Modification sugar constituents

Since sialic acid is a frequent terminal sugar constituent of the polysaccharide trees on glycoproteins, this method selectively forms reactive aldehydes on the most accessible parts for subsequent modifications. The carbohydrate polymer of a protein provides a long spacer arm that can be used to conjugate another large macromolecule, such as a second protein, with little steric problems. 

Bulk sweeteners are distinguished by high stability at elevated temperatures. They do not undergo caramelisation reactions like sucrose. They do not react with common food constituents either. As a result products containing bulk sweeteners instead of carbohydrates may be more pale than sugar-based products and may have a slightly different flavour. Such differences can, however, be compensated for by slight modifications of recipes, if necessary. 

Interaction of volatile and nonvolatile constituents in foods results in flavor modifications of varying intensities. The effects of 5 -nucleotides on the flavor threshold of octanal (23) and the effects of acid, sugar, and pectin on the flavor threshold of limonene (24) have been studied in orange juice. 

Recent studies on modified oligonucleotides have shown that a modification of one of the three components of the constituent nucleotides, i.e., the nucleobase, the sugar moiety, and the phosphate backbone, alters both their stability and overall structure. The actual involvement of stereoelectronic effects in the observed structural changes has been initially addressed only qualitatively [41-45]. 

The Englyst procedure uses enzymatic and chemical methods to measure NSP. (For detailed working protocols, see Further Reading.) All starch is hydrolyzed enzymatically and NSP are measured as the sum of the constituent sugars released by acid hydrolysis. The sugars may be measured by GC or by HPLC to obtain values for individual monosaccharides, or a single value for total sugars may be obtained by colorimetry. Values may be obtained for total, soluble, and insoluble NSP, and a small modification allows cellulose to be measured separately. 

The mutarotations of the sugars listed in Table III and those for many other sugars follow the first-order equation. The activation energy averages about 17,000 cal./mole this value corresponds to an increase in rate of 2.5 times for a 10° rise in temperature. The conformity of the mutarotation data to the first-order equation makes it probable that the main constituents of the equilibrium solution are the a- and jS-pyranose modifications. The actual composition may be calculated from the optical rotations of the equilibrium solution when the rotations of the pure a- and /3-isomers are known. Data of this type are included in Table III. Independent confirmation of the composition of the equilibrium solutions is provided by studies of the rates of bromine oxidation of the sugars, the results of which are also found in Table III. 

Occurrence. The sugar is encountered infrequently. Cathartic-acting glycosides (aloins) such as barbaloin, isobarbaloin, nataloin, and homo-nataloin from plants of the genus Aloe A. barbadensis) yield D-arabinose 39). The glycosidic union is very resistant to hydrolysis. The sugar occurs in the furanose modification as a constituent of the polysaccharide fraction of tubercle bacilli 40). 

Not only is it a constituent of the nucleic acids but also of several vitamins and coenzymes (Chapters VIII and XIII). The sugar occurs in these natural products in the furanose modification. Solutions of ribose probably contain considerable quantities of the furanose form, and the mutarotation is complex and exhibits a minimum. Its metabolism is discussed in Chapters XIII and XIV. 

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