Food Carbohydrate Chemistry

Ronald E. Wrolstad

• Publisher: Wiley-Blackwell
• Year: 2011
• Print ISBN: 9780813826653
• eBook ISBN: 9781119949152
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Not since "Sugar Chemistry" by Shallenberger and Birch (1975) has a text clearly presented and applied basic carbohydrate chemistry to the quality attributes and functional properties of foods. Now in Food Carbohydrate Chemistry, author Wrolstad emphasizes the application of carbohydrate chemistry to understanding the chemistry, physical and functional properties of food carbohydrates. Structure and nomenclature of sugars and sugar derivatives are covered, focusing on those derivatives that exist naturally in foods or are used as food additives. Chemical reactions emphasize those that have an impact on food quality and occur under processing and storage conditions. Coverage includes: how chemical and physical properties of sugars and polysaccharides affect the functional properties of foods; taste properties and non-enzymic browning reactions; the nutritional roles of carbohydrates from a food chemist's perspective; basic principles, advantages, and limitations of selected carbohydrate analytical methods. An appendix includes descriptions of proven laboratory exercises and demonstrations. Applications are emphasized, and anecdotal examples and case studies are presented. Laboratory units, homework exercises, and lecture demonstrations are included in the appendix. In addition to a complete list of cited references, a listing of key references is included with brief annotations describing their important features.

Students and professionals alike will benefit from this latest addition to the IFT Press book series. In Food Carbohydrate Chemistry, upper undergraduate and graduate students will find a clear explanation of how basic principles of carbohydrate chemistry can account for and predict functional properties such as sweetness, browning potential, and solubility properties. Professionals working in product development and technical sales will value Food Carbohydrate Chemistry as a needed resource to help them understand the functionality of carbohydrate ingredients. And persons in research and quality assurance will rely upon Food Carbohydrate Chemistry for understanding the principles of carbohydrate analytical methods and the physical and chemical properties of sugars and polysaccharides.

1

Classifying, Identifying, Naming, and Drawing Sugars and Sugar Derivatives

Structure and Nomenclature of Monosaccharides

Aldoses and Ketoses

Configurations of Aldose Sugars

D- vs. L-Sugars

Different Ways of Depicting Sugar Structures

Fischer, Haworth, Mills, and Conformational Structures

Classifying Sugars by Compound Class—Hemiacetals, Hemiketals, Acetals, and Ketals

Structure and Nomenclature of Disacchaarides

Structure and Optical Activity

A Systematic Procedure for Determining Conformation (C-1 or 1-C), Chiral Family (D or L), and Anomeric Form (α or β) of Sugar Pyranoid Ring Structures

Structure and Nomenclature of Sugar Derivatives with Relevance to Food Chemistry

Glycols (Alditols)

Glyconic, Glycuronic, and Glycaric Acids

Deoxy Sugars

Amino Sugars and Glycosyl Amines

Glycosides

Sugar Ethers and Sugar Esters

Vocabulary

References

Structure and Nomenclature of Monosaccharides

Sugars are polyhydroxycarbonyls that occur in single or multiple units as monosaccharides, disaccharides, trisaccharides, tetrasaccharides, or oligosacharides (typically three to ten sugar units). Monosaccharides (also known as simple sugars) exist as aldoses or ketoses, with glucose and fructose being the most common examples. Glycose is a generic term for sugars. Sugars are also classified according to the number of carbon atoms in the molecule (e.g., trioses, tetroses, pentoses, hexoses, heptoses, etc.).

Figure 1.1 Structure and nomenclature of glucose, fructose, and arabinose.

Aldoses and Ketoses

Aldoses contain an aldehyde functional group at carbon-1 (C-1), whereas ketoses contain a carbonyl group that is almost always located at carbon-2 (C-2). C-1 for aldoses and C-2 for ketoses are the reactive centers for these molecules and are known as the anomeric carbon atoms. Figure 1.1 shows the structure for D-glucose, D-fructose, and, in addition, D-arabinose. Sugars have common or trivial names with historical origins from chemistry, medicine, and industry. There is also a systematic procedure for naming sugars (some examples are shown in Table 1.1). Glucose is also commonly known as dextrose. In systematic nomenclature, its suffix is hexose, indicating a 6-carbon aldose sugar, and the prefix is gluco-, which shows the orientation of the hydroxyl groups around carbons 2–5. The symbol D refers to the orientation of the hydroxyl group on C-5, the highest numbered asymmetric carbon atom, also known as the reference carbon atom. Since fructose (also known as levulose) has just three asymmetric carbon atoms, its configurational prefix is the same as that for the pentose sugar arabinose. Thus, the systematic name for glucose is D-gluco-hexose and fructose is D-arabino-hexulose.

Table 1.1 Trivial and Systematic Names of Selected Sugars

Trivial (or Common)	Systematica
D-Erythrose	D-erythro-tetrose
D-Threose	D-threo-tetrose
D-Arabinose	D-arabino-pentose
D-Lyxose	D-lyxo-pentose
D-Ribose	D-ribo-pentose
D-Xylose	D-xylo-pentose
D-Allose	D-allo-hexose
D-Altrose	D-altro-hexose
D-Galactose	D-galacto-hexose
D-Glucose	D-gluco-hexose
D-Gulose	D-gulo-hexose
D-Idose	D-ido-hexose
D-Mannose	D-manno-hexose
D-Talose	D-talo-hexose
aIn the systematic name, the configurational prefix is italicized, and the stem name indicates the number of carbon atoms in the molecule.

Configurations of Aldose Sugars

Figure 1.2 shows all possible configurations around the asymmetric carbon atoms for the triose, tetrose, pentose, and hexose D-aldose sugars. Diastereoisomers are molecular isomers that differ in configuration about one or more asymmetric carbon atoms; there are eight hexose diastereoisomers. Epimer is yet another term in sugar chemistry that refers to diastereoisomers that differ in configuration about only one asymmetric carbon atom (e.g., D-galactose is the 4-epimer of D-glucose). The term has historical significance because the melting point of dinitrophenylhydrazone derivatives was a classical procedure used in identifying sugars. The 2-epimers (e.g., glucose and mannose, allose and altrose, etc.) gave identical dinitrophenylhydrazone derivatives.

Figure 1.2 Structures of the D-aldoses containing from 3 to 6 carbon atoms as depicted by the Rosanoff shorthand convention.

Figure 1.3 D- and L-glucose as depicted in the Fischer and conformational projections.

D- vs. L-Sugars

L-sugars are the mirror images of D-sugars. Figure 1.3 depicts the structures of D- and L-glucose in the Fischer and conformational projections. (Note: When drawing an L-sugar, the orientation of the hydroxyl groups on every asymmetric carbon atom need to be reversed; a frequent error is to only change the orientation on the reference carbon atom.) D- and L-glucose are enantiomers, nonsuperimposable stereoisosmeric molecules that are mirror images. L-sugars occur rarely in nature. A pair of enantiomers are identical in chemical reactivity, and they have the same taste properties. They are handled differently in biological systems, however. Although humans absorb L-sugars, L-sugars are not metabolized and thus have no caloric value.

Figure 1.4 Furanose and pyranose structures of β-D-glucose and β-D-fructose.

Figure 1.5 β-D-glucopyranose as depicted by the Haworth, Mills, and conformational conventions.

Figure 1.6 Basic chair and boat conformations for β-D-glucopyranose.

Different Ways of Depicting Sugar Structures

Fischer, Haworth, Mills, and Conformational Structures

It is important to realize that pentose and hexose sugars exist as ring forms, and only a small amount will occur in the acyclic form. Thus, the Fischer projections shown in Figure 1.2 are in no way representative...

Table of contents

• Cover
• Series One
• Title Page
• Copyright
• Series Two
• Dedication
• Contributors
• Acknowledgments
• Introduction
• Chapter 1: Classifying, Identifying, Naming, and Drawing Sugars and Sugar Derivatives
• Chapter 2: Sugar Composition of Foods
• Chapter 3: Reactions of Sugars
• Chapter 4: Browning Reactions
• Chapter 5: Functional Properties of Sugars
• Chapter 6: Analytical Methods
• Chapter 7: Starch in Foods
• Chapter 8: Plant Cell Wall Polysaccharides
• Chapter 9: Nutritional Roles of Carbohydrates
• Appendices
• Index
• Food Science and Technology