Classification of Carbohydrates

1. Glucose: honey, fruits, corn syrup, sweet grapes, sweet corn; hydrolysis of starch and cane sugar. Physiologically the most important sugar; the “sugar” carried by the blood and the principal one used for tissues.
2. Fructose: honey, ripe fruits, some vegetables; hydrolysis of sucrose insulin. Can be changed to glucose in the liver and intestine and is an intermediate metabolite in glycogen breakdown.
3. Galactose: not found free in nature; digestive end product of lactose hydrolysis. Can be changed to glucose in the liver; synthesized in body to make lactose and is a constituent of glycolipids.
4. Mannose: found in legumes; hydrolysis of plant mannosans and gums. A constituent of polysaccharide of albumins, globulins, and mucoids.

1. Arabinose: derived from gum arabic plus plum and cherry gums; not found free in nature. Has no known physiologic function in man; used in metabolism studies of bacteria.
2. Ribose: derived from nucleic acid of meats and seafoods. Structural element of nucleic acids, ATP, and coenzymes (NAD and FAD).
3. Ribulose: formed in metabolic processes. Intermediate in direct oxidative pathway of glucose breakdown.
4. Xylose: wood gums, corncobs, and peanut shells; not found free in nature. Very poorly digested and has no known physiologic function; used medicinally as a diabetic food.

1. Sucrose: cane and beet sugar, maple syrup, molasses, and sorghum. Hydrolyzed to glucose and fructose; a non-reducing sugar.
2. Maltose: malted products and germinating cereals; an intermediate product of starch digestion. Hydrolyzed to two molecules of glucose; a reducing sugar; does not occur free in tissues.
3. Lactose: milk and milk products; formed in the body from glucose nature. Hydrolyzed to glucose and galactose; may occur in urine during pregnancy; a reducing sugar.

1. Raffinose: cottonseed meal, molasses, sugar beets and stems. Only partially digestible but can be hydrolyzed by enzymes of intestinal bacteria to glucose, fructose, and galactose.
2. Melizitose: honey, poplars, and conifers. Composed of one fructose unit and two glucose units.

1. Glycogen: meat products and seafoods; polysaccharides of the animal body, often called animal starch; storage form of carbohydrates in body, mainly in liver and muscle.
2. Starch: cereal grains, unripe fruits, vegetables, legumes, and tubers. Most important food source of carbohydrates; storage form of carbohydrates in plants. Composed chiefly of amylose and amylopectin; hydrolyzed to glucose.
3. Dextrin: toasted bread, intermediate product of starch digestion. Formed in course of hydrolytic breakdown of starch.

1. Inulin: tubers and roots of dahlias, artichokes, dandelions, onions, and garlic. Hydrolizable to fructose; used in physiologic investigation for determination of glomerular filtration rate.
2. Mannosan: legumes and plant gums. Hydrolyzable to mannose but digestion incomplete; further splitting by bacteria may occur in large bowel.

1. Cellulose: skins of fruits, outercoverings of seeds, plus stalks and leaves of vegetables. Not subject to attack of digestive enzymes in man, thus an important source of “bulk” in diet; may be partially split to glucose by bacterial action in large bowel.
2. Hemicellulose and pectin: woody fibers and leaves. Less polymerized than cellulose; may be digested to some extent by microbial enzymes, yielding xylose.

Indigestible is another name for indigestable polysaccharides is dietary fiber which is comprised of 2 groups:

1. Insoluble dietary fibers (cellulose, lignin, and cutin) which are the most abundant organic compounds in the world. They help prevent constipation, colon cancer, and diverticulosis, but not hypercholesterolemia.
2. Soluble dietary fibers (hemicellulose, pectins, gums, and algal polysaccharides) which are useful in decreasing serum cholesterol and in regulating blood glucose levels.