Lecture 5: Lipids Flashcards
Lipids
Triglycerides
Sterols
Phospholipids
Comprised of carbon, hydrogen, oxygen
Are hydrophobic
Lipids in food
Provide 9kcal/g
Provides taste and mouthfeel
Fatty Acids
- Building block for TG and phospholipids
- Chain of carbons containing acid group at alpha end and methyl group at omega end
Categorizing Fatty Acids
There are 20 different fatty acids that vary:
* By carbon chain length
* By saturation
* By double bond location
* By shape
Categorizing by Chain Length
- Short chain (2-4 C): liquid at room temperatures and cold
- Medium chain (6-10 C): liquid at room temp solid at cold temp
- Long chain (>12 C): solid at room temp and cold
Categorizing by Saturation
- Saturated Fat
- Unsaturated Fat
~Monounsaturated
~Polyunsaturated
~Omega-3 (n-3)
Degree of Saturation
Determined by whether the carbons are held together by a double or single bond.
Saturated Fatty Acids
- All the carbons on the fatty acid are bound to hydrogen.
- There are no double bonds.
- They are solid at room temperature.
- They have a higher melting point.
Unsaturated Fatty Acids
- Some carbons on fatty acid form a double bond with
each other instead of binding to hydrogen. - They tend to be liquid at room temperature.
- They have a lower melting point.
Two types of Unsaturated Fatty Acids:
~Monounsaturated fatty acid (MUFA)
~Polyunsaturated fatty acid (PUFA)
Monounsaturated fatty acid (MUFA)
Has one double bond
Polyunsaturated fatty acid (PUFA)
Has two or more double bonds
Categorizing by double bond location
Count from methyl/omega end
Categorizing by Shape
Unsaturated fatty acids form two different shapes based
on the position of the hydrogen atoms around the double
bond:
Cis form: hydrogens on same side of double bond
Trans form: hydrogens on opposite sides of double bond
Triglycerides
- Major form of lipid in body
~Stores as adipose tissue for energy
~In bloodstream - high levels risk factor for heart
disease - Major form of lipid in food
~Add texture
~Make meat tender
~Preserve freshness
Structure of triglyceride
Have a glycerol backbone + 3 fatty acids
Contains a mixture of fatty acids
Phospholipids
- Have hydrophilic and hydrophobic ends
- 2 fatty acids + glycerol + phosphate group
- Synthesized by liver
- Emulsify fats
- Part of lipid bilayer in cell membrane (lecithin)
Sterols
- Four connecting rings of carbon and hydrogen
- No caloric value
- In animals (e.g. dietary cholesterol): not required in diet since liver makes what body needs
- In plants (phytosterols, phytostanols): can help reduce blood
cholesterol
Lipid digestion
- Fats, phospholipids, sterol break down to free fatty acids, monoglycerides and glycerol
Process of Lipid digestion
- Mouth: Chewing
- Stomach: Gastric lipase breaks down fat into diglyceride and one fatty acid
- Small intestine: most digestion occurs here
~Bile acids: emulsify fat, break fat globules into smaller
pieces
~Pancreatic lipase: two fatty acids and monoglyceride
~Phospholipids (lecithin) in bile is packaged with
monoglycerides and fatty acids to create micelles (small
carriers) for absorption
~Short and medium-chain fatty acids enter bloodstream
and travel to liver
~Long-chain fatty acids enter lymph and need transport
carriers
Sterol Digestion
Not digested
* Bile emulsifies sterols
* Carried by the micelle and absorbed intact through intestinal wall
* Some cholesterol goes back into the small digestion
- If lipids are undigested and not absorbed in the small intestine, they:
~Bind with fiber
~Are eliminated in the feces