Sugar humic acid

Humic acids - anitro-humic acid, sugar-humic acid, ligno-humic acid, meta ligno-humic acid. Soluble in alkali and... 

Recall from Chapter 23.2.4 that humic substances are isolated from seawater by adsorption on a hydrophobic resin followed by elution using solvents of varying pH. The desorbed compounds are fractionated into two classes, humic acids fulvic acids based on their solubility behavior. A model structure for a humic acid is illustrated in Figure 23.10a in which fragments of biomolecules, such as sugars, oligosaccharides. 

Phenolic compounds can be condensed forming aryl-aryl and aryl-oxygen-aryl (ether linkages) bonds to yield diaryl and diaryl ether polymers (59). These are in many ways similar to natural humic acids, confirming earlier research by others (60-62) that humic acids are formed from the copolymerization of phenolic compounds with amino acids, peptides, and amino sugars. 

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). 

Another major problem associated with the extraction of DNA from archaeological specimens is that the procedure often co-extracts impurities that can later complicate, or prevent, the study of the extracted DNA by inhibiting PCR amplification (reviewed by 5). Commonly encountered inhibitory substances found in aDNA extracted from teeth, bones, mummified tissue, and coprolites include humic acids, ftilvic acids, tannins, porphyrin products, phenolic compounds, hematin, and collagen type I (37—42). The formation of Maillard products, commonly encountered in coprolite samples, can also prevent PCR amplification by causing DNA to become inaccessibly trapped in these sugar-derived condensation products (12). As the negative results in many aDNA studies are attributed to the presence of PCR inhibitors, our extraction method outlined below pays particular attention to the problem and offers a simple test for the presence of PCR inhibitors in DNA extracts. 

Spectrophotometric and chromatographic studies indicated that the color-bearing compounds responsible for the sugar color development were 5-HMF, caramel, humic acids, and melanoidins. Reduction of these compounds by improving first carbonation technique to minimize reducing sugar destruction would improve color development of the carbonation sugar. 

A number of poorly defined terms have been used for distinguishing various types of colorant that may occur in sugar materials. It appears probable that precise spectrophotometry may eventually help to show whether the distinctions which have been made between the various colorants (such as caramels, humin, humic acids, melanoidins, etc.) are justified from this point of view. 

In contrast to the selective preservation theory, the condensation pathway proposes that humic substances are derived from the polymerization and condensation of low-molecular-weight molecules that are products of the partial microbial degradation of organic residues (Kogel-Knabner, 1993). Under this scheme of increasing complexa-tion, fulvic acids would be the first humic substances synthesized, followed by humic acids and then humin (Stevenson, 1994). The two commonly accepted condensation models are the polyphenol theory and the sugar-amine or mela-noidin theory. 

Non-volatile organic compounds can be characterized by c.g.c. if pyrolyzed directly into the injector chamber of a g.c. [56, 57 ]. It has been shown that size exlusion chromatography and gel permeation chromatography are adequate techniques for fractionation of non-volatile components from water samples. The fractions are then to pyrolysis-g.c.— mass spectrometry for the characterization of humic acid and fulvic acids, sugars, and proteins [57 ]. ... 

Humic and flilvic acids are traditionally extracted from soils and sediment samples as the sodium salts by using sodium hydroxide solution. The material that remains contains the insoluble humin fraction (Figure 3). The alkaline supernatant is acidified to pH 2 with HCl. The humic acid precipitates and the fulvic acid remains in solution with other small molecules such as simple sugars and amino acids. These molecules can be separated by passing the solution through a hydrophobic resin, such as the methacrylate cross-linked polymer, XAD-8. The fulvic acids will sorb to the resin while the more hydrophilic molecules pass through the column. The fulvic acid can be removed with dilute base. 

Amino Acids. Kemp and Mudrochova (1973) determined amino acids and amino sugars by ion-exchange chromatography in 6N HCl hydrolysates of humic and fulvic acids from Lake Ontario sediments. They obtained total amino acids of 21.5% for humic acid and 12.6% for fulvic acid. Total amino sugars accounted for only 1.9 and 1.3% for humic acid and fulvic acid, respectively. They found the amino acid distribution in the humic acid resembled that of zooplankton and suspended sediment samples, with the exception of glycine which was higher in the sediments. This lends support for the assumed autochthonous nature of lake sediment organic matter. On the other hand, basic amino acid concentrations were low in the fulvic acid and its amino acid distribution resembled the combined form in the interstitial waters. 

A gradual decrease of carbohydrates with depth in humic substances in Lake Haruna sediments was shown by Uzaki (unpublished). Uzaki analyzed carbohydrates (neutral sugars) in humic acid, fulvic acid, and humin [Fig. 7(B)-(D)]. 

Acid hydrolysis is often used to release amino acids and carbohydrates from the total sediment or from isolated humic acids. This method was first applied to marine sediments by Degens et al. (1964). However, since the apparent distribution of amino acids and sugars seems to depend strongly on... 

By examination of the recent literature as reviewed by Tissot and Welte (1978), one gets the impression that the diagenesis of humic substances to form kerogen is well understood. In effect, many consider kerogen to be formed via condensation mechanisms in which aquatic plant substances are microbially degraded to form soluble monomers that condense to form humic polymers that eventually condense to form kerogen. The melanoidin pathway (sugar-amino acid condensation products) has been invoked by some to explain the structures formed (Nissenbaum and Kaplan, 1972 Hue and Durand, 1973, 1977 Welte, 1973 Nissenbaum, 1974 Stuermer et al. 1978 Tissot and Welte, 1978). 

Table 4 shows mean values for the relative distribution of amino acids in acid hydrolyzates of humic acids and fulvic acids extracted from the same soils. These data are expressed as a-amino nitrogen of each amino acid x 100/total amino acid nitrogen. An inspection of the data in Table 4 indicates, with few minor exceptions, similarities in the amino acid composition of humic acids and fulvic acids. Acid hydrolysis appears to destroy about one-half of the amino sugars and there are losses of threonine and serine (Sowden, 1959, 1969). No corrections are made for their decomposition because the ammonia-nitrogen would then require correction, and a valid correction for it is not possible. The ammonia nitrogen increases with length of time of hydrolysis (Khan and Sowden, 1971). 

Table 5 presents data on the distribution of nitrogen in humic acids, fulvic acids, and humin extracted from tropical soils. Especially noteworthy are the relatively high proportions of amino acid nitrogen in all humic fractions, and the unusually high percentages of total nitrogen identified. Humin is especially rich in amino sugars. 

---