CARBOHYDRATES KRAUSE'S FOOD & THE NUTRITION CARE PROCESS(THIRTEENTH EDITION, 2012,chapter3) Presentation by: Dr. M. Ekramzadeh PhD in Nutrition Science Department of Nutrition Shiraz University of Medical Sciences

Polysaccharides Polysaccharides are carbohydrates with more than 10 monosaccharide units. Plants store these carbohydrates as starch granules formed by linking glucose in straight chains and branching into a complex granular structure. Plants make two types of starch: amylose /amylopectin

Amylose is a smaller, linear molecule that is less than 1% branched whereas amylopectin is highly branched because of its larger size, amylopectin is more abundant in the food supply, especially in grains and starchy tubers Starches from corn, rice, potato, and other plants are glucose polymers with the same chemical composition. Their unique character, taste, texture, and absorbability are determined by the relative numbers of glucose units in straight (amylase) and branched configurations (amylopectin) and the degree of accessibility to digestive enzymes

Resistant Starch Raw starch from raw potato or grains is poorly digested Moist cooking causes the granules to swell, gelatinizes the starch, softens and ruptures the cell wall, and makes the starch more digestible by pancreatic amylase Starch that remains intact throughout cooking, recrystallizes after cooling, resists enzyme breakdown, and yields limited amounts of glucose for absorption

Dextrins result from the digestive process and are large, linear glucose polysaccharides of intermediate lengths cleaved from high amylose starch by alpha- amylase Limit dextrins are cleaved from amylopectin containing branch points and are subsequently digested into glucose by the mucosal enzyme isomaltase

Glycogen In contrast to plants, animals use carbohydrates primarily to maintain blood glucose concentrations between feedings. To ensure a readily available supply, liver and muscle cells store carbohydrate as glycogen. Glycogen is stored hydrated with water; thus the water makes glycogen large, cumbersome, and unsuitable for long-term energy storage.

The 70-kg "average" man stores only an 18-hour fuel supply as glycogen, compared with a 2-month supply stored as fat If all human energy stores were glycogen, humans would need to weigh 60 additional pounds Approximately 150 g of glycogen is stored in muscle, which can be increased fivefold with physical training but is not available to maintain blood glucose directly It is the glycogen store in the human liver (approximately 90 g) that is involved in the hormonal control of blood sugar

The recommended amount of digestible carbohydrate required in the diet ranges between 45% and 65% of total calories The Dietary Guidelines for Americans recommend that consumers select fruits, vegetables, and whole grains for higher fiber intake while decreasing sugar-added food choices.

Dietary Fiber and Functional Fiber Dietary fiber refers to intact plant components that are not digestible by gastrointestinal (GI) enzymes Functional fiber refers to nondigestible carbohydrates that have been extracted or manufactured from plants Both of these types of fiber have been shown to have beneficial physiologic functions in the GI tract and in reducing risk of certain disease states

Homopolysaccharides contain repeating units of the same molecule Homopolysaccharides contain repeating units of the same molecule. An example is cellulose, which cannot be hydrolyzed by amylase enzymes. Cellulose is the most abundant organic compound in the world, constituting 50% or more of all the carbon in vegetation.

The long cellulose molecule folds back on itself and is held in place by hydrogen bonding, thus giving cellulose fibrils great mechanical strength but limited flexibility Cellulose is found in carrots and other vegetables

Other homopolymers called beta-glucans(glucopyranose) occur with branching, which makes them more soluble; examples include oats and barley

Heteropolysaccharides are made by modifying the basic cellulose structure to form compounds with different water solubilities Hemicellulose is a glucose polymer substituted with different sugar molecules that have different water solubilities. The predominant sugar is used to name the hemicellulose (e.g., xylan, galactan, mannan, arabinose, galactose) Pectins and gums contain sugars and sugar alcohols that make these molecules more water soluble

The galacturonic acid structure of pectin absorbs water and forms a gel that it is widely used for making jams and Jellies The galacturonic acid backbone has rhamnose units inserted at intervals and side chains of arabinose and galactose Pectin is found in apples, citrus fruit, strawberries, and other fruits

Gums and mucilages (e.g., guar gum) are similar to pectin, except their galactose units are combined with other sugars(e.g., glucose) and polysaccharides Gums are found in plant secretions and seeds. The specific textural qualities of gums and mucilages are commercially useful when added to processed foods such as ice cream

Fructans are composed of fructose polymers, often linked with an initial glucose Fructooligosaccharides (FOSs) Fructans Inulin Inulin-type fructans oligofructose Inulin is a diverse group of fructose polymers widely distributed in plants as a storage carbohydrate

Oligofructose is a subgroup of inulin with fewer than 10 fructose units. All are poorly digested in the upper GI tract and thus supply only approximately 1 kcal/g Fructans contain fructose; have a sweet, clean flavor; and are half as sweet as sucrose

wheat, onions, garlic, bananas, and chicory Major sources of fructans include: wheat, onions, garlic, bananas, and chicory Other sources include: tomatoes, barley, rye, asparagus, and Jerusalem artichokes Inulin compounds are widely used to improve the flavor and sweetness of low-calorie foods and to improve the stability and acceptability of fat-reduced foods. Because they are not absorbed in the proximal intestine, fructans have been used as a sugar replacement for diabetic Patients.

Prebiotics are nondigestible food substances that selectively stimulate the growth or activity of beneficial bacterial species already resident in the colon (Probiotics) and are beneficial to the host Various prebiotics: inulin, inulin-type fructans, and FOSs, stimulate the growth of intestinal bacteria, principally bifidobacteria. Fructans (synthesized or extracted) have prebiotic properties and are considered to be functional fiber (commonly added to liquid nutrition supplements and tube feeding formulas)

Algal polysaccharides (e. g Algal polysaccharides (e.g., carrageenan) are extracted from seaweed and algae and are used as thickening and stabilizing agents in infant formulas, ice cream, milk pudding, and sour cream products. Algal polysaccharides are used commercially because they form weak gels with proteins and stabilize food mixtures, preventing suspended ingredients from settling. Carrageenan damages human cells in culture and destroys human mammary myoepithelial cells at concentrations as low as 0.00014%.

Polydextrose and other polyols are synthetic polymers of sugar alcohols that are used as sugar substitutes in foods. They are not digestible, contribute to increased fecal bulk, and may be fermented in the small intestine. They are not yet classified as functional fibers.

Lignin is a woody fiber found in the stems and seeds of fruits and vegetables and the bran layer of cereals. It is not a carbohydrate but is a polymer composed of phenylpropyl alcohols and acids. The phenyl groups contain conjugated double bonds, which make them excellent antioxidants. Flaxseed lignin also has phytoestrogen activity and can mimic estrogen at its receptors on reproductive organs and bone.

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