ECHNOLOGY OF CEREALS Olig The smallest oligosaccharide glycosidic link. Although this may appear to be association it is capable of considerable FIG 3. 2 Formation of the glycosidic link according to the configuration of the dic link and the position of the hydroxyl group involved in the bonding. Three important glucose. It is the monomeric unit of starch, variants among disaccharides involving only ellulose and beta-D-glucans a-D-glucopyranose are shown in Fig. 3.3 The most important pentoses are the poly. In these compounds the reducing group of only hydroxyaldehydes D-xylose and L-arabinose, one of the monosaccharide molecules is involved because of their contribution to cell wall polymers. in the glycosidic link and the reducing group of The structures of these compounds and of some the other remains functional other monosaccharides found in cereals are shown In sucrose, another important disaccharide found in plants, fructose and glucose residues are The most abundant derivatives of monosaccha- joined through the reducing groups of both rides are those in which the reducing group forms hence their reducing properties are lost. Sucrose a glycosidic link with the hydroxyl group of is readily hydrolyzed under mildly acid condi another organic compound(as in Fig. 3.2), fre- tions, or enzymically, to yield its component quently another molecule of the same species monomers which of course again behave as reduc- or another monosaccharide. Sugar molecules ing sugars. Sucrose is the main carbon compound may be joined to form short or long chains involved in translocating photosynthate to the by a series of glycosidic links thus producing grain. It features prominently during develop oligosaccharides or polysaccharides ment rather than in the mature grain because it CH2OH B-D-glucopyranosyl-(1-4)-a-D-glucopyranose),(3)isomaltose(a-D-glucopyrand pyrano54 TECHNOLOGY OF CEREALS Oligosaccharides The smallest oligosaccharide, the disaccharide, comprises two sugar molecules joined by a glycosidic link. Although this may appear to be a simple association it is capable of considerable variation according to the configuration of the glycosidic link and the position of the hydroxyl group involved in the bonding. Three important D-glucose. It is the monomeric unit of starch, variants among disaccharides involving only cellulose and beta-D-ghcans. a-D-glucopyranose are shown in Fig. 3.3. The most important pentoses are the poly- In these compounds the reducing group of only hydroxyaldehydes D-xylose and L-arabinose, one of the monosaccharide molecules is involved because of their contribution to cell wall polymers. in the glycosidic link and the reducing group of The structures of these compounds and of some the other remains functional. other monosaccharides found in cereals are shown In sucrose, another important disaccharide in Fig. 3.1. found in plants, fructose and glucose residues are The most abundant derivatives of monosaccha- joined through the reducing groups of both; rides are those in which the reducing group forms hence their reducing properties are lost. Sucrose a glycosidic link with the hydroxyl group of is readily hydrolyzed under mildly acid condi￾another organic compound (as in Fig. 3.2), fre- tions, or enzymically, to yield its component quently another molecule of the same species monomers which of course again behave as reduc￾or another monosaccharide. Sugar molecules ing sugars. Sucrose is the main carbon compound may be joined to form short or long chains involved in translocating photosynthate to the by a series of glycosidic links, thus producing grain. It features prominently during develop￾oligosaccharides or polysaccharides. ment rather than in the mature grain because it -0 H -y + HO-I3 T A-I3 OH H20 FIG 3.2 Formation of the glycosidic link. CH20H HO HQOGw HO He0 Ho0 H OH H OH CHZOH H OH (1) (2) HO H OH I HO HQH H OH (3) FIG 3.3 Structural conformation of (1) maltose (a-D-ghcopyronosyl-( 1-+4)-a-D-glucopyranose), (2) cellobiose (~-~-glucopyranosyl-( 1+4)-a-~-glucopyranose), (3) isomaltose (a-D-glucopyranosyl- ( 1+6)-P-D-glucopyranose)