Lipids

ANSC303

Lipids

generally insoluble in water; important source of energy (dietary and storage) used in the cell membrane (lipid bilayer and MPL); supply essential fatty acids; synthesis of hormones; absorption of fat soluble vitamins; increase the palatability of feed (BUT, too much lipid can decrease the palatability of feed)

Fatty acids

straight chain hydrocarbons; terminate in a carboxyl group; make up complex lipids

Carboxyl group

CH₃ — (CH₂)_n — COOH

Saturated fatty acids

contains no carbon—carbon double bonds; missing 2H per double bond; the double bonds can either be cis or trans

Oil

liquid at room temperature; has more double bonds

Fat

solid at room temperature; very few double bonds

Triacylglycerol (TAG)

how we store lipids; approximately 95% of the lipids we consume (humans/pigs) are TAGs

Lingual Lipase

mammalian enzyme produced by the salivary glands; produced continuously; production increases with increased fat intake; stable and active in the low pH of the stomach; act in the short chain FA at the Sn3 position in the mouth and the stomach of non-ruminants

Gastric Lipase

mammalian enzyme produced by chief cells in the stomach; produced continuously; production increases with increased fat intake; stable and active on the low pH of the stomach; act on the short chain FA at the Sn3 position in the stomach of non-ruminants

Emulsification

increase the surface area of a fat droplet by turning it into many small fat droplets

Physical emulsification

mixing that occurs in the stomach and as food enters the duodenum

Chemical emulsification

occurs in the proximal small intestine; bile is mixed with digesta at the duodenum

Bile

made in the liver; stored in the gallbladder; synthesized from cholesterol; has both a hydrophobic region and a hydrophilic region allowing it to interact with hydrophobic lipids and the aqueous environment

Pancreatic lipase

mammalian enzyme; hydrolyzes fatty acids from S_n1 and S_n3 position; requires colipase for optimal activity

Colipase

produced by the pancreas in the inactive form, procolipase; procolipase is activated to colipase by trypsin; colipase contains a hydrophobic region that interacts with the fat droplet; colipase is NOT and enzyme, it just creates a binding site for pancreatic lipase

AcylCoA Synthetase

enzyme that reforms TAG in the enterocyte

B-48

apolipoprotein; stabilizes the lipoprotein as it moves through circulation; confers specificity (like a name tag) which tells the liver to leave it alone; enables lipoprotein lipase to hydrolyze TAG into DAG and FFA on the surface of muscle and adipose cells

Chylomicron

complete fat particle; exocytosed into lymphatic circulation and then slowly moves into the blood stream; 82% TAG, 7% phospholipid, 2% cholesterol, 9% protein, and some A, D, E, and K

Adsorb

to become stuck to

Desorb

become released from

Lysolecithin

desorbs saturated fatty acids from feed particle

Emulsification by bile

large fat droplet + bile → emulsified fat droplets

Enzymatic digestion by pancreatic lipase

triglyceride + lipase → fatty acids (monoglyceride) and some free glycerol is also formed

Absorption of products of fat digestion depends on size

short and medium-chained fatty acids and glycerol (small products) → absorbed into blood via capillary

long-chain fatty acids and monoglycerides (large products) → form into triglycerides and are transported in chylomicrons into lymph vessels

Glycolipid

found in grasses and plants, contains a sugar at S_n1; primary lipid source in grazing animals

Phospholipids

primary source of digested in the small intestine of ruminants; can come from microbes (MPL)

Lipase

microbial enzyme that hydrolyzes TAG into glycerol and 3 FFA

Galactolipase

microbial enzyme that hydrolyzes glycolipids into glycerol, 2 FFA, and sugar

Phospholipase

microbial enzyme that hydrolyzes phospholipids into glycerol, 2 FFA, and the polar head group

Lipids supply essential fatty acids which…

aids in the synthesis of hormones

What are the fat soluble vitamins

A, D, E, and K

How does palatability affect ruminants?

they dislike added fat

How does fat affect palatability of food/feed?

Increases palatability

How do lipids condition the feed?

Decreased dust, decreased fines, decreased sorting

Lipid structure: TAG

CH₃— (CH₂)_n—- COOH

straight chain hydrocarbon

fatty acids are used to synthesized more complex lipids

2 types of fatty acids

saturated and unsaturated fatty acids

Saturated fatty acids

contain no C-C double bonds

contain all of the H they can contain

maximal energy value

Unsaturated fatty acids

contain one or more C-C double bonds

missing 2H

less energy with every additional double bond

Monounsaturated fatty acid

contain 1 C-C double bond

missing 2H

Polyunsaturated fatty acids

contain >1 C-C double bond

missing 2H per double bond

What determines fluidity of the lipid?

The number of double bonds

Increased number of double bonds = decrease in melting point

Mouth (non-ruminant lipid digestion)

minimal digestion of TAG; lingual lipase

physical emulsification: TAG + H₂O and LL → DAG

Stomach (non-ruminant lipid digestion)

TAG,_DAG,FFA

Gastric lipase and physical emulsification at S_n3

TAG+ H₂O and GL or LL → DAG

Small intestine (non-ruminant lipid digestion)

TAG,_DAG,FFA

primary site of digestion and only site of absorption

Phase 1 emulsification: make and maintain small fat droplets; increased the surface area of the fat droplets

Phase 2 enzymatic digestion: pancreatic lipase; S_n1 and S_n3; procolipase + trypsin → colipase

Physical digestion

mixing; chewing; movement of digesta

mouth, stomach, duodenum

Chemical digestion

maintain the small fat droplet

bile

Phase 3 absorption through passive diffusion

TAG + H₂O and PL → DAG

DAG + H₂O and PL → MAG

What hydrolyzes ester bonds at S_n3?

lingual lipase and gastric lipase

What hydrolyzes ester bonds at S_n1 and S_n3?

Pancreatic lipase which requires colipase for optimal activity

Trypsin

Prodeolytic

breakes peptide bonds

activates procolipase → colipase (interacts with the fat droplet)