Polysaccharides: Origin, Source and Properties. Chapter 2

Polysaccharides are natural polymers that can be extracted from various sources. They can be extracted from plant cell walls (such as pectin, cellulose and starch); from seeds (guar gum (GG), locust bean gum (LBG) and tara gum (TG)); from tubers or roots (konjac mannan); and from seaweed (alginate and agarm carrageenan). In some cases, the source is tree exudates (gum arabic (GA), ghatti gum and karaya gum) or animals (hyaluronan, chitosan and chondroitin sulphate). Some types of bacteria and fungi are also a source of polysaccharides (xanthan, gellan, wellan, dextran, pullulan and cellulose). In their natural environment, polysaccharides provide structural support, gelation, hydration and lubrication, and play a role in cell signalling. They are commonly referred to as hydrocolloids, particularly in the food industry, but this term also includes proteins. Owing to their remarkable properties, polysaccharides are currently used as thickening, stabilizing, gelling, film forming and emulsifying agents in various industrial sectors. Furthermore, the quest to understand how they function in their natural assembly, whether as part of a cell wall or in connective tissues, has led to their use as a source of dietary fibre, as a therapeutic agent to restore lubrication in diseased osteoarthritic joints, as plant growth promoters and in anti-ageing applications, among others; they may find many more applications in the future. This chapter will explore the origins, molecular structures and conformations of natural polymers, with an emphasis on functionality. Also, methods employed for the modification of polysaccharides to enhance their functionality or produce novel materials, as well as those using radiation processing, will be briefly mentioned.