Search results for "CITRIC ACID"

Speciation of Low Molecular Weight Carboxylic Ligands in Natural Fluids: Protonation Constants and Association with Major Components of Seawater of O…

1999

Abstract The interaction of oxydiacetate and citrate with the major components of seawater has been studied potentiometrically, at 25°C, in an artificial seawater (containing Na+, K+, Ca2+, Mg2+, Cl− and SO42−) at different salinities (5–45‰). Apparent protonation constants were calculated, from potentiometric data, and estimated, using an appropriate complex formation model. Formation constants of complexes formed by oxydiacetate and citrate and the cation of seawater (the inorganic content of seawater being considered as a single 1 : 1 salt) were determined. The single salt approximation for the major inorganic components of seawater, which is a good tool in estimating the mean strength o…

Mathematic predictive models for calculating copper, iron and zinc dialysability in infant formulas

2001

Differences in the dialysability of a mineral element from infant formulas of the same type were detected in a previous study. As these may be due to the effects that different levels of the components of the formulas could have on dialysability, we attempted to establish mathematical models to predict the dialysability of Cu, Fe and Zn from infant formulas according to their ascorbic, citric, or selected amino acid contents. A simple linear regression was applied between the ascorbic acid, citric acid and amino acid contents and the Cu, Fe and Zn dialysability of 18 powdered infant formulas of different types. Significant correlations (P<0.05) were obtained between the dialysability of Fe …

l-Valine biosynthesis during batch and fed-batch cultivations of Corynebacterium glutamicum: Relationship between changes in bacterial growth rate an…

2007

Abstract A transition in the bacterial growth rate to below maximum was found to be an optimum parameter of cellular physiology to increase the activity of acetohydroxy acid synthase, a regulatory enzyme in l -valine synthesis, and amino acid overproduction by Corynebacterium glutamicum ATCC 13032 recombinants under batch and fed-batch cultivation conditions. An increase in l -valine synthesis under transient situations when cellular growth rate was downregulated was correlated to a decrease in the activity of aconitase, a key enzyme in the tricarboxylic acid cycle (TCA) of C. glutamicum , and, in contrast, to an increase in the activity of glucose-6-phosphate dehydrogenase, a key enzyme in…

Metabolomics approach to studying minimally processed peach (Prunus persica) fruit

2012

Fresh-cut fruit products for both retail and food service applications have increasingly appeared in the market place in recent years. Among different fruit types, peaches can be used and are highly appreciated as fresh-cut product although their commercial success is limited due to their short shelf-life and the quick onset of wounding-related physiological reactions. In this work we analyzed the technological and physiological changes induced by fresh-cut preparation in three different types of peach cultivars: 'Fayette' (melting), 'Wilhelmina' (non-melting) and 'Ghiaccio3' (stony hard). We performed a metabolite targeting profiling to focus on the changes in organic acid levels, importan…

Citrate Sensing by the C 4 -Dicarboxylate/Citrate Sensor Kinase DcuS of Escherichia coli : Binding Site and Conversion of DcuS to a C 4 -Dicarboxylat…

2007

ABSTRACT The histidine protein kinase DcuS of Escherichia coli senses C 4 -dicarboxylates and citrate by a periplasmic domain. The closely related sensor kinase CitA binds citrate, but no C 4 -dicarboxylates, by a homologous periplasmic domain. CitA is known to bind the three carboxylate and the hydroxyl groups of citrate by sites C1, C2, C3, and H. DcuS requires the same sites for C 4 -dicarboxylate sensing, but only C2 and C3 are highly conserved. It is shown here that sensing of citrate by DcuS required the same sites. Binding of citrate to DcuS, therefore, was similar to binding of C 4 -dicarboxylates but different from that of citrate binding in CitA. DcuS could be converted to a C 4 -…

Citric Acid Based Carbon Dots with Amine Type Stabilizers: pH-Specific Luminescence and Quantum Yield Characteristics

2020

We report the synthesis and spectroscopic characteristics of two different sets of carbon dots (CDs) formed by hydrothermal reaction between citric acid and polyethylenimine (PEI) or 2,3-diaminopyridine (DAP). Although the formation of amide-based species and the presence of citrazinic acid type derivates assumed to be responsible for a blue emission is confirmed for both CDs by elemental analysis, infrared spectroscopy, and mass spectrometry, a higher abundance of sp2-hybridized nitrogen is observed for DAP-based CDs, which causes a red-shift of the n-π* absorption band relative to the one of PEI-based CDs. These CD systems possess high photoluminescence quantum yields (QY) of ∼40% and ∼48…

Inhibition of Plant Lactate Dehydrogenase Isoenzymes by Benzoic Acid and Cinnamic Acid Derivatives

1976

Summary Several phenolic compounds such as derivatives of benzoic and cinnamic acid were investigated with respect to their inhibitory effect on potato tuber lactate dehydrogenase isoenzymes. Ki values were determined and it was found that they were in the range of 10−2 M for several benzoic acid derivatives while they were in the range of 10−5 M for several hydroxylated cinnamic acid derivatives such as 3,4-dihydroxy cinnamic acid, p(m)nitrocinnamic acid, and 7,8-dihydroxy-4-methyl coumarin as well as kynurenic acid. Also coumaric acid derivatives revealed a very strong inhibition: The K1 values for coumarin and p-coumaric acid were in the range of 10−4 M. The inhibition by all aromatic co…

Effects of Citric Acid on Human Gingival Epithelium

1987

Determination of Homovanillic Acid in Human Plasma Using HPLC with Electrochemical Detection and Automated Solid Phase Extraction

1993

Abstract An isocratic HPLC method with electrochemical detection for the quantification of homovanillic acid (HVA) is described. The method included automated solid phase extraction on C-18-reversed phase material, followed by separation on a 3-μm Nucleosil 100 C18 column (250 mm × 4.6 mm I. D.) with a 100 mM citric acid solution (pH 6.6) containing 4% acetonitrile (v/v) as eluent at a flow rate of 0.6 ml/min. Isovanillinic acid served as internal standard. Extractability of both analytes was ca. 80 %. After extraction of 1 ml of plasma, coefficients of variation of replicate analyses were below 10 % in the naturally occuring concentration range.

Effect of proteins, phytates, ascorbic acid and citric acid on dialysability of calcium, iron, zinc and copper in soy-based infant formulas.

2000

The possible effect of ascorbic acid, citric acid, proteins and phytate on dialysability of Ca, Fe, Zn and Cu in soy-based infant formulas is studied, taking dialysability as a measure of the amount of element available for absorption. Different dialysis percentages for similar element contents in different formulas are found. A regression analysis was applied between Ca, Zn, Cu and Fe dialysis percentages and soy-based formula components to estimate the possible influence of the latter on the dialysability of the elements. Significant correlations were found between citric acid contents and dialysability of Zn and Fe. No correlations were found between protein, ascorbic acid and phytic aci…