Final 8 - Lipids

Question 1

Draw structure of triglyceride provided with fatty acids

Answer 1

do it

Question 2

Structure of STEARIC ACID

Answer 2

18 carbon, zero double bonds

Question 3

Structure of LINOLEIC ACID

Answer 3

Omega-6 (18:2, Cis-9, cis-12)

Question 4

Structure of LINOLENIC ACID

Answer 4

Omega-3 (18:3, cis-9, cis-12, cis-15)

Question 5

What is the relationship between melting points and fatty acid structure?

Answer 5

• Melting points increase with chain length
• Decrease with increase of unsaturation
- Linear/saturated FA is packed very tight, takes higher energy to separate, so high melting point
- Unsaturated FAs are more spread out, so easier to break up - lower melting point

Question 6

Describe the polarity and structure of a fatty acid

Answer 6

• Contains an end with carboxyl group (double bond with oxygen and then an -OH group), which performs as the acid in a system (hydrophilic)
• Other end has short or long chain of carbons with covalent hydrogen bonds (CH2)n (saturated) or form a double bond with each other (unsaturated)

Question 7

What is the difference between mono-, di-, triglyceride?

Answer 7

MONO - one fatty acid on glycerol backbone
- Amphiphilic - glycerol wants to dissolve in water because of hydrophilic carboxyl group; fatty acid wants to dissolve in fat (hydrophobic); can carry across cell membrane; moves freely in both water base and lipid base

DI - two fatty acids on glycerol backbone with one -OH end

TRI - three fatty acids attached to glycerol
most common, because can be so many different combinations

Question 8

Of mono-, di-, and triglycerides, which can be used as an emulsifier?

Answer 8

• mono- and di-glyceride are both amphiphilic that can serve as emulsifier.
• Tri-glyceride is hydrophobic, since it does not contain any -OH group

Question 9

What type of solvents do lipids dissolve in?

Answer 9

Only in organic solvents

Question 10

Lipids serve as a solvent for what type of compounds?

Answer 10

Non-polar

Non-polar mixes well with non-polar; polar well with polar

Question 11

Describe the structure of a phospholipid

Answer 11

Third -OH group of glycerol has phosphorus group attached to it instead of fatty acid

Question 12

Describe the structure and polarity of lecithin from egg yolk

Answer 12

• Amphiphilic, so can be used as an emulsifier

* Phospholipid, so glycerol backbone with two fatty acids and one phosphorous group

Question 13

Why is lecithin an important emulsifier in many products?

Answer 13

When two immiscible liquids are mixed together

Question 14

What is continuous phase and dispersed phase of an emulsion?

Answer 14

• Continuous phase is the major part of the emulsion mixture

* Dispersed is the smaller proportion which you’re trying to disperse in small droplets

Question 15

Describe mayo as an emulsion. Pick out the emulsifier, the continuous phase and dispersed phase

Answer 15

Mayo- (high fat egg yolk base you’re trying to disperse water into)

Water-in-oil emulsion

• Fat/lipids are the continuous phase
• Water is the dispersed phase
• Egg yolk/lecithin is the emulsifier

Question 16

Describe milk as an emulsion. Pick out the emulsifier, the continuous phase and dispersed phase

Answer 16

12% fat/88% water

Oil-in-water emulsion

• Water is continuous phase
• Fat is dispersed phase

Question 17

What is a free radical?

Answer 17

Chemical species containing one or more unpaired electrons (unstable and highly reactive). Tries to steal any electrons it can- will attack anything next to it.

Question 18

Describe the free radical chain reaction from initiation to ending

Answer 18

• Free radical X (unknown) attacks anything next to it- usually a lipid because they have a lot of H. Grabs the electron from the lipid and leaves the lipid impaired with a single electron, becomes a free radical.
• Free radical lipid will attack any oxygen in the air/container and creates another free radical, which attacks another lipid next to it, generating a new free radical
• Continues until all the oxygen is used up
If metals exist in system the peroxidative lipid will react with metal and create its own cycle until most of the lipids become free radicals
• When free radicals bump into each other they can form electron pairs and become more stable; are not lipids anymore, are highly volatile and have a different smell (rancid)

Question 19

Give basic chain reactions for lipid oxidation (initiation, propagation, and termination)

Answer 19

Initiation: LH + X* → L* + XH

Chain propagation:
L* + O2 → LOO*
LOO* + LH → LOOH + L*

Chain termination:
LOO* + L* → LOOL
LO* + L* → LOL

Question 20

How can lipid rancidity or fat rancidity be prevented in food products?

Answer 20

1. LIGHT
   • Selection of packaging material
   • Storage in the dark
2. OXYGEN CONCENTRATION
   • Vacuum packaging
   • Nitrogen flushing
3. HEAVY METAL CONCENTRATION
   • Selection of packaging material
   • Metal chelating agents (eg: polyphosphates in meat products)
4. ANTIOXIDANT CONCENTRATION
   • Antioxidants may occur naturally in foods (vitamins D, E, and A)
   • Natural or synthetic antioxidants can be added
5. TEMPERATURE - Storage and distribution at low temperatures
6. DEGREE OF UNSATURATION - selection of fat/oil
   • Unsaturated FAs become rancid quicker than saturated FAs usually

Question 21

Explain how fat functions as flavor enhancer

Answer 21

• Adds creamy mouth feel

* Carries many different flavor compounds - a lot of flavors can only dissolve in fats (not water)

Question 22

Is there a good quality fat replacer? Why/why not

Answer 22

No
• Fat has lubrication effect, where flavors slide on your tongue giving you creamy mouth feel
• Enhances flavor, so when replace fat a lot of flavors are removed at same time