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
Fat Sources
• Forages
• Glycolipids
• Grains & Concentrates
• Triglycerides
• Fat Supplements
• Triglycerides (by products)
• Free fatty acids (rumen-protected)
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
• Glycerol backbone, 2 fatty acids, and one or
two galactose
• Major lipid class in forages
• Rich in linolenic acid (18:3)
Galactose-Galactose
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
Nomenclature and general structure:
O
A.
20
B.
1
18
3
16
5
14
7
12
9
10
11
8
13
6
15
4
17
2
19
OH
20:4 D5, 8, 11, 14
O
OH
20:4 w or n- 6
Unsaturated Essential Fatty Acids
Most FA can be synthesized by the cell: de novo, but these two can’t
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Both FA are found in high concentrations in most plants
Nomenclature and Structure
Saturated – single bonds
R1
C
C
C
C
C
R2
C
R2
Unsaturated – double bonds
R1
C
C
C
C
Nomenclature and Structure
cis
H
H
H
H
C
C
C
C
H
H
trans
C
C
H
C
C
H
H
H
H
H
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 + High pressure + H2
varying saturation
Ni++
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
Nomenclature and Structure
non-conjugated
H
H
H
H
H
C
C
C
C
C
H
conjugated
H
H
H
H
C
C
C
C
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
• Hydrolysis of ester linkages of triglycerides,
glycolipids and phospholipids
• Extensive, > 85%
• Bacterial lipases
• Glycerol + Free fatty acids
• Prerequisite for biohydrogenation
Lipids
Unsaturated
Hydrolysis
Biohydrogenation
Free fatty acids
Saturated
Rumen Hydrolysis
Fermented
to VFA’s
Biohydrogenation
• Converts:
unsaturated fatty acids → saturated fatty acids
• Biochemical pathways
• Biohydrogenation intermediates
Isomerization
Cis Cis
Oriented
Oriented
Double
Bond
Double
Bond
Bacterial
Isomerases
Trans Oriented
Double Bond
Biohydrogenation
Unsaturated
Double Bond
Bacterial
+ 2 H+
Hydrolyases
Saturated
Bond
Hydrogenation
Rumen Lipid Metabolism
Absorbed
Diet
Forages (galactolipids)
VFA
Concentrates (TG’s)
Glycerol
Galactose
Free Fatty Acids
(unsaturated)
Saturated Fatty Acids
(C 18:0 & C 16:0)
Rumen
Small Intestine
Fat Source
Fat Suppl.
Forages
Grains
Oil Seeds
Fat Type
FA or TG
GL
TG
TG
Rumen
TG
FA
Hydrolysis
TG
esophagus
GL
O-FA=
O-FA=
O-FA=
O-sugar
O-FA=
O-FA=
Biohydrogenation
OH
OH + 3 FA=
OH
OH
OH + 2FA=
OH
FA= CLA transsaturated FA
TG
FA
Sugar  VFAs
TG
FA
TG: Triglyceride; GL: Glycolipid; FA: Fatty acid
FA=: Fatty acid with double bond
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.
Biohydrogenation
• Converts:
unsaturated fatty acids → saturated fatty acids
• Biochemical pathways
• Biohydrogenation intermediates
Digestion in the Rumen
Linoleic Acid (18:2) in Dairy cows
200
consumed
g/day
160
120
80
40
0
1
2
3
4
5
6
7
8
9
10
11
Study
Jenkins, FAT University
Digestion in the Rumen
Linoleic Acid (18:2) in Dairy cows
200
consumed
duodenum
g/day
160
120
80
40
0
1
2
3
4
5
6
7
8
9
10
11
Study
Jenkins, FAT University
Digestion in the Rumen
Stearic Acid (18:0) in Dairy cows
500
consumed
g/day
400
300
200
100
0
1
2
3
4
5
6
7
8
9
10 11
Study
Jenkins, FAT University
Digestion in the Rumen
Stearic Acid (18:0) in Dairy cows
500
consumed
g/day
400
duodenum
300
200
100
0
1
2
3
4
5
6
7
8
9
10 11
Study
Jenkins, FAT University
Traditional Pathways for Rumen Biohydrogenation
cis-6, cis-9, cis-12
( -linolenic acid)
cis-6, cis-9, trans-11
(conj. Octadecatrienoic acid)
cis-9, cis-12
(linoleic acid)
cis-9, trans-11
cis-9,cis-12, cis-15
( -linolenic acid)
cis-9, trans-11, cis-15
(conj. Octadecadienoic acid) (conj. Octadecatrienoic acid)
cis-6, trans-11
trans-11, cis-15
(octadecadienoic acid)
(octadecadienoic acid)
trans-11
(vaccenic acid)
C18:0
(stearic acid)
Griinari & Bauman 1999
Rumen Biohydrogenation
linoleic acid
(cis-9, cis-12 C18:2 )
Change in rumen pH
conjugated linoleic acid
(cis-9, trans-11 CLA)
conjugated linoleic acid
trans-10, cis-12 CLA
trans-11 C18:1
trans-10 C18:1
stearic acid (C18:0 )
stearic acid (C18:0 )
Griinari and Bauman, 1999
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.