Vegetables polysaccharides

Inuline is a vegetable polysaccharide of low molecular weight (M % 5,400) and fairly narrow molecular weight distribution (lkl-5). It consists of B(l >2) linked D-fructofuranoside units (figure 5). 

Polysaccharides are macromolecules which make up a large part of the bulk of the vegetable kingdom. Cellulose and starch are, respectively, the first and second most abundant organic compounds in plants. The former is present in leaves and grasses the latter in fruits, stems, and roots. Because of their abundance in nature and because of contemporary interest in renewable resources, there is a great deal of interest in these compounds. Both cellulose and starch are hydrolyzed by acids to D-glucose, the repeat unit in both polymer chains. 

Cellulose is the most abundant of naturally occurring organic compounds for, as the chief constituent of the eell walls of higher plants, it comprises at least one-third of the vegetable matter of the world. The cellulose eontent of such vegetable matter varies from plant to plant. For example, oven-dried cotton contains about 90% cellulose, while an average wood has about 50%. The balance is composed of lignin, polysaccharides other than cellulose and minor amounts of resins, proteins and mineral matter. In spite of its wide distribution in nature, cellulose for chemical purposes is derived commerically from only two sources, cotton linters and wood pulp. 

Mannans (Tagut Nut, Corajo, Vegetable Ivory, Carobean), (CgHioOg, mw 162.14. Poly-, meric polysaccharides which yield mannose on hydrolysis. They can be acetylated and nitrated... 

Knee, M., Bartley, I.M. (1981). Composition and metabolism of cell wall polysaccharides in ripening fruits. In Friend, J., Rhodes , M.J.C. (eds.). Recent advances in the biochemistry of fruits and vegetables. Academic Press, New York, 133-148. 

Within the gut, oxidative damage may be prevented by phytic acid, obtained from cereals and vegetables (Graf et al., 1987), and by soluble non-starch polysaccharides like pectin (Kohen et al., 1993). The use of antioxidant vitamins in the treatment of inflammatory bowel disease has also been su ested (Evans et al., 1990). 

Cellulose, the most abundant biological substance on earth, is the basic and major component of most plant tissues it is the substance that makes up the walls of vegetable cells and therefore the framework of vegetable fibers. The molecules of cellulose are long, linear polysaccharides, made up of many (several hundreds and even over 1000) aligned glucose monomers... 

Polysaccharides are polymers made up of many monosaccharides joined together by glycoside bonds, and include cellulose, starch, vegetable mucilage and plant gums. 

Nowadays there is scientific evidence that, besides plant polysaccharides and lignin, other indigestible compounds such as resistant starch, oligosaccharides, Maillard compounds, and phytochemicals—mainly polyphenols—can be considered DF constituents (Saura-Calixto and others 2000). Of these substances, resistant starch is a major constituent in cereals, whereas phytochemicals are the most important such substance in fruits and vegetables. Here, we address mainly polyphenols and carotenoids associated with DF in fruits and vegetables because of the important biological properties derived from them. 

Englyst HN, Bingham SA, Runswick SA, Collinson E and Cummings JH. 1988. Dietary fibre (non-starch polysaccharides) in fruit, vegetables and nuts. J Hum Nutr Diet 1 247-286. 

The extractability of the polysaccharides of plants can be profoundly affected by the chemical and physical changes which occur between the end of active vegetative growth and the time the plant parts are subjected to chemical extraction. 

Bourquin LD, Titgemeyer EC, Fahey GC Jr. Vegetable fiber fermentation by human fecal bacteria cell wall polysaccharide disappearance and short-chain fatty acid production during in vitro fermentation and water-holding capacity of unfermented residues. J Nutr 1993 123 860-869.. 

The starches, the most important vegetable reserve carbohydrate and polysaccharides from plant cell walls, are discussed in greater detail on the following page. Inulin, a fructose polymer, is used as a starch substitute in diabetics dietary products (see p.l60). In addition, it serves as a test substance for measuring renal clearance (see p.322). 

Carbohydrates serve as a general and easily available energy source. In the diet, they are present as monosaccharides in honey and fruit, or as disaccharides in milk and in all foods sweetened with sugar (sucrose). Meta-bolically usable polysaccharides are found in vegetable products (starch) and animal products (glycogen). Carbohydrates represent a substantial proportion of the body s energy supply, but they are not essential. 

An attempt has been made to classify gums into two main groups (a) real gums which are those plant products which form a clear solution in water and (b) vegetable mucilages which are those which swell but do not dissolve completely in water. This classification is useful but not entirely satisfactory since there are exceptions. Thus gum traga-canth, a tree exudate and a true plant gum, is only partially soluble in water and exhibits those properties normally attributed to mucilages. In this section of the article the term plant gum will be restricted to those complex acid polysaccharides which are exuded from trees either spontaneously or after mechanical injury. 

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