Polysaccharides reserve food

The origin and function of xylan in the cell wall are also not explained. Postulations that it is a plasticizer or is a reserve food are not fully substantiated. Its derivation from cellulose through the decarboxylation of an intermediary polyglucuronic acid seems very unlikely. There is evidence from a number of sources to indicate that the xylan polysaccharide is deposited along with cellulose in cell wall elaboration. 

Generally, reinforcing, cell-wall polysaccharides are least soluble while emollients, mucilaginous, and food reserve polysaccharides represent the most soluble group. Exceptions to the generalization that reserve food polysaccharides are easily soluble occur in starch amylose and seed mannan. Starch amylose is readily dispersible in most of its natural forms since it occurs mixed with easily soluble amylopectin which facilitates the dissolution of the amylose. 

Polyfructoses are widely distributed as reserve food materials in plants. Usually these water-soluble polysaccharides can be extracted from their sources (e.g., tubers) without use of drastic reagents, since they are found in solution in cell sap. 

By far the most important polysaccharides are cellulose and starch. Both are produced in plants from carbon dioxide and water by the process of photosynthesis, and both, as it happens, are made up of D-(+)-glucose units. Cellulose is the chief structural material of plants, giving the plants rigidity and form. It is probably the most widespread organic material known. Starch makes up the reserve food supply of plants and occurs chiefly in seeds. It is more water-soluble than cellulose, more easily hydrolyzed, and hence more readily digested. 

Inulin, Dahlin alantin alant starch. Mol wt approx 5000. Polysaccharide of Compositae which partially or completely replaces starch as a reserve food. Isoln from dahlia tubers McDonald, "Polyfructosans and Difructose Anhydrides" in Advan. Carbohyd. Chem. vol. 2, 254 (1946) from Jerusalem artichoke tubers Bacon, Edelman, Biochem. J. 48, 114 (1951). Structure E. G. V. Percival. Structural Carbohydrate Chemistry (J. Garnet Miller, London, 2nd ed., 1962) p 274. 

Plants store polysaccharides as food reserve in all types of cell but primarily in special storage cells or organs such as parenchymous cells or roots, tubers, and pith. The most important of these food reserves are starches, fructans, mannans, and galactomannans. The mannans are sometimes food reserves and sometimes structural material in the plant cell wall. In animals the chief reserve polysaccharide is glycogen, which in chemical structure is much like one of the components of starch (see Part II of this chapter.). 

Although most seeds contain starch as the principal food reserve, many contain other polysaccharides and some have industrial utility. The first seed gums used commercially were quince, psyUium, flax, and locust bean gum. However, only locust bean gum is stiU used, particularly in food appHcations quince and psyllium gums are only used in specialized appHcations. 

It has been estimated that >90% of the carbohydrate mass in nature is in the form of polysaccharides. In living organisms, carbohydrates play important roles. In terms of mass, the greatest amounts by far are stmctural components and food reserve materials, in that order and both in plants. However, carbohydrate molecules also serve as stmctural and energy storage substances in animals and serve a variety of other essential roles in both plants and animals. 

Considering the close resemblance in general structure and food-reserve function of these polysaccharides, a certain similarity in properties might be expected, and this similarity will be discussed in later Sections. Also, the parent polysaccharides cellulose, mannan, and esparto xylan are all intrinsically water-insoluble the progressive introduction of the monosaccharide and disaccharide stubs, if... 

Ivory nut mannan such as that from palm seed is the only identified water insoluble food reserve polysaccharide which occurs in nearly pure form. It dissolves in 5% alkaline solution, and its food reserve nature is indicated by its disappearance when the seed germinates. Perhaps its lack of solubility permits the palm seeds to withstand rather long soaking periods before germination. Most other mannans found in other biological sources are branched and more readily water soluble. 

A second very widely distributed polysaccharide is starch, which is stored in the seeds, roots, and fibers of plants as a food reserve — a potential source of glucose. The chemical composition of starch varies with the source, but in any one starch there are two structurally different polysaccharides. Both consist entirely of glucose units, but one is a linear structure (amylose) and the other is a branched structure (amylopectin). 

Polysaccharides, proteins, and lipids are involved in different structures of the plant and animal tissues used for food. The structures built from these materials are responsible for the form and tensile strength of the tissues and create the necessary conditions for the metabolic processes to occur. Compartmentation resulting from these structures plays a crucial biological role in the organisms. Some other saccharides, proteins, and lipids are stored for reserve purposes. Other constituents are either bound to different cell structures or distributed in soluble form in the tissue fluids. 

Starch, a food-reserve substance from plant grains, is a mixture of two polysaccharides, amylose and amylopectin (Kennedy and White 1988). Amylose is... 

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