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2) Food Chemistry I > Lipids VII > Flashcards

Lipids VII Flashcards

(93 cards)

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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

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2
Q

What other mechanisms can decrease autoxidation?

A
  • Stabilization of hydroperoxides
  • Competitive binding of O2
  • Retardation of the initiation step
  • Removal of oxygen
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3
Q

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

A

Interrupting or retarding the propagation step

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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

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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

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6
Q

How do antioxidants prefer to end their free radical states?

A

By combining with other free radicals to form neutral species

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7
Q

What do antioxidants typically give their free radical to?

A

Generally a peroxy radical

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8
Q

What do antioxidants lengthen?

A

They lengthen the induction period

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9
Q

Are antioxidants consumed?

A

Yes, slowly

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10
Q

Compounds with good antioxidant properties are generally _______ compounds.

A

Phenolic

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11
Q

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

A
  • Seed oils

- They are less susceptible to autoxidation than animal fats

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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

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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)

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14
Q

In phenolic antioxidants, what donates hydrogens?

A

Always the OH groups

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15
Q

Which antioxidants does the public prefer?

A

Complex antioxidants found in natural products (rosemary extract)

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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

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17
Q

Are antioxidants used alone?

A

Usually used as combinations because mixtures tend to be more effective

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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

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19
Q

What happens if the amounts of antioxidant surpass 200 ppm?

A
  • Antioxidant can become a pro-oxidant

- Can be toxic

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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)

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21
Q

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

A

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

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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

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23
Q

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

A

Through volatilization as a fat is heated

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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

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25
How does citric acid slow down oxidation? Is it an antioxidant?
- No, it is a preservative | - Natural way to chelate metals, which slows down oxidation
26
What are powerful catalysts for lipid oxidation? How?
- Metal ions | - Assist in catalyzing the breakdown of hydroperoxides
27
Metal ions shorten the ____________ and increase the overall __________
induction period, rate of the reaction
28
What amount of metal ions are required to bring about a significant change in the reaction rate?
Only a small amount (ppm)
29
Does metal ion catalysis favour the second or third oxidation state reaction? What does it form?
Favours the second oxidation state; forms an alkoxy
30
What does the third oxidation state of a metal ion form?
A peroxy
31
Why do metal ions speed up the autoxidation reaction?
Since they catalyze the breakdown of ROOH to form Alkoxy and Peroxy radicals
32
What does the chelation of metal ions cause?
- Causes steric hindrance | - Eliminates the catalytic role metal ions would otherwise play
33
Do chelating agents interfere with the primary autoxidation mechanisms? What are they called?
- No - Not true antioxidants - Synergistic agents to synergists
34
Give examples of synergists.
Ascorbic acid, phosphates, EDTA, phospholipids, chelating agents
35
Why are metal ions largely unavoidable?
Since almost all processing equipment is metallic
36
How are metal ions contributed naturally?
- By raw materials | - In the form of chlorophyll or myoglobin
37
Metal ions allow the formation of more reactive ___________, which can attack lipids directly
singlet oxygen
38
Where is lipoxygenase realtively abundant?
In plant tissues
39
What does lipoxygenase catalyse?
Catalyses the direct oxidation of polyunsaturated fatty acids which have a cis-cis 1,4 pentadiene group in its molecular structure
40
What do enzymes catalyze in the lipid of plant tissues?
- Catalyzes the formation of hydroperoxides | - Instigates the free radical mechanism
41
What happens to frozen/dehydrated vegetables if they are not blanched?
- Undergo rapid autoxidation | - Produce hay like/cardboard aroma
42
What does the bleaching of pigments (chlorophyll, beta-carotene) occur as a result?
Result of autoxidation initiated by lipoxygenase
43
Why is heat applied to the oilseed crush?
To reduce the effects of lipoxygenase and lipase
44
What is responsible for the development of characteristic flavours and aromas in living plant systems?
Lipoxygenase
45
How can the autoxidation reaction be controlled?
- Antioxidants - Synergists (chelating agents) - Protection from light (brown bottles) - Replacement of air with nitrogen
46
What are the 11 factors that affect autoxidation?
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
Why can fatty acids chelate?
Because they have a carboxyl group
48
Which radical is the most reactive?
Hydroxy radical
49
How many hydroperoxides does oleic acid form?
4
50
How do the energy levels of triplet and singlet oxygen compare?
Triplet: 0 Singlet: 22.5 kcal
51
How does the nature of triplet and singlet oxygen compare?
Triplet: diradical Singlet: no radical
52
How does the reaction of triplet and singlet oxygen compare?
Triplet: radical Singlet: electron-rich
53
How does the degradation of linoleic acid compare if its done with triplet or singlet oxygen?
Triplet: slower Singlet: much faster
54
What are dye photosynthesizers?
Methylene blue, crystal violet
55
What are pigment photosynthesizers?
Chlorophyll, riboflavin
56
Photosynthesizers absorb light in the ____ - ____ range
380-900
57
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
light absorbed short fluorescence intersystem crossing
58
Prior to the development of rancidity, what is the reversion flavor in soybean oil like?
Beany and grassy flavor
59
What are the detrimental effects of lipoxygenase?
- Destruction of the essential fatty acids - Free radicals produced damage other compounds - Development of off-flavor and odor in beans and peans
60
Lipoxygenase exhibits substrate specificity for what?
cis-cis-penta-1,4-diene unit
61
What does enzyme-catalyzed oxidation form?
- Abstracts a hydrogen, O2 reacts with the free radical, which produces a hydroperoxide - Same thing as regular oxidation
62
What is the role of preventative antioxidants?
Minimizes the formation of initiating radicals
63
Name some preventative antioxidants.
- Superoxide dismutase - Catalase - Singlet-oxygen quencher
64
What is the role of radical scavenging antioxidants?
Breaks the free radical chain reactions by donating hydrogen to free radicals
65
Name some radical scavenging antioxidants.
- Vitamin C - Tocopherol - Anthocyanin
66
___________ are opposite to synergists.
Pro-oxidants
67
The greater the reduction potential in mV, the ______ the species affinity for electrons and the ______ its tendency to be reduced
greater | greater
68
What are the two ways to minimize lipid oxidation with antioxidants?
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
What kind of compounds are antioxidants usually?
Monohydroxy or polyhydroxy phenol compounds
70
Do antioxidants have a low or high activation energy?
Low activation energy to donate hydrogen
71
Why don't antioxidant free radicals initiate another free radical?
Due to the stabilization of the delocalization of the radical electron
72
Are antioxidant free radicals subject to oxidation?
No, since they are quite stable
73
What is the function of metal chelators?
Deactivate trace metals that are free of fatty acids by the formation of complex ion or coordination compounds
74
Give examples of metal chelators.
- EDTA (very efficient) - Citric acid - Phosphoric acid
75
When does synergism occur in lipid oxidation?
When mixtures of antioxidants produce a more pronounced activity than the sum of the activities of the individual antioxidants when used separately
76
What are primary antioxidants often used with to maximize efficiency?
- Other phenolic antioxidants | - Various metal chelating agents
77
What are 5 factors affecting the efficiency of antioxidants?
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
What are the two types of antioxidants?Give examples.
- Natural: tocopherols | - Synthetic: BHA, BHT, PG
79
What are some factors that affect our choices of antioxidants?
- 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
What are the 6 tests that can be used to evaluate the quality of the flavour of an oil?
1) Sensory evaluation 2) Peroxide value 3) Benzidine test 4) TBA test 5) GC for volatile compound analysis 6) Active Oxygen Method (AOM)
81
What does the Benzidine test indicate?
If you have a yellow measurement, you have aldehydes in your oil
82
What does the TBA test indicate?
If you have an intense red colour, you have aldehydes in your oil (extensive oxidation)
83
Do decadienals (aldehydes) increase/decrease with light exposure? Does that increase/decrease the flavour score?
- Increase | - Decrease
84
What can be used to predict oil flavour by GC? Why?
- Linear regression | - To only have to use one taste test panel
85
What does the AOM method determine? What does it mean?
- Oxygen is bubbled at a controlled rate - You can determine if the oil is prone to reversion within minutes - Active Oxygen Method
86
What happens if an oil is used too long for deep-frying? (2)
1) Aldehydes and ketones will accumulate, which can be toxic | 2) Product can be dehydrated to a solid black "rock"
87
In the lipoxygenase reaction, where is the electron or hydrogen abstracted from? What does that produce?
- Abstracted from the omega-8 position | - Creates a free radical at omega-8
88
Do efficient antioxidants have low or high activation energies?
Low
89
Do efficient antioxidants have low or oxidation potentials?
High
90
Do efficient antioxidants have low or high reduction potentials?
Low
91
Do efficient antioxidants have low or high solubility in oil?
High
92
Name 3 factors that affect your choice of antioxidant.
- Safety - Off-odor - Stability to pH and food processing
93
What are the 3 main reactions that occur during deep-frying? What are their consequences?
- Oxidation (alcohols, ketones, aldehydes) - Dehydration - Hydrolysis (FFA, diacylglycerols)

2) Food Chemistry I (31 decks)

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