ABSTRACT

Plant gums are generally taken to include all plant polysaccharides other than starch that can be hydrated and have a commercial application. The most abundant plant polysaccharide, cellulose, is in a slightly ambiguous position, as naturally occurring, it is clearly insoluble and would appear difficult to consider as a gum. However, although microcrystalline cellulose and soluble modified cellulose are important commercial gums, these are outside the scope of this chapter, which is concerned solely with naturally occurring gums. A polysaccharide can be regarded as mucilage when a high degree of solubility is accompanied by easy hydration and a reduced viscosity. There is also a difference in the origin of gums and mucilages. Mucilages are usually of secretory nature whereas the gums are either cell wall components or intended as reserve polysaccharides to provide energy store for the plant. These categories are not entirely exclusive because highly soluble wall components such as pectins can be readily liberated from the wall and function as mucilage when the wall is fully hydrated. Also, an important class of gums are produced as plant surface exudates, usually as a consequence of plant damage. Algal gums are derived from the wall mucilage of seaweeds.