09012011FNTR342-CarbFiberDigest

09012011FNTR342-CarbFiberDigest - Digestion, Absorption,...

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Digestion, Absorption, and Properties of Carbohydrates and Dietary Fiber Reading: Gropper 4 th ed, Ch 4, pp. 72–80; Ch 5, pp. 108–119 Gropper 5 th ed, Ch 3, pp. 63–72; Ch 4, pp. 108–121; Ch 2, pp. 53–55
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2 Objectives for today: Review chemical structures of carbohydrates Review sites of digestion and mechanisms of absorption of carbohydrates Understand mechanism of lactose intolerance and related syndromes
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3 Objectives for today (cont.): Review types of dietary fiber Review effects of dietary fiber on GI tract and impact on health Briefly examine the interface between GI tract and immune system
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4 Definition: Carbohydrates are compounds made up of single or multiple sugars and composed of carbon, hydrogen, and oxygen atoms; formula = (CH 2 O) n provide 4 kcal/g the preferred energy source, especially for the brain and nervous system and red blood cells
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5 Carbohydrate classification: Simple Carbohydrates: Monosaccharides: 1 sugar moiety Cannot be reduced further by hydrolysis hexoses = glucose , fructose, galactose Disaccharides: 2 sugar moieties linked covalently sucrose , lactose, maltose Complex Carbohydrates: Oligosaccharides: 3 or more glucose moieties dextrins; derived from breakdown of starch or glycogen Polysaccharides: 10s to 1000s glucose moieties starch, fibers and glycogen
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Monosaccharides have: Anomeric carbon at the carbonyl end (C=O) that exists as either an aldehyde (glucose) or ketone (fructose) Hydroxyl ends that react with carbonyl group to cyclize the molecule 6 Organic Chemistry Beginner Style CH O reducing group OH OH OH OH H H H H C C C C CH 2 OH 1 2 3 4 5 6 D-Glucose (open chain)
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7 OH OH OH O H H H H H H C C C C C O CH 2 OH 6 1 O CH 2 OH O H OH OH OH 6 1 α -anomer of glucose O CH 2 OH O H OH OH 6 1 β - anomer of glucose Glucose in its ring forms
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8 Table 4-1, p. 75 8
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9 Glucose Dietary sources of glucose: Disaccharides Sucrose (table sugar; 50% glucose/50% fructose) Lactose (milk sugar) Maltose (malt) High Fructose Corn Syrup (45% glucose + 55% fructose) Complex carbohydrates Animal starch (glycogen)
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10 Disaccharides Monosaccharides attached by acetal bonds (glycosidic bonds) where –OH of anomeric Carbon binds to -OH (C4/C6) of another This bond can be in α or β orientation Major disaccharides Sucrose = Glucose + Fructose Lactose = Glucose + Galactose Maltose = Glucose + Glucose
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11 O CH 2 OH O O CH 2 OH SUCROSE (glucose-fructose) α -1,2-bond OH CH 2 OH O O O LACTOSE (galactose-glucose) β -1,4-bond OH OH CH 2 OH CH 2 OH O O O MALTOSE (glucose-glucose) OH OH CH 2 OH CH 2 OH -1,4-bond O O O OH OH CH 2 OH CH 2 OH -1,1-bond TREHALOSE (glucose-glucose) Structures of the most common disaccharides 1 2 1 4 1 1 1 4
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12 Disaccharides Sources of disaccharides Sucrose (table or cane sugar): major sweetener in fruits and vegetables
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09012011FNTR342-CarbFiberDigest - Digestion, Absorption,...

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