Lipid digestion/absorption

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Lipid digestion/absorption

• AnSci 520

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Rumen Lipid Metabolism
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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

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Fat Sources

• Forages
• Glycolipids
• Grains Concentrates
• Triglycerides
• Fat Supplements
• Triglycerides (by products)
• Free fatty acids (rumen-protected)

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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 (182)

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Galactolipids

• Glycerol backbone, 2 fatty acids, and one or two
  galactose
• Major lipid class in forages
• Rich in linolenic acid (183)

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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)

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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.

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Structures of Lipids Fatty Acids
Nomenclature and general structure
O
A.
5, 8, 11, 14
D
204
OH
20
18
16
14
12
10
8
6
4
2
O
6
204
w or n-
B.
OH
1
3
5
7
9
11
13
15
17
19
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Unsaturated Essential Fatty Acids
Most FA can be synthesized by the cell de novo,
but these two cant
Both FA are found in high concentrations in most
plants
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Nomenclature and Structure

• Saturated single bonds

Unsaturated double bonds
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Nomenclature and Structure
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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 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
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Nomenclature and Structure
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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.

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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.

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Hydrolysis

• Hydrolysis of ester linkages of triglycerides,
  glycolipids and phospholipids
• Extensive, gt 85
• Bacterial lipases
• Glycerol Free fatty acids
• Prerequisite for biohydrogenation

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LipidsFree fatty acids
UnsaturatedSaturated
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Rumen Hydrolysis
Fermented to VFAs
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Biohydrogenation

• Converts
• unsaturated fatty acids ? saturated fatty acids
• Biochemical pathways
• Biohydrogenation intermediates

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Isomerization
Cis Oriented Double Bond
Cis Oriented Double Bond
Bacterial Isomerases
Trans Oriented Double Bond
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Biohydrogenation
Unsaturated Double Bond
Bacterial Hydrolyases
2 H
Saturated Bond
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Hydrogenation
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Rumen Lipid Metabolism
Absorbed
Diet
Forages (galactolipids) Concentrates (TGs)
VFA
Glycerol Galactose Free Fatty Acids (unsaturated)
Saturated Fatty Acids (C 180 C 160)
Rumen
Small Intestine
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Rumen
TG FA
Hydrolysis
Biohydrogenation
O-FA O-FA O-FA
OH OH 3 FA OH
TG
FA? CLA ?trans?saturated FA
esophagus
TG FA
GL
O-sugar O-FA O-FA
OH OH 2FA OH Sugar ? VFAs
TG FA
TG Triglyceride GL Glycolipid FA Fatty
acid FA Fatty acid with double bond
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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.

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Biohydrogenation

• Converts
• unsaturated fatty acids ? saturated fatty acids
• Biochemical pathways
• Biohydrogenation intermediates

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Linoleic Acid (182) in Dairy cows
Digestion in the Rumen
Jenkins, FAT University
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Linoleic Acid (182) in Dairy cows
Digestion in the Rumen
Jenkins, FAT University
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Stearic Acid (180) in Dairy cows
Digestion in the Rumen
500
consumed
400
300
g/day
200
100
0
1
2
3
4
5
6
7
8
9
10
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Study
Jenkins, FAT University
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Stearic Acid (180) in Dairy cows
Digestion in the Rumen
Jenkins, FAT University
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Rumen Biohydrogenation
linoleic
acid
linoleic
acid
(
cis
-
9,
cis
-
12 C
)
(
cis
-
9,
cis
-
12 C
)
Change in rumen pH
182
182
conjugated
linoleic
acid
conjugated
linoleic
acid
conjugated
linoleic
acid
conjugated
linoleic
acid
(
cis
-
9,
trans
-
11 CLA)
trans
-
10,
cis
-
12 CLA
(
cis
-
9,
trans
-
11 CLA)
trans
-
10,
cis
-
12 CLA
trans
-
11 C
trans
-
10 C
trans
-
11 C
trans
-
10 C
181
181
181
181
stearic
acid (C
)
stearic
acid (C
)
stearic
acid (C
)
stearic
acid (C
)
180
180
180
180
Griinari and Bauman, 1999

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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.