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Food Antioxidants Flashcards

1
Q

What are food antioxidants?

A

Substances that protect foodstuffs from oxidative damage. They act by interacting with highly reactive species such as free radicals, and converting them into stable and less reactive forms.

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2
Q

What are free radicals?

A

Uncharged molecules or ions with unpaired electrons.

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3
Q

What is auto-oxidation?

A

spontaneous oxidation of molecules caused by atmospheric O2.

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4
Q

What are the two types of rancidity?

A

oxidative

hydrolytic

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5
Q

What is oxidative rancidity?

A

off-flavorscausedbyproductsof

oxidation, e.g., aldehydes, ketones, alcohols.

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6
Q

What is hydrolytic rancidity?

A

off-flavorscausedbyliberationof free fatty acids.

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7
Q

Oxidative rancidity is accelerated by

A

trace metals (Fe, Cu and Zn), salt, light, bacteria, and molds.

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8
Q

Hydrolytic rancidity is accelerated by

A

water, lipases and phospholipases from bacteria, and molds.

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9
Q

What is total antioxidant capacity (TAC)?

A

the full or total antioxidant activity against various reactive
oxygen/nitrogen species.

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10
Q

What is oxygen radical absorbance capacity (ORAC)?

A

determines the degradation of an antioxidant (e.g.,

fluorescein) after being mixed with free radical generators such as peroxyl radicals.

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11
Q

What is total radical antioxidant potential (TRAP)?

A

the time required to deplete antioxidant(s) by reactive species produced at a given rate.

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12
Q

Give examples of reactive species

A 
• Free radicals (superoxide radical (O2−), hydroxyl
radical)
• Singlet oxygen (O2*)
• Hydrogen peroxide (H2O2)
• Peroxynitrite (ONO2−)
• Hypochlorous acid (HClO)§
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13
Q

Agents that promote oxidation are:

A
  • Molecular oxygen
  • High temperature
  • UV radiation & exposure to light
  • Metal ions (pro-oxidants)
  • Unsaturated biomolecules
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14
Q

What are the steps of auto-oxidation

A
  1. initiation
  2. propagation
  3. termination
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15
Q

What are the reactions that occur in the initiation step in auto-oxidation?

A

X• + R−H –> R• + H−X

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16
Q

What are the reactions that occur in the propagation step of auto-oxidation?

A

R• + O2 –>ž ROO•

ROO• +R−H –> žROO−H+ R•

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17
Q

What are the reactions that occur in the termination step of auto-oxidation?

A

2 ROO• –>ž ROO−R + O2
ROO• + R• ž–> ROO−R
R• +R• –> žR−R

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18
Q

What can be reactions of “alternative initiation”?

A

ROO−H –>ž RO• + •OH

2ROO−Hž –> RO• + ROO• + H2O

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19
Q

What are the reactions of metal ion induced alternative initiation?

A

Mn++ROO−Hž –> RO•+−OH +M(n+1)+

M(n+1)+ + ROO−H –>ž ROO• + H+ + Mn+

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20
Q

What are the types of antioxidants?

A

Primary antioxidants (free radical scavengers)

Secondary antioxidants (non free radical deactivators)

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21
Q

Give examples of primary antioxidants (free radical scavengers)

A
  • vitamin C
  • vitamin E
  • carotenoids
  • flavonoids
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22
Q

Demonstrate the reaction that phenolic antioxidant (tocopherol) can undergo

A

in the slides (16)

23
Q

What are the two types of secondary antioxidants?

A

Preventive Antioxidants

The non free radical deactivators

24
Q

Give examples for preventive antioxidants

A
  • Metal ion chelators (ferretin, lactoferrin, amino acids, peptides, proteins)
  • Non-radical decomposition of hydroperoxides & hydrogen peroxide
25
Q

Give examples for the non free radical deactivators

A

• Metal ion chelators (e.g.,ascorbicacid,citricacid,
EDTA)
• UV radiation absorbers (e.g.,arylsalicylates,
formamidine, Ciba TINOSORB, phenylphthalisomides)
• Conversion of hydroperoxides to non-radical species (via reduction to alcohols with lithium aluminum hydride, or cleavage to ketones & alcohols)
• Deactivation of reactive oxygen species.

26
Q

Give examples for non-radical reactive oxygen species

A 
Molecular oxygen (O2) 
Hydroperoxide (H2O2) 
Peroxynitrite (ONOO-) 
Singlet oxygen (1O2) 
Organic peroxide (ROOR’)
27
Q

Give examples for radical reactive oxygen species

A 
Superoxide anion (O2.-) 
Hydroxyl radical (.OH)
Nitric oxide (NO.) 
Peroxyl radical (RO.)
28
Q

Examples of a free radical reaction:

29
Q

Give examples for antioxidant enzymes

A
  • catalase
  • glutathione peroxidase (a.k.a.glutathione-S- transferase, or glutathione reductase)
  • superoxide dismutase (SOD)
30
Q

What is the reaction of catalase

A

2H2O2 →2H2O+O2

31
Q

The reaction of glutathione peroxidase:

A

2 GSH + H2O2 → GS–SG + 2 H2O

GSH represents reduced monomeric glutathione, and GS–SG represents glutathione disulphide.

32
Q

Glutathione reductase then reduces the oxidized glutathione to complete the cycle:

A

GS–SG + NADPH + H+ → 2 GSH + NADP+

33
Q

The half-reactions of superoxide dismutase (SOD):

cytoplasm, mitochondria and extracellular

A

SOD catalyses the dismutation of superoxide:
M(n+1)+-SOD + O2− → Mn+-SOD + O2
Mn+-SOD + O2− + 2H+ → M(n+1)+-SOD + H2O2

where M = Cu (n=1) ; Mn (n=2) ; Fe (n=2) ; Ni (n=2)

34
Q

What are the categories of food antioxidants?

A

natural

artificial/synthetic

35
Q

Examples of Natural Antioxidants:

A

• vitamins E, C and A
• phenolic acids (cinnamic acid, vanillic acid, coumaric
acid, caffeic acid, p-hydroxy benzoic acid)
• flavonoids (anthocyanins, quercitin, catechin)
• chlorophyll
• carotenoids (β-carotene & lycopene)
• glutathione
• selenium
• coenzyme Q, and
• melatonin

36
Q

Give examples of food containing anthocyanin pigments

A

cyanidin, malvinidin, delphinidin – found in foodstuffs such as grapes and cranberries.

37
Q

Give examples of food containing carotenoid pigments

A

β-carotene, lutein, lycopene and cryptoxanthin) - pumpkin, mangoes, carrots, peppers, and green leafy vegetables (e.g., spinach).

38
Q

Give examples of food containing Vitamin E

A

vegetable oils, avocados, nuts, seeds and whole grains.

39
Q

Give examples of food containing (Poly) phenolics

A

catechins, caffeic acid, vanillic acid, etc. – found in food products such as red wine, tea, thyme and oregano.

40
Q

Give examples of food containing flavonoids

A

tea, green tea, citrus fruits, red wine, onion, apples, soybeans, tofu, lentils, peas and milk.

41
Q

Give examples of food containing selenium

A

seafood, offal, lean meat and whole grains.

42
Q

Give examples of food containing vitamin C

A

oranges, blackcurrants, kiwi fruit, mangoes, broccoli, spinach, peppers and strawberries.

43
Q

Examples of synthetic food antioxidants

A
  • Butylated Hydroxy Anisole (BHA)
    Molecular Formula: C11H16O2
  • Propyl Gallate (PG)
    Molecular Formula: C10H12O5
  • Butylated Hydroxytoluene (BHT)
    Molecular formula C11H16O2
  • Tertiary Butyl Hydroquinone (t-BHQ)
    Molecular Formula: C10H14O2
44
Q

What is the limit of synthetic food antioxidants in food products?

A

maximum limit of 0.02% in foodstuff

45
Q

In what products is tocopherol used? and what are desirable effects?

A

Tocopherols are relatively heat stable (used in food products like crackers, baked goods, and fried foods)

46
Q

Structure of betacarotene and flavone

47
Q

What are the sources of food antioxidants?

A
  • Plant products
  • Animal products
  • Microbial sources
48
Q

Plant sources of food antioxidants are

A
  • Oil seeds (sunflower, canola, flaxseed, cottonseed)
  • Nuts (cashew, hazel nuts, peanuts, pecans)
  • Legumes (peas, beans)
  • Cereals (barley, wheat, oat, corn)
  • Fruits (citrus, berries, grapes)
  • Root & tuberous vegetables (carrots, potato, beetroot)
  • Spices (thyme, ginger, savory, oregano)
  • Teas (green tea, oolong tea, black tea)
49
Q

Animal sources of food antioxidants are

A
  • Antioxidant enzymes
  • Peptides / amino acids / proteins (metal ion chelators)
  • Carotenoids
50
Q

Microbial/Plant cell sources of food antioxidants are

A
  • Carotenoids
  • Anthocyanins / flavonoids (Vitis vinifera)
  • Atrovenetin (from Penicillium species)
  • Mycotrienin II, trienomycin A (from Streptomyces sp.)
51
Q

Uses of artificial antioxidant in food products

A
  • Oils and fats
  • Crackers, cookies
  • Potato-chips
  • Margarine
  • Dry cereals
52
Q

Food antioxidants as antimicrobial agents:

A

Phenolic antioxidants (e.g., BHA) also exhibit antimicrobial activity against several bacteria.

Flavonoids (e.g., isof lavones) also have antimicrobial activity against plant pathogens.

Tannins (polymers of f lavanols), have been reported to inhibit the growth of Aeromonas, Bacillus, Clostridium botulinum, C. perfringens, Enterobacter, Klebsiella, Proteus, Pseudomonas, Shigella, Staphylococcus aureus, Streptococcus, and Vibrio (Chung et al., 1998)

Antioxidants => highly effective preservatives for foods.

53
Q

Future of antioxidants and consumer views

A

Consumers are becoming increasingly cynical about the safety of synthetic compounds for food use.

  • More of natural instead of artificial / synthetic
  • More incorporation of herbs & spices in sensitive foods such as polyunsaturated oils (tea extracts, herbs such as sage and rosemary)
  • Tissue culture products (e.g., rosmarimic acid and isof lavones)
  • GMO could be used to enhance the production of compounds with improved resistance to oxidation

Food Chemistry II (8 decks)

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