Artery

4. Carbohydrate Digestion Mouth 1. Mastication

5. Carbohydrate Digestion Mouth 1. Mastication 2. Saliva – moistens feed, together with mastication disrupts structure

6. Carbohydrate Digestion Mouth 1. Mastication 2. Saliva – moistens feed, together with mastication disrupts structure 3. Salivary amylase – attacks 1,4 linkages within starch

8. Carbohydrate Digestion Stomach 1. Low pH – denatures amylase

9. Carbohydrate Digestion Stomach 1. Low pH – denatures amylase 2. Acid helps disrupt H-bonds within complex carbohydrates

10. Carbohydrate Digestion Stomach 1. Low pH – denatures amylase 2. Acid helps disrupt H-bonds within complex carbohydrates 3. N0 CHO digesting enzymes

11. Induced Fit Model of Enzyme Function The active site is in the “induced conformation”

12. Carbohydrate Digestion Duodenum Pancreatic amylases break down starches to dextrins, maltotriose, maltose Amylase hydrolyzes -1,4 linkages Amylose ->->-> maltose Amylopectin ->->-> maltose, dextrin

13. Carbohydrate Digestion Duodenum Pancreatic amylases break down starches to dextrins, maltotriose, maltose The major brush border carbohydrases are: Maltase (maltose, maltotriose) – > -> glucose Isomaltase (dextrins) -> -> glucose Lactase (lactose) -> -> galactose, glucose in the enterocyte Sucrase (sucrose) ->-> fructose, glucose

15. Carbohydrate Digestion Duodenum Pancreatic amylases break down starches to dextrins, maltotriose, maltose The major brush border carbohydrases are: Maltase (maltose, maltotriose) – > -> glucose Isomaltase (dextrins) -> -> glucose Lactase (lactose) -> -> galactose, glucose in the enterocyte Sucrase (sucrose) ->-> fructose, glucose

16. Carbohydrate Digestion Enterocytes Only absorb monosaccharides Final breakdown products are glucose, galactose, fructose Fructose ->->-> lactic acid, glucose Galactose ->->-> glucose

19. Absorption of Glucose Across the Intestinal Epithelium The transporter for glucose and galactose into the enterocyte is the SODIUM DEPENDENT HEXOSE TRANSPORTER (SGLUT-1).

20. Absorption of Glucose Across the Intestinal Epithelium The transporter for glucose and galactose into the enterocyte is the SODIUM DEPENDENT HEXOSE TRANSPORTER (SGLUT-1). The molecule transports both glucose and sodium into the cell (won’t transport either alone).

21. Glucose Transporter The transporter is initially oriented facing the lumen – can only bind sodium, not glucose. After sodium is bound, a conformational change occurs, opening a glucose pocket. After glucose is bound, the transporter reorients in the membrane and is moved inside the cell.

22. Glucose Transport cont’d Sodium dissociates inside the cytoplasm and this destabilizes the glucose – transporter bond. Glucose dissociates within the cytoplasm and the free transporter is reoriented outward facing the lumen. Glucose is transported out of the enterocyte via a different transporter (GLUT – 2) in the basolateral membrane.

25. Important Carbohydrates

26. Dietary Carbohydrate Composition Monosaccharides – glucose from the hydrolysis of starch, fructose (keto-hexose) is 140% sweeter than sucrose and is very reactive with amino acids (maillard reactivity)

27. Disaccharides – sucrose is the major disaccharide in most diets (in foods, is often responsible for functional qualities including sweetness, mouth-feel, textural characteristics).

28. Disaccharides – sucrose is the major disaccharide in most diets (in foods, is often responsible for functional qualities including sweetness, mouth-feel, textural characteristics). Decreased use in soft drinks because of replacement with high-fructose corn syrup (increased availability and lower cost).

29. Disaccharides – sucrose is the major disaccharide in most diets (in foods, is often responsible for functional qualities including sweetness, mouth-feel, textural characteristics). Decreased use in soft drinks because of replacement with high-fructose corn syrup (increased availability and lower cost). Lactose (galactose-glucose) – milk products

30. Oligosaccharides – galactosucroses and fructo-oligosaccharides Galactosucroses – range from 5-8% DM Fructo-oligosaccharides – 60-70% DM of Jerusalem artichoke, do not undergo maillard reactivity (non-reducing)

31. Polysaccharides Starch – the most important, abundant polysaccharide. It is the reserve polysaccharide in leaves, stems, roots (tuber), seeds, fruit.

32. Polysaccharides Starch – the most important, abundant polysaccharide. It is the reserve polysaccharide in leaves, stems, roots (tuber), seeds, fruit. It occurs as discrete, crystalline granules whose size, shape, and gelatinization temperature are dependent on plant species.

33. Starch cont’d Seed starches – wheat, corn, rice, barley are located within protein matrices (poor quality protein sources for non-ruminants) Root starch – potato, casava

34. Starch cont’d Starch is a homopolysaccharide (repeating glucose units) with a mixture of two polymers, amylose and amylopectin

35. Amylose – is largely a linear polymer (1, 4 linkages) and a small percentage of 1, 6 branch points Amylopectin – highly branched (5-6% 1,6 branch points

36. Most common cereal starches contain 20-30% amylose Waxy starches (corn, rice, sorghum, barley) have no amylose and are essentially 100% amylopectin

37. Starch Gelatinization Starch granules hydrate in aqueous environments, swelling about 10%. Addition of heat takes the granules from an organized to disorganized state, this is the gelatinization temperature . Digestion of starch by amylase is greatly enhanced if it has been gelatinized.

38. Starch Gelatinization Retrograde starch – realignment of starch granules within amylose and amylopectin, “not normal” and may lead to decline in digestive efficiency.