part 4 Flashcards
what are antioxidants used for?
preservation of food by stopping deterioration, rancidity, discolouration due to oxidation
what is oxidation?
electron removal/abstraction from comp by ROS
examples of ROS?
hydrogen peroxide, hydroxyl radical, alkoxy, superoxide
why oxidation prob?
off flavour and colour, loss of flavour/aroma, discolouration, texture chage, decrease nutr. value, toxic byproducts
why decrease in nutr value by oxidation>
essential fatty acid and vitamin destruction
fatty acids in nature are present in form of :
triacylglycerols
common unsaturated fatty acids in foods
oleic, linoleic (omega 6), linolenic (omega 3)
system we use instead of trans and cis?
E and Z
why do unsaturated oxidize?
contain allylic hydrogens which are sensitive to abstraction by reactive O species–>autoxidation rxn
which is more stable, conjugated or nonconjugated?
conjugated
E=__, Z=___
trans;cis
what are the 2 types antioxidants?
phenolic comps, organic acids and their salts/esters
ex. of organic acids?
ascorbic/citric acid
how do citric acid work?
chelate and bind metals (metals take triplet state O to single state)
examples of synthetic phenolic antioxidants?
BHA, BHT (no longer GRAS), PG, TBHQ (approved)
BHT is produced through this mech:
catalytic alkylation of p-cresol with isobutylene
phys properties of synth phenolic antiox?
white/off-white solids with high purity, may react with metals to produce off-colours, poor water sol (except PG), tasteless odourless
why poor water sol good for synth phenolic antiox?
so it can protect lipophilic substances
mech of antioxidant?
gives up H and e-, generate resonance structures that make hard for oxidation to happen, produce free radical way less reactive than original
food uses of synth phenolics?
permitted lvls wt:wt, alone or in combo, based on lipid content–cereal, baking, edible oils, candy, margarine, packaging
what is carry through?
the ability of antiox to survive processing steps and impart stability to finshed product
why BHA/BHT good carry through?
most sterically hindered
antiox improves:
shelf life
toxicity of synth phenolics?
potential carcinogen (but in rats forestomach, low validity study); Netherlands cohort study show no association with stomach cancer
industrial uses of BHT:
food, pet food, pharma and cosmetics, fuel additive, plastics, rubber
main mechanism for detox w/ synth phenolic antiox?
phase 1: oxidation (enzyme mediated, cytochrome P-450), becomes more water sol. (gallic acid)
phase 2: methylation (go from meta, less water sol, steric hindrance, to ortho conjugates of hydroxyl grp)
phase 3: conjugation (enzyme mediated), make much more water sol.
natural phenolic antiox include:
tocopherols (racemic D and L), sesamol, gossypol, quercitin, avenanthramides, rosmaridiphenol, ferulic acid, resveratrol, rutin
phys properties of tocopherols?
pale-yellow viscous oils, readily destroy by heat and UV, easily oxidized by nitrate and metal ions
tocopherols antioxidant activity highest in ____ and owest in ___
delta; alpha
why alpha less active?
cuz it is most stericallly hindered
possible carcinogen, GI/liver toxicity, antifungal found in sesame seed oil
sesamol
found to be toxic in non ruminants (reduce O2 availability), natural in cottonseeds, insecticide, male contraceptive
gossypol
first edible oil produced commercially, number one in WW2?
cottonseed oil
naturally in fruits and veg, tea leaves, with only half free radical scavenging ability of BHA/BHT
quercitin (flavonoid)
found in oats
avenanthramides
what form of avenanthramide is for asthma?
tranilast (no phenolics/hydroxyl)
naturally occuring phenolic in flax seed
ferulic acid
found in brown skin of peanut and in red wine:
resveratrol
found in buckwheat
rutin
other synth phenolics?
Ionox 100, THBP
organic acids and salts/esters are ___ soluble
water
product of citric acid/ascorbic acid?
dehydroascorbic acid (quenched the radical!)
most reactive radical?
hydroxyl
why add saturated fats to organic acids?
so don’t react with ROS
organic acid esters have ___ effect when used with phenolic antiox
synergestic; get rid of ALL free radicals!
max. addition lvls of organic acid esters depends on:
lipid content
organic acid esters sold as ____, aids in stabilizing ____
natural health product, veg oil
sources of free radicals?
internal and external
ex. of human diseases and free radicals?
organ damage, arterial wall lesions, CHD plaque formation, retina damage, DNA breakage, a.a oxidation, membrane damage, joint damage, resp distress, alzheimers, asthma, diabetes, arthritis, parkinson’s
what are some cellular protection mechanisms?
enzymes like SOD, catalase, peroxidase; glutathione
examples of chemopreventive agents?
BHA, BHT, PG, TBHQ
what are anthocyanins found in?
berries!
anthocyanins break down into:
PGA, PCA
anthocyanins are ___ soluble, but CHO can be removed
water
produced from eggs, fish, rice/corn/soy, potato, etc:
antioxidant peptides
how antiox peptides work (mechanism)?
free radical scavenging (like BHT) and chelation (like citric acid)
how does antioxidant peptides incorporate rational design?
5-16 a.a., hydrophobic (Leu/Val), random coil, Tyr/Phe/His/pro for H/e- donation
antioxidant peptides have ___ structure
phenol
