TECHNOLOGY OF CEREALS 4)-B-D-XYLp)-(-4)-B-D-XYLp)-(-4)-B-D-XYLp)-(-4)-B-D-XYL(p)- FIG 3.4 Structure of arabinoxylan of wheat aleurone and starchy endosperm cell walls. p, represents ne pyranose or 6-membered ring form; f, represents the furanose or 5-membere Pentosans which appear white when seen as a bulk powder While glucans are polymers of a single face. They have a refractive index of about 1.5 sugar species the common pentosans (polymers Specific gravity depends upon moisture content of pentose sugars) comprise two or more different species, each in a different isomeric form. Thus but it is about 1. 5. The mysteries of granule arabinoxylans, found in endosperm walls of wheat structure, development and behaviour have and other cereals, have a xylanopyranosyl back- exercized the minds of scientists for hundreds of bone to which are attached single arabinofuranosyl years and continue to do so. Granules from residues(Fig. 3. 4). different species differ in their properties and there is even variation in form among granules from the same storage organ Shape is determined Starch in part by the way that new starch is added to Starch is the most abundant carbohydrate in existing granules, in part by physicochemical all cereal grains, constituting about 64% of the conditions existing during the period of growth re wheat grain(about 70% and in part by composition of the endosperm), about 73% of the dry matter composition of the dent maize grain and 62% of the proso millet grain. It occurs as discrete granules of up The main way in which composition varies is to 30 um diameter and characteristic of the species the relative proportions of the two macro- In shape molecular species of which granules consist Starch granules are solid, optically clear bodies (Fig. 3.5) CH2OH CH2OH CH2OH OH CH2OH CH, OH FIG 3.5 Structural representation of amylose (i)and amylopectin(ui)56 TECHNOLOGY OF CEREALS -4)-B-D-XYL(p)-(l-4)-~-D-XYL(p)-(I-4)-~-D-XYL(p)-(I-4)-~-D-XYL (p)- (I- 3 3 I I I I a-L-ARA(f) a-L-ARA(f) FIG 3.4 Structure of arabinoxylan of wheat aleurone and starchy endosperm cell walls. p, represents the pyranose or &membered ring form; f, represents the furanose or 5-membered ring form. Pentosans which appear white when seen as a bulk powder because of light scattering at the starch-air inter￾Whi1e glucans are po1ymers Of a sing1e face. They have a refractive index of about 1.5. sugar species the common pentosans (polymers Specific gravity depends upon moisture content of pentose sugars) comprise two or more different but it is about 1.5. The mysteries of granule species, each in a different isomeric form. Thus structure, development and behaviour have arabinoxylans, found in endosperm walls of wheat exercized the minds of scientists for hundreds of and other cereals, have a xylanopyranosyl back￾years and continue to do so. Granules from bone to which are attached single arabinofuranosyl different species differ in their properties and residues (Fig. 3.4). there is even variation in form among granules from the same storage organ. Shape is determined Starch in part by the way that new starch is added to existing granules, in part by physicochemical Starch is the most abundant carbohydrate in conditions existing during the period of growth all cereal grains, constituting about 64% of the and in part by composition. dry matter of the entire wheat grain (about 70% Composition of the endosperm), about 73% of the dry matter of the dent maize grain and 62% of the proso millet grain. It occurs as discrete granules of up The main way in which composition varies is to 30 pm diameter and characteristic of the species in the relative proportions of the two macro￾in shape. molecular species of which granules consist Starch granules are solid, optically clear bodies (Fig. 3.5). CH20H CH20H CH,OH CH20H ---o p&oQoQoQ O--- H OH H OH (i) H OH H OH CH 20H CH20H --.oJQ0q (Ii) 0 I CH2OH CH20H ---o ~o~o&oJF& 0 --- H OH H OH H OH H OH FIG 3.5 Structural representation of amylose (i) and amylopectin (ii)