ABSTRACT
The chemical modication of oligosaccharides and polysaccharides is of interest to food science1,2 and the broad area of biomaterials; biomaterials would include applications in regenerative medicine3,4 as well as hydrogels in drug delivery.5,6 Chemical degradation is used for structural analysis7-10 and for the preparation of derivative forms from biological tissue.11,12 Heparin, for example, is derived from porcine intestine or bovine lung by mild alkaline hydrolysis followed by other purication steps.13-15 Low-molecular-weight heparin (LMWH) is derived from unfractionated heparin by fractionation after enzymatic or chemical degradation.16 Methylation (permethylation)17 and acetylation (peracetylation)18,19 of polysaccharides have been used to prepare samples for compositional analysis by gas-liquid chromatography (GLC)20 and are used today to prepare samples for mass spectrometry.21,22
Polysaccharides are composed of monomer units, which are polyols and are similar in structure. The term glycan is used to describe polysaccharides and is most frequently used to describe a polysaccharide moiety to a protein or lipid. The term protein polysaccharide refers to a glycoconjugate obtained from a plant source, while the term proteoglycan is used to refer to a glycoconjugate derived from an animal source.23 A glycoside is a mixed acetal with a glycosyl reacting with non-acyl group (RO). A glycosamine is an N-glycoside, while a C-glycosyl has a C-glycosidic linkage. The reader is directed to several sources for a consideration of carbohydrate nomenclature.24-26
The monomer units of polysaccharides may be modied in vivo to contain amino groups and may be sulfated. A glycosaminoglycan is a polysaccharide that contains amino sugars. The hydroxyl groups in the monomer monosaccharide unit are quite unreactive and can only be modied under rigorous conditions.27,28 Polysaccharides are polar molecules capable of hydrogen bonding, interaction with solvent and can exist in conformation equlibirum.29 Morris30 has discussed the levels of conformation of polysaccharides in solution showing that, as with proteins, there are four levels of structure: primary, secondary, tertiary, and quaternary. The behavior of polysaccharides in solution is critical for their function in foods. In particular, for fabricated foods, thickening and jellying properties31 are characteristics that can be modulated by processing including chemical modication.1,2,32 The rheological properties of nonfood carbohydrates can also be modulated by chemical modication.33,34 In the case of a water-insoluble polysaccharide such as cellulose, function depends on physical strength and chemical inertness.35
