Optimization of soy protein isolate, microbial transglutaminase and glucono-δ-lactone in gluten-free rice noodles

BACKGROUND

Rice flour does not contain gluten and lacks cohesion and extensibility, which is responsible for the poor texture of rice noodles. Different technologies have been used to mitigate this challenge, including hydrothermal treatments of rice flour, direct addition of protein in noodles, use of additives such as hydrocolloids and alginates, and microbial transglutaminase (MTG). Recently, the inclusion of soy protein isolate (SPI), MTG, and glucono-δ-lactone (GDL) in the rice noodles system yielded rice noodles with improved texture and more compact microstructure, hence the need to optimize the addition of SPI, MTG, and GDL to make quality rice noodles.

RESULTS

Numerical optimization showed that rice noodles prepared with SPI, 68.32 (g kg^-1 of rice flour), MTG, 5.06 (g kg^-1 of rice flour) and GDL, 5.0 (g kg^-1 of rice flour) gave the best response variables; hardness (53.19 N), springiness (0.76), chewiness (20.28 J), tensile strength (60.35 kPa), and cooking time (5.15 min). The pH, sensory, and microstructure results showed that the optimized rice noodles had a more compact microstructure with fewer hollows, optimum pH for MTG action, and overall sensory panelists also showed the highest preference for the optimized formulation, compared to other samples selected from the numerical optimization and desirability tests.

CONCLUSION

Optimization of the levels of SPI, MTG, and GDL yielded quality noodles with improved textural, mechanical, sensory, and microstructural properties. This was partly due to the favourable pH value of the optimized noodles that provided the most suitable conditions for MTG crosslinking and balanced electrostatic interaction of proteins. © 2020 Society of Chemical Industry.

A simple enzymatic assay for the quantification of C1-specific cellulose oxidation by lytic polysaccharide monooxygenases

OBJECTIVE

The development of an enzymatic assay for the specific quantification of the C1-oxidation product, i.e. gluconic acid of cellulose active lytic polysaccharide monooxygenases (LPMOs).

RESULTS

In combination with a β-glucosidase, the spectrophotometrical assay can reliably quantify the specific C1- oxidation product of LPMOs acting on cellulose. It is applicable for a pure cellulose model substrate as well as lignocellulosic biomass. The enzymatic assay compares well with the quantification performed by HPAEC-PAD. In addition, we show that simple boiling is not sufficient to inactivate LPMOs and we suggest to apply a metal chelator in addition to boiling or to drastically increase pH for proper inactivation.

CONCLUSIONS

We conclude that the versatility of this simple enzymatic assay makes it useful in a wide range of experiments in basic and applied LPMO research and without the need for expensive instrumentation, e.g. HPAEC-PAD.

The Molting Biomarker Molecule Exists as 2-Acetamido-2-deoxy-gluconic Acid in Urine of Blue Crabs and Helmet Crabs

N-Acetyl-d-glucosamino-1,5-lactone 1 has been reported as a candidate component of the sex pheromone mixture of female blue crabs, Callinectes sapidus, since it is present in the urine of reproductive females and males detect it. Theoretically, 1 can convert to a 1,4-lactone isomer 2 or to the corresponding carboxylic acid, 2-acetamido-2-deoxygluconic acid 3 by hydrolysis in aqueous solution. In this study, we examined the biologically relevant state of equilibrium mixture of 1, 2, and 3 in crab urine using ESI-MS and NMR analyses. The ESI-MS analysis showed that the dominant form of solubilized synthetic 1 is lactone 1 and/or 2, immediately after solubilization in deuterated water, seawater, and phosphate buffer and gradually changing to carboxylic acid 3 which becomes most predominant in phosphate buffer. The NMR analysis showed that synthetic 1 converts to other forms in deuterated water and seawater, and reaches an equilibrium mixture of at least three forms within 24 h. In contrast, 1 converts to a single state of another form in deuterated water with 35 mm phosphate buffer pH 7.6 within 24 h, which is identical to the state in urine with or without phosphate buffer. Thus, we conclude that the molting biomarker sensed by male crabs is 3.

Terahertz time-domain spectroscopy and quantitative analysis of metal gluconates

A series of metal gluconates (Na(+), K(+), Mg(2+), Ca(2+), Fe(2+), Cu(2+), and Zn(2+)) were investigated by terahertz (THz) time-domain spectroscopy. The absorption coefficients and refractive indices of the samples were obtained in the frequency range of 0.5-2.6 THz. The gluconates showed distinct THz characteristic fingerprints, and the dissimilarities reflect their different structures, hydrogen-bond networks, and molecular interactions. In addition, some common features were observed among these gluconates, and the similarities probably come from the similar carbohydrate anion group. The X-ray powder diffraction measurements of these metal gluconates were performed, and the copper(II) gluconate was found to be amorphous, corresponding to the monotonic increase feature in the THz absorption spectrum. The results suggest that THz spectroscopy is sensitive to molecular structure and physical form. Binary and ternary mixtures of different gluconates were quantitatively analyzed based on the Beer-Lambert law. A chemical map of a tablet containing calcium D-gluconate monohydrate and α-lactose in the polyethylene host was obtained by THz imaging. The study shows that THz technology is a useful tool in pharmaceutical research and quality control applications.

Root metabolic response of rice (Oryza sativa L.) genotypes with contrasting tolerance to zinc deficiency and bicarbonate excess

Plants are routinely subjected to multiple environmental stresses that constrain growth. Zinc (Zn) deficiency and high bicarbonate are two examples that co-occur in many soils used for rice production. Here, the utility of metabolomics in diagnosing the effect of each stress alone and in combination on rice root function is demonstrated, with potential stress tolerance indicators identified through the use of contrasting genotypes. Responses to the dual stress of combined Zn deficiency and bicarbonate excess included greater root solute leakage, reduced dry matter production, lower monosaccharide accumulation and increased concentrations of hydrogen peroxide, phenolics, peroxidase and N-rich metabolites in roots. Both hydrogen peroxide concentration and root solute leakage were correlated with higher levels of citrate, allantoin and stigmasterol. Zn stress resulted in lower levels of the tricarboxylic acid (TCA) cycle intermediate succinate and the aromatic amino acid tyrosine. Bicarbonate stress reduced shoot iron (Fe) concentrations, which was reflected by lower Fe-dependent ascorbate peroxidase activity. Bicarbonate stress also favoured the accumulation of the TCA cycle intermediates malate, fumarate and succinate, along with the non-polar amino acid tyrosine. Genotypic differentiation revealed constitutively higher levels of D-gluconate, 2-oxoglutarate and two unidentified compounds in the Zn-efficient line RIL46 than the Zn-inefficient cultivar IR74, suggesting a possible role for these metabolites in overcoming oxidative stress or improving metal re-distribution.

Determination of vitamin B6 by means of differential spectrophotometry in pharmaceutical preparations in the presence of magnesium compounds

The content of pyridoxine hydrochloride in two-component pharmaceutical preparations containing various magnesium compounds was examined. The UV differentiation spectrophotometry was devised and compared with the reference method of high performance liquid chromatography (HPLC). The analysis of the absorbance spectra (A) and its first (D1) and second (D2) derivatives made it possible to establish the appropriate analytical wavelengths (A: 290 nm; D1: 302 nm; D2: 308 nm). It was proved that spectrum differentiation significantly corrects errors resulting from overlapping background especially when the magnesium hydroaspartate, lactate or magnesium lactogluconate is present together with vitamin B6.

A new amperometric bienzymatic biosensor based on biocomposites for the determination of gluconic acid in wines

A new amperometric bienzymatic biosensor for gluconic acid based on the coimmobilization of gluconokinase (EC 2.7.1.12) and phosphogluconate dehydrogenase (EC 1.1.1.44) by polysulfone membrane entrapment onto the surface of a graphite-epoxy composite is reported. This biosensor represents an alternative to gluconate dehydrogenase (EC 1.1.99.3) based methods, which is no longer commercially available. Measurements were done at an applied potential of +0.800 V, room temperature and phosphate buffer pH 7.50; obtaining a linear response range for gluconic acid extended from 7.0 × 10(-6) to 2.5 × 10(-4)M. Constructed biosensors showed good reproducibility for calibrations using different electrodes (RSD of 1.74%). Finally, biosensor was applied to real wine samples, and the results obtained were validated by comparison with those provided by a reference laboratory. Good correlation was found when the biosensor results were plotted vs. the reference values (slope=1.03 ± 0.04, intercept=0.01 ± 0.02, r(2)=0.995).

Use of a Schizosaccharomyces pombe mutant to reduce the content in gluconic acid of must obtained from rotten grapes

Schizosaccharomyces pombe YGS-5 and Saccharomyces cerevisiae G1 strains were used in order to develop an effective method for reducing the gluconic acid content of musts without altering the development of alcoholic fermentation or detracting from quality in the resulting wines. The best results in synthetic media were obtained by using a temperature of 24 degrees C and a sulfur dioxide rate below 100 mg/L under semiaerobic conditions. Sequential inoculation of the musts with YGS-5 first and fermentative G1 yeasts then reduced their gluconic acid content by 85% within 43 h; by contrast, simultaneous inoculation with YGS-5 and G1 provided a reduction of only 40%. The wines with the best sensory and analytical properties were obtained by sequentially inoculating the musts with YGS-5 and, once gluconic acid was removed, G1. The wine obtained by sequential inoculation without removing YGS-5 was that exhibiting the highest odorant activity value (OAV) for the volatile compounds in the floral odor series. A protocol for treating musts containing gluconic acid was developed and tested at the pilot plant scale. The treatment reduced the gluconic acid content by 70% within 46 h with no adverse effect on the analytical or sensory quality of the resulting wines.

Integrated electrochemical gluconic acid biosensor based on self-assembled monolayer-modified gold electrodes. Application to the analysis of gluconic acid in musts and wines

An integrated amperometric gluconic acid biosensor constructed using a gold electrode (AuE) modified with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA) on which gluconate dehydrogenase (GADH, 0.84 U) and the mediator tetrathiafulvalene (TTF, 1.5 micromol) were coimmobilized by covering the electrode surface with a dialysis membrane is reported. The working conditions selected were Eapp=+0.15 V and 25+/-1 degrees C. The useful lifetime of one single TTF-GADH-MPA-AuE was surprisingly long. After 53 days of continuous use, the biosensor exhibited 86% of the original sensitivity. A linear calibration plot was obtained for gluconic acid over the 6.0x10(-7) to 2.0x10(-5) M concentration range, with a limit of detection of 1.9x10(-7) M. The effect of potential interferents (glucose, fructose, galactose, arabinose, and tartaric, citric, malic, ascorbic, gallic, and caffeic acids) on the biosensor response was evaluated. The behavior of the biosensor in a flow-injection system in connection with amperometric detection was tested. The analytical usefulness of the biosensor was evaluated by determining gluconic acid in wine and must samples, and the results obtained were validated by comparison with those provided by using a commercial enzyme test kit.

Optimal biostimulation strategy for phenol degradation with indigenous rhizobium Ralstonia taiwanensis

This study provides a first attempt from a perspective of Gaden's classification of fermentation and phase-plane to put forward phenol degradation using various augmented nutrient media for biostimulation. It aimed to identify the most promising nutrient source(s) to attenuate synergistic interactions with phenol for optimal phenol degradation. Therefore, the growth association of phenol degradation using various nutrient media in place of combined toxic interactions was established via Gaden's classification scheme of fermentation and phase-plane analysis. In cultures grown on medium bearing dual carbon sources (glycerol and phenol) or phenol alone, phenol was found to be firstly biodegraded for microbial growth (i.e., growth-associated degradation). In contrast, when yeast extract or acetate was supplemented, a diauxic growth behavior was observed as the augmented nutrient was primarily utilized while phenol degradation was repressed. Moreover, using glycerol as the nutrient source, phenol degradation seemed to be enhanced simultaneously during the consumption of glycerol for cellular growth after ca. 2h response lag in growth. Although gluconic acid could enhance cell growth as well as phenol degradation, the phenol degradation performance was still not as good as that of glycerol. Thus, biostimulation with glycerol appeared to show the most favorable metabolic characteristics against phenol toxicity on Ralstonia taiwanensis, leading to better degradation efficiency of the toxic pollutant. Phase-plane trajectories also clearly confirmed that glycerol was the optimal biostimulating nutrient source for phenol degradation.

The protons of gluconic acid are the major factor responsible for the dissolution of tricalcium phosphate by Burkholderia cepacia CC-Al74

Burkholderia cepacia CC-Al74 with a high ability for solubilizing tricalcium phosphate (TCP) was used to study the P-solubilization mechanism. We collected filtrates able to solubilize TCP from the cultures of strain CC-Al74 and demonstrated that the P-solubilization increased from 0 microg ml(-1) to 200 microg ml(-1) during exponential growth, when the pH decreased from 8 to 3. HPLC-analysis revealed that the solubilization of TCP was mainly caused by the release of 16.3 mM gluconic acid. At this concentration, gluconic acid was capable of solubilizing 376 microg ml(-1) of TCP whereas water at pH 3 only solubilized 35 microg ml(-1). The difference is due to the final H+ concentrations which were 13.5 mM and 1 mM in 16.3 mM gluconic acid and deionized water, respectively at pH 3.

Redox Polymer and Probe DNA Tethered to Gold Electrodes for Enzyme-Amplified Amperometric Detection of DNA Hybridization

The detection of nucleic acids based upon recognition surfaces formed by co-immobilization of a redox polymer mediator and DNA probe sequences on gold electrodes is described. The recognition surface consists of a redox polymer, [Os(2,2'-bipyridine)2(polyvinylimidazole)(10)Cl](+/2+), and a model single DNA strand cross-linked and tethered to a gold electrode via an anchoring self-assembled monolayer (SAM) of cysteamine. Hybridization between the immobilized probe DNA of the recognition surface and a biotin-conjugated target DNA sequence (designed from the ssrA gene of Listeria monocytogenes), followed by addition of an enzyme (glucose oxidase)-avidin conjugate, results in electrical contact between the enzyme and the mediating redox polymer. In the presence of glucose, the current generated due to the catalytic oxidation of glucose to gluconolactone is measured, and a response is obtained that is binding-dependent. The tethering of the probe DNA and redox polymer to the SAM improves the stability of the surface to assay conditions of rigorous washing and high salt concentration (1 M). These conditions eliminate nonspecific interaction of both the target DNA and the enzyme-avidin conjugate with the recognition surfaces. The sensor response increases linearly with increasing concentration of target DNA in the range of 1 x 10(-9) to 2 x 10(-6) M. The detection limit is approximately 1.4 fmol, (corresponding to 0.2 nM of target DNA). Regeneration of the recognition surface is possible by treatment with 0.25 M NaOH solution. After rehybridization of the regenerated surface with the target DNA sequence, >95% of the current is recovered, indicating that the redox polymer and probe DNA are strongly bound to the surface. These results demonstrate the utility of the proposed approach.

Arsenic Species in Solutions for Parenteral Nutrition

BACKGROUND

In spite of its high toxicity, arsenic is a common contaminant in pharmaceuticals. This is stated by pharmacopoeias' monographs where it is not generically included with other heavy metals, but has its own specifications. Arsenic should not exceed 0.1 mg/L in most pharmaceutical products for IV administration. This limit, however, was established without taking into consideration the specific arsenic species which contribute to this amount. In this work, the presence of arsenite and arsenate species in solutions of amino acids, salts, vitamins, and lipids commercialized for IV administration was investigated.

METHODS

The measurements were done by hydride generation atomic absorption spectrometry.

RESULTS

The results showed that all commercial formulations contain both arsenic species in some level; however, the total arsenic content exceeded the allowed limit in only a few samples. Calcium gluconate, sodium bicarbonate, heparin, and vitamin solutions were the most contaminated, presenting total arsenic concentration ranging from 62 to 249 microg/L. The most important finding, however, was the different ratios As(V)/As(III) among the formulations. Whereas practically only As(V) was found in ampoules containing water for injection and salt solutions (NaCl, KC1, phosphates), As(III) predominated in solutions of vitamins, gluconate, and glucose. As these are reducing substances, we investigated the possibility of their reaction with As(V) and its conversion into As(III). The heating of As(V) in the presence of gluconate, glucose, ascorbic acid, methionine, isoleucine, sodium chloride, and pure water, in autoclave for 15 minutes, showed that, whereas no As(III) was found in pure water and sodium chloride solution, approximately 50% of As(V) was converted into As(III) in the remainder of the solutions.

CONCLUSIONS

The results showed that As(V), the main species in these formulations, may be converted into As(III), depending on the presence of reducing substances among the formulation constituents.

Effect of Schizosaccharomyces pombe on aromatic compounds in dry sherry wines containing high levels of gluconic acid

Volatile compounds have been determined in control dry sherry wines and those supplemented with gluconic acid, which were inoculated with the Schizosaccharomyces pombe 1379 (ATCC 26760) yeast strain. These compounds were grouped, according to volatiles exhibiting the identical odor quality, into nine groups of the same odor character (aromatic series) as a way of establishing the aroma profile for the studied wines. Control and supplemented wines showed changes in the balsamic, spicy, roasty, and fruity aromatic series, and tasters judged the aroma as typical of wines subjected to biological aging. This fission yeast may be used as a treatment to reduce gluconic acid contents in wines obtained from rotten grapes, making feasible the incorporation of these wines into the biological aging process. In addition, this procedure may also help to accelerate the traditional biological aging in sherry winemaking due to the contribution of some specific compounds by S. pombe to the wine.

Changes in gluconic acid, polyols and major volatile compounds in sherry wine during aging with submerged flor yeast cultures

The traditional biological process by which sherry wines are aged can be accelerated by using submerged Saccharomyces cerevisiae var. capensis (G1) strain cultures previously grown in glycerol. The used controlled shaking conditions raise the acetaldehyde, acetoin, and meso 2,3-butanediol contents in the wine, and increases the consumption of gluconic acid by flor yeast relative to traditional biological aging under flor yeast velum.

Gluconic acid consumption in wines by Schizosaccharomyces pombe and its effect on the concentrations of major volatile compounds and polyols

Schizosaccharomyces pombe 1379 (ATCC 26760) yeast strain in wine substantially increases acetaldehyde and 1,1-diethoxyethane concentrations and to decreases levo-2,3-butanediol, glycerol, acetoin, and gluconic acid concentrations. In this study, S. pombe has been used for the first time to reduce gluconic acid in wine under aerobic conditions. Only acetaldehyde and acetoin exhibited significantly higher levels in the wines containing gluconic acid. The high in vitro specific activity of alcohol dehydrogenase observed may be directly related to the high production of acetaldehyde by the studied fission yeast.

Oral amiloride treatment decreases taste sensitivity to sodium salts in C57BL/6J and DBA/2J mice

Sodium taste transduction is thought to occur via an amiloride-sensitive, sodium-selective pathway and an amiloride-insensitive, cation nonselective, anion-dependent pathway(s). It has been shown by others that amiloride, an epithelial sodium channel (ENaC) blocker, significantly reduces the chorda tympani nerve response to lingually applied NaCl in C57BL/6 (B6) mice but not in DBA/2 (D2) mice, suggesting that the latter strain might not possess functional ENaCs in taste receptor cells. We psychophysically measured and compared taste detection thresholds of NaCl and sodium gluconate (NaGlu) prepared with and without 100 microM amiloride in these two strains (eight/strain). Mice were trained and tested in a two-response operant signal detection procedure conducted in a gustometer. Surprisingly, no strain effect was found for the detection thresholds of both salts (approximately 0.05-0.06 M). Moreover, these thresholds were increased by almost an order of magnitude by amiloride adulteration of the solutions. This marked effect of amiloride on sodium detection thresholds suggests that ENaCs are necessary for normal sensitivity to sodium salts in both strains. In addition, because NaGlu is thought to stimulate primarily the amiloride-sensitive pathway, especially at low concentrations, the similarity of NaCl and NaGlu thresholds (r > 0.81 both strains) suggests that ENaCs are also sufficient to support the detection of sodium in weak solutions by B6 and D2 mice.

Gluconic acid, its lactones, and SO(2) binding phenomena in musts from botrytized grapes

Intramolecular gluconic acid esterification reactions led to the formation of two lactones, gamma- and delta-gluconolactone (glucono-1,4-lactone and glucono-1,5-lactone). The presence of the first has not yet been reported in must or wine. These lactones are in equilibrium with gluconic acid, gamma- and delta-gluconolactone representing, respectively, 5.8 and 4.1% of the acid level. Correlations between must SO(2) binding power, gluconic acid, and consequently its lactones are shown. The SO(2) affinity of a mixture containing this acid and gamma- and delta-gluconolactone was determined, and gluconic acid appeared to be indirectly responsible for approximately 8% of the bindable SO(2) in musts from botrytized grapes.

Identification and quantification of antioxidant components of honeys from various floral sources

Little is known about the individual components of honey that are responsible for its antioxidant activity. The present study was carried out to characterize the phenolics and other antioxidants present in honeys from seven floral sources. Chromatograms of the phenolic nonpolar fraction of the honeys indicated that most honeys have similar but quantitatively different phenolic profiles. Many of the flavonoids and phenolic acids identified have been previously described as potent antioxidants. A linear correlation between phenolic content and ORAC activity was demonstrated (R(2) = 0.963, p < 0.0001). Honeys were separated by solid-phase extraction into four fractions for sugar removal and separation based on solubility to identify the relative contribution of each fraction to the antioxidant activity of honey. Antioxidant analysis of the different honey fractions suggested that the water-soluble fraction contained most of the antioxidant components. Specific water-soluble antioxidant components were quantified, including protein; gluconic acid; ascorbic acid; hydroxymethylfuraldehyde; and the combined activities of the enzymes glucose oxidase, catalase and peroxidase. Of these components, a significant correlation could be established only between protein content and ORAC activity (R(2) = 0.674, p = 0.024). In general, the antioxidant capacity of honey appeared to be a result of the combined activity of a wide range of compounds including phenolics, peptides, organic acids, enzymes, Maillard reaction products, and possibly other minor components. The phenolic compounds contributed significantly to the antioxidant capacity of honey but were not solely responsible for it.

Determination of carboxylic acids in vinegars and in Aceto Balsamico Tradizionale di Modena by HPLC and GC methods

The presence of carboxylic acids in grape products has been investigated for a long time by researchers, from both the qualitative and quantitative points of view. Evaluation of carboxylic acids requires the study and optimization of some operative variables which are strictly related to the matrix. In particular, the determination of organic acids in real matrixes such as Aceto Balsamico Tradizionale of Modena (ABTM; a traditional balsamic vinegar made from cooked grape must) is often difficult because of the presence of numerous interferences that need to be removed by separation techniques. To this aim, in the present work a solid-phase extraction (SPE) method with C18 and NH(2) exchangers was used to clean the ABTM samples prior to analysis or further treatments. Both HPLC and GC techniques were used to determine organic acids. The efficiency of these two different analytical techniques in the study of ABTM acidic composition has been evaluated. Both methods separately were not able to supply all the data related to carboxylic acids. In particular, HPLC allows acetic and lactic acids quantification, but gluconic and succinic acids are better determined by GC. As far as tartaric, citric, and malic acids are concerned, both HPLC and GC methods give statistically equivalent results. The variation of the single acidic species composition along a series of casks furnished interesting information regarding the chemical transformations taking place during the aging process of this product.

[Direct UV detection of glucose and its derivatives in capillary zone electrophoresis]

UV labeling detection has been commonly used to determine the association constants between lectins and saccharides, but the interaction is always between the labeled carbohydrates, rather than the truly underivatized carbohydrates, and lectins. In order to directly detect saccharides during the study on the interaction of glucose and its derivatives with lectins (e.g., concanavalin A), a capillary zone electrophoretic method with detection at a wavelength of 195 nm has been developed. The influences of various separation conditions including buffer concentration, pH and voltage were investigated. By using an uncoated silica capillary (50 microns i.d., 375 microns o.d., 48.5 cm of total length, and 44.0 cm to the detector) and 50 mmol/L Na2HPO(4)-50 mmol/L NaH2PO4 solution (near to the physiological pH of 7.4) as buffer, the underivatized sugars, including glucosamine, N-acetylglucosamine, glucose, and sodium gluconate, were sufficiently separated within 11 min at an applied voltage of 10 kV. On-column UV monitoring allowed the detection of these compounds at less than 4 mmol/L level, and quantification by the peak area method allowed reproducible determination of them at least at their respective concentration ranges. The method is characterized by its simplicity, rapidity, and reproducibility, and should be useful for the analysis of the interaction of glucose and its derivatives with lectins.

On-line coupling of a miniaturized bioreactor with capillary electrophoresis, via a membrane interface, for monitoring the production of organic acids by microorganisms

Capillary electrophoresis (CE) can be a valuable tool for on-line monitoring of bioprocesses. Production of organic acids by phosphorus-solubilizing bacteria and fermentation of UHT milk were monitored and controlled by use of a membrane-interfaced dialysis device and a home-made microsampler for a capillary electrophoresis unit. Use of this specially designed sampling device enabled rapid consecutive injections without interruption of the high voltage. No additional sample preparation was required. The time resolution of monitoring in this particular work was approximately 2 h, but could be reduced to 2 min. Analytes were detected at low microg mL(-1) levels with a reproducibility of approximately 10%. To demonstrate the potential of CE in processes of biotechnological interest, results from monitoring phosphate solubilization by bacteria were submitted to qualitative and quantitative analysis. Fermentation experiments on UHT milk showed that monitoring of the processes by CE can provide good resolution of complex mixtures, although for more specific, detailed characterization the identification of individual substances is needed.

Quantification of intracellular metabolites in Escherichia coli K12 using liquid chromatographic-electrospray ionization tandem mass spectrometric techniques

The quantitative comprehension of microbial metabolic networks is a prerequisite for an efficient rational strain improvement ("metabolic engineering"). It is therefore necessary to accurately determine the concentration of a large number of reactants (i.e., metabolites, nucleotides, cofactors) in order to understand "in vivo" reaction kinetics. Quantification of intracellular concentrations of glycolytic intermediates and nucleotides in Escherichia coli K12 using a perchloric acid extraction and an LC-ESI-MS method was achieved. Intracellular metabolites (e.g., glucose 6-phosphate, fructose 1,6-bisphosphate, 6-phospho gluconate, acetyl-CoA, adenine nucleotides) were quantified under defined (glucose-limited steady-state) growth conditions. The method was verified by comparing the intracellular metabolite concentrations measured via LC-ESI-MS with enzymatic determinations. It is thus possible to identify and quantify more than 15 intracellular metabolites in parallel with a minimal amount of sample volume.

Changes in major components of tea fungus metabolites during prolonged fermentation

Changes in major components and microbes in tea fungus broth (or kombucha; teakwass) prepared from nine different sources during a prolonged fermentation of up to 60 days were investigated. Cell concentrations of both yeasts and acetic acid bacteria in broth were generally higher than those in the cellulosic pellicles. The residual sucrose concentration decreased linearly with time, although the rate fell after the first month. Metabolic fates of glucose and fructose produced as a result of the hydrolysis of sucrose were different. Glucose was not produced in parallel with fructose (0.085 g 100 ml(-1) d(-1)) but was produced with a lower initial rate (0.041 g 100 ml(-1) d(-1)). Both titratable acidity and gluconic acid increased steadily with time for all samples, although gluconic acid was not generated for 6 days until the fermentation had begun. Acetic acid increased slowly to a maximum value of 1.1 g 100 ml(-1) after 30 days; thereafter, it decreased gradually. Gluconic acid contributed to the titratable acidity and thus, the taste of tea fungus broth, during the final stage of fermentation. It is concluded that the desired quality or composition of kombucha can be obtained through the proper control of fermentation time.

Two-dimensional NMR spectroscopy and structures of six lipid A species from Rhizobium etli CE3. Detection of an acyloxyacyl residue in each component and origin of the aminogluconate moiety

The chemical structures of six lipid A species (A, B, C, D-1, D-2, and E) purified from Rhizobium etli CE3 were investigated by one- and two-dimensional NMR spectroscopy. The R. etli lipid A subtypes each contain an unusual acyloxyacyl residue at position 2' as part of a conserved distal glucosamine moiety but differ in their proximal units. All R. etli lipid A species lack phosphate groups. However, they are derivatized with an alpha-linked galacturonic acid group at position 4', as shown by nuclear Overhauser effect spectroscopy. Component B, which had been not been reported in previous studies, features a beta, 1'-6 linked disaccharide of glucosamine acylated at positions 2, 3, 2', and 3' in a pattern that is typical of lipid A found in other Gram-negative bacteria. D-1 contains an acylated aminogluconate unit in place of the proximal glucosamine residue of B. C and E lack ester-linked beta-hydroxyacyl chains at position 3, as judged by their H-3 chemical shifts, and may be synthesized from B and D-1, respectively, by the R. etli 3-O-deacylase. D-2 is an isomer of D-1 that forms nonenzymatically by acyl chain migration. A may be an elimination product derived from D-1 during hydrolysis at 100 degrees C (pH 4.5), a step needed to release lipid A from lipopolysaccharide. Based on these findings, we propose a biosynthetic scheme for R. etli lipid A in which B is generated first by a variation of the E. coli pathway. The aminogluconate unit of D-1 could then be made from B by enzymatic oxidation of the proximal glucosamine. As predicted by our hypothesis, enzyme(s) can be demonstrated in extracts of R. etli that convert (14)C-labeled B to D-1.

Mineralization of benzo[a]pyrene by Marasmiellus troyanus, a mushroom isolated from a toxic waste site

Mycelia from the mushroom Marasmiellus troyanus were grown in the presence of radiolabeled benzo[a]pyrene in liquid culture. After 15 days, 8.1% of the label from M. troyanus cultures was recovered in CO2 as compared to 1.1% for Phanerochaete chrysosporium and 0.2% for Aspergillus niger. M. troyanus efficiently transformed B[a]P into water soluble metabolites with 64% of the label recovered in the water soluble fraction as compared to 11.7% for P. chrysosporium and 4.1% for A. niger. Glucuronic acid and sulfate conjugates of B[a]P were identified from the aqueous fraction of cultures of M. troyanus, after 17 days.

High-performance liquid-phase separation of glycosides. III. Determination of total glucosinolates in cabbage and rapeseed by capillary electrophoresis via the enzymatically released glucose

A selective and sensitive method for the determination of total glucosinolates (GSs) in plant extracts by capillary electrophoresis-laser-induced fluorescence (LIF) detection was developed. It was based on the enzymatically released glucose from glucosinolates in the presence of the hydrolyzing enzyme myrosinase. The released glucose was converted to gluconic acid (GA) by the action of glucose oxidase. The resulting GA was then labeled selectively with the fluorescent tag 7-aminonaphthalene-1, 3-disulfonic acid (ANDSA). The peak area resulting from the GA-ANDSA derived from free and bound glucose was subtracted from the peak area of the GA-ANDSA resulting from the free glucose in the sample. This gave the total glucosinolates in the sample. The peak areas were normalized to the internal standard, N-acetylneuraminic acid derivatized with ANDSA. The method was validated using four different plant extracts, white cabbage leaves, rapeseed leaves, rapeseed roots, and rapeseed seeds. Furthermore, a capillary electrophoresis-UV detection method for profiling GS in plant extracts was developed. In addition to providing a fingerprint of the glucosinolates in plant extracts, the method allowed the experimenter to rapidly check the various steps involved in the extraction and sample cleanup.

Expression of genes from Rahnella aquatilis that are necessary for mineral phosphate solubilization in Escherichia coli

Rahnella aquatilis is a Gram-negative bacterium that can fix atmospheric nitrogen and also has the ability to solubilize mineral phosphate. We have cloned the genes that confer the mineral phosphate solubilizing (Mps) trait from this organism by mobilizing a cosmid library of R. aquatilis into Escherichia coli HB101. A 7.0-kb EcoRI fragment from a cosmid, when transferred into E. coli strains HB101 and DH5 alpha, conferred the ability to solubilize hydroxyapatite and the production of gluconic acid to E. coli. The relative amounts of soluble phosphate and gluconic acid produced by the cloned 7.0-kb EcoRI fragment in E. coli were significantly higher than those of R. aquatilis. Nucleotide sequence analysis revealed two complete open reading frames (ORF1 and ORF2) and a partial ORF, ORF1 and ORF2 encoded proteins of molecular mass 10 kDa and 44 kDa. The 44-kDa protein showed extensive sequence similarity to pqqE of Erwinia herbicola, Klebsiella pneumoniae and A. Acinetobacter calcoaceticus. The 10-kDa protein revealed strong similarity to the pqqD of K. pneumoniae and A. calcoaceticus.

Biochemical basis for glucose-induced inhibition of malolactic fermentation in Leuconostoc oenos

The sugar-induced inhibition of malolactic fermentation in cell suspensions of Leuconostoc oenos, recently reclassified as Oenococcus oeni (L. M. T. Dicks, F. Dellaglio, and M. D. Collins, Int. J. Syst. Bacteriol. 45:395-397, 1995) was investigated by in vivo and in vitro nuclear magnetic resonance (NMR) spectroscopy and manometric techniques. At 2 mM, glucose inhibited malolactic fermentation by 50%, and at 5 mM or higher it caused a maximum inhibitory effect of ca. 70%. Galactose, trehalose, maltose, and mannose caused inhibitory effects similar to that observed with glucose, but ribose and 2-deoxyglucose did not affect the rate of malolactic activity. The addition of fructose or citrate completely relieved the glucose-induced inhibition. Glucose was not catabolized by permeabilized cells, and inhibition of malolactic fermentation was not observed under these conditions. 31P NMR analysis of perchloric acid extracts of cells obtained during glucose-malate cometabolism showed high intracellular concentrations of glucose-6-phosphate, 6-phosphogluconate, and glycerol-3-phosphate. Glucose-6-phosphate, 6-phosphogluconate, and NAD(P)H inhibited the malolactic activity in permeabilized cells or cell extracts, whereas NADP+ had no inhibitory effect. The purified malolactic enzyme was strongly inhibited by NADH, whereas all the other above-mentioned metabolites exerted no inhibitory effect, showing that NADH was responsible for the inhibition of malolactic activity in vivo. The concentration of NADH required to inhibit the activity of the malolactic enzyme by 50% was ca. 25 microM. The data provide a coherent biochemical basis to understand the glucose-induced inhibition of malolactic fermentation in L. oenos.

Quantitation of the glycation intermediate 3-deoxyglucosone by oxidation with rabbit liver oxoaldehyde dehydrogenase to 2-keto-3-deoxygluconic acid followed by high-performance liquid chromatography

A simple and sensitive method for the detection of 3-deoxyglucosone was developed using oxidation with crude oxoaldehyde dehydrogenase to 2-keto-3-deoxygluconic acid followed by high-performance liquid chromatography (HPLC). Oxoaldehyde dehydrogenase was prepared from rabbit liver and partially characterized. 2-Keto-3-deoxygluconic acid produced from 3-deoxyglucosone by oxoaldehyde dehydrogenase was derivatized with 1,2-diamino-4,5-methylenedioxybenzene, and the fluorescent products were detected and quantitated by HPLC using a solvent containing borate. In the presence of borate, 2-keto-3-deoxygluconic acid was completely separated from N-acetylneuraminic acid. The detection limit of 3-deoxyglucosone was 2.5 pmol/injection (10 microliters) at a signal-to-noise ratio of 3. This method was used to confirm the inhibitory effect of aminoguanidine on glycation.

Detection of metabolites of the Entner-Doudoroff pathway by HPLC with pulsed amperometry: application to assays for pathway enzymes

Three major metabolites in the Entner-Doudoroff pathway, 6-phosphogluconate, 2-keto-3-deoxy-6-phosphogluconate, and pyruvate can be detected and quantified by HPLC with pulsed amperometric detection. Resolution is achieved by ion-exchange chromatography at alkaline pH with isocratic elution in 5 to 10 min. Detection limits are in the subnanomolar range, and detector response is linear over 3-4 orders of magnitude. This method can be employed for the assay of the enzymes of the pathway, 6-phosphogluconate dehydratase (EC 4.2.1.12) and 2-keto-3-deoxy-6-phosphogluconate aldolase (EC 4.1.2.14), eliminating the need for coupling enzymes as in the previously employed spectrophotometric assays. The lag in pyruvate production seen in the coupled enzyme spectrophotometric assay for 6-phosphogluconate dehydratase is absent in the HPLC/pulsed amperometric detection assay. This lag represents an artifact of a slow tautomerism of 2-keto-3-deoxy-6-phosphogluconate which must precede its utilization by the coupling enzyme, 2-keto-3-deoxy-6-phosphogluconate aldolase. Kinetic data on the approach to equilibrium of 2-keto-3-deoxy-6-phosphogluconate aldolase-catalyzed interconversion of 2-keto-3-deoxy-6-phosphogluconate, pyruvate, and glyceral-dehyde-3-phosphate can be also accurately quantified by HPLC with pulsed amperometric detection.

Development of a process-FIA system using mediator-modified enzyme electrodes

A computer-controlled process-FIA system for monitoring industrial bioprocesses was developed using mediator-modified enzyme electrodes. The single-line FIA system was modified by replacing the mixing coil with a flexible operating sample dilution unit. By this way, the analyzer offers automatic procedures for self-calibration 'real-time' dilution and recalibration based on the current analyte concentration. In regard to the dynamic range of the sensors, the FIA system is able to self-adapting to any analyte concentration of the bioprocess. The technique was tested for control of glucose during microbial fed-batch processes of gluconic acid production.

Mutants of Escherichia coli producing pyrroloquinoline quinone

In glucose minimal medium a PTS- strain of Escherichia coli [delta (ptsH ptsI crr)] could grow slowly (doubling time, d = 10 h). When the population reached 5 x 10(6) to 2 x 10(7) cells ml-1, mutants growing rapidly (d = 1.5 h) appeared and rapidly outgrew the initial population. These mutants (EF mutants) do not use a constitutive galactose permease for glucose translocation. They synthesize sufficient pyrroloquinoline quinone (PQQ) to yield a specific activity of glucose dehydrogenase (GDH) equivalent to that found in the parent strain grown in glucose minimal medium supplemented with 1 nM-PQQ. Membrane preparations containing an active GDH oxidized glucose to gluconic acid, which was also present in the culture supernatant of EF strains in glucose minimal medium. Glucose utilization is the only phenotypic trait distinguishing EF mutants from the parent strain. Glucose utilization by EF mutants was strictly aerobic as expected from a PQQ-dependent catabolism. The regulation of PQQ production by E. coli is discussed.

Changes in the concentration of metabolites in milk from cows fed on diets supplemented with soyabean oil or fatty acids

Cows were fed on diets supplemented with soyabean oil or soyabean fatty acids which in some cases were protected from rumen hydrogenation. The fat-containing diets reduced the output of short- and medium-chain fatty acids in milk. Associated with this fall in short- and medium-chain fatty acids was a decrease in the concentration of 2-oxoglutarate and an increase in that of isocitrate and citrate. Protection of polyunsaturated fat from rumen hydrogenation had no significant effect. Milk yields were unaffected by diet, but the variation in milk yield among cows correlated positively with the concentration of glucose in milk.

The adverse effects of high oral osmolal mixtures in neonates. A review and a study of the osmolality of calcium preparations

In both animals and humans, there are numerous clinical, physiologic, and morphologic alterations that occur when hypertonic solutions are introduced into the alimentary tract. The most serious adverse effect observed in the human infant is necrotizing enterocolitis. A short in vitro study analyzing osmolalities of drug-formula mixtures at various dilutions, conducted by the authors, showed that an unacceptable degree of high osmolality may be achieved in the preparation of common medications used in newborn nurseries. Although review of the literature confirms that, in general, the osmolalities of mixtures fed to newborns should not exceed 460 mOsm/kg H2O, lower levels would be preferable in ill and low birth weight newborns. When possible, consideration should be given to the use of parenteral medication for the critically ill neonate. Ideally, the osmolalities of mixtures fed to newborns should be measured if they are not known or cannot be calculated.

Determination of calcium gluconate by selective oxidation with periodate

A modified analytical method was developed which can accurately quantitate calcium gluconate and its pharmaceutical preparations in the presence of other calcium compounds or other cations able to complex with EDTA. The proposed method was based on the principle of the Malaprade reaction, according to which gluconic acid is selectively and quantitatively oxidized by sodium periodate. The content of calcium gluconate was calculated from the amount of gluconic acid found. The selective oxidation proceeded at 50 degrees C for 10 min, yielding approximately 100% recovery of calcium gluconate. The proposed method was accurate, precise, and superior to the compendia EDTA- complexometric method in terms of specificity.

Gas chromatographic determination of glucono-delta-lactone in foods

A method is described for the gas chromatographic (GC) determination of glucono-delta-lactone in foods. A sample was homogenized with 60-70 degrees C water and filtered. The filtrate was buffered with NH4OH-NH4Cl pH 10 solution, and was passed through a QAE-Sephadex A25 column. The column was washed with water and glucono-delta-lactone was eluted with 0.1N HCl. An aliquot of the eluate was evaporated to dryness and derivatized with pyridine, N,O-bis(trimethylsilyl)trifluoroacetamide, and trimethylchlorosilane at room temperature. GC separation of glucono-delta-lactone as the TMS derivative was performed on a 2% OV-17 column at 180 degrees C. Recoveries from bread, jelly, soybean curd, and other foods fortified with 0.1% glucono-delta-lactone ranged from 92 to 106%, with standard deviations from 2.2 to 9.8%. The detection limit was approximately 0.025%.

Effect of chlorhexidine gluconate on acute nonmicrobial inflammation reaction

The effects of chlorhexidine on the appearance of leukocytes and some hydrolytic enzymes were studied in an experimental acute nonmicrobial inflammation reaction caused by implanation of viscose sponge beneath the backskin. The results showed that chlorhexidine gluconate decreased the number of leukocytes in the inflammatory exudate. The drug used had no measurable effect on the distribution of different types of leukocytes. Chlorhexidine has a clear inhibitory effect on the appearance of phosphatases, glycosidases and peptidases. On the other hand the effect on proteinases was small.

Fluorescence densitometric method for the determination of gluconic and lactobionic acids ("sugar acids") in pharmaceutical preparations

An in situ fluorimetric method has been developed for the quantitation of gluconic and lactobionic acids and their salts in tablet formulations. The method is based on glycol cleavage with lead tetraacetate followed by treatment with dichlorofluorescein. Calcium gluconate and lactobionate were determined in Calcium-Sandoz and Ca-C 1000 Sandoz effervescent tablets. The reproducibility corresponded to relative standard deviations between 0.7 and 3.5% (usually below 2%). Detection limits of 0.2 mug per spot can be obtained. Interfering compounds such as citric acid, sugars and ascorbic acid can be separated from the "sugar acids". The linearity of the calibration graphs between 0.5 and 5 mug per spot is satisfactory (r = 0.994-0.999). The method is simple and could be applied to the routine analysis of suitable pharmaceutical formulations. Other compounds with glycol structures should also be adaptable to this technique.