Lipids Flashcards
Lipids
lipids = fat = ether extract
Dictionary definitions of FAT
- Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water.
- A greasy water-insoluble solid or semi-solid chemical compound that is among the chief nutritional components of food;
- Animal or vegetable tissue made up of cells that contain large amounts of triglycerides;
- A solid or liquid substance such as butter or soybean oil that is derived from animals or plants and is used as a cooking medium or ingredient
Classifications of lipids
- Simple lipids
- Compound lipids
3. Non-glycerol, non-fatty acid based lipids
4. Derived Lipids -
Classifications of lipids
- Simple lipids
- Esters of fatty acids with various alcohols;
- Fats and oils are esters of fatty acids with glycerol;
- Waxes are esters of fatty acids with alcohols other than glycerol.
Classifications of lipids
2. Compound lipids
- Esters of fatty acids containing non-lipid substances such as:
phosphorus, CHO, or proteins
- Examples: phospholipids, glycolipids, lipoproteins
Classifications of lipids
3. Non-glycerol, non-fatty
acid based lipids
- Cholesterol
- Plant-based sterols
- Waxes
- Many pigments
Classifications of lipids
4. Derived Lipids
substances obtained by hydrolysis of compound lipids.
Practical considerations…
1. Lipids are less dense than water;
(thus they float!)
2. Lipids yield more energy (~9 kcals/gram) than
carbohydrates and proteins (~4 kcals/g); thus
they are often used as a concentrated source of
energy in animal feeds; (Helpful in winter)
3. Dietary fats are mostly triglycerides
(typically greater than 95%) .
All carbons have to have 4 bonds
Fatty acids
- This is the building block of all simple and compound lipids;
• Hydrocarbon chain with carboxylic acid at one
end; thus making it an “acid”
;
• Typically, even # of © w/o branching;
• Ruminants tissues & products will have some
fatty acids that are odd # and/or branched that
come from microbial sources.
Unsaturated Fatty acids
- Unsaturation involves the loss of hydrogens from two adjacent C, thus a double bond must be formed in order for all C to have a total of 4 bonds;
lysine- limiting in soybeans
Glycine-poultry
Fatty Acid Nomenclature
Saturated and Unsaturated
Myristic acid- 14 carbons; 0 double bonds
Palmitic acid- 16 carbons;0 double bonds
Stearic acid: 18 carbons; 0 double bonds
Oleic Acid: 18 carbons; 1 double bond
Linoleic acid: 18 carbons; 2 double bonds
Polyunsaturated fatty acids (PUFA)
Arachidonic acid (ARA)- 20 carbons; 4 double bonds
Alpha-Linolenic acid (ALA)- 18 carbons; 3 double bonds
Eicosapentanoic acid (EPA)- 20 carbons; 5 double bonds
Docosahexanoic acid (DHA)- 22 carbons; 6 double bonds
Animal Fats
Lard
Tallow
Butter
Lard is from pigs
Tallow is from cattle
Butter is from dairy cows
Triglyceride Profiles of Fats are NOT the same as the
fatty acid profile.
1. Fats are mixtures of various triglycerides;
2. Fatty acids are not uniformly distributed on glycerol backbone
(see Table 8.3, p. 98)
4 Key ways to Describe the properties of Dietary Fats
- Melting point
- Iodine Number
- Saponification number
- Reichert-Meissl (RM) number
- Melting point (MP)
(4 things associated with MP)
- Melting point (MP)- is a key way to describe poperties of Dietary Fats
a) Temperature at which solid fat turns liquid;
b) Depends on chain length and unsaturation;
c) As chain length increases, MP increases;
d) As unsaturation increases, MP decreases;
*Melting point is an important characteristic
of fats/oils, b/c it affects “functionality”.
2. Iodine number
(4 things associated with this)
2. _Iodine numbe_r- a key way to describe the properties of Dietary Fats
a) Grams of iodine taken up by 100 g of fat;
b) Iodine reacts with double bonds;
c) The more unsaturated the fat the higher the iodine #;
d) The higher the iodine # the lower
the oxidative stability of the fat/oil.
Oxidative Stability of fats/oils
- Oxygen from the air and heat combine to degrade fatty acids;
- Sat. & mono are more stable than PUFA;
- The degradation can produce destructive free radicals and off-flavors;
- The end-point is rancidity!
3. Saponification number
(3 things associated with it)
3. Saponification number- a key way to Describe the Properties of Dietary Fats
a) Milligrams of alkali (NaOH or KOH) it takes to hydrolyse 1 gram of fat;
b) Reaction between alkali and fat yields soaps;
c_) The shorter the average fatty acid chain length
the higher the saponification number_
d) (see Table 8.3 - p. 95)
4. Reichert-Meissl (RM) number
( things associated with this)
4. Reichert-Meissl (RM) number- A key way to describe the properties of Dietary Fats
a) Milliliters of 0.1 N KOH needed to neutralize amount
of volatile fatty acids released from the hydrolysis of 5 grams of fat
b) A measure of water-soluble volatile (SHORT-CHAIN)
fatty acids in a fat
c) Butterfat has a RM = 17-35
“Fake” Fats
1. In the olestra chemical structure, sucrose takes the place of glycerol.
2. The olestra molecule is too large to be metabolized
and passes through the body unchanged.
3. Because it acts as a lipid in the GI tract, it can cause
depletion of fat-soluble vitamins.
Digestion of Fats
Most digestion and absorption of fats occurs in the small intestine;
- EMULSIFICATION by bile is critical
- LIPASES
EMULSIFICATION
EMULSIFICATION by bile is critical…
- Increases solubility of fat; “ (watch in-class demonstration)
- Increases surface area, thus increases access to digestive enzymes;
- Without bile, fat digestion is very poor.
- With bile, fat digestibility is high (typically 90-95_%)
LIPASES
LIPASES breakdown complex lipids to fatty acids and other components…
