Initial Amino Acid Concentration Research Articles

Evaluating the impact of Torulaspora delbrueckii and amino acid concentration on the nitrogen metabolism of Oenococcus oeni

This study investigates the impact of Saccharomyces cerevisiae and Torulaspora delbrueckii inoculation strategies and amino acid supplementation on nitrogen metabolism and malolactic fermentation (MLF) performance in Oenococcus oeni. Oenococcus oeni has low demand of nitrogen and typically prefers peptides over amino acids. In this work we studied the nitrogen metabolism (proteins, peptides, amino acids and biogenic amines (BA)) of three O. oeni strains. Higher initial amino acid concentrations generally accelerated MLF, particularly with the PSU-1 strain, which exhibited stuck fermentation in some conditions with low initial amino acid concentration related with coinoculation of yeasts. Nitrogen metabolism in O. oeni showed a preference for peptide-bound amino acids, and gene expression analyses highlighted a general upregulation in response to increased amino acid concentrations. BA production, particularly cadaverine and putrescine, was strain-dependent and associated with the presence of the odc gene. Besides, the production of 2-phenylethylamine was related with alcoholic fermentation (AF) inoculation strategy. Overall, the study demonstrates the complexity of nitrogen metabolism in O. oeni, emphasizing that it is influenced by both the yeast species used in AF and the initial amino acid composition, highlighting the importance of peptide composition, offering a potential tool for optimizing MLF in winemaking.

Occurrence of acrylamide carcinogen in Arabic coffee Qahwa, coffee and tea from Saudi Arabian market

The present work describes the outcomes of the assessment on acrylamide contents in a number of thermally treated foods (Arabic coffee Qahwa, coffee and tea) obtained from the Saudi Arabian markets. A total of 56 food samples of different brands and origin were studied, the amounts of acrylamide in Arabic coffee Qahwa, coffee and tea were obtained in the range of 10 to 682 μg kg−1. In comparison to coffee (152–682 μg kg−1), the Arabic coffee Qahwa (73–108 μg kg−1) and tea (10–97 μg kg−1) contain lower amounts of acrylamide. Among the analyzed samples, the green tea contained low amounts of acrylamide ranged from 10 to 18 μg kg−1, and thus the green tea could be considered as a healthier hot drink. A great variation of acrylamide formation has been observed in these food products. This divergence may be due to the initial concentration of amino acids especially asparagines and reducing sugars in food products, in addition to roasting temperature and time, pH and water activity. The obtained data can also be used in epidemiological investigation to estimate the acrylamide exposure from nutritional survey.

Amino acids and biogenic amines in red varietal wines: the role of grape variety, malolactic fermentation and vintage

This work studies for the first time the amino acid and biogenic amine composition of Rioja red wines made with the red minority varieties Vitis vinifera cv. Monastel and Maturana Tinta de Navarrete, using Tempranillo as a reference variety. The role of malolactic fermentation and vintage on these compounds was also analysed, and discriminate analyses were applied to achieve a possible differentiation of the wines. Amino acid composition allowed a differentiation of wines according to grape variety. Monastel was characterised by the highest value in β-alanine and Maturana Tinta de Navarrete by its highest value in OH-proline. However, biogenic amines were no able to classify varietal wines. The malolactic fermentation had significant changes on the amino acid and biogenic amine content, and allowed distinguishing wines that underwent this process from wines without malolactic fermentation. No correlation was found between total amino acids and total biogenic amines after malolactic fermentation, suggesting that a higher initial concentration of amino acids in the medium did no affect the concentration of biogenic amines after malolactic fermentation. Vintage influenced the amino acid and biogenic amine pattern, obtaining a clear separation of wines by vintages. Monastel and Maturana Tinta de Navarrete wines showed a minor varietal character and were more influenced by the climatic conditions of each vintage than Tempranillo wines. All the wines showed histamine levels below the human physiological threshold and implemented regulations.

Separation of Two Amino Acids by Microemulsion Bulk Liquid Membrane

In this research work the potentialities of microemulsion bulk liquid membrane for the selective transport of L-tryptophan (L-Trp) and L-tyrosine (L-Tyr) are investigated at 298.15 K. Reversed micelle formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in dichloroethane, was used as mobile carrier to transport amino acids between a source and a receiving aqueous phase. The effects of pH, surfactant concentration and initial amino acid concentration on the extraction efficiency and transfer rate of the amino acids were studied. It is verified that for a mixture of two amino acids, L-Trp can be extracted selectively by using this type of the bulk liquid membrane with optimized condition.

Dynamics of pore synthesis and degradation in protocells

Liposomes have found countless applications as microreactors or for studying the evolution of protocells. However, to keep reactions ongoing, exchange with the environment is required. Based on experiments with nanopores expressed by an enclosed gene expression system, we developed a model describing the observed growth dynamics quantitatively. The model depends on one parameter only and allowed estimations of hitherto unknown parameters: the diffusion coefficient of amino acids through a single pore and the initial amino acid concentration. The long-term consequences of different degradation mechanisms are also discussed: we found a surprisingly sharp threshold deciding on the question of survival of the protocell.

Malolactic fermentation of Tempranillo wine: contribution of the lactic acid bacteria inoculation to sensory quality and chemical composition

Malolactic fermentation (MLF) of Tempranillo Rioja wines (Spain) inoculated with two lactic acid bacteria (LAB) strains were studied and compared with spontaneous MLF. Inoculation with selected Oenococcus oeni lyophila shortened MLF duration up to 19days and lead to wines with more fresh and fruity characters, especially when implantation was 100%. We demonstrated modifications in the concentration of volatile and nitrogenous compounds and a good correlation between analytical and sensory attributes was also noted. In addition, the low initial amino acid concentration and the consumption of these compounds by the inoculated yeast strain during alcoholic fermentation resulted in wines with very low biogenic amines levels (under 3.75mgL -1) after MLF and 3month storage period in all cases. The results showed the significance of choose the most suitable starter to elaborate quality wines and suggest the control of amino acid content in must and wine to prevent the formation of biogenic amines. © 2011 The Authors. International Journal of Food Science and Technology © 2011 Institute of Food Science and Technology.

Quantification of Amino Acids in Fermentation Media by Isocratic HPLC Analysis of Their α-Hydroxy Acid Derivatives

In this paper we describe a novel method for quantification of amino acids. First, α-hydroxy acid derivatives of amino acids were formed after reaction with dinitrogen trioxide by the van Slyke reaction. Second, the α-hydroxy acid derivatives were separated on an Aminex HPX-87H column (Bio-Rad) eluted isocratically with 5 mM H(2)SO(4) and quantified by refractive index detection. We were able to measure the reaction products of 13 of the 20 classical amino acids: glycine, l-alanine, l-valine, l-leucine, l-isoleucine, l-methionine, l-serine, l-threonine, l-asparagine, l-glutamine, l-aspartic acid, l-glutamic acid, and l-proline. We obtained linear relationships between the product peak areas and initial amino acid concentration, whereby the concentrations of these amino acids could be quantified on the basis of the quantification of their products. The method can be used to analyze amino acids in parallel with other small molecules, such as sugars or short chain fatty acids, and was used for parallel quantification of glycine, l-alanine, or l-glutamic acid, and glucose uptake in cultures of the heterotrophic dinoflagellate Crypthecodinium cohnii . The method can also be used to quantify other amines, as demonstrated by detection of Tris (2-amino-2-(hydroxymethyl)propane-1,3-diol).

Enrichment of Amino Acids by Ultrasonic Atomization

Dilute aqueous solutions of two amino acids, tryptophan (Trp) and phenylaramine (Phe), were atomized ultrasonically, and it was found that the amino acids were enriched in the collected mist droplets. The enrichment ratio increased with decreasing initial concentration of amino acids. An enrichment model was proposed and was verified with experimental results. The mechanism is analogous to that of nonfoaming adsorptive bubble separation (NFBS) reported previously. The model explained well the experimental results, and the specific surface area of the mist droplets was estimated. In the case of ultrasonic atomization, the estimated specific surface areas for both Trp and Phe were larger than those of NFBS. This suggests that smaller droplets will be formed by ultrasonic atomization. The present method will be available to separate gas−liquid interfaces where surface-active substances adsorb and to enrich them from dilute aqueous solution.

Response surface optimization of the separation of dl-tryptophan using an emulsion liquid membrane

Response surface methodology was applied to optimize the separation of dl-tryptophan from aqueous solution. dl-tryptophan was extracted into an emulsion liquid membrane containing Aliquat-336 in oleyl alcohol. The carrier concentration (10–30%, by volume), pH (10–14) and initial amino acid concentrations (1–7 mM) were the critical components of the separation optimized. Experiments were performed at 150 rpm stirring rate, for 30 min extraction time with equal volumes of organic and aqueous phases. The response surface equation to predict the extraction yield in the above range of critical components is Y=100.72+31.83x 1+0.15x 2+3.38x 3−21.41x 1 2−5.39x 2 2−7.11x 3 2+1.19x 1x 2−3.26x 1x 3−2.30x 2x 3 where Y is the response, (extraction yield). Maximum Y (100%) was obtained by employing the following predicted optimum extraction conditions: a pH of 12.46, a carrier concentration of 22.22%, and an initial amino acid concentration of 4.97 mM.

Amino acid solubilization in cationic reversed micelles: factors affecting amino acid and water transfer

The aim of this work is to investigate the driving forces involved in amino acid solubilization in cationic reversed micelles, and to determine in which way different parameters affect the reversed micellar structure and amino acid solubilization, in order to select the best conditions to optimize amino acid extraction. To this end, extraction equilibrium experiments were performed using different experimental conditions and three amino acids with different structures: aspartic acid - a hydrophilic amino acid, phenylalanine - a slightly hydrophobic amino acid, and tryptophan - a hydrophobic amino acid. The study of the effect of amino acid related parameters, such as pH and the initial amino acid concentration in the aqueous phase, and the effect of parameters that influence the reversed micellar structure, such as surfactant concentration, ionic strength and co-surfactant concentration, provides useful information about the driving forces involved, solute-micelle interfacial interactions and solute location in the cationic system trioctylmethylammonium chloride (TOMAC)/ hexano1/n-heptane. These parameters can be adjusted to optimize amino acid extraction. It is shown that amino acids with the same isoelectric point can be selectively separated by exploring the different interactions they establish with the reversed micellar interface.

Counterion effect of amino acids in reverse micelles

The effect of amino acids at zwitterionic condition on the water uptake of Aerosol-OT (AOT) reverse micellar system has been studied. The experimental results for different initial surfactant and salt concentrations, and different amino acids showed that the water uptake increased almost linearly with the initial amino acid concentration. The variation of the water uptake with the amino acid concentration is purported to be due to the counterion effect of amino acids. A simple model is proposed to account for the counterion effect of amino acids. The model accurately predicts the water uptake by the reverse micelles.

Kinetics of the extraction of phenylalanine and glutamic acid by ion-exchange carriers

Biological transport of amino acids is usually mediated by carrier proteins buried in biomembranes. The application of models to such transport systems has long been desired in the separation science and technology of amino acids and is an active area of research. Recently, the application of commercial metal extractants as mobile carriers in the liquid membrane technology has attracted increasing attention due to their potential capability in the field of bioseparation. In the development of such a novel separation technique, knowledge of the extraction kinetics is necessary in addition to knowledge of the extraction equilibrium. Due to their zwitterionic character, it is possible to extract amino acids with ion-exchange carriers by controlling the pH of aqueous amino acid solutions. A modified Lewis-type cell experiment was used to study the extraction kinetics of glutamic acid (system I) and phenylalanine (system II) by naphthenic acid, and that of phenylalanine by a quarternary ammonium salt, Aliquat 336 (system III). The effects of agitation, interfacial area, carrier concentration, pH, and initial concentration of amino acids on the extraction rate were discussed. A rate equation involving the mass transfer terms was derived, based on an interfacial chemical reaction mechanism. It was found that the limiting case, based on an interfacial reaction rate-determining mechanism, was in good agreement with the experimental results. The intrinsic chemical reaction is controlled by the formation of an amino acid/ carrier complex at the interface. The mechanism of extraction proposed in this study is applicable to both glutamic acid and phenylalanine in the two ionic carrier systems.

Stability of fluconazole and amino acids in parenteral nutrient solutions

The stability of fluconazole and amino acids in parenteral nutrient (PN) solutions was studied. Amino acids at three concentrations (1.0%, 2.5%, and 5.0%) with 25% dextrose injection were combined with a high (1.75 mg/mL) or a low (0.5 mg/mL) concentration of fluconazole to form six combinations of PN solution and fluconazole. The solutions were visually inspected for precipitate, color change, or gas formation and tested for pH. By using high-performance liquid chromatography, the solutions were assayed for fluconazole concentration at zero, one, and two hours after preparation. The PN solution containing fluconazole 1.75 mg/mL and 5.0% amino acids was assayed for 14 amino acids at the same time points. There was no visual evidence of incompatibility in any of the fluconazole and PN solutions, and the pH of the solutions did not vary appreciably throughout the study period. The mean percentage of initial fluconazole concentration remaining at one and two hours was greater than 97% for all of the solutions studied. The mean percentage of initial amino acid concentration remaining at one and two hours was greater than 93% for each of the 14 amino acids assayed. When fluconazole 0.5 mg/mL or 1.75 mg/mL is mixed with PN solution containing 1.0%, 2.5%, or 5.0% amino acids and 25% dextrose injection, both fluconazole and amino acids are stable for up to two hours.

Comparison of fluorescamine and o‐phthaldialdehyde methods for measuring amino acid exchange in marine organisms

Two methods routinely used to quantify total primary amine concentrations in seawater are the fluorescamine bulk assay and o‐phthaldialdehyde derivatization with chromatographic separation (OPA‐HPLC). Investigators using OPA‐HPLC have observed net amino acid uptake by marine invertebrates; those using fluorescamine observe excretion of primary amines. We systematically compared the two methods with amino acid and ammonium standards and also conducted two excretion experiments with two species of bivalve molluscs. Mytilus edulis exhibits both uptake and excretion of primary amines and the flux is correlated with the initial concentration of amino acids. The two methods give comparable results, particularly after correcting the fluorescamine data for differences in relative fluorescence among amino acids. Mercenaria mercenaria exhibits net uptake of amino acids when flux is measured by OPA‐HPLC and net excretion of fluorescamine‐positive substances. Small peptides may contribute to the discrepancy between assay methods.

Lysine and methionine transport by bovine jejunal and ileal brush border membrane vesicles.

Lysine (LYS) and methionine (MET) transport were studied using brush border membrane vesicles from bovine jejunal and ileal tissues. Total transport of LYS and MET was divided into mediated and diffusion components. Mediated uptake was further divided into sodium (Na)-dependent and Na-independent systems. Total LYS and MET uptake by ileal brush border (BB) vesicles tended to be higher than that by jejunal BB vesicles at all concentrations evaluated but differences were significant (P less than .05) at 2.5 and 7.5 mM for LYS and 5, 12.5 and 15 mM for MET. The greater capacity of ileal BB vesicles appeared to be due to the Na-dependent component of LYS uptake and the diffusion component of MET uptake. Transporters had less affinity but higher capacity than for LYS transport in both ileal and jejunal tissue. Methionine transport was greater (P less than .05) than LYS transport in both ileal and jejunal BB vesicles when the initial amino acid concentration was 7.5 mM. But when the initial amino acid concentration was 1.25 mM, MET uptake was greater (P less than .13) than LYS uptake in jejunal, but not in ileal, BB vesicles. The relative contribution of mediated and diffusion uptake systems to total MET and LYS uptake was found to be dependent on substrate concentration. Both intestinal site and substrate concentration influenced the contributions of Na-dependent, Na-independent and diffusion systems to total methionine and lysine uptake.

The absorption of amino acids from the rumen of the sheep. I. The loss of amino acids from solutions placed in the washed rumen in vivo

L-histidine, glycine, and L-amino acid mixtures were placed in the washed rumen of sheep in concentrations similar to those found under normal feeding conditions. The amounts of individual amino acids lost from the rumen over a 4 hr period ranged from virtually zero to 50% of the initial concentration of amino acids placed in the rumen. It was calculated that this could account for 6% of the total nitrogen absorption from the rumen. The amount of L-amino acids lost from the rumen depended on their initial concentration and on the concentration of other amino acids present. The branched chain amino acids showed the most rapid absorption.

Influence of amino acid supply on ribosomes and protein synthesis of perfused rat liver.

1. The livers of rats were perfused in situ with medium containing mixtures of amino acids in multiples of their concentration in normal rat plasma. The incorporation of labelled amino acid into protein of the liver and of the perfusing medium increased with increasing amino acid concentration. During 60min. perfusions, labelling of liver protein reached a plateau, and labelling of medium protein was inhibited when the initial concentration of the amino acid mixture was more than ten times the normal plasma value. 2. Examination of polysome profiles derived from livers perfused without amino acids in the medium showed that the number of large aggregates was decreased and the number of small aggregates, particularly monomers and dimers, was increased with time of perfusion. The addition of amino acids to the perfusion medium reversed this polysome shift to an extent that was dependent on the initial concentration of amino acids. Polysome profiles derived from livers perfused for 60min. with ten times the normal plasma concentration of amino acids were essentially the same as the polysome profiles of normal non-perfused livers. 3. The ability of ribosome preparations from perfused livers to incorporate amino acids into protein in vitro decreased with increasing time of perfusion when no amino acids were added to the medium, but increased as the concentration of amino acids in the perfusion medium was increased. 4. The ability of cell sap from perfused livers to support protein synthesis in vitro was not influenced by the amino acid concentration of the perfusion medium. 5. Livers were perfused for 60min. with medium containing amino acid mixtures at ten times the normal plasma concentration but deficient in one amino acid. Maximal incorporation of labelled amino acid into liver protein, the stability of the polysome profile and the ability of ribosome preparations to incorporate amino acids into protein were found to depend on the presence of 11 amino acids: arginine, asparagine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine, tryptophan and valine. A mixture of these 11 amino acids, at ten times their normal plasma concentration, stimulated the incorporation of labelled amino acid into liver protein, stabilized the polysome profile and increased the ability of ribosome preparations to incorporate amino acids into protein to the same extent as the complete mixture. 6. It is concluded that the availability of certain amino acids plays an important role in the control of protein synthesis, possibly by stimulating the ability of ribosomes to become, and to remain, attached to messenger RNA.

KINETICS OF INTESTINAL ACTIVE TRANSPORT OF FIVE NEUTRAL AMINO ACIDS.

Rates of transport against a concentration gradient by everted segments of hamster small intestine were determined for five monoaminomonocarboxylic acids. Values varied considerably from animal to animal. A graph of reciprocal of transport rate as a function of reciprocal of initial amino acid concentration revealed a linear relationship for each amino acid. Values for Kt, the concentration at which half-maximal transport is observed, diminished with increasing length of side chain for glycine, l-alanine, l-valine, and l-leucine. The Kt for α-aminoisobutyric acid was much higher than the others. Values for Vmax, the apparent limiting transport rate, decreased as chain length increased. With increasing initial amino acid concentration transport rate rose to a maximum and then declined. At concentrations producing this decline no gross mucosal damage was noted. The apparent inhibitory effect of these high concentrations was not a permanent one.