Polysaccharides chemical classification

Chemical classification of polysaccharides is the least ambiguous system of grouping these macromolecules. Polysaccharides of different origins can have similar structures, as Kravtchenko et al. (1992) discovered in lemon and apple pectin. Likewise, polysaccharides of the same origin can have different structures, as for example, the concentration of pyruvate and acetyl substituents in xanthan, depending on incubation conditions (Pettitt, 1982). 

As indicated in the first part of the chapter, this type of classification based on the occurrence of polysaccharides offers some disadvantages, particularly in that some materials such as chitin, hyaluronic acid, and cellulose occur in plants or microorganisms as well as in animals. However, until more chemical work is done, a strictly chemical classification does not seem feasible. The conflicting classifications and nomenclature in this field need standardization and agreement. 

Such a chemical classification is necessarily incomplete, since detaik of structure are not available for all known polysaccharides. Table II, however, lists the more important polysaccharides classified according to this scheme... 

Different classifications for the chiral CSPs have been described. They are based on the chemical structure of the chiral selectors and on the chiral recognition mechanism involved. In this chapter we will use a classification based mainly on the chemical structure of the selectors. The selectors are classified in three groups (i) CSPs with low-molecular-weight selectors, such as Pirkle type CSPs, ionic and ligand exchange CSPs, (ii) CSPs with macrocyclic selectors, such as CDs, crown-ethers and macrocyclic antibiotics, and (iii) CSPs with macromolecular selectors, such as polysaccharides, synthetic polymers, molecular imprinted polymers and proteins. These different types of CSPs, frequently used for the analysis of chiral pharmaceuticals, are discussed in more detail later. 

The descriptive phase of biology is an essential prerequisite for the healthy growth of biochemistry, and the serological classification of the Salmonellas and related Enterobacteria has allowed a comprehensive and reproducible series of analyses to be made where otherwise a chaotic situation could have arisen. The Kauffmann-White Schema embraces more than the specificities due to polysaccharides of the O antigens. The H antigens, for example, are specificities due to the protein components of the flagella, and these are probably beyond the scope of chemical methods available at this time. 

There is no ideal system of polysaccharide classification [3]. The best system should be that based on chemical structure. However, because of their polymolecularity, which limits descriptions to statistical structures in many cases, and the great variety of structures, classifying polysaccharides in this way has limitations. Combinations of the following categories are used [3] ... 

Polysaccharides are found in plants and animals. In higher plants and algae, they are components of either the cell wall or the cell interior. In bacteria and fungi, they can be both cell components and metabolic products. Consequently, in addition to classification according to their chemical structure, polysaccharides are often classified according to their function or use ... 

Classification of the pectic substances is an area that grabbed much attention of the polymer biochemistry. Pectic polysaccharides are in fact, recognized in several forms and accordingly, they have been classified into distinct groups. The American Chemical Society classified pectic substances into fom main groups as follows (Kertesz, 1951). 

Biosurfactants are classified based on their chemical composition and microbial origin. The chemical structure of biosurfactants contains hydrophilic and hydrophobic groups. Amino acids, peptides and polysaccharides can be present as hydrophilic moieties and saturated or unsaturated fatty acids can be present as hydrophobic moieties in the structure. Structure based classification has following major classes of biosurfactants (Guerra-Santos et al., 1987 Kooper and Goldenberg, 1987) (i) Glycolipids (Rhamnolipids, Trehalolipids and Sophorolipids) (ii) Lipopeptide and lipoprotein (iii) Fatty acids, phospholipids and neutral lipids (iv) Pol5mieric biosurfactants, and (v) Particulate biosurfactants. 

In the past [4-6] it was common to characterize amphiphiles according to their major performance in food systems (1) emulsification and stabilization, (2) protein interactions, (3) polysaccharide complexation, (4) aeration, and (5) crystal structure modification of fats. Such classifications correlate the surfactant chemical structure to its interaction (chemical or physical) with substrates such as fats, polysaccharides, and proteins. It was confirmed fhat certain surfactants interact molecularly with macromolecules, forming complexes and/or hybrids, and alter the macromolecular behavior at the interface. Such activity is an important new contribution of cosurfactants to the surface performance of other surfactants [7]. Such interactions are sometimes a very important contribution of amphiphiles to food systems. 

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