarrowia lipolytica, an oleaginous yeast, is recognized for its potential to produce single cell oils and citric acid from different feedstocks. These versatilities of Y. lipolytica with regards to substrate utilization make it an attractive host for biorefinery application. However, to develop a commercial process for the production of citric acid by Y. lipolytica, it is necessary to better understand the primary metabolism and its regulation, especially for growth on mixed substrate.

RESULTS

Controlling the dissolved oxygen concentration (pO2) in Y. lipolytica cultures enhanced citric acid production significantly in cultures grown on glucose in mono- or dual substrate fermentations, whereas with glycerol as mono-substrate no significant effect of pO2 was found on citrate production. Growth on mixed substrate with glucose and glycerol revealed a relative preference of glycerol utilization by Y. lipolytica. Under optimized conditions with pO2 control, the citric acid titer on glucose in mono- or in dual substrate cultures was 55 and 50 g/L (with productivity of 0.6 g/L*h in both cultures), respectively, compared to a maximum of 18 g/L (0.2 g/L*h) with glycerol in monosubstrate culture. Additionally, in dual substrate fermentation, glycerol limitation was found to trigger citrate consumption despite the presence of enough glucose in pO2-limited culture. The metabolic behavior of this yeast on different substrates was investigated at transcriptomic and 13C-based fluxomics levels.

CONCLUSION

Upregulation of most of the genes of the pentose phosphate pathway was found in cultures with highest citrate production with glucose in mono- or in dual substrate fermentation with pO2 control. The activation of the glyoxylate cycle in the oxygen limited cultures and the imbalance caused by glycerol limitation might be the reason for the re-consumption of citrate in dual substrate fermentations. This study provides interesting targets for metabolic engineering of this industrial yeast.

Dissolved organic matter affects the bioaccumulation of copper and lead in Chlorella pyrenoidosa: A case of long-term exposure

This study evaluated the impact of dissolved organic matter (DOM) of varying molecule weights (MWs) on long-term exposure to Cu and Pb in Chlorella pyrenoidosa. Citric acid, fulvic acid, and humic acid, in the order of increasing MWs, were selected to represent DOM. The results showed that DOM with larger MWs had stronger inhibitory effects on the bioavailability of Cu to algae. However, the biosorption isotherm of Pb in the presence of DOM was different: as Pb equilibrium concentration increased, the biosorption capacity increased sharply to a maximum, then decreased. The maximum values ranged between 0.186 and 0.398 mmol g^-1, as the solution DOM concentration and MW changed, exhibiting a stoichiometric relationship between DOM, Pb and algae. The ternary complex of Pb-DOM-alga formed in a limited Pb concentration range, and increased the percentage of internalized Pb. This research helps to understand the role of DOM in metal uptake in phytoplankton.

Unusual Root Canal Irrigation Solutions

Microorganisms and their by-products play a critical role in pulp and periradicular pathosis. Therefore, one of the main purposes of root canal treatment is disinfection of the entire system of the canal. This aim may be obtained using mechanical preparation, chemical irrigation, and temporary medication of the canal. For this purpose, various irrigation solutions have been advocated. Common root canal irrigants, such as sodium hypochlorite, chlorhexidine, and a mixture of tetracycline, acid, and detergent have been extensively reviewed. The aim of this review was to address the less common newer root canal irrigation solutions, such as citric acid, maleic acid, electrochemically activated water, green tea, ozonated water, and SmearClear.

Experimental design data for the biosynthesis of citric acid using Central Composite Design method

In the present investigation, we report that statistical design and optimization of significant variables for the microbial production of citric acid from sucrose in presence of filamentous fungi A. niger NCIM 705. Various combinations of experiments were designed with Central Composite Design (CCD) of Response Surface Methodology (RSM) for the production of citric acid as a function of six variables. The variables are; initial sucrose concentration, initial pH of medium, fermentation temperature, incubation time, stirrer rotational speed, and oxygen flow rate. From experimental data, a statistical model for this process has been developed. The optimum conditions reported in the present article are initial concentration of sucrose of 163.6 g/L, initial pH of medium 5.26, stirrer rotational speed of 247.78 rpm, incubation time of 8.18 days, fermentation temperature of 30.06 °C and flow rate of oxygen of 1.35 lpm. Under optimum conditions the predicted maximum citric acid is 86.42 g/L. The experimental validation carried out under the optimal values and reported citric acid to be 82.0 g/L. The model is able to represent the experimental data and the agreement between the model and experimental data is good.

Overexpression of a C4-dicarboxylate transporter is the key for rerouting citric acid to C4-dicarboxylic acid production in Aspergillus carbonarius

Background

C₄-dicarboxylic acids, including malic acid, fumaric acid and succinic acid, are valuable organic acids that can be produced and secreted by a number of microorganisms. Previous studies on organic acid production by Aspergillus carbonarius, which is capable of producing high amounts of citric acid from varieties carbon sources, have revealed its potential as a fungal cell factory. Earlier attempts to reroute citric acid production into C₄-dicarboxylic acids have been with limited success.

Results

In this study, a glucose oxidase deficient strain of A. carbonarius was used as the parental strain to overexpress a native C₄-dicarboxylate transporter and the gene frd encoding fumarate reductase from Trypanosoma brucei individually and in combination. Impacts of the introduced genetic modifications on organic acid production were investigated in a defined medium and in a hydrolysate of wheat straw containing high concentrations of glucose and xylose. In the defined medium, overexpression of the C₄-dicarboxylate transporter alone and in combination with the frd gene significantly increased the production of C₄-dicarboxylic acids and reduced the accumulation of citric acid, whereas expression of the frd gene alone did not result in any significant change of organic acid production profile. In the wheat straw hydrolysate after 9 days of cultivation, similar results were obtained as in the defined medium. High amounts of malic acid and succinic acid were produced by the same strains.

Conclusions

This study demonstrates that the key to change the citric acid production into production of C₄-dicarboxylic acids in A. carbonarius is the C₄-dicarboxylate transporter. Furthermore it shows that the C₄-dicarboxylic acid production by A. carbonarius can be further increased via metabolic engineering and also shows the potential of A. carbonarius to utilize lignocellulosic biomass as substrates for C₄-dicarboxylic acid production.

Production of added-value metabolites by Yarrowia lipolytica growing in olive mill wastewater-based media under aseptic and non-aseptic conditions

Yarrowia lipolytica ACA-YC 5033 was grown on glucose-based media in which high amounts of olive mill wastewaters (OMWs) had been added. Besides shake-flask aseptic cultures, trials were also performed in previously pasteurized media while batch bioreactor experiments were also done. Significant decolorization (∼58%) and remarkable removal of phenolic compounds (∼51% w/w) occurred, with the latter being amongst the highest ones reported in the international literature, as far as yeasts were concerned during their growth on phenol-containing media. In nitrogen-limited flask fermentations the microorganism produced maximum citric acid quantity ≈19.0 g/L [simultaneous yield of citric acid produced per unit of glucose consumed (Y_Cit/Glc)≈0.74 g/g]. Dry cell weight (DCW) values decreased at high phenol-containing media, but, on the other hand, the addition of OMWs induced reserve lipid accumulation. Maximum citric acid concentration achieved (≈52.0 g/L; Y_Cit/Glc≈0.64 g/g) occurred in OMW-based high sugar content media (initial glucose added at ≈80.0 g/L). The bioprocess was successfully simulated by a modified logistic growth equation. A satisfactory fitting on the experimental data occurred while the optimized parameter values were found to be similar to those experimentally measured. Finally, a non-aseptic (previously pasteurized) trial was performed and its comparison with the equivalent aseptic experiment revealed no significant differences. Yarrowia lipolytica hence can be considered as a satisfactory candidate for simultaneous OMWs bioremediation and the production of added-value compounds useful for the food industry.

Citric acid: emerging applications of key biotechnology industrial product

Owing to new biotechnological production units mostly located in China, global supply of citric acid in the course of the last two decades rose from less than 0.5 to more than 2 million tonnes becoming the single largest chemical obtained via biomass fermentation and the most widely employed organic acid. Critically reviewing selected research achievements and production trends, we identify the reasons for which this polycarboxylic acid will become a key chemical in the emerging bioeconomy.Graphical abstract

Citric acid application for denitrification process support in biofilm reactor

The study demonstrated that citric acid, as an organic carbon source, can improve denitrification in Anaerobic Sequencing Batch Biofilm Reactor (AnSBBR). The consumption rate of the organic substrate and the denitrification rate were lower during the period of the reactor's acclimatization (cycles 1-60; 71.5 mgCOD L^-1 h^-1 and 17.81 mgN L^-1 h^-1, respectively) than under the steady state conditions (cycles 61-180; 143.8 mgCOD L^-1 h^-1 and 24.38 mgN L^-1 h^-1). The biomass yield coefficient reached 0.04 ± 0.02 mgTSS· mgCOD_re^-1 (0.22 ± 0.09 mgTSS mgN_re^-1). Observations revealed the diversified microbiological ecology of the denitrifying bacteria. Citric acid was used mainly by bacteria representing the Trichoccocus genus, which represented above 40% of the sample during the first phase of the process (cycles 1-60). In the second phase (cycles 61-180) the microorganisms the genera that consumed the acetate and formate, as the result of citric acid decomposition were Propionibacterium (5.74%), Agrobacterium (5.23%), Flavobacterium (1.32%), Sphaerotilus (1.35%), Erysipelothrix (1.08%).

An accurate description of Aspergillus niger organic acid batch fermentation through dynamic metabolic modelling

BACKGROUND

Aspergillus niger fermentation has provided the chief source of industrial citric acid for over 50 years. Traditional strain development of this organism was achieved through random mutagenesis, but advances in genomics have enabled the development of genome-scale metabolic modelling that can be used to make predictive improvements in fermentation performance. The parent citric acid-producing strain of A. niger, ATCC 1015, has been described previously by a genome-scale metabolic model that encapsulates its response to ambient pH. Here, we report the development of a novel double optimisation modelling approach that generates time-dependent citric acid fermentation using dynamic flux balance analysis.

RESULTS

The output from this model shows a good match with empirical fermentation data. Our studies suggest that citric acid production commences upon a switch to phosphate-limited growth and this is validated by fitting to empirical data, which confirms the diauxic growth behaviour and the role of phosphate storage as polyphosphate.

CONCLUSIONS

The calibrated time-course model reflects observed metabolic events and generates reliable in silico data for industrially relevant fermentative time series, and for the behaviour of engineered strains suggesting that our approach can be used as a powerful tool for predictive metabolic engineering.

Determination of the Relative Effectiveness of Four Food Additives in Degrading Aflatoxin in Distillers Wet Grains and Condensed Distillers Solubles

The food additives sodium bisulfite, sodium hypochlorite, citric acid, and ammonium persulfate were evaluated for their effectiveness in degrading aflatoxin in samples of distillers wet grains (DWG) and condensed distillers solubles (CDS) obtained from an industrial ethanol plant. Aqueous food additive solutions, 0.5% by weight, were added to DWG or CDS at the level of 0.5 ml/g of sample, and the materials were heated at 90°C for 1 h. Sodium bisulfite was not effective in degrading aflatoxin in either DWG or CDS. Among the four food additives tested, sodium hypochlorite was the most effective. However, it bleached the substrate and left an off-odor. Citric acid and ammonium persulfate reduced aflatoxin levels by 31 to 51%. Citric acid is the most promising additive for degrading aflatoxin because it has been classified as generally recognized as safe by the U.S. Food and Drug Administration. Aflatoxin reduction was enhanced by increasing the citric acid addition level and prolonging the heating time. Reductions of 65 and 80% in DWG and CDS, respectively, were obtained by the addition of 2.5% (by weight) citric acid and heating at 90°C for 1 h. Aflatoxin levels in DWG and CDS were gradually reduced with prolonged heating at 90°C, even without the addition of food additives. Aflatoxin reductions of 53 and 73% were achieved in DWG and CDS as a result of heating at 90°C for 5 h.

Co-application of 6-ketone type brassinosteroid and metal chelator alleviates cadmium toxicity in B. juncea L

Plant growth regulator-assisted phytoremediation has been assessed as a novel strategy to improve phytoremediation potential of plants. In the present work, potential of castasterone, a plant growth regulator, combined with citric acid was explored for phytoremediation of cadmium in Brassica juncea seedlings. The seedlings were raised under controlled laboratory conditions for 7 days. Results revealed that 0.6 mM cadmium exposure induced toxicity in the seedlings, which was reflected through root growth inhibition, accumulation of hydrogen peroxide and malondialdehyde, and loss of cell viability. Pre-sowing treatment of castasterone supplemented with citric acid enhanced cadmium accumulation in the roots (from 752 μg/g DW to 1192 μg/g DW) and shoots (from 88 μg/g DW to 311 μg/g DW) and also improved root length, shoot length, fresh weight, and dry weight of seedlings by 81, 17, 39, and 35 %, respectively. The co-application reduced malondialdehyde accumulation by 39 % and reduced oxidative stress by enhancing the activities of antioxidant enzymes (superoxide dismutase, guaiacol peroxidase, catalase, ascorbate peroxidase, dehydroascorbate, glutathione reductase, glutathione peroxidase, glutathione-S-transferase, polyphenol oxidase), maximum enhancement (82 %) being in polyphenol oxidase. Similarly, the contents of water- and lipid-soluble antioxidants were found to increase by 31 and 4 %, respectively. Confocal microscopy revealed enhanced content of NO. Results suggested that binary combination of castasterone and citric acid is helpful in improving cadmium accumulation and ameliorating metal toxicity in B. juncea seedlings.

Click chemistry improved wet adhesion strength of mussel-inspired citrate-based antimicrobial bioadhesives

For the first time, a convenient copper-catalyzed azide-alkyne cycloaddition (CuAAC, click chemistry) was successfully introduced into injectable citrate-based mussel-inspired bioadhesives (iCMBAs, iCs) to improve both cohesive and wet adhesive strengths and elongate the degradation time, providing numerous advantages in surgical applications. The major challenge in developing such adhesives was the mutual inhibition effect between the oxidant used for crosslinking catechol groups and the Cu(II) reductant used for CuAAC, which was successfully minimized by adding a biocompatible buffering agent typically used in cell culture, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), as a copper chelating agent. Among the investigated formulations, the highest adhesion strength achieved (223.11 ± 15.94 kPa) was around 13 times higher than that of a commercially available fibrin glue (15.4 ± 2.8 kPa). In addition, dual-crosslinked (i.e. click crosslinking and mussel-inspired crosslinking) iCMBAs still preserved considerable antibacterial and antifungal capabilities that are beneficial for the bioadhesives used as hemostatic adhesives or sealants for wound management.

Fermentative production of high titer citric acid from corn stover feedstock after dry dilute acid pretreatment and biodetoxification

The aim of this work is to study the citric acid fermentation by a robust strain Aspergillus niger SIIM M288 using corn stover feedstock after dry dilute sulfuric acid pretreatment and biodetoxification. Citric acid at 100.04g/L with the yield of 94.11% was obtained, which are comparable to the starch or sucrose based citric acid fermentation. No free wastewater was generated in the overall process from the pretreatment to citric acid fermentation. Abundant divalent metal ions as well as high titer of potassium, phosphate, and nitrogen were found in corn stover hydrolysate. Further addition of extra nutrients showed no impact on increasing citric acid formation except minimum nitrogen source was required. Various fermentation parameters were tested and only minimum regulation was required during the fermentation. This study provided a biorefining process for citric acid fermentation from lignocellulose feedstock with the maximum citric acid titer and yield.