Carbohydrates in Food: An IntroductionOpen image in new window
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.
KeywordsGlycosidic Bond Aldehyde Group Sugar Alcohol Glucose Molecule Ketone Group
Sugar containing an aldehyde group monosaccharide—single sugar unit.
The anomeric hydroxyl group is on the opposite face of the ring from carbon-6 (i.e., the two groups point in opposite directions).
The carbon atom that is part of the free carbonyl group in the straight-chain form of a sugar.
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).
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).
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.
Decomposition of sugars at very high temperatures resulting in brown color.
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.
Glucose polymers joined by α-1,6-glycosidic bonds. Produced by some bacteria and yeasts.
Glucose polymers joined by α-1,4-glycosidic bonds. Product of starch hydrolysis. Found in corn syrups.
Two sugar units joined together by a 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.
The ─OH group on the carbon atom.
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.
Sugar containing a ketone group.
Nonenzymatic browning reaction involving a reducing sugar and a free amino acid group on a protein.
Single sugar unit.
Several (3–10) sugar units joined together by a glycosidic bond.
Many (hundreds or thousands of) sugar units joined together.
Sugar that contains a free carbonyl group.
The highest-numbered asymmetric carbon atom; C5 in glucose and fructose.
The hydroxyl group attached to the reference carbon atom.
The result of reduction of carbonyl group to a hydroxyl group.
Solution that contains more solute than could normally be dissolved at a particular temperature.
Three sugar units joined together by a glycosidic bond.
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