Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

2) Food Chemistry I > Lipids VII > Flashcards

Lipids VII Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Gourmet Food flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

What is the major function of true antioxidants?

A

Have the property of being able to interrupt the PROPAGATION step of the autoxidation process

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What other mechanisms can decrease autoxidation?

A
  • Stabilization of hydroperoxides
  • Competitive binding of O2
  • Retardation of the initiation step
  • Removal of oxygen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the most important mechanism to slow the autoxidation process?

A

Interrupting or retarding the propagation step

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the two properties of an antioxidant?

A

1) Ability to give a hydrogen more readily than a fatty acid

2) Has a poor tendency to react with molecular oxygen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How do antioxidant free radicals differ from free fatty acid radicals?

A

Antioxidant free radicals have a poor tendency to react with molecular oxygen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How do antioxidants prefer to end their free radical states?

A

By combining with other free radicals to form neutral species

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What do antioxidants typically give their free radical to?

A

Generally a peroxy radical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What do antioxidants lengthen?

A

They lengthen the induction period

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Are antioxidants consumed?

A

Yes, slowly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Compounds with good antioxidant properties are generally _______ compounds.

A

Phenolic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is vitamin E present in? What does that cause?

A
  • Seed oils

- They are less susceptible to autoxidation than animal fats

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Are seed oils or animal fat oils more susceptible to autoxidation?

A

Animal fats are more susceptible since they do not have antioxidants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the main antioxidants used for food?

A

1) BHA
2) BHT
3) PG
4) Tert-butyl Hydroquinone (not used in Canada)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

In phenolic antioxidants, what donates hydrogens?

A

Always the OH groups

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Which antioxidants does the public prefer?

A

Complex antioxidants found in natural products (rosemary extract)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the disadvantage of using oils with natural antioxidants?

A

Oils contain natural antioxidants at variable levels; they can be lost during processing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Are antioxidants used alone?

A

Usually used as combinations because mixtures tend to be more effective

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the antioxidant legal limit? What is it based on?

A
  • Under 0.02% (200 ppm)

- Based on the fat content of the product

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What happens if the amounts of antioxidant surpass 200 ppm?

A
  • Antioxidant can become a pro-oxidant

- Can be toxic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What does an antioxidant free radical form when it accepts hydrogen?

A
  • Forms resonance stabilized antioxidant free radical

- Resonance delocalization (free radical can change spots)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How does gamma-Tocopherol change the quality of an oil?

A

Prolongs the freshness (less hexanal for longer) through its antioxidants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What happens to antioxidants (like propyl gallate) in frying fats or in systems of high pH?

A
  • Can form a blue complex with ferrous ions

- Discolors a fat, such as lard

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How can BHA and BHT (normally stable) be lost? Why?

A

Through volatilization as a fat is heated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How are the vapor pressures of BHA and BHT?

A
  • Quite low

- But, high enough to allow the migration of the antioxidant impregnated into packaging material to migrate to the food

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How does citric acid slow down oxidation? Is it an antioxidant?

A
  • No, it is a preservative

- Natural way to chelate metals, which slows down oxidation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What are powerful catalysts for lipid oxidation? How?

A
  • Metal ions

- Assist in catalyzing the breakdown of hydroperoxides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Metal ions shorten the ____________ and increase the overall __________

A

induction period, rate of the reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What amount of metal ions are required to bring about a significant change in the reaction rate?

A

Only a small amount (ppm)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Does metal ion catalysis favour the second or third oxidation state reaction? What does it form?

A

Favours the second oxidation state; forms an alkoxy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What does the third oxidation state of a metal ion form?

A

A peroxy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Why do metal ions speed up the autoxidation reaction?

A

Since they catalyze the breakdown of ROOH to form Alkoxy and Peroxy radicals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What does the chelation of metal ions cause?

A
  • Causes steric hindrance

- Eliminates the catalytic role metal ions would otherwise play

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Do chelating agents interfere with the primary autoxidation mechanisms? What are they called?

A
  • No
  • Not true antioxidants
  • Synergistic agents to synergists
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Give examples of synergists.

A

Ascorbic acid, phosphates, EDTA, phospholipids, chelating agents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Why are metal ions largely unavoidable?

A

Since almost all processing equipment is metallic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

How are metal ions contributed naturally?

A
  • By raw materials

- In the form of chlorophyll or myoglobin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Metal ions allow the formation of more reactive ___________, which can attack lipids directly

A

singlet oxygen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Where is lipoxygenase realtively abundant?

A

In plant tissues

39
Q

What does lipoxygenase catalyse?

A

Catalyses the direct oxidation of polyunsaturated fatty acids which have a cis-cis 1,4 pentadiene group in its molecular structure

40
Q

What do enzymes catalyze in the lipid of plant tissues?

A
  • Catalyzes the formation of hydroperoxides

- Instigates the free radical mechanism

41
Q

What happens to frozen/dehydrated vegetables if they are not blanched?

A
  • Undergo rapid autoxidation

- Produce hay like/cardboard aroma

42
Q

What does the bleaching of pigments (chlorophyll, beta-carotene) occur as a result?

A

Result of autoxidation initiated by lipoxygenase

43
Q

Why is heat applied to the oilseed crush?

A

To reduce the effects of lipoxygenase and lipase

44
Q

What is responsible for the development of characteristic flavours and aromas in living plant systems?

A

Lipoxygenase

45
Q

How can the autoxidation reaction be controlled?

A
  • Antioxidants
  • Synergists (chelating agents)
  • Protection from light (brown bottles)
  • Replacement of air with nitrogen
46
Q

What are the 11 factors that affect autoxidation?

A

1) Energy in the form of heat and light
2) Catalysts
3) Double bonds
4) Enzymes
5) Chemical oxidants
6) Oxygen content and types of oxygen
7) Natural antioxidants
8) Phospholipids
9) Fatty acids
10) Mono- and Di-glycerides
11) Polymers

47
Q

Why can fatty acids chelate?

A

Because they have a carboxyl group

48
Q

Which radical is the most reactive?

A

Hydroxy radical

49
Q

How many hydroperoxides does oleic acid form?

A

4

50
Q

How do the energy levels of triplet and singlet oxygen compare?

A

Triplet: 0
Singlet: 22.5 kcal

51
Q

How does the nature of triplet and singlet oxygen compare?

A

Triplet: diradical
Singlet: no radical

52
Q

How does the reaction of triplet and singlet oxygen compare?

A

Triplet: radical
Singlet: electron-rich

53
Q

How does the degradation of linoleic acid compare if its done with triplet or singlet oxygen?

A

Triplet: slower
Singlet: much faster

54
Q

What are dye photosynthesizers?

A

Methylene blue, crystal violet

55
Q

What are pigment photosynthesizers?

A

Chlorophyll, riboflavin

56
Q

Photosynthesizers absorb light in the ____ - ____ range

A

380-900

57
Q

The singlet state is produced first by the _______________, but it has a _____ lifetime, decaying to _______________ to the ground state and by _________________ to the triplet state

A

light absorbed
short
fluorescence
intersystem crossing

58
Q

Prior to the development of rancidity, what is the reversion flavor in soybean oil like?

A

Beany and grassy flavor

59
Q

What are the detrimental effects of lipoxygenase?

A
  • Destruction of the essential fatty acids
  • Free radicals produced damage other compounds
  • Development of off-flavor and odor in beans and peans
60
Q

Lipoxygenase exhibits substrate specificity for what?

A

cis-cis-penta-1,4-diene unit

61
Q

What does enzyme-catalyzed oxidation form?

A
  • Abstracts a hydrogen, O2 reacts with the free radical, which produces a hydroperoxide
  • Same thing as regular oxidation
62
Q

What is the role of preventative antioxidants?

A

Minimizes the formation of initiating radicals

63
Q

Name some preventative antioxidants.

A
  • Superoxide dismutase
  • Catalase
  • Singlet-oxygen quencher
64
Q

What is the role of radical scavenging antioxidants?

A

Breaks the free radical chain reactions by donating hydrogen to free radicals

65
Q

Name some radical scavenging antioxidants.

A
  • Vitamin C
  • Tocopherol
  • Anthocyanin
66
Q

___________ are opposite to synergists.

A

Pro-oxidants

67
Q

The greater the reduction potential in mV, the ______ the species affinity for electrons and the ______ its tendency to be reduced

A

greater

greater

68
Q

What are the two ways to minimize lipid oxidation with antioxidants?

A

1) Preventative antioxidants: inhibit the formation of free alkyl radicals in the initiation step
2) Radical scavenging antioxidants: interrupt the propagation step of the free radical chain

69
Q

What kind of compounds are antioxidants usually?

A

Monohydroxy or polyhydroxy phenol compounds

70
Q

Do antioxidants have a low or high activation energy?

A

Low activation energy to donate hydrogen

71
Q

Why don’t antioxidant free radicals initiate another free radical?

A

Due to the stabilization of the delocalization of the radical electron

72
Q

Are antioxidant free radicals subject to oxidation?

A

No, since they are quite stable

73
Q

What is the function of metal chelators?

A

Deactivate trace metals that are free of fatty acids by the formation of complex ion or coordination compounds

74
Q

Give examples of metal chelators.

A
  • EDTA (very efficient)
  • Citric acid
  • Phosphoric acid
75
Q

When does synergism occur in lipid oxidation?

A

When mixtures of antioxidants produce a more pronounced activity than the sum of the activities of the individual antioxidants when used separately

76
Q

What are primary antioxidants often used with to maximize efficiency?

A
  • Other phenolic antioxidants

- Various metal chelating agents

77
Q

What are 5 factors affecting the efficiency of antioxidants?

A

1) Activation energy of antioxidants to donate hydrogen should be low
2) Oxidation potential should be high (should not strip an electron)
3) Reduction potential should be low (can reduce or donate an electron)
4) Stability to pH and processing
5) Solubility in oil should be high

78
Q

What are the two types of antioxidants?Give examples.

A
  • Natural: tocopherols

- Synthetic: BHA, BHT, PG

79
Q

What are some factors that affect our choices of antioxidants?

A
  • Safety
  • Antioxidant effectiveness
  • Off-odor
  • Off-color
  • Convenience of antioxidant incorporation to foods
  • Carry-through effect
  • Stability to pH and food processing
  • Availability
  • Cost
  • Non-adsorbable, if possible
80
Q

What are the 6 tests that can be used to evaluate the quality of the flavour of an oil?

A

1) Sensory evaluation
2) Peroxide value
3) Benzidine test
4) TBA test
5) GC for volatile compound analysis
6) Active Oxygen Method (AOM)

81
Q

What does the Benzidine test indicate?

A

If you have a yellow measurement, you have aldehydes in your oil

82
Q

What does the TBA test indicate?

A

If you have an intense red colour, you have aldehydes in your oil (extensive oxidation)

83
Q

Do decadienals (aldehydes) increase/decrease with light exposure? Does that increase/decrease the flavour score?

A
  • Increase

- Decrease

84
Q

What can be used to predict oil flavour by GC? Why?

A
  • Linear regression

- To only have to use one taste test panel

85
Q

What does the AOM method determine? What does it mean?

A
  • Oxygen is bubbled at a controlled rate
  • You can determine if the oil is prone to reversion within minutes
  • Active Oxygen Method
86
Q

What happens if an oil is used too long for deep-frying? (2)

A

1) Aldehydes and ketones will accumulate, which can be toxic

2) Product can be dehydrated to a solid black “rock”

87
Q

In the lipoxygenase reaction, where is the electron or hydrogen abstracted from? What does that produce?

A
  • Abstracted from the omega-8 position

- Creates a free radical at omega-8

88
Q

Do efficient antioxidants have low or high activation energies?

A

Low

89
Q

Do efficient antioxidants have low or oxidation potentials?

A

High

90
Q

Do efficient antioxidants have low or high reduction potentials?

A

Low

91
Q

Do efficient antioxidants have low or high solubility in oil?

A

High

92
Q

Name 3 factors that affect your choice of antioxidant.

A
  • Safety
  • Off-odor
  • Stability to pH and food processing
93
Q

What are the 3 main reactions that occur during deep-frying? What are their consequences?

A
  • Oxidation (alcohols, ketones, aldehydes)
  • Dehydration
  • Hydrolysis (FFA, diacylglycerols)

2) Food Chemistry I (31 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions