Chemistry
Reducing vs Non reducing sugars
Reducing sugars are carbohydrates that can donate electrons to other molecules, while non-reducing sugars cannot. This ability to reduce other substances is due to the presence of a free aldehyde or ketone group in the reducing sugar molecule. Non-reducing sugars lack this functional group and therefore cannot undergo the same chemical reactions as reducing sugars.
Written by Perlego with AI-assistance
Related key terms
1 of 5
4 Key excerpts on "Reducing vs Non reducing sugars"
eBook - ePub- Ronald E. Wrolstad(Author)
- 2011(Publication Date)
- Wiley-Blackwell(Publisher)
Disaccharides are formed from the reaction of an anomeric carbon atom with the hydroxyl group of another sugar. This acetal or ketal linkage is also referred to as a glycosidic linkage. The hydroxyl group reacting with the anomeric carbon may be an alcohol functional group of another sugar, or it could be the hydroxyl substituent located on the anomeric carbon. When the condensation is between two anomeric carbons, the compound will not contain a hemiacetal or hemiketal functional group, and it will be a nonreducing sugar. Reducing disaccharides are systematically named by having the nonreducing sugar moiety be a substituting group on the reducing sugar. The nature of the glycosidic linkage, whether α or β, the number of the carbon atom where the sugar is substituted, and the ring size all need to be indicated. Importantly, reducing disaccharides have an -ose suffix. For example, the systematic name for lactose is 4-O-β-D-galactopyranosyl-D-glucopyranose. Reducing disaccharides will have both α and β forms, the designation being for the orientation of the anomeric hydroxyl, not the glycosidic linkage. If the glycosidic linkage is changed from β to α, a different sugar is formed (e.g., the sugar will no longer be lactose). The structures along with systematic and trivial names for disaccharides that are important in foods are shown in Figure 1.9
No longer available |Learn moreMCAT Biochemistry Review 2024-2025
Online + Book
- (Author)
- 2023(Publication Date)
- Kaplan Test Prep(Publisher)
Tollens' or Benedict’s reagents.- Sugars with a –H replacing an –OH group are termed deoxy sugars.
- Sugars can react with carboxylic acids and their derivatives, forming esters (esterification). Phosphorylation is a similar reaction in which a phosphate ester is formed by transferring a phosphate group from ATP onto a sugar.
- Glycoside formation is the basis for building complex carbohydrates and requires the anomeric carbon to link to another sugar.
Complex Carbohydrates
- Disaccharides form as result of glycosidic bonding between two monosaccharide subunits; polysaccharides form by repeated monosaccharide or polysaccharide glycosidic bonding.
- Common disaccharides include sucrose (glucose-α-1,2-fructose), lactose (galactose-β-1,4-glucose), and maltose (glucose-α-1,4-glucose).
- Polysaccharides play various roles:
- Cellulose is the main structural component for plant cell walls and is a main source of fiber in the human diet.
- Starches (amylose and amylopectin) function as a main energy storage form for plants.
- Glycogen functions as a main energy storage form for animals.
ANSWERS TO CONCEPT CHECKS
4.1
- Aldopentose; ketohexose
- D -Glucose’s epimers are D -mannose (C-2), D -allose (C-3), and D -galactose (C-4). None of the D -stereoisomers is an enantiomer for glucose; L -glucose is the enantiomer of D -glucose.
4.2
- During hemiacetal or hemiketal formation, the carbonyl carbon becomes chiral and is termed the anomeric carbon. The orientation of the –OH substituent on this carbon determines if the sugar molecule is the α- or β-anomer.
4.3
- Esterification is the reaction by which a hydroxyl group reacts with either a carboxylic acid or a carboxylic acid derivative to form an ester. Glycoside formation refers to the reaction between an alcohol and a hemiacetal (or hemiketal) group on a sugar to yield an alkoxy group.
eBook - ePubFood Carbohydrates
Chemistry, Physical Properties, and Applications
- Steve W. Cui(Author)
- 2005(Publication Date)
- CRC Press(Publisher)
Figure 1.21 ). The trehaloses are nonreducing sugars because the two hemiacetal hydroxyl groups are engaged in the glycosidic bond and, therefore, no free anomeric groups are available. The acetal linkage between the monosaccharide residues is called a glycosidic linkage. Each of the 11 disaccharides has distinctive chemical and physical properties, although structurally they differ only in the type of glycosidic bond that joins the two moieties. For example, maltose has α-1→4 linkage, cellobiose has β-1→4 linkage, isomaltose has α-1→6 linkage, whereas α,α-trehalose has α-1→1 linkage.FIGURE 1.18A β-1→2 linked disaccharide.A few of the 11 glucose-glucose disaccharides are quite common. Maltose, although it rarely occurs in plants, can be readily produced by hydrolysis of starch. Maltose is therefore present in malted grains and various food items containing starch hydrolysis products (e.g., corn syrup). α,α-Trehalose occurs in the spores of fungi and it is also produced by yeasts. Isomaltose constitutes the branch point of amylopectin and glycogen. Cellobiose is a product of bacterial hydrolysis of cellulose by enzymes such as endo-cellulases and cellobiohydrolases. Laminaribiose is a repeating unit found in the polysaccharides, laminarin (brown algae), pachyman (fungi), and callose.Disaccharides can be divided into heterogeneous and homogeneous types, according to their monosaccharide composition, and into reducing or nonreducing disaccharides, depending whether they possess a free anomeric carbon. Homodisaccharides contain two identical monosaccharide units, whereas heterodisaccharides are composed of two different monomers. Reducing disaccharides, in contrast to nonreducing ones, contain a reactive hemiacetal center that can be easily modified chemically (e.g., via oxidation or reduction).
eBook - ePub- Robert J. Ouellette, J. David Rawn(Authors)
- 2015(Publication Date)
- Elsevier(Publisher)
Figure 13.8 ), is a disaccharide in which the anomeric centers are linked 1,2ʹ.Figure 13.8 SucroseSucrose has both an acetal and a ketal functional group. Neither ring can exist in equilibrium with either an aldehyde or ketone. As a result, sucrose cannot mutarotate, nor is it a reducing sugar. The systematic name, α-D -glucopyranosyl-β-D -fructofuranoside, ends in the suffix -oside , which indicates that sucrose exists as a glycoside, and so is not a reducing sugar.Problem 13.12 Describe the structure of the following disaccharide.SolutionThe hemiacetal center located on the aglycone ring (at the right) has a hydroxyl group in the β-configuration. The glycosidic bond is from C-1 of the acetal ring (on the left) to C-3 of the aglycone ring (on the right). Furthermore, the oxygen bridge is formed through a β-glycosidic bond. Thus, the bridge is β-1,3’. Next, we examine both rings to determine the identity of the monosaccharides. The ring on the left is β-D -galactopyranose: all of its hydroxyl groups are equatorial except the one at C-4, which is axial. The ring on the right is β-D -glucopyranose. The compound is 3-O-(β-D -galactopyranosy1)-β-D -glucopyranoside.Problem 13.13 Describe the structure of the following disaccharide.13.9 Polysaccharides
Polysaccharides are high molecular weight substances consisting of monosaccharides linked to one another by glycosidic bonds. Because the structures of heteropolysaccharides are more complex than those of homopolysaccharides, we will only consider homopolysaccharides in this section.The homopolysaccharides starch and cellulose, found in plants, contain only glucose. About 20% of starch is amylose, which is soluble in cold water; the remaining 80%, called amylopectin, is insoluble in water. Starch is present in potatoes, rice, wheat, and other cereal grains. The amount of amylose and amylopectin in starch is variable and depends on its source.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
