Carbohydrates in Food: An Introduction

Abstract

Carbohydrates are organic compounds containing carbon, hydrogen, and oxygen, and they may be simple or complex molecules. Historically, the term “carbohydrate” has been used to classify all compounds with the general formula C _n (H₂O) _n as the hydrates of carbon. Important food carbohydrates include simple sugars, dextrins, starches, celluloses, hemicelluloses, pectins, and gums. They are an important source of energy or fiber in the diet, and they are also important constituents of foods because of their functional properties. Carbohydrates may be used as sweeteners, thickeners, stabilizers, gelling agents, and fat replacers.

For use with subsequent Carbohydrate food chapters

Glossary

Aldose

Sugar containing an aldehyde group monosaccharide—single sugar unit.

Alpha-anomer

The anomeric hydroxyl group is on the opposite face of the ring from carbon-6 (i.e., the two groups point in opposite directions).

Anomeric carbon atom

The carbon atom that is part of the free carbonyl group in the straight-chain form of a sugar.

Anomers

Isomers that differ only in the orientation of the hydroxyl group on the anomeric carbon atom; there are two forms—alpha (α) and beta (β).

Beta-anomer

The anomeric hydroxyl group is on the same face of the ring as carbon-6 (i.e., the two groups point in the same direction).

Carbonyl group

Contains an oxygen atom double-bonded to a carbon atom. The aldehyde group and the ketone group can both be described as a carbonyl group.

Caramelization

Decomposition of sugars at very high temperatures resulting in brown color.

Cross-planar bond

Formed when the hydroxyl groups on the carbon atoms involved in the formation of a glycosidic bond are oriented on opposite faces of the sugar rings. Cross-planar bonds occur in cellobiose and in cellulose. They also occur in pectin. They are not digested in the human digestive system.

Dextrans

Glucose polymers joined by α-1,6-glycosidic bonds. Produced by some bacteria and yeasts.

Dextrins

Glucose polymers joined by α-1,4-glycosidic bonds. Product of starch hydrolysis. Found in corn syrups.

Disaccharide

Two sugar units joined together by a glycosidic bond.

Furanose

Five-membered ring.

Glycosidic bond

Bond that links two sugar units together; it is formed between the free carbonyl group of one sugar and a hydroxyl group of another sugar; the orientation (α or β) and position (e.g., 1,4) of the link must be specified.

Hydroxyl group

The ─OH group on the carbon atom.

Invert sugar

An equimolar mixture of glucose and fructose, formed by hydrolysis of sucrose, either by acid and heat, or by enzymes such as invertase or sucrase.

Ketose

Sugar containing a ketone group.

Maillard reaction (Maillard browning reaction)

Nonenzymatic browning reaction involving a reducing sugar and a free amino acid group on a protein.

Monosaccharide

Single sugar unit.

Oligosaccharide

Several (3–10) sugar units joined together by a glycosidic bond.

Polysaccharide

Many (hundreds or thousands of) sugar units joined together.

Pyranose

Six-membered ring.

Reducing sugar

Sugar that contains a free carbonyl group.

Reference carbon atom

The highest-numbered asymmetric carbon atom; C5 in glucose and fructose.

Reference hydroxyl group

The hydroxyl group attached to the reference carbon atom.

Sugar alcohol

The result of reduction of carbonyl group to a hydroxyl group.

Supersaturated solution

Solution that contains more solute than could normally be dissolved at a particular temperature.

Trisaccharide

Three sugar units joined together by a glycosidic bond.