Chromatographic determination of amino acid enantiomers in beers and raw materials used for their manufacture

Simultaneous analysis of DL-Amino acids in foods and beverages using a highly sensitive chiral resolution labeling reagent

Amino acids with various functions are abundant in living organisms and foods. Recent advances in analytical technology show that trace amounts of D-amino acids exist in living organisms and foods. In addition, studies show that these amino acids are involved in various physiological functions that differ from those of L-amino acids. Thus, a technique for analyzing DL-amino acids is required. However, the simultaneous separation and highly sensitive detection of DL-amino acids are complicated; therefore, highly sensitive analytical methods that can rapidly separate and identify compounds are required. We previously developed our original chiral resolution labeling reagents for the separation and highly sensitive detection of DL-amino acids. Here, we developed a simple method for the rapid separation and highly sensitive detection of DL-amino acids in various foods and beverages by liquid chromatography-mass spectrometry (LC-MS) using an octadecyl (C18) column after labeling with 1-fluoro-2,4-dinitrophenyl-5-D-leucine-N,N-dimethylethylenediamineamide (D-FDLDA; enantiomeric excess > 99.9 %). In addition, we synthesized a stable isotope (13C6)-labeled D-FDLDA (13C6-D-FDLDA) and established an analytical method that can accurately identify the peak of each DL-amino acid. MS sensitivity of DL-amino acids labeled with our labeling reagent was higher than that of conventional labeling reagents (Marfey's reagents). The labeling reagent was neither desorbed from each DL-amino acid nor degraded for at least 1 week at 4 °C. Furthermore, we determined the DL-amino acid contents in foods and beverages using the proposed method, and differences in the total amino acid content and D/L ratio in each food and beverage were observed.

Occurrence and Levels of Biogenic Amines in Beers Produced by Different Methods

The concentration of biogenic amines (BAs) in beer depends, among other factors, on the activity of microorganisms, in particular lactic acid bacteria. In this work an analytical method based on derivatization with tosyl chloride and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was used to determine 17 BAs in samples of commercially available beers, and to monitor the changes in concentration of several BAs throughout the fermentation process. In some of the analysed samples the concentration of BAs exceeded the safety threshold for consumers. During the fermentation stage of home-brewing of ale the concentration of spermine in the wort increased until the end of the stormy fermentation, to then drop below the initial concentration at the end of fermentation, and below the LOQ after refermentation. The results of the study indicate that monitoring the total content of BAs is required due to the potential risk to human health.

Antihypertensive and Probiotic Effects of Hidakakombu (Saccharina angustata) Fermented by Lacticaseibacillus casei 001

Hidakakombu (Saccharina angustata), commonly known as kelp, is an edible macroalgae mainly grown in the Hidaka region of Hokkaido. Hidakakombu is graded based on its shape and color. Low-grade Hidakakombu has low value and is distributed at a low price. It is desired to establish a method to add value to low-grade Hidakakombu. In this study, low-grade Hidakakombu was fermented by Lacticaseibacillus casei 001 to add value. Fermentation of Hidakaombu enhanced the inhibition of blood pressure elevation due to ACE inhibition. L. casei 001 in fermented Hidakakombu remained viable in simulated gastric and intestinal juices. The ACE inhibitory component in L. casei 001-fermented Hidakakombu was isolated from the fraction below 3 kDa using high-performance liquid chromatography. The purified amino acid was identified as D-Trp using nuclear magnetic resonance, mass spectroscopy, and optical rotation measurements. This is the first report on the ACE inhibitory activity of D-Trp in L. casei 001-fermented Hidakakombu. Hidakakombu fermented by L. casei 001 was shown to be a source of probiotics and functional components against hypertension. Therefore, fermentation by L. casei 001 was found to be an effective means of adding high value to low-grade Hidakombu.

Identification of d-amino acids in tea leaves

During manufacturing processes and in the storage period of tea, amino acids may undergo enantiomeric isomerization, converting their l- to d-forms. To examine the hypothesis, a method was developed for the analysis of the enantiomers in tea leaves. After enriched by ion-exchange solid-phase extraction, the enantiomeric pairs were separated by a chiral high performance liquid chromatography (HPLC) and subsequently detected and identified by using a high resolution quadrupole time-of-flight mass spectrometry (QTOF MS). Only l-forms of amino acids were found in fresh tea leaves. A total of 11 d-amino acids were found in 19 tea samples, ranging from trace amount to 43 µg/g. The results indicated that the enantioisomerization of amino acids occurred in post-harvest tea leaves, and affected by process conditions and storage time.

D-amino acids in foods

With the only exception of glycine, all amino acids exist in two specular structures which are mirror images of each other, called D-(dextro) and L-(levo) enantiomers. During evolution, L-amino acids were preferred for protein synthesis and main metabolism; however, the D-amino acids (D-AAs) acquired different and specific functions in different organisms (from playing a structural role in the peptidoglycan of the bacterial cell wall to modulating neurotransmission in mammalian brain). With the advent of sophisticated and sensitive analytical techniques, it was established during the past few decades that many foods contain considerable amounts of D-AAs: we consume more than 100 mg of D-AAs every day. D-AAs are present in a variety of foodstuffs, where they fulfill a relevant role in producing differences in taste and flavor and in their antimicrobial and antiaging properties from the corresponding L-enantiomers. In this review, we report on the derivation of D-AAs in foods, mainly originating from the starting materials, fermentation processes, racemization during food processing, or contamination. We then focus on leading-edge methods to identify and quantify D-AAs in foods. Finally, current knowledge concerning the effect of D-AAs on the nutritional state and human health is summarized, highlighting some positive and negative effects. Notwithstanding recent progress in D-AA research, the relationships between presence and nutritional value of D-AAs in foods represent a main scientific issue with interesting economic impact in the near future.

Recent Applications of Mass Spectrometry at Clarkson University

Mass spectrometry (MS) is a powerful technique that has various applications including the identification and characterization of proteins, protein-protein interactions and protein post translational modifications, as well as other molecules (i.e. metabolites, lipids, nucleotides and polynucleotides). However, not too many undergraduate students within the USA and around the world have access to (and are trained in) MS. The undergraduate students in our department are taught to analyze proteomics and metabolomics data obtained from MS analysis, including de novo sequencing of peptides and to interpret the MS and MS/MS data acquired in positive and negative ionization modes. Here, we give some examples of MS data analyzed in the Biochemistry I class and then examples of some independent research projects performed by students over the years in the Biochemistry and Biotechnology laboratory, where MS is used for both proteins, peptides and metabolites analysis, thus demonstrating the applicability of MS analysis in diverse fields. The projects discussed include analysis of the protein content present in yogurt, beer, protein shakes, contact lenses, or milk of animal or vegetal origin.

Rapid Determination of Amino Acids of Nitraria tangutorum Bobr. from the Qinghai-Tibet Plateau Using HPLC-FLD-MS/MS and a Highly Selective and Sensitive Pre-Column Derivatization Method

Amino acids are indispensable components of living organisms. The high amino acid content in Nitraria tangutorum Bobr. fruit distinguishes it from other berry plants and is of great significance to its nutritional value. Herein, using 10-ethyl-acridine-3-sulfonyl chloride as a fluorescent pre-column labeling reagent, a method for the efficient and rapid determination of amino acid content in N. tangutorum by pre-column fluorescence derivatization and on-line mass spectrometry was established and further validated. The limits of detection (signal-to-noise ratio = 3) were between 0.13 and 1.13 nmol/L, with a linear coefficient greater than 0.997 and a relative standard deviation between 1.37% and 2.64%. In addition, the method required a short analysis time, separating 19 amino acids within 20 min. Subsequently, the method was used to analyze the amino acid content of Nitraria tangutorum Bobr. from tissues retrieved from seven regions of the Qinghai-Tibet Plateau. Nitraria tangutorum Bobr. was shown to contain a large amount of amino acids, with the total content and main amino acid varying between the different tissues. This research supports the nutritional evaluation, quality control, and development and utilization of Nitraria tangutorum Bobr.

Determination of enantiomeric excess of some amino acids by second-order calibration of kinetic-fluorescence data

In this investigation a new non-separative kinetic-spectroflourimetric method is proposed for the determination of lysine (lys), leucine (leu) and phenylalanine (phe) enantiomers as their o-phthaldialdehyde (OPA) derivatives in the presence of an optically active chiral thiol compound, 1-mercapto-2-propanol (MP). At ambient temperature and in the borate buffer media of pH 9.6, MP, OPA, as highly selective fluorogenic reagents, and amino acid (AA) enantiomers reacts with each other to yield two fluorescent diasteriomers of D and L-AA with maximum difference in fluorescence intensity at about 450 nm. To achieve information from the small spectral changes, the data are analyzed by Multivariate Curve Resolution Alternating Least Squares (MCR-ALS) method. Linear calibration curves are achieved to distinct D and L-lys, leu and phe in different mole ratios by applying appropriate constraints in MCR-ALS procedures. This is the first application of MCR-ALS in determination of enantiomeric excess (ee) using OPA/MP adduct as chiral reagent, which benefits from direct time dependent-fluorescence spectral analysis and does not require prior separation of chiral analytes. Both the cross-validated correlation coefficient (Q²) and root mean squares error of prediction (RMSEP) indicated satisfactory prediction ability of this method.

Characterization of Lactobacillus salivarius alanine racemase: short-chain carboxylate-activation and the role of A131

Many strains of lactic acid bacteria produce high concentrations of d-amino acids. Among them, Lactobacillus salivarius UCC 118 produces d-alanine at a relative concentration much greater than 50 % of the total d, l-alanine (100d/d, l-alanine). We characterized the L. salivarius alanine racemase (ALR) likely responsible for this d-alanine production and found that the enzyme was activated by carboxylates, which is an unique characteristic among ALRs. In addition, alignment of the amino acid sequences of several ALRs revealed that A131 of L. salivarius ALR is likely involved in the activation. To confirm that finding, an L. salivarius ALR variant with an A131K (ALR(A131K)) substitution was prepared, and its properties were compared with those of ALR. The activity of ALR(A131K) was about three times greater than that of ALR. In addition, whereas L. salivarius ALR was strongly activated by low concentrations (e.g., 1 mM) of short chain carboxylates, and was inhibited at higher concentrations (e.g., 10 mM), ALR(A131K) was clearly inhibited at all carboxylate concentrations tested (1-40 mM). Acetate also increased the stability of ALR such that maximum activity was observed at 35 °C and pH 8.0 without acetate, but at 50 °C in the presence of 1 mM acetate. On the other hand, maximum ALR(A131K) activity was observed at 45 °C and around pH 9.0 with or without acetate. It thus appears that A131 mediates the activation and stabilization of L. salivarius ALR by short chain carboxylates.

Crystallographic studies of aspartate racemase from Lactobacillus sakei NBRC 15893

Aspartate racemase catalyzes the interconversion between L-aspartate and D-aspartate and belongs to the PLP-independent racemases. The enzyme from the lactic acid bacterium Lactobacillus sakei NBRC 15893, isolated from kimoto, is considered to be involved in D-aspartate synthesis during the brewing process of Japanese sake at low temperatures. The enzyme was crystallized at 293 K by the sitting-drop vapour-diffusion method using 25%(v/v) PEG MME 550, 5%(v/v) 2-propanol. The crystal belonged to space group P3121, with unit-cell parameters a = b = 104.68, c = 97.29 Å, and diffracted to 2.6 Å resolution. Structure determination is under way.

Data-fusion for multiplatform characterization of an Italian craft beer aimed at its authentication

Five different instrumental techniques: thermogravimetry, mid-infrared, near-infrared, ultra-violet and visible spectroscopies, have been used to characterize a high quality beer (Reale) from an Italian craft brewery (Birra del Borgo) and to differentiate it from other competing and lower quality products. Chemometric classification models were built on the separate blocks using soft independent modeling of class analogies (SIMCA) and partial least squares-discriminant analysis (PLS-DA) obtaining good predictive ability on an external test set (75% or higher depending on the technique). The use of data fusion strategies - in particular, the mid-level one - to integrate the data from the different platforms allowed the correct classification of all the training and validation samples.

Chiral amino acid analysis of Japanese traditional Kurozu and the developmental changes during earthenware jar fermentation processes

Enantioselective amino acid metabolome analysis of the Japanese traditional black vinegars (amber rice vinegar, Kurozu) was performed using two-dimensional high-performance liquid chromatography combining a microbore-monolithic ODS column and narrowbore-enantioselective columns. d-Amino acids, the enantiomers of widely observed l-amino acids, are currently paid attention as novel physiologically active substances, and the foodstuffs and beverages containing high amounts of d-amino acids are the subjects of interest. In the present study, the amino acid enantiomers were determined by two-dimensional HPLC techniques after pre-column fluorescence derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole. In the first dimension, the amino acid enantiomers are separated as their d plus l mixtures by the reversed-phase mode, then the d-amino acids and their l-counterparts are separately determined in the second dimension by the enantioselective columns. As a result, large amounts of d-Ala (800-4000nmol/mL), d-Asp (200-400nmol/mL) and d-Glu (150-500nmol/mL) were observed in some of the traditionally produced Kurozu vinegars. Relatively large or small amounts of d-Ser (50-100nmol/mL), d-Leu (10-50nmol/mL) and d-allo-Ile (less than 20nmol/mL) were also present in these samples. Developmental changes in the d-amino acid amounts during the fermentation and aging processes have also been investigated.

Distribution of D-amino acids in vinegars and involvement of lactic acid bacteria in the production of D-amino acids

Levels of free D-amino acids were compared in 11 vinegars produced from different sources or through different manufacturing processes. To analyze the D- and L-amino acids, the enantiomers were initially converted into diastereomers using pre-column derivatization with o-phthaldialdehyde plus N-acethyl-L-cysteine or N-tert-butyloxycarbonyl-L-cysteine. This was followed by separation of the resultant fluorescent isoindol derivatives on an octadecylsilyl stationary phase using ultra-performance liquid chromatography. The analyses showed that the total D-amino acid level in lactic fermented tomato vinegar was very high. Furthermore, analysis of the amino acids in tomato juice samples collected after alcoholic, lactic and acetic fermentation during the production of lactic fermented tomato vinegar showed clearly that lactic fermentation is responsible for the D-amino acids production; marked increases in D-amino acids were seen during lactic fermentation, but not during alcoholic or acetic fermentation. This suggests lactic acid bacteria have a greater ability to produce D-amino acids than yeast or acetic acid bacteria.

On-line sample preconcentration by sweeping and poly(ethylene oxide)-mediated stacking for simultaneous analysis of nine pairs of amino acid enantiomers in capillary electrophoresis

This study proposes a sensitive method for the simultaneous separation and concentration of 9 pairs of amino acid enantiomers by combining poly(ethylene oxide) (PEO)-based stacking, β-cyclodextrin (β-CD)-mediated micellar electrokinetic chromatography (MEKC), and 9-fluoroenylmethyl chloroformate (FMOC) derivatization. The 9 pairs of FMOC-derivatized amino acid enantiomers were baseline separated using a discontinuous system, and the buffer vials contained a solution of 150 mM Tris-borate (TB), 12.5% (v/v) isopropanol (IPA), 0.5% (w/v) PEO, 35 mM sodium taurodeoxycholate (STDC), and 35 mM β-CD, and the capillary was filled with a solution of 1.5 M TB, 12.5% (v/v) IPA, 35 mM STDC, and 35 mM β-CD. Based on the difference in viscosity between the sample zone and PEO solution and because of the STDC sweeping, the discontinuous system effectively stacked 670 nL of the 9 pairs of FMOC-derivatized amino acid enantiomers without losing chiral resolution. Consequently, the limits of detection for the 9 pairs of FMOC-derivatized amino acid enantiomers were reduced to 40-60 nM. This method was successfully used to determine d-Tryptophan (Trp), l-Trp, d-Phenylalanine (Phe), l-Phe, d-Glutamic acid (Glu), and l-Glu in various types of beers.

Greater enhancement of Bacillus subtilis spore yields in submerged cultures by optimization of medium composition through statistical experimental designs

Bacillus subtilis spore preparations are promising probiotics and biocontrol agents, which can be used in plants, animals, and humans. The aim of this work was to optimize the nutritional conditions using a statistical approach for the production of B. subtilis (WHK-Z12) spores. Our preliminary experiments show that corn starch, corn flour, and wheat bran were the best carbon sources. Using Plackett-Burman design, corn steep liquor, soybean flour, and yeast extract were found to be the best nitrogen source ingredients for enhancing spore production and were studied for further optimization using central composite design. The key medium components in our optimization medium were 16.18 g/l of corn steep liquor, 17.53 g/l of soybean flour, and 8.14 g/l of yeast extract. The improved medium produced spores as high as 1.52 +/- 0.06 x 10(10) spores/ml under flask cultivation conditions, and 1.56 +/- 0.07 x 10(10) spores/ml could be achieved in a 30-l fermenter after 40 h of cultivation. To the best of our knowledge, these results compared favorably to the documented spore yields produced by B. subtilis strains.

Occurrence of D-serine in rice and characterization of rice serine racemase

Germinated, unpolished rice was found to contain a substantial amount of D-serine, with the ratio of the D-enantiomer to the L-enantiomer being higher for serine than for other amino acids. The relative amount of D-serine (D/(D+L)%) reached approximately 10% six days after germination. A putative serine racemase gene (serr, clone No. 001-110-B03) was found in chromosome 4 of the genomic DNA of Oryza sativa L. ssp. Japonica cv. Nipponbare. This was expressed as serr in Escherichia coli and its gene product (SerR) was purified to apparent homogeneity. SerR is a homodimer with a subunit molecular mass of 34.5kDa, and is highly specific for serine. In addition to a serine racemase reaction, SerR catalyzes D- and L-serine dehydratase reactions, for which the specific activities were determined to be 2.73 and 1.42nkatal/mg, respectively. The optimum temperature and pH were respectively determined for the racemase reaction (35 degrees C and pH9.0) and for the dehydratase reaction (35 degrees C and pH9.5). SerR was inhibited by PLP-enzyme inhibitors. ATP decreased the serine racemase activity of SerR but increased the serine dehydratase activity. Kinetic analysis showed that Mg(2+) increases the catalytic efficiency of the serine racemase activity of SerR and decreases that of the serine dehydratase activity. Fluorescence-quenching analysis of the tryptophan residues in SerR indicated that the structure of SerR is distorted by the addition of Mg(2+), and this structural change probably regulates the two enzymatic activities.

Rapid classification of enzymes in cleaning products by hydrolysis, mass spectrometry and linear discriminant analysis

A method for the rapid classification of proteases, lipases, amylases and cellulases used as enhancers in cleaning products, based on precipitation with acetone, hydrolysis with HCl, dilution of the hydrolysates with ethanol, and direct infusion into the electrospray ion source of an ion-trap mass spectrometer, has been developed. The abundances of the ([M+H]+ ions of the amino acids, from the hydrolysates of both the enzyme industrial concentrates and the detergent bases spiked with them, were used to construct linear discriminant analysis models, capable of distinguishing between the enzyme classes. For this purpose, the variables were normalized as follows: (A) the ion abundance of each amino acid was divided by the sum of the ion abundances of all the amino acids in the corresponding mass spectrum; (B) the ratios of pairs of ion abundances were obtained by dividing the ion abundance of each amino acid by each one of the ion abundances of the other 17 amino acids in the corresponding mass spectrum. Using normalization procedure B, excellent class-resolution between proteases, lipases, amylases and cellulases was achieved. In all cases, enzymes in industrial concentrates and manufactured cleaning products were correctly classified with >98% assignment probability.

Effect of reaction pH on enolization and racemization reactions of glucose and fructose on heating with amino acid enantiomers and formation of melanoidins as result of the Maillard reaction

This study investigates the effect of reaction pH on enolization and racemization reactions of glucose and fructose on heating with amino acid enantiomers, can influence the formation of melanoidins as result of the Maillard reaction. Remarkable enolization reaction of sugars was observed in the course of the Maillard reaction. Especially, the degree of sugar enolization was increased as the pH levels increased, which was higher in fructose than glucose systems. Otherwise, enolization of sugars on heating with amino acid was higher in glucose than fructose systems. Formation of isomer in Glc/d-Lys, Fru/d-Asn and Fru/d-Lys were increased upon increase of pH levels. The relative amounts of isomers in Glc/l-Asn and Glc/d-Asn were decreased upon increase of pH levels. Browning development was dependent on the pH levels, being more significant for model systems apart from heated glucose solution alone. Browning development of fructose systems was higher than glucose-amino acid systems. The l- and d-isomers both showed different absorption in the UV-vis spectra and that these occur at similar shape. Every peak has a stable absorbance appeared in the range between 260 and 320nm, characteristic of melanoidins.

Classification of vegetable oils according to their botanical origin using amino acid profiles established by direct infusion mass spectrometry

Amino acid profiles, established by direct infusion mass spectrometry, have been used to classify vegetable oils according to their botanical origin. The proteins present in hazelnut, sunflower, corn, soybean, olive, avocado, peanut and grapeseed oils were precipitated with acetone, and the residue was hydrolyzed in acid medium, diluted in a hydrochloric acid/ethanol mixture, and infused into the mass spectrometer. The spectra of the hydrolyzed protein extracts showed [M+H]+ ions of the following amino acids: glycine, alanine, serine, proline, valine, threonine, cysteine, isoleucine + leucine, aspartic acid, lysine, glutamic acid, methionine, histidine, phenylalanine, arginine and tyrosine. These ions were used to construct linear discriminant analysis (LDA) models. The ratios of the ion signal intensities selected by pairs were used as predictors. With the sequential application of three LDA models, the eight botanical origin categories of the samples were well resolved.

Enantiomeric analysis of amino acids by using comprehensive two-dimensional gas chromatography

The chiral separation of amino acids (AA) derivatised with ethyl chloroformate by using comprehensive two-dimensional gas chromatography is reported. A commercially available enantioselective capillary column (Chirasil-l-Val) has been tested as first-dimension column. Two nonenantioselective stationary phases (BPX50 and BP1) with different column lengths were combined with the enantioselective column, which represent chiral/polar and chiral/low-polarity column sets, respectively. These column sets were evaluated to determine the most useful column combination to provide improved separation efficiency of enantioselective AA analysis. Separations of AA mixtures derivatised either as their N-trifluoroacetyl methyl esters or with methyl chloroformate, performed on a chiral/low-polarity column set, are also shown. The method was demonstrated for chiral analysis of AAs in different beer samples. The major AA in the beer samples was proline with amounts ranging from around 65-95% with minor contents of glycine and the l-enantiomers of alanine, valine, leucine, and isoleucine. Small amounts of d-alanine, at about 1, 1.5, and 15% were detected in the three samples.