Dissolved carbohydrates

The relatively specific method outUned here combines a number of well-known reactions in carbohydrate chemistry it is based on a procedure described by Johnson and Sieburth (1977) with minor modifications. Since formaldehyde is the only product actually detected, the responses of various sugars are fairly uniform. The method offers several advantages over earlier techniques especially as it avoids the use of concentrated mineral acids. 

A number of steps are involved in the method and hence it is relatively time-consuming. On the other hand, a large number of samples may be processed at once, as only 1 mL of seawater is required. The technique is almost free of interferences and appears to detect monosaccharides only (MCHO). After a simple hydrolysis procedure the method may be employed to estimate concentrations of polysaccharides in seawater or in marine particulates. Since (in addition to glassware and chemicals) a photometer is the only equipment required, few problems are encountered when using the method in the field. 

Briefly, the method comprises reduction of the monosaccharides to the respective sugar alcohols, periodate oxidation to formaldehyde and detection of this compound as a coloured complex with 3-methyl-2-benzothiazolinone hydrazone at 635 nm. After subtraction of a blank value and comparison with a standard curve the results are reported in glucose equivalents. 

However, in addition to monosaccharides the technique will determine all compounds containing a 1,2-diol moiety such as alditols, amino sugars and uronic acids. Non-reducing disaccharides remain undetected by this procedure reducing disaccharides show a somewhat lower response. Of the organic compounds tested so far only serine interferes at concentration levels higher than those exf ected in seawater. 

Sodium borohydride Make sure that the crystalline sodium borohydride is stored in a desiccator use fresh chemicals only. Immediately before use dissolve 70 mg of sodium borohydride in 5 mL of distilled water (5 °C). 

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The carbonyl group of carbohydrates can be reduced to an alcohol function Typi cal procedures include catalytic hydrogenation and sodium borohydnde reduction Lithium aluminum hydride is not suitable because it is not compatible with the solvents (water alcohols) that are required to dissolve carbohydrates The products of carbohydrate reduc tion are called alditols Because these alditols lack a carbonyl group they are of course incapable of forming cyclic hemiacetals and exist exclusively m noncyclic forms... 

The transformation of carbohydrates, proteins and lipids has been investigated during transport in an intercepting gravity sewer under aerobic conditions. It was seen that dissolved carbohydrates and, to some extent, proteins were removed, whereas the concentration of lipids was almost unchanged (Figure 3.9). 

TABLE 3.4. Total and Dissolved Carbohydrates, Proteins and Lipids as a Percentage of Total and Dissolved COD, Respectively. 

Dissolved carbohydrate (grrr3) Dissolved carbohydrate (grrr3)... 

FIGURE 3.9. Concentrations of dissolved carbohydrate and protein in wastewater during transport in a gravity sewer under aerobic conditions (Raunkjaer et al., 1995). 

Although the investigations of both Raunkjaer et al. (1995) and Almeida (1999) showed that removal of COD — measured as a dissolved fraction — took place in aerobic sewers, a total COD removal was more difficult to identify. From a process point of view, it is clear that total COD is a parameter with fundamental limitations, because it does not reflect the transformation of dissolved organic fractions of substrates into particulate biomass. The dissolved organic fractions (i.e., VFAs and part of the carbohydrates and proteins) are, from an analytical point of view and under aerobic conditions, considered to be useful indicators of microbial activity and substrate removal in a sewer. The kinetics of the removal or transformations of these components can, however, not clearly be expressed. Removal of dissolved carbohydrates can be empirically described in terms of 1 -order kinetics, but a conceptual formulation of a theory of the microbial activity in a sewer in this way is not possible. The conclusion is that theoretical limitations and methodological problems are major obstacles for characterization of microbial processes in sewers based on bulk parameters like COD, even when these parameters are determined as specific chemical or physical fractions. 

The complete hydrolysis of the soluble cellulose derivative required gradual addition of water and, preferably, acid. Water can act on cellulose acetate hydrogensulfate in three ways (a) saponification of sulfate groups, (b) saponification of acetate groups, and (c) hydrolysis of glycosidic bonds. Reaction (a) is most rapid and occurs under the mildest conditions. As Table II shows, the product is not any more water soluble (Entries 1-4). Under more severe conditions, the deacetylation (b) has proceeded to water-soluble products, the total amount of dissolved carbohydrates corresponding to theory (Entries 5-10). How-... 

The electron micrographs of the enzyme-treated sprucewood holo-cellulose revealed the loci of the removed substances when compared with untreated samples. The relative intensity of degradation at the ultra-structural level corresponded to the results obtained by chemical analysis of the dissolved carbohydrates. 

Q. Liu, M. H. A. Janssen, F. van Rantwijk, and R. A. Sheldon, Room-temperature ionic liquids that dissolve carbohydrates in high concentrations, Green Chem., 7 (2005) 39 42. 

Gremm, T. J., and L. A. Kaplan. 1997. Dissolved carbohydrates in streamwater determined by HPLC and pulsed amperometric detection. Limnology and Oceanography 42 385-393. 

Johnson, K. M., and J. M. Sieburth. 1977. Dissolved carbohydrates in seawater. I. A precise spectrophotometric analysis for monosaccharides. Marine Chemistry 5 1-13. 

Munster, U. 1984. Distribution, dynamic and structure of free dissolved carbohydrates in the PlulSsee, a north German eutrophic lake. Verhandlungen Internationale Vereinigung fiir Theoretische und Angewandte Limnologie 22 929-935. 

Senior, W., and L. Chevolot. 1991. Studies of dissolved carbohydrates (or carbohydrate-like substances) in an estuarine environment. Marine Chemistry 32 19—35. 

As mentioned earlier, the abundance of carbohydrates in ocean DOM relative to river DOM does not reflect the biochemical compositions of terrestrial plants and marine phytoplankton. It appears that carbohydrates in plant litter are largely degraded in soils, resulting in relatively low concentrations in river DOM. Carbohydrates are the major components of exudates from phytoplankton (Biddanda and Benner, 1997 Biersmith and Benner, 1998), and herbivorous grazing also releases carbohydrates to the DOM reservoir (Strom et al., 1997). The in situ production of dissolved carbohydrates in the surface ocean appears to result in a greater relative abundance of carbohydrates in the ocean relative to rivers. 

Note See the cited references for details about the bioassay incubation conditions. A spectrophotometric assay for dissolved carbohydrates was used rather than a chromatographic assay of individual neutral sugars. 

Burney, C. M. 1986. Bacterial utilization of total in situ dissolved carbohydrate in offshore waters. Limnology and Oceanography 31 427-431. 

Nineteen different compounds (or compound classes) that are known to be rapidly assimilated by bacterioplankton have been identified as DOM photoproducts (Table I). Five of these photoproducts are formed with source DOM from both freshwater and marine environments acetaldehyde, formaldehyde, glyoxylate, pyruvate, and amino acids. Nine others have been reported only from freshwater systems (acetate, butyrate, citrate, formate, levulinate, malonate, oxalate, succinate, and dissolved carbohydrates), whereas five have been reported only from marine systems (acetone, butanal,... 

Gremm, Th.J. and L.A. Kaplan. 1998. Dissolved carbohydrate concentration, composition, and bioavailability to microbial heterotrophs in stream water. Acta Hydrochim. Hydrobiol. 26 167-171. 

Cheng X. and Kaplan L. A. (2001) Improved analysis of dissolved carbohydrates in stream water with HPLC-PAD. Anal. Chem. 73, 458-461. 

Ionic liquids are able to dissolve carbohydrates to high concentrations as mentioned in the previous section. The use of ionic liquids in cellulose dissolution and functionalisation is particularly significant considering the problems associated with conventional processes such as the cupramonium and xanthate processes [117, 118, 120, 134-136], Lignin is soluble in ionic liquids, as discussed in Sect. 4.2. 

Zhao H, Baker GA, Song Z et al (2008) Designing enzyme-compatible ionic liquids that can dissolve carbohydrates. Green Chem 10 696-705... 

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