Pyruvic acid, detection

Since the best results were obtained with the W and W-based oxide catalysts, the reaction was studied in more detail using 20 g portions of these catalysts. The reaction was performed at 230°C, with feed rates of pyruvic acid, air, and water = 10.5, 350, and 480 mmol/h. The contact time defined as volume of catalyst (ml)/rate of gaseous feed (ml/s) was about 5.2 s. The main products were citraconic anhydride and CO2. The amount of acetic acid was very small. No other products were detected except for very small amounts of CO, acetone, and acetaldehyde. A relatively large discrepancy was observed between the amount of consumed pyruvic acid and that of the sum of produced citraconic anhydride and acetic acid. This discrepancy was defined as "loss". 

The results obtained appeared quite promising, but the real sensation was the detection of pyruvate, the salt of 2-oxopropanoic acid (pyruvic acid), which is one of the most important substances in contemporary metabolism. Pyruvic acid was first obtained in 1835 by Berzelius from dry distillation of tartaric acid. The labile pyruvate was detected in a reaction mixture containing pure FeS, 1-nonanethiol and formic acid, using simulated hydrothermal conditions (523 K, 200 MPa). The pyruvate yield, 0.7%, was certainly not overwhelming, but still remarkable under the extreme conditions used, and its formation supports Wachtershauser s theory. Cody concludes from these results that life first evolved in a metabolic system prior to the development of replication processes. 

Experiments with glyceraldehyde and dihydroxyacetone showed them to be fermentable, but results with methyl glyoxal were conflicting. With Lebedev juice no lactic acid was formed, but with top yeast Neuberg reported that lactic acid was detectable. In 1913 he and Kerb therefore proposed sugar was converted to methyl glyoxal from which pyruvic acid and ethanol were derived ... 

With a molar ratio of propylene glycol to H2O2 of 2.5, the selectivity to hydroxyacetone at 32% conversion of the glycol was 94%, and the selectivity based on H202 was 85%. Small amounts of acetic acid and formic acid were detected. The initial oxidation proceeds with high selectivity for the secondary alcohol group. Further oxidation affords oxidative cleavage products rather than pyruvic acid, as is observed when the oxidation of hydroxyacetone is carried out with 02 and noble metal catalysts. 

Other types of enzymes When no oxidase or dehydrogenase is available for a target analyte, other types of enzymes have been used for biospedfic recognition e.g. for citric acid detection, citrate lyase, and amperometric detection was possible by coupling to two more enzymatic reactions oxaloacetate decarboxylase and pyruvate oxidase, which convert citric add into H2O2 with the latter being monitored amperometrically with an H202 probe. For detection of acetic add, acetate kinase is used, coupled to pyruvate kinase and pyruvate oxidase [34,35]. 

Mechanism of reaction. The adduct of malvidin-3-glucoside with pyruvic acid, also known as vitisin A(Fig. 9A.3h), was firstly detected in fortified red wines (Bakker et al. 1997) and in a grape marc (Fulcrand et al. 1998) and further isolated and characterized by NMR (Bakker et al. 1997 Fulcrand et al. 1998). According to Fulcrand et al. (1998), the reaction between pyruvic acid and grape anthocyanins occurs through a series of steps similar to those previously described for the hydroxyphenyl-pyranoanthocyanins (Sect. 9A.2.4.1 Fig. 9A.3f). Later studies performed by NMR (Mateus et al. 2001b) and mass spectrometry (Asenstorfer et al. 2001 Hayasaka and Asenstorfer 2002) have confirmed the structure proposed by Fulcrand et al. (1998). This mechanism is extended to the condensation reaction between anthocyanins and other enolizable precursors found in wine (Benabdeljalil et al. 2000). 

Gorton et al. reported carbon paste electrodes based on Toluidine Blue O (TBO)-methacrylate co-polymers or ethylenediamine polymer derivative and NAD" " with yeast alcohol dehydrogenase for the analysis of ethanol [152,153] and with D-lactate dehydrogenase for the analysis of D-lactic acid [154]. Use of electrodes prepared with dye-modified polymeric electron transfer systems and NAD+/NADH to detect vitamin K and pyruvic acid has also been reported by Okamoto et al. [153]. Although these sensors showed acceptable performances, insensitivity to ambient oxygen concentration, sensor stability and lifetime still need to be improved to obtain optimal dehydrogenase based enzyme biosensors. 

Fig. 5 Separation of the organic acid on CIM disk monolithic column. Conditions—mobile phase 130 mM NaCl in 20 mM phosphate buffer, pH 8.0 separation unit CIM disk monolithic column comprising of four CIM QA disks flow rate 5 mL/ min sample (1) 0.03 g/L pyruvic acid, (2) 0.5 g/L malic acid, (3) 0.2 g/L a-ketoglutaric acid, (4) 0.007 g/L fumaric acid, (5) 2 g/L citric acid, and (6) 2 g/L isocitric acid injection volume 20 pL detection UV at 210 nm. (From Ref. [17].)...

An attempt was made to detect ozone as a product of the photolysis of 20 p.p.m. of pyruvic acid in 1 atm. of oxygen. None was detected, though a few tenths of 1 p.p.m. of ozone would have produced an identifiable absorption band. 

Krampitz and Hardebeck (48) and Hardebeck et al. (19) have found that thermal polyamino acids accelerate the decarboxylation of pyruvic acid. Carbon dioxide (from C-1 of p5n uvate) and acetic acid (from C-2 and C-3 of pyruvate) were the main products. Small amounts of acetaldehyde and acetoin were also detected. The finding of acetic acid as a main product indicates, as the authors pointed out, that an oxidation as well as a decarboxylation must occur. The process is thus somewhat similar to that observed by Fox and Krampitz (46) with... 

Figure 1.10 HPLC analysis of organic acids in Cabernet Sauvignon wine using after sample preparation by C18 SPE followed by isolation of organic acids a 500-mg amine-quaternary resin (Figure 1.9). 1. tartaric acid, 2. malic acid, 3. lactic acid, 4. acetic acid, 5. citric acid, 6. pyruvic acid, 7. shikimic acid. Analytical conditions column C18 (250 x 4mm, 5 pun) at room temperature, detection at wavelength 210nm, sample volume injected 20p.L, solvent H3P04 5 x 10 3M with isocradc elution at flow rate 0.6mL/min (Flamini and Dalla Vedova, 1999)...

Fig. 4-10. Separation of organic acids on IonPac ICE-AS5. - Eluent 0.0016 mol/L perfluorobu-tyric acid flow rate 0.3 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations fully dissociated compounds (1), 10 ppm oxalic acid (2), 25 ppm pyruvic acid (3), and tartaric acid (4), 30 ppm malonic acid (5), lactic acid (6), malic acid (7), and acetic acid (8), 20 ppm isodtric acid (9), 30 ppm citric acid (10), 40 ppm / -hydroxybutyric acid (11), succinic acid (12), and propionic acid (13).

Fraction A obtained from the elution of a two-year-old Port wine through Toyopearl gel column with 20% aqueous ethanol was found to be mainly comprised of eight pigments which structural identities were ascertained by LC-MS (Table 1). The number attributed to each compoimd in Table 1 corresponds to the elution order by HPLC in the condition described herein. The three major pigments detected were isolated by semi-preparative HPLC and their structures were fully elucidated by mass spectrometry and NMR. Based on their UV-visible characteristics and structural analysis, these pigments were found to correspond to the pyruvic acid adducts of malvidin 3-glucoside (3A), malvidin... 

Figure 1. Structures of the major anthocyanin-pyruvic acid adducts detected in...

As shown in Equations 1 and 2, cystine lyase produces cysteine, pyruvate, ammonia and sulfur from cystine. The cysteine is further acted upon to give pyruvate, hydrogen sulfide and ammonia. Hydrogen sulfide and ammonia formation probably account for the sulfhydryl compound and ammonia aromas detected in the unblanched sample. The pyruvic acid (at the pH of the samples) may account for the sour aroma detected in the unblanched sample, as well as samples treated with lyase and lipase separately. 

A number of polysaccharides, of microbial origin, contain nonsugar substituents, such as ketals of pyruvic acid, that are stable under the conditions of methylation analysis but are acid labile. Unless precautions are taken, such groups can easily lead to the misidentification of branchpoint residues. However, most plant cell wall polysaccharides contain noncarbohydrate substituents that are either alkali labile (e.g., 0-acetyl and phenolic esters) or stable to base and acid hydrolysis (e.g., 0-methyl ethers). The detection and location of 0-methyl ethers can be achieved by performing the methylation with deuterated methyl iodide (Ring and Selvendran, 1980 Selvendran, 1983b) or ethyl iodide. 

Detection systems for GC are chosen for their sensitivity and selectivity for a particular class of VOCs. Detectors for GC include FID, the BCD, the photoionization detector (PID), the pulsed discharge detector (PDD), and the reduction gas detector (RGD). A variety of mass spectrometers can also be interfaced with a GC for confirmation of molecular structure and quantitation. Singlewavelength ultraviolet-visible detectors (190 to 600 nm) and diode array detectors are used to detect carbonyls as their 2,4-dinitrophenylhydrazone derivatives. The absorption maxima for aliphatic carbonyls, aromatic carbonyls, and dicarbonyls are near 360 nm, 385 to 390 nm, and 415 to 430 nm, respectively. Formic, acetic, and pyruvic acid are detected by ion conductivity. 

We are aware of no reports finding dehydroalanine in food proteins. During acid hydrolysis the dehydroalanine is broken down to ammonia and pyruvic acid therefore, only the ammonia would be detected in routine amino acid analysis. In summarizing the many reactions of dehydroalanine in proteins, Friedman (25) reported that 14 crossiinked amino acids can be formed in proteins. If one considers the isomeric forms that could exist, the number expands to at least 53 derivatives. 

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