B) Antioxidants
- Class IV preservatives (Canada Food and Drug Regulations)
Function:
Function: preservation of food by delaying its deterioration, rancidity or discolouration due to oxidation (‘lipid’) [Code of Federal Regulations (CFR) 170.3] (key is that it delays, not prevents
What is oxidation?
electron removal/abstraction from a compound by a reactive oxygen species - reactive oxygen species in foods include: hydrogen peroxide (H2O2), hydroxyl radical (HO.)(most common in foods), perhydroxyl/ hydroperoxyl radical (HOO.), alkoxy radical (RO.), and the superoxide radical (O2-.)
Antioxidants
Why is oxidation a problem in foods?
- off flavour and odour production (i.e. rancidity)
- loss of flavour and aroma (real interest in creating more flavor for the ageing population)
- discolouration due to structural changes of natural pigments (e.g. anthocyanins, β-carotene, chlorophyll)
- texture changes (e.g. organoleptic organoleptic (based on the sences- mouthfeel- soft, crisp, dry, juicy, smooth, flky, crunchy) properties)
- decrease in nutritional value due to essential fatty acid and vitamin (A,C,D,E and K) destruction
this is why food additives can make it more nutritious, wider choice, safer food supply and lower price)
-formation of toxic (carcinogens and mutagens) by-products
Antioxidants
Unsaturated fatty acid oxidation is the major problem in foods
- fatty acids in nature are present in the form of triacylglycerols (TAG)
- common unsaturated fatty acids in foods:oleic acid: C18:1 Δ9linoleic acid: C18:2 Δ9,12—omega 6linolenic acid (-linolenic): C18:3 Δ9,12,15 - omega 3
- less common: eicosapentaenoic acid: C20:5 Δ5,8,11,14,17 and
docosahexaenoic acid: C22:6 Δ4,7,10,13,16,19
Geometric confirmation: cis or Z
Trans is E
B) Antioxidants
Why?
Why?
- because they contain allylic hydrogens, which are sensitive to abstraction by reactive oxygen species (‘autoxidation reaction’)
allyl group: (a methylene) -CH2-CH=CH2 Oleic acid: HOOC-(CH2)6-CH2-CH=CH-CH2-(CH2)6-CH3 Linoleic acid: HOOC-(CH2)6-CH2-CH=CH-CH2-CH=CH-CH2-(CH2)3-CH3 Linolenic acid: HOOC-(CH2)6-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-CH2-CH3
Whats more stable? Trans , they prefer to be in non-conjugated forms: single single double single single double
look at slide 5
j
lipid is in simple stae (only 1) while 02 comes in triples (3O2) something needs to happen to get it to react with each other
) Antioxidants
Two types:
!!! understand them
Phenolic compounds (both synthetic and natural)
Organic acids and their salts and esters (e.g. ascorbic and citric acid)
- based on the structure of
phenols
Synthetic phenolic antioxidants
BHA (butylated hydroxyanisole) BHT (butylated hydroxytoluene)
TBHQ (tert-butylhydroquinone) [approved for food use in Canada in 1999]
Synthetic phenolic antioxidants
Physical Properties
- all are white or off-white solids with high purity (99.8%); may react with metals to produce off-colours (pink)
- with the exception of gallates (e.g. PG: 3.5 mg/mL) all have poor water solubility (‘not soluble in water’; e.g. BHT: 0.6 mg/L @25 oC)
All have excellent oil solubility (e.g. BHT :g/100ml)
Tateless and odourless
Vary in antioxidant activity, thermal stability and volatility
genrated free radical (o-) on the antioxydant but is way less reactive and less impactful because it can transfer the free radical all through the structure- resonate structure
f-
an example of rational design -drugs, foods, food additives
- “carry through”:
the ability of an antioxidant to survive processing steps (e.g. frying, baking) and impart stability to the finished product
usually have multiple antioxydants-use it with BHT (most sterically hindered antioxydant- best carry through-
By adding antioxidant you improve shelf life
Synthetic phenolic antioxidants
Toxicity
continued toxicity testing for >60 years (animals and humans)
- 1982 study showed benign tumors in the forestomach of rats (2.0% of total diet) significance? As humans don’t have forestomach – never went through peer reviewed - Netherlands cohort study (NLCS) of 120,000 (men and women; 54 to 65 years of age) risk factors for stomach cancer (antioxidants included). Based on dietary studies (1986-1999) “no significant association with normal (0.5 mg/day) dietary intakes of BHT/BHA with stomach cancer”
Toxicity
- safety continues to be a ‘hot topic’ of discussion for consumers always a push for banning these compounds-BHT LD50 (rats, rabbits): 2930 mg/kg bwt
Never need to know the ld50 on exam - BHA LD50 (rats): >2000 mg/kg bwt; PG LD50 (rats/mice): 3800 mg/kg bwt
Synthetic phenolic antioxidants
Toxicity (cont.)
- BHA LD50 (rats): >2000 mg/kg bwt; PG LD50 (rats/mice): 3800 mg/kg bwt
- life-time carcinogenicity studies (rats) at dietary levels of 0.2 to 1.0%; two-generation (rats) studies at 25-500 mg/kg of body weight; 2-year studies (mice) at dietary levels of 0.02 to 0.5%; two-generation studies (dogs, hamsters, mice and rats) at dietary levels of 1-2% no tumour incidence;
- reproductive toxicity (hamsters, mice, monkeys, rabbits & rats): at dietary levels of 0.1 to 0.5%, and oral doses ranging from 50 to 320 mg/kg of body weight no adverse effects;
Synthetic phenolic antioxidants
Toxicity (cont.)
no cmta (carcinogenicmutagenic)
- NOEL/NOAEL (bht): 25 MG/KG BWT/DAY
- ADI (BHT) : 0.3 [FAO/WHO) and 0.05mg/kg bwt [EU] (estimated intake: 0.051 mg/day based on assumption of maximum permitted levels; 0.2mg/day [BHA+ PG ]; 0.25 mg/day [BHA +BHT +PG])
- industrial uses of BHT:
food (11%); pet food (11%); pharmaceuticals and cosmetics (12%); fuel additive (15%); plastics (25%); rubber (27%)
- industrial uses of BHT:
Synthetic phenolic antioxidants
Mechanisms (main) for Detoxification
Phase I: oxidation (enzyme mediated rxn; cytochrome P-450)
[E] (propyl gallate) [.35G/100ML] (gallic acid) [1.5G/100ML] (INCREASE SOLUBILITY BUT STILL NOT VERY SOLUBLE
Natural phenolic antioxidants
Tocopherol(s)
- pale-yellow viscous oils (impart colour to food)
-readily destroys by heat frying: 50-75% loss; 1 minute boiling: 5-20% loss); destroyed by UV light ; easily oxidized in the prescence of nitrate and metal ions
(delta is the most active because very availableleast hindered- alpha has the least because it’s the most sterically hindered)
antioxidant activity: alpha > beta > gamma >delta
But vitamin E is the exact opposite
- significant colour change (yellow brown) with heat
The present and future
A. Other naturally occurring phenolics (sesame seeds)
Sesamol
- found in sesame seed oil at levels of 0.3 to 0.5%;
- possible carcinogen (mice and rat studies in 2002; CA Proposition 65 list(needs to be on label))
- GI/liver toxicity
- antifungal activity (when attacked by microbe it releases toxic compounds)
Purity? Solubility? New formulation required? Effective in foods> stability? Cost? Cross reactivity? Taste? Colour? Ease of use? Toxicity?
A. Other naturally occurring phenolics
flavanoids(quercitin)
- naturally present in fruits and vegetables (e.g. apples: 4.4 mg/ 100 g; broccoli: 3.2 mg/100 g; tea leaves: 204-255 mg/100 g)
- free radical scavenging ability (in vitro) was ~50% that of BHA and BHT
- toxicity? Effective in foods? Stability? Cost? Others?
avenanthramides
naturally occuring phenolicsnaturally present in oats (~0.2 mg/100 g) av c is the most active
The present and future
B. Other synthetic phenolics
Ionox 100: approved for food use in
the EU since 1967
THBP: approved for food use in
the EU, Asia, India and Mexico
since 1963
the most reactive oxygen species
oh.
Organic acids and their salts and esters (e.g. ascorbic and citric acid)
- the radical scavenging (reaction with free radicals) mechanism is the same as observed in synthetic/natural phenolics
no lipid solublilty
very water water soluble
- ascorbyl palmitate and stearate (commercial products)
- has a synergistic effect when used with phenolic antioxidants
- maximum addition level of 0.02%; typically used at 0.01% (based on food lipid content)
you add it to ascorbic acid so that it can be lipid soluble which is good
GRAS status ; used under GMP in Canad
Aids in the stabilization of vegetable oils
No cmta
ascorbic acid can regenerate the antioxydants (a-) and make dihydroascorbate acid - no free radicals
Biological Toxicity of Free Radicals
- HO., RO., H2O2, RO.- are all examples of reactive oxygen species (ROS)
Sources of these compounds are both internal [ endogenous] (eg. Electron transport chain, enzyme system) abd external (e.g. foods, environment) - research has shown that oxidative damage of cells is an important mechanism by which carcinogenesis is initiated; in addition, it is certainly why we age and why our body mechanisms deteriorate
- Human diseases and free radicals: :
- organ damage (liver, lungs and kidneys); arterial wall lesions (CHD); lipid oxidation products (plaque formation CHD); retina damage (blindness)
- DNA strand breaks/damage; amino acid oxidation (enzyme inactivation); membrane damage; neutrophil (type of white blood cell) production joint damage, respiratory distress
- have been implicated with Alzheimer’s, asthma, diabetes, Parkinson’s and rheumatoid arthritis
- cellular protection mechanisms: enzymes (catalase, peroxidase, superoxide dismutase) and glutathione (tripeptide, GSH)
- a number of dietary components such as Vitamins C & E, and ß-carotene have been linked (correlative evidence) with protecting cells from oxidative deterioration
- BHA, BHT, PG, tbhq have been shown to have aticarcinogenic
properties (in vitro and cell-line studies) reduction in free radicals
formation has been proposed as the mechanism for these
chemopreventive agents
