Carbohydrates uronic acids

The ratio of fulvic to humic acid is also significant both, together with carbohydrates (uronic acids and sugars), are linearly related to the SOC. The humic acid increases and the fulvic acid decreases as the SOC increases (McGrath, 1997). 

One must be cautious in interpreting data on carbohydrates, hydroxyl acids, and uronic acids in humic substances. As Thurman and Malcolm 11983) have pointed out, the amount of these materials in a fulvic acid is a function of the way that it was isolated. They have shown that nonassociated carbohydrates, uronic acids, and hydroxyl acids may be separated from fulvic acid by adsorption chromatography on XAD resins. For example, a prairie soil fulvic acid contained 20% carbohydrate before XAD adsorption chromatography and only 5% after chromatography. In the fulvic acid isolated by Sposito et al. (1978) adsorption chromatography was not used in the purification process and therefore some of the carbohydrate that they report may not be an integral part of the fulvic acid structure. 

Composition (g/100g) 2 Non-cellulosic carbohydrates Uronic acids Cellulose Starch Lignin Protein... 

Uronic acids (Section 25 19) Carbohydrates that have an aide hyde function at one end of their carbon chain and a car boxyhc acid group at the other... 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can be reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. Monosaccharides can also be chain-lengthened by the multistep Kiliani-Fischer synthesis and can be chain-shortened by the Wohl degradation. 

Pyruvate ketals add to the anionic nature of the exopolysaccharide and are usually present in stoichiometric ratios with the carbohydrate component Pyruvate is normally attached to the neutral hexoses but may also be attached to uronic adds. In the absence of uronic acids, pyruvate alone contributes to the anionic nature of the exopolysaccharide. 

In tandem with his studies of polysaccharides, Stacey had a research group investigating the chemistry of the unusual sugars found as components of carbohydrate macromolecules. In this context, derivatives of simple sugars, di- and trisaccharides, uronic acids, deoxy sugars, amino sugars, sugar sulfates, and phosphates were studied. 

Table II. Carbohydrate compositions (weight percentage) of individual oligomer peaks purified (QAE-Sephadex or HPLC ion-exchange separation, respectively) from mixtures of citrus pectin oligomers or B fruit extracts Compositions shown are for peaks whose biological activity is described in Figure 4. Uronic acid values are based on colorimetric assay. Proportions of neutral sugars were determined by GC and adjusted so that totals equal 100%. In fact, some oligomers (G7 peaks 8, 9 and 10. B extract peak 10) produced small (less than 1 % of the total integrated area), unknown peaks in the GC chromatograms.

Uronic acid was estimated by the rw-hydroxyphenyl method [4], O-Acetyl contents by the method of Hestrin [5], carbohydrate by the phenol-sulfuric acid method [6] and protein by the Hartree method [7]. 

Table V. Determination of carbohydrates, proteins, uronic acids and 0-acetyl of Fractions from aqueous extractions from seeds of C. speciosa.

De Ruiter, G. A., Schols, H. A., Voragen, A. G. J., and Rombouts, F. M., Carbohydrate analysis of water-soluble uronic acid-containing polysaccharides with high-performance anion-exchange chromatography using methanolysis combined with TFA hydrolysis is superior to four other methods, Anal. Biochem., 207, 176, 1992. 

Determination of xylan is frequently made by estimation of furfural production. Data so obtained, even when appropriately corrected for furfural that arises from uronic acid, may be high if araban is present in the polysaccharide preparation. In the absence of interfering carbohydrates, furfural estimation may lead to accurate xylan values. 

A uronic acid is formed when a carbohydrate is oxidized to a carboxylic acid but still retains the aldehyde group. 

A double mediatory system consisting of modified TEMPO and halide ion or metal ion was also exploited for the oxidation of alcohols [53-55]. A number of carbohydrates have been chemoselectively oxidized at the primary hydroxyl group to uronic acids [56]. 

Partially protected carbohydrates can be selectively oxidized at the primary hydroxy group to uronic acids at the nickel hydroxide electrode. At the same electrode, in polyhydroxy steroids, a preferential oxidation of the sterically better accessible hydroxyl groups is achieved [142]. By way of the mediator, TEMPO, carbohydrates that are only protected at the anomeric hydroxyl group are selectively oxidized at the primary hydroxyl group (Fig. 27) [143-145]. 

Chaplin used methanolysis for the analysis of carbohydrates in glycoproteins. His method was a variation of the foregoing procedures, with an improvement of using tert-hvAyX alcohol to remove hydrogen chloride by coevaporation, instead of prolonged trituration with silver carbonate. His method is useful for samples containing uronic acids and lipids. Mononen studied methanolysis, followed by deamination and reduction with borohydride, for determination of the monosaccharide constituents of glycoconjugates. This method was applied to a lipid-free, protein fraction of rat brain. 

Carbohydrate/O-acetyl content of P. deltoides LCCs appears in Table III. All purified LCCs were 0-acetylated moieties containing varying amounts of glucose, mannose, xylose, and uronic acids. Relative to xylose, the highest levels of uronic acid and 0-acetyl content were encountered in LCCs 1 and 2. LCC 1 was the sole moiety to contain galactose. Xylose was the most abundant sugar found in both LCCs 3 and 4, both of which also contained nearly equimolar amounts of glucose and mannose. 

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