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

http://upload.wikimedia.org/wikipedia/commons/1/19/Rasyslami.jpg

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.