lipid digestion/absorption ansci 520. rumen lipid metabolism
TRANSCRIPT
Lipid digestion/absorption
AnSci 520
Rumen Lipid Metabolism
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
• Forages• Glycolipids
• Grains & Concentrates• Triglycerides
• Fat Supplements• Triglycerides (by products)
• Free fatty acids (rumen-protected)
Fat Sources
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)
Galactolipids
Galactose-Galactose
• Glycerol backbone, 2 fatty acids, and one or two galactose
• Major lipid class in forages
• Rich in linolenic acid (18:3)
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)
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.
Structures of Lipids & Fatty Acids
20 18 16 14 12 10 8 6 4 2OH
O
1 3 5 7 9 11 13 15 17 19OH
20:4 5, 8, 11, 14
20:4 w or n- 6O
Nomenclature and general structure:
A.
B.
©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
Unsaturated Essential Fatty AcidsMost FA can be synthesized by the cell: de novo, but these two can’t
Both FA are found in high concentrations in most plants
Saturated – single bonds
Nomenclature and Structure
Unsaturated – double bonds
R1 C R2C CC C
R1 C R2C CC C
CCC
H
C
H H
H HH
trans
CC
H H
C
H
HC
H
H
cis
Nomenclature and Structure
Cis vs. Trans Bondsof 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 + High pressure + H2 varying saturationNi++
PUFA: Polyunsaturated fatty acids • Spontaneously oxidize with molecular O2 at their double bonds • Form epoxide rings and breaking the chain - rancidity • Prevented by addition of anti-oxidants
conjugated
CC
H H
C
H
C
H
non-conjugated
H H
C CC
H H
C
H
C
H
Nomenclature and Structure
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.
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.
• Hydrolysis of ester linkages of triglycerides, glycolipids and phospholipids
• Extensive, > 85%
• Bacterial lipases
• Glycerol + Free fatty acids
• Prerequisite for biohydrogenation
Hydrolysis
Lipids
Free fatty acids
Unsaturated
Saturated
Hydrolysis
Biohydrogenation
Rumen Hydrolysis
Fermented to VFA’s
• Converts:
unsaturated fatty acids → saturated fatty acids
• Biochemical pathways
• Biohydrogenation intermediates
Biohydrogenation
Isomerization
Cis Oriented Double Bond
Cis Oriented Double Bond
Trans Oriented Double Bond
Bacterial Isomerases
Biohydrogenation
Unsaturated Double Bond
Saturated Bond
Bacterial Hydrolyases + 2 H+
Hydrogenation
Rumen Lipid Metabolism
DietForages (galactolipids)
Concentrates (TG’s)
Rumen
Glycerol
Galactose
Free Fatty Acids (unsaturated)
VFA
Absorbed
Saturated Fatty Acids (C 18:0 & C 16:0)
Small Intestine
Hydrolysis Biohydrogenation
TG
GL
O-FA=O-FA=O-FA=
O-sugarO-FA=O-FA=
OHOH + 3 FA=OH
OHOH + 2FA=OH
Sugar VFAs
FA= CLA transsaturated FA
Fat Source Fat Suppl. Forages Grains Oil Seeds
Fat Type FA or TG GL TG TG
TGFA
TGFA
TGFA
TG: Triglyceride; GL: Glycolipid; FA: Fatty acidFA=: Fatty acid with double bond
esophagus
Rumen
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.
• Converts:
unsaturated fatty acids → saturated fatty acids
• Biochemical pathways
• Biohydrogenation intermediates
Biohydrogenation
Linoleic Acid (18:2) in Dairy cows
Digestion in the Rumen
0
40
80
120
160
200
1 2 3 4 5 6 7 8 9 10 11
Study
g/d
ay
consumed
Jenkins, FAT University
Linoleic Acid (18:2) in Dairy cows
Digestion in the Rumen
0
40
80
120
160
200
1 2 3 4 5 6 7 8 9 10 11
Study
g/d
ay
consumed
duodenum
Jenkins, FAT University
Stearic Acid (18:0) in Dairy cows
Digestion in the Rumen
0
100
200
300
400
500
1 2 3 4 5 6 7 8 9 10 11
Study
g/d
ay
consumed
Jenkins, FAT University
Stearic Acid (18:0) in Dairy cows
Digestion in the Rumen
0
100
200
300
400
500
1 2 3 4 5 6 7 8 9 10 11
Study
g/d
ay
consumed
duodenum
Jenkins, FAT University
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
linoleic acid(cis-9, cis-12 C18:2)
conjugated linoleic acid(cis-9, trans-11 CLA)
trans-11 C18:1
stearic acid (C18:0)
conjugated linoleic acid trans-10, cis-12 CLA
trans-10 C18:1
stearic acid (C18:0)
Rumen Biohydrogenation
linoleic acid(cis-9, cis-12 C18:2)
conjugated linoleic acid(cis-9, trans-11 CLA)
trans-11 C18:1
stearic acid (C18:0)
conjugated linoleic acid trans-10, cis-12 CLA
trans-10 C18:1
stearic acid (C18:0)
Griinari and Bauman, 1999
Change in rumen pH
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.