8/29/2014 1 Course Outline Introduction, Overview of Industry I. Nutrient Analysis II. Digestive Tract Anatomy / Function - Anatomy - Digestive enzymes - Introduction to Gut Hormones III. Classes of Nutrients Digestive Enzymes • Carbohydrates: – Starch, disaccharides digested to monosaccharides – Fiber not digested by animal, but may be digested by microorganisms • Protein – Digested to free amino acids and dipeptides • Lipids – Mainly triglycerides (triacylglycerol) digested to free fatty acids, mono- and diglycerides and glycerol – Phospholipids and cholesterol ester of lesser importance. Source Enzyme Method of Activationor optimal conditions foractivitySubstrate end productSalivary gland salivary amylase(minor role, only inhuman, pig)pH 6.6-6.8 Starch maltose, maltotrioseLingual gland lingual lipase(minor importance)pH 3.0-6.0 Triglycerideat #3positionFatty acid plus 1,2-diglycerideStomach:Chief cellspepsin pepsinogen converted to pepsinby Hcl.Optimal pH 1-2Protein peptidesStomach: gastric lipasesame as lingual lipasePancreas: trypsin trypsinogen converted totrypsin by enterokinase inintestineoptimal pH 5.2-6.0Protein peptideschymotrypsin chymotrysinogen converted toactive by trypsinoptimum pH 8.0Protein peptidescarboxypeptidase procarboxypeptidase activatedby trypsincarboxylend ofproteinsmall peptides,free amino acidselastase proelastase activated bytrypsin Protein peptidespancreaticamylasepH 7.1 Starch maltose,maltotriosepancreatic lipase activated by bile salts,phospholipids, colipase, pH 8.0Triglycer-idesfree fatty acids,mono-glyceride,glycerolphospholipase activated by trypsin phospho-lipidsfatty acids,lysophospholipidcholesterol esterhydrolaseactivated by bile salts cholesterolestersfree cholesterol,fatty acidsDigestive Enzymes: Salivary, gastric, pancreatic8/29/2014 2 Source Enzyme Method ofActivationor optimalconditions foractivitySubstrate end productIntestinalepithelial cells,mainlyduodenumaminopeptidase polypeptides small peptides,free amino acidsdipeptidases dipeptides free amino acidssucrase pH 5-7.0 Sucrose glucose, fructosemaltase pH 5.8-6.2 Maltose glucoselactase pH 5.4-6.0 Lactose glucose,galactoseisomaltase 1,6-glucoside glucoseDigestive Enzymes: Intestinal epithelial cells Carbohydrate and Protein Digestion in Humans Carbohydrases Source Type Targets Amylase alpha- beta- Salivary, pancreatic Bacteria, plants Endo- Exo- α1-4 Glucosidase Sucrase (Invertase) Brush border - Maltase Brush border - α1-4 glucosidase Isomaltase Brush border - α1-6 glucosidase Lactase Brush border - β –galactosidase8/29/2014 3 Proteases Source Type Amino acid targets Pepsin Chief cells in stomach Endo- Leu, Phe, Tyr, Trp Between hydrophobic and aromatic Trypsin Pancreas Endo- Lysine, arginine Chymotrypsin Pancreas Endo- Tyr, trp, phe (lys, met) Elastase Pancreas Endo- Gly, ala, val Carboxypeptidase pancreas Exo- A- aromatic or BCAA B- arg, lys Aminopeptidase Brush border Exo- ? Dipeptidase Brush border - - Nutrient Absorption CHO – active and facilitiated Glucose Transporters: SGLT 1 = active transport (intestine and kidney) GLUT 1-5 = facilitated transport various tissues different affinities for glucose8/29/2014 4 Development of Carbohydrate Digesting Enzymes in the Pig Sucrase Maltase 2 Isomaltase Maltase 3 Lactase Trehalase Br. Poultry Sci 42:389-395, 2001 Sucrase Maltase Lactase Trehalase Lactose Digestion • In pigs: Lactose has a ME value of 3435 kcal/kg – Whey is 75% or more lactose – In birds, lactose causes diarrhea and can be toxic. (may be used as a probiotic at < 10%) CP Ca P DM Fiber Lipid ME, Pig ME, Poultry Whey 12.1 0.87 0.79 100% available 94 0 0.7 3190 19008/29/2014 5 J. Nutr. 2003 Wolf and Domestic dog are > 99% similar at DNA level (humans and chimps >98%) Expression of 3 genes related to carbohydrate (starch) digestion are different: amylase maltase sodium dependent glucose transporter (SGLT1) Amylase Maltase March 2013 Lipid digestion in humans8/29/2014 6 Dietary TG Digestion and Absorption Bile-salt activated lipase • Found in human and certain other primates breast milk – Also in dog and cat – Not in pig, horse, cattle, rat, guinea pig, rhesus monkey – (Higher primates and carnivores) • May be important in species with milk fatty acid profiles containing mainly LCFA • Rodents, herbivores, have SCFA and MCFA in milk TG which are digested by lingual and gastric lipases8/29/2014 7 Digestive Enzyme Development in the Young Pig (Lindemann et al., 1986) Age Body Wt, kg Lipase Amylase Chymotrypsin Trypsin Pepsin Birth 1.3 934 121 133 284 421 1 wk 2.0 2965 4422 470 770 3722 2 wk 3.3 12142 17614 840 1200 10550 3 wk 4.8 15421 37729 1350 1760 59320 4 wk 6.6 48756 62406 2222 3250 70400 Pancreatic enzymes expressed per pancreas. Pepsin expressed per stomach.8/29/2014 8 Deficiencies of digestive enzymes • Genetic Deficiencies • Young animal – Capacity to produce digestive enzymes in mammals is not fully developed at birth. • Human infant transition to solid food • Weaned pig lacks ability to digest starch • Older animals – Loose capacity to produce lactase • Lactose intolerance in humans • Incidence: Caucasians < 20%, Chinese and other Asians > 90%, Africans 95% Digestive Enzyme Substitution Therapy (J Anim Physiol and Anim Nutr 2005) • Pig model of exocrine pancreatic insufficiency – Relatively common in dogs – Humans - cystic fibrosis – Model – ligate pancreatic duct – +/- enzymes, phospholipids, omeprazole (Prilosec) – “Creon” = lipase, protease, amylase capsules – Diet: 18% CP, 19% EE, 6% CF, 40% starch Ileal Digestibility, % Organic matter Crude fat Crude protein Control 85 98 80 Pancreatic Ligation 44 16 29 PL + Creon 76 80 70 Dietary Fat and Obesity • High fat diets contribute to obesity • Limiting fat digestion and absorption may help with weight loss • Approaches – PL inhibitor – Fat substitute – Gastric bypass (affects all nutrients)8/29/2014 9 Olestra Side Effects -Fecal urgency -lower absorption of vitamin E and carotenoids Warning Label This product contains Olestra. Olestra may cause abdominal cramping loose stools. Olestra inhibits the absorption of some vitamins and other nutrients. Vitamins A,D, E and K have been added. Olestra = sucrose polyester R = fatty acid esterified to sucrose Regular Chips: 90 Calories from Fat