Food antioxidants Flashcards
Oxidation variously defined as (4)
- gain of O2
- loss of H
- loss of e-
- increase in oxidation state
paradox of O2
need O2 for carbs, fats and prot metabolism –> for ATP production
- BUT O2 is super reactive, can make Reactive oxygen species
what is a reactive oxygen species?
- examples (7)
- 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)
what are antioxidants?
- act by what?
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
what are free radicals?
- 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
what is auto-oxidation? (self-oxidation)
spontaneous oxidation of molecules caused by atmospheric O2
(ie benzaldehyde reacts with O2 and becomes benzoic acid)
2 types of rancidity?
- what?
- by what enzymes?
- accelerated by what?
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
2 different types of ROS + examples
NON-RADICALS:
- molecular oxygen (O2)
- hydroperoxides (H2O2)
- organic peroxide (ROOR’)
RADICALS:
- superoxide anion (O2°-)
- hydroxyl radical (°OH)
- nitric oxide (NO°)
- peroxyl radical (RO°)
primary vs secondary antioxidants + examples!!!
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
what are the 3 types of antioxidants?
- NATURAL:
- natural compounds that allow orgs to decrease oxidative stress
- ie vit C, A, E, carotenoids - SYNTHETICS:
- butylated hydroxianisole (BHA)
- butylated hydroxytoluene (BHT)
- tertiary butyl hydroxyquinone (TBHQ)
- propyl gallate (PA) - ANTIOXIDANT ENZYMES
- catalase, glutathione peroxidase (or glutathione reductase or glutathione-S-transferase) and superoxide dismutase (SOD)
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° = 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
how can FR cause diseases?
FR can react with and cause damage to various biomolecules like proteins and nucleic acids
how can vit C act as an antioxidant?
- vs a-tocopherol?
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
how do phenolics (flavonoids and tocopherols) act as antioxidants? 2 steps ish
- peroxyl radical (ROO°) abstracts a H from benzene ring with 2 OH –> forms a semi-quinone (benzene + 1 OH + O°)
- 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!
what are 2 ways to stabilize antioxidants that have H abstracted from them?
- conjugate systems (ie carotenoids) –> free radical formed on antioxidant can move along conjugated system and stay at the most stable place
- aromaticity through resonance
2 ways that peroxides can split up
- more common one?
- 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 - 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!
secondary antioxidants prevent which type of scission of peroxides?
- ie?
prevent homolytic scission!
- trivalent phosphate compound acts as 2° antioxidant to form non-reactive ROH and corresponding pentavalent phosphate compound
what are 4 agents that promote oxidation and create reactive species?
- molecular oxygen (O2)
- high temp
- UV radiation & exposure to light
- metal ions (pro-oxidants)
5 examples of 2° antioxidants (5) + examples!
- 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)
Name preventive antioxidants
- metal ion chelators: ferretin, lactoferrin, amino acids, peptides, proteins
- non-radical decomposition of hydroperoxides and hydrogen peroxide
what are the 3 antioxidant enzymes? and which reaction do they catalyze?
- Catalase: 2 H2O2 –> 2 H2O + O2
- Glutathione peroxidase or glutathione transferase:
2 GSH + H2O2 –> GS-SG + 2 H2O - superoxide dismutase:
2 O2- + 2 H+ –> H2O2 + O2
- H2O2 is less reactive than superoxide (O2-)
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?
- 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
how can you convert oxidized glutathione back to reduced glutathione?
- GS-SG + NADPH + H+ –> 2 GSH + NADP+
- catalyzed by glutathione reductase: reduces the oxidized glutathione to complete the cycle
- glutathione peroxidase converts H2O2 and organic peroxides into what?
- VS SOD breakdowns superoxide into what?
- H2O and ROH
- SOD –> into H2O2 and O2
give examples of natural antioxidants (8)
- 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)
Give examples of + what foods contain them
- anthocyanin pigments:
- CAROTENOID PIGMENTS
- POLYPHENOLICS
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
gives examples of what foods contains vit E, flavonoids, selenium, vitamin C
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
how do these compounds act as an antioxidants?
- chlorophyll:
- glutathione
- selenium
- coenzyme Q10
- melatonin
- 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
how do flavonoids, anthocyanins and vit E act as free e- scavengers? vs carotenoids
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
vitamin C: each step/abstraction of H+ will cause what?
- how can vit C act as an antioxidant? how can it stabilize itself?
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
what are the 4 types of synthetic antioxidants? + molecular formula?
- what is common btw all 4?
- maximum foodstuff limit?
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
what are the 3 sources of food antioxidants? + lots of examples!
- 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) - ANIMAL PRODUCTS
- antioxidant enzymes
- peptides/amino acids, proteins (metal ion chelators)
- carotenoids - MICROBIAL SOURCES
- carotenoids
- anthocyanins/flavonoids
- atrovenetin (from penicillium)
- mycotrienin II, trienomycin A (from streptomyces)
what type of antioxidants do these contain?
- oil seeds
- nuts
- legumes and cereals
- fruits
- roots, tubers, spices, teas
- 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
are natural or synthetic antioxidants more stable? ie in heat? –> give example of food product
- which are more used in food products?
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
what are 5 common food products where antioxidants are added?
- 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
which food antioxidants can act as preservative as antimicrobial agents? (3)
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
how do antioxidants control microbial growth and proliferation? (2)
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
Future of antioxidants:
- consumers are becoming more or less cynical about safety of synthetic compounds for food use?
- solutions? (4)
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
