1. Lipid digestion/absorption AnSci 520

2. Rumen Lipid Metabolism

3. Rumen Biohydrogenation Ruminant animals obtain lipids from three primary sources: Feed (seeds and forages) Diet supplementation (etc. tallow, palm oil, fish oil) De novo synthesis

4. Forages Glycolipids Grains & Concentrates Triglycerides Fat Supplements Triglycerides (by products) Free fatty acids (rumen-protected) Fat Sources

5. Triglycerides Glycerol backbone, and 3 fatty acids Major lipid class in concentrates Main lipid store in animal tissues Diverse range of fatty acids, rich in linoleic acid (18:2)

6. Galactolipids Galactose-Galactose Glycerol backbone, 2 fatty acids, and one or two galactose Major lipid class in forages Rich in linolenic acid (18:3)

8. Fatty Acids Long carbon chains that contain a methyl group (CH3) at one end and a carboxyl group (COOH) at the other Fatty acids are what make lipids energy-rich Characterized by: Number of carbons (chain length) Number of double bonds (degree of unsaturation) Location and orientation of these bonds (non-conjugated, conjugated; cis, trans)

9. Fatty acids vary in chain length and degree of unsaturation: Usually contain an even number of carbon atoms, typically between 14 and 24. The 16- and 18-carbon fatty acids are most common. May contain one or more double bonds. The double bonds in polyunsaturated fatty acids are separated by at least one methylene group (execpt when conjugated). The configuration of the double bonds in most unsaturated fatty acids is cis.

10. Structures of Lipids & Fatty Acids 2018161412108642 OH O 135791113151719 OH 20:4  5, 8, 11, 14 20:4 w or n- 6 O Nomenclature and general structure: A. B.

11. ©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license. Unsaturated Essential Fatty Acids Most FA can be synthesized by the cell: de novo, but these two can’t Both FA are found in high concentrations in most plants

12. Saturated – single bonds Nomenclature and Structure Unsaturated – double bonds R1CR2CCCC R1CR2CCCC

13. CCC H C HH HH H trans CC HH C H H C H H cis Nomenclature and Structure

14. Cis vs. Trans Bonds of Unsaturated Fatty Acids Trans: from food processing and rumen biohydrogenation (via microbial metabolism) Partial hydrogenation of polyunsaturated fats Lowers fluidity - becomes more solid at room temp. PUFA: Polyunsaturated fatty acids Spontaneously oxidize with molecular O 2 at their double bonds Form epoxide rings and breaking the chain - rancidity Prevented by addition of anti-oxidants

15. conjugated CC HH C H C H non-conjugated HH CCC HH C H C H Nomenclature and Structure

17. Rumen Biohydrogenation Traditionally, fat in ruminant diets has been limited to that provided in oil seeds and animal fat supplementation. Dietary fat is supplemented as an energy source since it provides more energy than carbohydrates. Too much fat in diet affects diet digestibility.

18. What Happens During Rumen Biohydrogenation? Dietary lipids hydrolyzed in the rumen to form free fatty acids and glycerol. Triglycerides- three fatty acids hooked onto glycerol backbone. (Found in animals, plants, and humans) Glycolipids- glycerol with two fatty acids + sugar “hanging off” SN3 position. (Found primarily in forages) Phospholipids- two fatty acids and phosphate group. Polyunsaturated fatty acids are also hydrogenated to saturated fatty acids and glycerol is converted to propionate.

19. Hydrolysis of ester linkages of triglycerides, glycolipids and phospholipids Extensive, > 85% Bacterial lipases Glycerol + Free fatty acids Prerequisite for biohydrogenation Hydrolysis

20. Lipids Free fatty acids Unsaturated Saturated Hydrolysis Biohydrogenation

21. Rumen Hydrolysis Fermented to VFA’s

22. Converts: unsaturated fatty acids → saturated fatty acids Biochemical pathways Biohydrogenation intermediates Biohydrogenation

23. Isomerization Cis Oriented Double Bond Trans Oriented Double Bond Bacterial Isomerases

24. Biohydrogenation Unsaturated Double Bond Saturated Bond Bacterial Hydrolyases + 2 H +

25. Hydrogenation

26. Rumen Lipid Metabolism Diet Forages (galactolipids) Concentrates (TG’s) Rumen Glycerol Galactose Free Fatty Acids (unsaturated) VFA Absorbed Saturated Fatty Acids (C 18:0 & C 16:0) Small Intestine

27. HydrolysisBiohydrogenation TG GL O-FA= O-sugar O-FA= OH OH + 3 FA= OH OH + 2FA= OH Sugar  VFAs FA=  CLA  trans  saturated FA Fat SourceFat Suppl.ForagesGrainsOil Seeds Fat TypeFA or TGGLTG FA TG FA TG FA TG: Triglyceride; GL: Glycolipid; FA: Fatty acid FA=: Fatty acid with double bond esophagus Rumen

28. Why Biohydrogenation? Aids in relieving the rumen of excess hydrogen ions caused by constant acid production through normal fermentation. Also, PUFA are highly toxic to rumen bacteria. –Survival process by bacteria. –Different groups of bacteria do different things.

29. Converts: unsaturated fatty acids → saturated fatty acids Biochemical pathways Biohydrogenation intermediates Biohydrogenation

30. Linoleic Acid (18:2) in Dairy cows Digestion in the Rumen 0 40 80 120 160 200 1234567891011 Study g/day consumed Jenkins, FAT University

31. Linoleic Acid (18:2) in Dairy cows Digestion in the Rumen 0 40 80 120 160 200 1234567891011 Study g/day consumed duodenum Jenkins, FAT University

32. Stearic Acid (18:0) in Dairy cows Digestion in the Rumen 0 100 200 300 400 500 1234567891011 Study g/day consumed Jenkins, FAT University

33. Stearic Acid (18:0) in Dairy cows Digestion in the Rumen 0 100 200 300 400 500 1234567891011 Study g/day consumed duodenum Jenkins, FAT University

34. cis-6, cis-9, cis-12 (  -linolenic acid) cis-9, cis-12 (linoleic acid) cis-9,cis-12, cis-15 (  -linolenic acid) cis-6, cis-9, trans-11 (conj. Octadecatrienoic acid) cis-9, trans-11 (conj. Octadecadienoic acid) cis-9, trans-11, cis-15 (conj. Octadecatrienoic acid) cis-6, trans-11 (octadecadienoic acid) trans-11, cis-15 (octadecadienoic acid) C18:0 (stearic acid) trans-11 (vaccenic acid) Traditional Pathways for Rumen Biohydrogenation Griinari & Bauman 1999

35. linoleicacid ( cis -9, cis -12 C 18:2 ) conjugatedlinoleicacid ( cis -9, trans -11 CLA) trans -11 C 18:1 stearicacid (C 18:0 ) conjugatedlinoleicacid trans -10, cis -12 CLA trans -10 C 18:1 stearicacid (C 18:0 ) Rumen Biohydrogenation linoleicacid ( cis -9, cis -12 C 18:2 ) conjugatedlinoleicacid ( cis -9, trans -11 CLA) trans -11 C 18:1 stearicacid (C 18:0 ) conjugatedlinoleicacid trans -10, cis -12 CLA trans -10 C 18:1 stearicacid (C 18:0 ) Griinari and Bauman, 1999 Change in rumen pH

36. Rumen By-pass Fatty acids can by-pass rumen: –Calcium salts –Protein coat –Formaldehyde Digestion and absorption of fatty acids in the small intestine is similar to monogastrics.