Chemical Components Carbohydrates importance, both in their contribution to the The terminology surrounding carbohydrates structural and storage components of the grain frequently serves to confuse rather than to clarify and to the behaviour of grains and their pro- Archaic and modern conventions are often inter. ducts during processing. In this context the most mixed and definitions of some terms are incon important monosaccharide, because of its abund sistent with their use. Even the term carbohydrate nce, is the six-carbon polyhydroxyaldehyde itself is not entirely valid It originated in the belief that naturally occurring compounds of this class could be represented formally as hydrates of carbon. i.e. Cx(H2O)y. This definition is too rigid however as the important deoxy sugars like hamnose, the uronic acids and compounds such acid and phloroglucinol would qualify for inch.C as ascorbic acid would be excluded and aceti sion. Nevertheless the term carbohydrate remains to describe those polyhydroxy compounds which reduce Fehlings solution either before or after hydrolysis with mineral acids(Percival, 1962) It is customary to classify carbohydrates ccording to their degree of polymerization Thus: monosaccharides(l unit), oligosaccharides (2-20 units)and polysaccharides(>20 units HOC Monosaccharides are the simplest carbohy drates; most of them are sugars. monosaccharides may have 3-8 carbon atoms but only those with 5 carbons (pentoses) and 6 carbons(hexoses) are common. Both pentoses and ses exist in a number of isomeric forms, they may be polyhydroxyaldehydes or polyhydroxyketones Structurally, they occur in ring form which may be six-membered (pyranose form five-membered (furanose form FIG 3. 1 Structural representations of (1)xylose xylopyranose),(2)arabinose(alpha-L-arabinofurar In mature cereal the mers are of glucose(beta-Dglucopyranose),(4) fructose(beta-D little importance in their own right but, as furanose, (5)D-galacturonic acid,(6) ribose ribofuranose),(7)deoxyribose(beta-D-deoxyribofuranose), and components of polymers, they are of extreme (8)mannose(alpha-D-mannopyrane3 Chemical Components Carbohydrates The terminology surrounding carbohydrates frequently serves to confuse rather than to clarify. Archaic and modern conventions are often inter￾mixed and definitions of some terms are incon￾sistent with their use. Even the term carbohydrate itself is not entirely valid. It originated in the belief that naturally occurring compounds of this class could be represented formally as hydrates of carbon. i.e. C,(H,O),,. This definition is too rigid however as the important deoxy sugars like rhamnose, the uronic acids and compounds such importance, both in their contribution to the structural and storage components of the grain, and to the behaviour of grains and their pro￾ducts during processing. In this context the most important monosaccharide, because of its abund￾ance, is the six-carbon polyhydroxyaldehyde: do HbH, HOCH, 4TQHHt HO H@H 1 tQoH CH,OH HfJcH,oH H:”;” HOCH, o HBOH I as ascorbic acid would be excluded and acetic ! ?H a, acid and phloroglucinol would qualify for inclu- (1) (2) sion. Nevertheless the term carbohydrate remains to describe those polyhydroxy compounds which reduce Fehlings solution either before or after It is customary to classify carbohydrates Thus: monosaccharides (1 unit), oligosaccharides (2-20 units) and polysaccharides (>20 units). Monosaccharides are the simplest carbohy￾b HO,CHz 0 4 hydrolysis with mineral acids (Percival, 1962). ‘;1 YH OH H according to their degree of polymerization. (3) (4) HOCH, o drates; most of them are sugars. Monosaccharides H OH OH OH may have 3-8 carbon atoms but only those with (5) (6) 5 carbons (pentoses) and 6 carbons (hexoses) are common. Both pentoses and hexoses exist in a number of isomeric forms, they may be polyhydroxyaldehydes or polyhydroxyketones. OH H HH H wy HO Structurally, they occur in ring form which (7) (8) may be six-membered (pyranose form) Or five-membered (furanose form). In mature cereal grains the monomers are of components of polymers, they are of extreme FIG 3.1 Structural representations of (1) xylose (beta-D￾xylopyranose), (2) arabinose (alpha-L-arabinofuranose), (3) glucose (beta-D-glucopyranose), (4) fructose (beta-D-fructo- furanose, (5) D-galacturonic acid, (6) ribose (beta+ (8) mannose (alpha-D-mannopyranose). little importance in their Own right but, as ribofuranose), (7) deoxyribose (beta-D-deoxyribofurose), and 53