Glucans 1—>4 - 3-, from plant cell-walls

Xyloglucans are classified as gum when they are extractable with hot water from seed endosperm cell walls, such as the tamarind seed xyloglucan, and as hemicelluloses because they are alkali-extractable from the cell walls of vegetative plant tissues where they are closely associated with cellulose [2]. Also /3-glucans with mixed linkages appear under the name gum as well as hemicellulose in the literature. 

Submicrofibril and triple-stranded left-hand helical microfibrils are found in tobacco primary cell wall and bacterial A. xylinum cellulose. We suspect from our results and the literature survey outlined in reference (1) that the triple stranded structures are prominent in the primary plant cell wall. The highly crystalline cellulose of plant and algae secondary cell wall appears by X-ray fiber diffraction (18,19) and TEM lattice imaging (20-23) to be largely crystalline arrays of planar straight chains of (l-4)-/3-D-glucan chains. 

Some workers refer to cotton lint (the normal fibers) as cellulose to distinguish it from seed cotton (fiber still on the seed) or the entire plant. Herein, the word cellulose has only the strict chemical meaning linear p-(1 4)-D-glucan. In the cell wall, cellulose occurs in small, crystalline microfibrils that are arranged in multilayer structures (see Figure 5.1). An especially important layer is the primary wall (see Figure 5.2) although it is a small fraction of the mature, fully developed fiber. 

Botanical polysaccharides exist as structural constituents of plant cell wall [64]. The main types of polysaccharides involved in cell wall are rigid fibrillar chitin (or cellulose) matrix-Uke (3-glucan, a-glucan, and glycoproteins [64-70]. Therefore, the selectirai of an effective extraction procedure for plant polysaccharides will have to depend on the cell wall structure [64]. In general, the basic theory of extraction of polysaccharides from botanical materials is to break the cell wall under certain conditions such as pH value, temperature, irradiation with microwave, and ultrasonic radiation [65,71]. 

Polysaccharides are made from linking multiple monosaccharide units. These long chain molecules are known as starch in the plant system and glycogen in the animal system. Starch polysaccharides primarily contain a-glucans. These include amylose, amylopectin, modihed starches, and resistant starches. Fiber, also known as nonstarch polysaccharides (NSP), primarily contains components derived from the plant cell wall such as cellulose, hemiceUulose, and pectin. Other polysaccharides include gums and hydrocoUoids. 

The components of dietary hber are derived mainly from the cell walls of plant material in the diet. These include cellulose, hemicellulose (P-glucans, arabinoxy-lans, etc.), and pectin, collechvely referred to as the NSP. Food gums, also called hydrocolloids, are polysaccharides and are considered dietary hber. Lignin, a noncarbohydrate component of the cell wall and a nonpolysaccharide, is also included as hber that is very tough. Most edible fruits and vegetables, with the excephon of carrots, contain low levels of lignin. 

Dietary fibers are polysaccharides from natural foods found primarily in plant cell walls, and include cellulose, hemicelluloses, and pectins. They are P-glucans that are not digestible by humans, and thereby provide noncaloric bulk in the diet. Dietary fibers also include polysaccharides such as pectins, alginates, exudate gums, carrageenans, and agar that are added to foods and are not digestible. 

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