Lecture 5: Lipids

Question 1

Lipids

Answer 1

Triglycerides
Sterols
Phospholipids

Comprised of carbon, hydrogen, oxygen

Are hydrophobic

Question 2

Lipids in food

Answer 2

Provide 9kcal/g
Provides taste and mouthfeel

Question 3

Fatty Acids

Answer 3

• Building block for TG and phospholipids
• Chain of carbons containing acid group at alpha end and methyl group at omega end

Question 4

Categorizing Fatty Acids

Answer 4

There are 20 different fatty acids that vary:
* By carbon chain length
* By saturation
* By double bond location
* By shape

Question 5

Categorizing by Chain Length

Answer 5

• 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

Question 6

Categorizing by Saturation

Answer 6

• Saturated Fat
• Unsaturated Fat
  ~Monounsaturated
  ~Polyunsaturated
  ~Omega-3 (n-3)

Question 7

Degree of Saturation

Answer 7

Determined by whether the carbons are held together by a double or single bond.

Question 8

Saturated Fatty Acids

Answer 8

• 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.

Question 9

Unsaturated Fatty Acids

Answer 9

• 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)

Question 10

Monounsaturated fatty acid (MUFA)

Answer 10

Has one double bond

Question 11

Polyunsaturated fatty acid (PUFA)

Answer 11

Has two or more double bonds

Question 12

Categorizing by double bond location

Answer 12

Count from methyl/omega end

Question 13

Categorizing by Shape

Answer 13

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

Question 14

Triglycerides

Answer 14

• 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

Question 15

Structure of triglyceride

Answer 15

Have a glycerol backbone + 3 fatty acids

Contains a mixture of fatty acids

Question 16

Phospholipids

Answer 16

• Have hydrophilic and hydrophobic ends
• 2 fatty acids + glycerol + phosphate group
• Synthesized by liver
• Emulsify fats
• Part of lipid bilayer in cell membrane (lecithin)

Question 17

Sterols

Answer 17

• 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

Question 18

Lipid digestion

Answer 18

• Fats, phospholipids, sterol break down to free fatty acids, monoglycerides and glycerol

Question 19

Process of Lipid digestion

Answer 19

• 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

Question 20

Sterol Digestion

Answer 20

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