Chapter 4 - The Carbohydrates, Sugars, Starches and Fibers Flashcards
Carbohydrate
Compounds composed of carbon, oxygen and hydrogen arranged as monosaccharides or multiples of monosaccharides. Most, but not all, carbohydrates have a ratio of one carbon molecule to one water molecule.
Carbo = carbon ( c), hydrate = with water (H2O)
All plant foods—whole grains, vegetables, legumes, and fruits—provide ample carbohydrate.
Our bodies receive glucose from carbs for immediate energy use and convert some glucose into glycogen for reserve energy.
Chemistry of Carbs
The dietary carbohydrate family includes:
- Monosaccharides: single sugars
- Disaccharides: sugars composed of pairs of monosaccharides
- Polysaccharides: large molecules composed of chains of monosaccharides
Monosaccharides and disaccharides (the sugars) are sometimes called simple carbohydrates, and polysaccharides (starches and fibers) are sometimes called complex carbohydrates.
Monosaccharide
Simple sugars. C6H12O6
These are simple carbohydrates. All have the same number and kinds of atoms. These differ in their arrangements of atoms, and the chemical differences account for the differing sweetness of each.
Mono = one Saccharides = sugar.
The most important sugars in nutrition:
Glucose
Fructose
Galactose
Glucose
Provides nearly all the energy the human brain uses daily.
Monosaccharide. Sometimes known as blood sugar in the body or dextrose in Foods.
Serves as an essential energy source for all the body’s activities. Significance to nutrition is tremendous.
Fructose
Monosaccharide. Intensely sweet. Sweetest of the sugars.
The arrangement of the atoms stimulates the taste buds on the tongue to produce sweet sensations.
Naturally in fruit and honey. Other sources include soft drinks, desserts, and high fructose corn syrup.
Galactose
Monosaccharide. Occurs naturally on foods as a simple sugar only in very small amounts.
Disaccharide
Pairs of three monosaccharides linked together. Glucose occurs in all three. The second member of the pair is fructose, galactose, or another glucose.
Whitney, Eleanor Noss; Rolfes, Sharon Rady. Understanding Nutrition (p. 98). Cengage Textbook. Kindle Edition.
Di = two.
These carbohydrates are put together and taken apart by condensation and hydrolysis
- Maltose (glucose + glucose)
- Sucrose (glucose + fructose)
- Lactose (glucose + galactose)
Condensation
To make a disaccharide.
Links two monosaccharides together.
A hydroxyl (OH) group from one monosaccharide and a hydrogen atom (H) from the other combine to create a molecule of water (H2O). The two originally separate monosaccharides link together with single oxygen (O).
In this chemical reaction, water is released and two molecules combine to form one larger product
Hydrolysis
A chemical reaction in which one molecule is split into two molecules, with hydrogen (H) added to one and a hydroxyl group (OH) to the other.
Hydro = water and lysis = breaking.
To break a disaccharide in two this chemical reaction occurs.
A molecule of water (H2O) splits to provide the H and OH needed to complete the resulting monosaccharide.
Commonly occurs during digestion.
Maltose
Disaccharide.
Composed of two glucose units.
Sometimes known as malt sugar. Produce whenever starch breaks down – in human digestion and the fermentation of alcohol. Only a minor part of a few foods including barley.
Sucrose
Disaccharide.
Composed of glucose and fructose.
Commonly known as table sugar, beet sugar or cane sugar. Also occurs in many fruits, some vegetables and grains.
Sweetest of the disaccharides because it contains fructose.
Lactose
Disaccharide.
Combination of galactose and glucose.
Principle carbohydrate of milk. Known as milk sugar.
Polysaccharide
Slightly more complex, containing many glucose units and, in some cases, a few other monosaccharides strung together.
Three types are important to nutrition: glycogen, starches, and fibers.
Glycogen is a storage form of energy in the body; starch is the storage form of energy in plants; and fibers provide structure in stems, trunks, roots, leaves, and skins of plants.
Glycogen
Polysaccharide.
An important storage form of energy in the body. Built of glucose units.
Found to only a limited extent in meats and not at all in plants. Food is not a significant source of glycogen.
Role is storage of glucose for future use in the liver and muscles. When our body sends hormonal messages to “release energy” enzymes respond by attacking the many branches of glycogen making a surge of glucose available
Starch
Polysaccharide.
Storage form of energy in plants.
Built of glucose units. Long, branched or unbranched chains of hundreds or thousands of glucose molecules linked together. Giant starch molecules are packed side by side in grains such as wheat or rice, in root crops and tubers such as yams and potatoes, and in legumes such as peas and beans.
When humans eat a plant, the body hydrolyzes the starch to glucose and uses the glucose for energy. Grains are the richest food source of starch.
Fibers
Polysaccharide.
The structural parts of plants and thus are found in all plant-derived foods—vegetables, fruits, whole grains, and legumes.
Composed of a variety of monosaccharides and other carbohydrate derivatives.
The bonds between their monosaccharides cannot be broken down by digestive enzymes in the body.
Because dietary fibers pass through the body undigested, they contribute no monosaccharides, and therefore little or no energy.
Researchers often sort dietary fibers into two groups according to their solubility; soluble and insoluble.
Soluble fibers
Dissolve in water, form gels (viscous) and are easily digested by bacteria in the colon (fermentable)
Commonly found in oats, barley, legumes, and citrus fruits, soluble fibers are most often associated with protecting against heart disease and diabetes by lowering blood cholesterol and glucose levels,
Insoluble fiber
Does not dissolve in water, do not form gels (non-viscous) and are less readily fermented.
Found mostly in whole grains (bran) and vegetables, insoluble fibers promote bowel movements, alleviate constipation, and prevent diverticular disease.