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Food Chemistry 2 > Food antioxidants > Flashcards

Food antioxidants Flashcards

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1
Q

Oxidation variously defined as (4)

A
  1. gain of O2
  2. loss of H
  3. loss of e-
  4. increase in oxidation state
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2
Q

paradox of O2

A

need O2 for carbs, fats and prot metabolism –> for ATP production
- BUT O2 is super reactive, can make Reactive oxygen species

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3
Q

what is a reactive oxygen species?
- examples (7)

A
  • produced from reactions with O2
  • molecules that contain at least 1 oxygen and 1 or more unpaired electron (ie free radicals)
  • much more reactive than O2 itself
    EXAMPLES:
  • free radicals (superoxide radical (O2°), hydroxyl radical(OH°), nitric oxide (NO°), alkoxy radical (RO°))
  • hydrogen peroxide (H2O2)
  • peroxynitrite (ONO2-)
  • hypochlorous acid (HClO)
  • singlet oxygen (O2^1)
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4
Q

what are antioxidants?
- act by what?

A

substances that protect foodstuffs from oxidative damage –> prevent oxidation from taking place
- act by interacting with highly reactive species such as free radicals and converting them into stable and less reactive forms

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5
Q

what are free radicals?

A
  • uncharged molecules or ions with unpaired electrons
  • abstract e-/H+ from neighbouring species to becomes stable –> produces more free radicals
  • can react with biological molecules and cause damage to themselves/cells –> can cause disease and health problems
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6
Q

what is auto-oxidation? (self-oxidation)

A

spontaneous oxidation of molecules caused by atmospheric O2
(ie benzaldehyde reacts with O2 and becomes benzoic acid)

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7
Q

2 types of rancidity?
- what?
- by what enzymes?
- accelerated by what?

A

OXIDATIVE:
- off-flavors caused by oxidation products (ie aldehydes, ketones, alcohol)
- by enzymes like lipoxygenase
- accelerated by trace metals (Fe, Cu, Zn), salt, light/air, bacteria/fungi and molds
HYDROLYTIC:
- off-flavors caused by liberation of free fatty acids due to hydrolysis of lipogenic enzymes
- lipase and phospholipase
- accelerated by water, lipases, phospholipases from bacteria and molds

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8
Q

2 different types of ROS + examples

A

NON-RADICALS:
- molecular oxygen (O2)
- hydroperoxides (H2O2)
- organic peroxide (ROOR’)
RADICALS:
- superoxide anion (O2°-)
- hydroxyl radical (°OH)
- nitric oxide (NO°)
- peroxyl radical (RO°)

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9
Q

primary vs secondary antioxidants + examples!!!

A

PRIMARY:
- free radical scavengers! –> absorb free radicals!
- include tocopherols (vit E), ascorbic acid (vit C), carotenoids and flavonoids (natural)
- BHA, TBHQ, PG and BHT (synthetic)
- all 3 antioxidant enzymes
SECONDARY:
- non free radical deactivators –> decompose non free radicals (ie decompose hydrogen peroxides or hydroperoxides) to non-radical species (via reduction to alcohol with lithium aluminum hydride)
- ie trivalent phosphates, metal chelators

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10
Q

what are the 3 types of antioxidants?

A
  1. NATURAL:
    - natural compounds that allow orgs to decrease oxidative stress
    - ie vit C, A, E, carotenoids
  2. SYNTHETICS:
    - butylated hydroxianisole (BHA)
    - butylated hydroxytoluene (BHT)
    - tertiary butyl hydroxyquinone (TBHQ)
    - propyl gallate (PA)
  3. ANTIOXIDANT ENZYMES
    - catalase, glutathione peroxidase (or glutathione reductase or glutathione-S-transferase) and superoxide dismutase (SOD)
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11
Q

A° + CH4 –> AH + CH3°
- which is not stable vs stable?
- how to make it stable?
- what is the created FR?
- which acts as antioxidants?

A
  • A° = not stable –> abstracts H from CH4 to become stable and neutral –> creates a new FR: CH3° –> new FR generated to continue cycle of FR generation –> cycle continues until rxns are terminated
  • created FR = CH3°
  • antioxidant = CH4! bc furnishes H+
  • AH and CH4 are stable
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12
Q

how can FR cause diseases?

A

FR can react with and cause damage to various biomolecules like proteins and nucleic acids

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13
Q

how can vit C act as an antioxidant?
- vs a-tocopherol?

A

VIT C:
- act as H+/e- donor to appropriate reactive species (FR) to stabilize and neutralize the latter
- can release 2 H+ + 2e-
VIT E:
- donates H+/e- to reactive species and itself becomes a FR

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14
Q

how do phenolics (flavonoids and tocopherols) act as antioxidants? 2 steps ish

A
  1. peroxyl radical (ROO°) abstracts a H from benzene ring with 2 OH –> forms a semi-quinone (benzene + 1 OH + O°)
  2. another peroxyl radical propagates reaction and abstracts H from semi quinone –> forms ROOH and quinone (benzene with 2 double bonds + 2 double bonded O)
    - quinone stabilizes by resonance!
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15
Q

what are 2 ways to stabilize antioxidants that have H abstracted from them?

A
  1. conjugate systems (ie carotenoids) –> free radical formed on antioxidant can move along conjugated system and stay at the most stable place
  2. aromaticity through resonance
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16
Q

2 ways that peroxides can split up
- more common one?

A
  1. HOMOLYTIC SCISSION:
    - shared e- in bond btw atoms are split equally btw 2 atoms –> each atom has an unpaired electron –> forms radicals!
    - products of splitting can be deactivated by species like trivalent phosphate to convert peroxide into its less reactive form (alcohol) and corresponding pentavalent phosphate compound
  2. HETEROLYTIC CLEAVAGE
    - occurs when 1 of species takes complete possession of shared e- to acquire negative charge, while other species that was deprived of its e- gets positive charge –> produces charged ions!
17
Q

secondary antioxidants prevent which type of scission of peroxides?
- ie?

A

prevent homolytic scission!
- trivalent phosphate compound acts as 2° antioxidant to form non-reactive ROH and corresponding pentavalent phosphate compound

18
Q

what are 4 agents that promote oxidation and create reactive species?

A
  • molecular oxygen (O2)
  • high temp
  • UV radiation & exposure to light
  • metal ions (pro-oxidants)
19
Q

5 examples of 2° antioxidants (5) + examples!

A
  • O2^1 quenchers (azide, octane, b-carotene)
  • ROOR decomposers (sulfenic acid, organosulfides)
  • metal ion chelators (EDTA, citric acid, ascorbic acid)
  • antioxidant enzyme inhibitors (SDS, PEG)
  • UV radiation absorbers (triazine benzophenone, acryl salicylatesm formamidine, ciba TINOSORB, phenylphthalisomides)
20
Q

Name preventive antioxidants

A
  • metal ion chelators: ferretin, lactoferrin, amino acids, peptides, proteins
  • non-radical decomposition of hydroperoxides and hydrogen peroxide
21
Q

what are the 3 antioxidant enzymes? and which reaction do they catalyze?

A
  1. Catalase: 2 H2O2 –> 2 H2O + O2
  2. Glutathione peroxidase or glutathione transferase:
    2 GSH + H2O2 –> GS-SG + 2 H2O
  3. superoxide dismutase:
    2 O2- + 2 H+ –> H2O2 + O2
    - H2O2 is less reactive than superoxide (O2-)
22
Q

which 3 aa form GSH?
- is GSH reduced or oxidized? –> will it lose or gain H+? from/to which aa?
- what is GS –> oxidized or reduced?

A
  • glutamate, glycine and cysteine
  • GSH = reduced monomeric glutathione –> thiol group from cysteine will furnish H+ to convert H2O2 and H2O
  • GS (gluthathione) = oxidized –> forms sulfide bond with another GS to form glutathione disulfide: GS-SG
23
Q

how can you convert oxidized glutathione back to reduced glutathione?

A
  • GS-SG + NADPH + H+ –> 2 GSH + NADP+
  • catalyzed by glutathione reductase: reduces the oxidized glutathione to complete the cycle
24
Q
  • glutathione peroxidase converts H2O2 and organic peroxides into what?
  • VS SOD breakdowns superoxide into what?
A
  • H2O and ROH
  • SOD –> into H2O2 and O2
25
Q

give examples of natural antioxidants (8)

A
  • vitamins E, C and A
  • phenolic acids (cinnamic acid, vanillic acid, coumaric acid, caffeic acid, p-hydroxy benzoic acid)
  • flavonoids (anthocyatnins, quercitin, catechins)
  • chlorophyll
  • carotenoids (b-carotene and lycopene)
  • glutathione
  • selenium (exists in many oxidation states)
  • coenzyme Q (ubiquinone)
26
Q

Give examples of + what foods contain them
- anthocyanin pigments:
- CAROTENOID PIGMENTS
- POLYPHENOLICS

A

ANTHOCYANINS pigments:
- cyanidin, malvinidin, delphinidin –> grapes and cranberries
CAROTENOIDS pigments:
- b-carotene, lutein, lycopene, cryptoxanthin –> pumpkn, mangoes, carrots, peppers, green leafy veg (spinach)
POLYPHENOLICS:
- catechins, caffeic acid, vanillic acid) –> red wine, tea, thyme, oregano

27
Q

gives examples of what foods contains vit E, flavonoids, selenium, vitamin C

A

VITAMIN E:
- vegetable oils, avocados, nuts, seeds, whole grains
FLAVONOIDS
- tea, green tea, citrus fruits, red wine, onions, apples, soybeans, tofu, lentils, peas and milk
SELENIUM:
- seafood, offal, lean meat and whole grains
VITAMIN C:
- oranges, blackcurrants, kiwi, mangoes, broccoli, spinach, peppers, strawberries

28
Q

how do these compounds act as an antioxidants?
- chlorophyll:
- glutathione
- selenium
- coenzyme Q10
- melatonin

A
  • CHLOROPHYLL: by virtue of its unsaturated system in the tetrapyrol ring structure
  • GLUTATHIONE: by virtue of its thiol group
  • SELENIUM: bc of ease at which it releases and picks up electrons –> exists in 4 oxidation states:
    -2, 0, +4, +6 –> enables it to act on a potential antioxidant
  • COENZYME Q: participates in redox reactions of ETC for energy generation
  • MELATONIN: hormone produce by brain under influence of farkness –> acts as antioxidant by virtue of its capacity to scavenge free radicals, stimulate antioxidant enzymes and also acts as metal ion chelator
29
Q

how do flavonoids, anthocyanins and vit E act as free e- scavengers? vs carotenoids

A

by virtue of their aromaticity that enables them to stabilize their free radicals by resonance
- carotenoids: scavenge free radicals and delocalize FR generated along the unsaturated system to stabilize it

30
Q

vitamin C: each step/abstraction of H+ will cause what?
- how can vit C act as an antioxidant? how can it stabilize itself?

A

will decrease vit C activity
- can donate H+ from its OH groups to FR –> forms intermediate FR that can form a common bond to stabilize the molecules

31
Q

what are the 4 types of synthetic antioxidants? + molecular formula?
- what is common btw all 4?
- maximum foodstuff limit?

A

BUTYLATED HYDROXYTOLUENE: C11H16O2
BUTYLATED HYDROXYANISOLE: C11H16O2
PROPYL GALLATE: C10H12O5
TERTIARY BUTYL HYDROXYQUINONE: C10H14O2
- all have an aromatic ring that enables them to stabilize FR by resonance
- 0.02% in foodstuff

32
Q

what are the 3 sources of food antioxidants? + lots of examples!

A
  1. PLANT PRODUCTS
    - oil seeds (sunflower, canola, flaxseed, cottonseed)
    - nuts (cashew, hazelnut, peanuts, pecans)
    - cereals (barley, wheat, oat, corn)
    - legumes (peas, beans)
    - fruits (citrus, berries, grapes)
    - root and tuberous vegs (carrots, potato, beetroot)
    - spices (thyme, ginger, savory oregano)
    - teas (green tea, oolong tea, black tea)
  2. ANIMAL PRODUCTS
    - antioxidant enzymes
    - peptides/amino acids, proteins (metal ion chelators)
    - carotenoids
  3. MICROBIAL SOURCES
    - carotenoids
    - anthocyanins/flavonoids
    - atrovenetin (from penicillium)
    - mycotrienin II, trienomycin A (from streptomyces)
33
Q

what type of antioxidants do these contain?
- oil seeds
- nuts
- legumes and cereals
- fruits
- roots, tubers, spices, teas

A
  • oil seeds: carotenoids and fat soluble vits (A and E)
  • nuts: chlorophylls, polyphenolics (flavonoids)
  • legumes and cereals: chlorophylls, phytochemicals (flavonoids), carotenoids
  • fruits: ascorbic and citric acid (water soluble), carotenoids
  • roots, tubers, spices, teas: chlorophylls and various phytochemicals and carotenoids
34
Q

are natural or synthetic antioxidants more stable? ie in heat? –> give example of food product
- which are more used in food products?

A

synthetics are more stable! especially in high temp like for frying potato chips
- synthetics are mostly used in food produces especially those requiring long time storage or heat treatment bc they are relatively more stable and effective in low amoounds

35
Q

what are 5 common food products where antioxidants are added?

A
  • oils and fats –> prevent rancidity during storage
  • crackers and cookies –> fat content can become significant after dehydration = rancidity
  • potato chips –> bc of high temp frying –> protect from rancidity
  • margarine
  • dry cereals –> to prevent rancidity
36
Q

which food antioxidants can act as preservative as antimicrobial agents? (3)

A

PHENOLIC ANTIOXIDANTS (ie BHA) –> exhibit antimicrobial activity against bacteria
FLAVONOIDS (isoflavones) –> have antimicrobial activity against plant pathogens
TANNINS (polymers of flavonols) –> can inhibit growth of aeromonas, bacillus, c. boulinum, c. perfringens, enterobacter, klebsiella, proteus, pseudomonas, shigella, s. aureus, streptococcus, vibrio

37
Q

how do antioxidants control microbial growth and proliferation? (2)

A

by disrupting cell walls to cause cellular material to leak out of organism to kill it + some are able to act as metal ion chelators and protect against oxidation potentiated by metal ions

38
Q

Future of antioxidants:
- consumers are becoming more or less cynical about safety of synthetic compounds for food use?
- solutions? (4)

A

MORE!
- more of natural instead of artificial/synthetic
- more incorporation of herbs and spices in sensitive foods such as polyunsaturated oils (tea extracts, herbs like sage and rosemary)
- tissue culture products –> rosmarimic acid and isoflavones
- GMO could be used to enhance production of compounds with improved resistance to oxidation

Food Chemistry 2 (7 decks)

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