fdsc - food antioxidants

• antioxidants are substances that act to prevent or inhibit oxidation of other molecules
• donate H to prevent autoxidation 
• donation or obstruction of electrons
• addition or removal of O₂

• in living organisms, nutrients get oxidized via glycolysis, TCA cycle and ETC → to release energy
• energy is released together with highly reactive species ( e.g. free radicals)
• the reactive species are potentially harmful as they abstract protons/ donate electrons to other biomolecules to gain stability

• spontaneous oxidation of biomolecules by molecular O₂ 
• commonly happens to unsaturated biomolecules (e.g. lipids/fatty acids)
• as a result of autoxidation, changes happen in the same biomolecules in terms of size and order
• some of the changes may be undesirable
• the off flavours are described as RANCID flavours
• this type of rancidity induced by oxidation is known as oxidative  rancidity
• there is HYDROLYTIC RANCIDITY caused by the splitting of lipid molecules by enzymes (lipases/phospholipases) from microorganisms in the presence of H₂O
• some of the breakdown products (FFA) may impact objectionable flavours to * reactive oxygen species → oxygen containing components with ↑ reactivity

• hydroperoxides
• singlet oxygen
• superoxide - free radical
• peroxintrite - free radical
• HClO
• nitrite oxide
• free radicals - OH, ONO₂, O₂

• are species with unpaired electrons in their orbital 
• as a result they are highly unstable and reactive

• "free scavengers"
• are those that act as scavenge or remove free radicals and prevent them from eliciting their harmful effects
• inhibit oxidation by terminating chain reactions
• they possess reactive OH or NH groups
• transfer protons from these groups to free radicals species to stabilize the radicals and inhibit their reactivity

• Examples:
• vitamin C
• vitamin E
• citric acid
• B-caroteine and other carotenoids
• lutein and lycopene
• polyphenolics, flavanoids and anthocyonins

• refers those that act by breaking into non-radical, non reactive and thermaly stable products
• also levin as preservative antioxidants, act in various ways
• eg. decomposition of hydrogen peroxides/peroxides
• eg. reducing agents such as sodium borohsydride or lithium aluminium hydroxide
• also, enzymes like catalase and superoxide disseminates

• 2° antioxidants inhibit oxidations in several ways:
• ex. chelating metal ions, inhibiting enzymes that produce ROS, absorption of UV light
• ex. EDTA, citric acid, catalase, superoxide dismutase (SOD)

• molecular oxygen
• ↑ temperature
• exposure to light
• UV radiation
• unsaturated biomolecules (fatty acids)
• metal ions (pro oxidants)
• some enzymes that promote formation of given radicals

induced by free radicals

• 1. Initiation step
•         X· + R−H → R· + H−X

• 2. Propagation steps
•         R· + O₂ → ROO·
•         ROO· + R−H → ROO−H + R·
• 3. Termination steps
•         2ROO· → ROO−R +O₂
•         ROO· + R· → ROO−R
•         R· + R· → R-R

• oils
• fats
• dairy
• meat
• improperly dried cereals

• Non radical
• molecular oxygen (O₂)
• hyperoxide (H₂O₂)
• peroxynitrite (ONOO^-)
• singlet oxygen (¹O₂)
• organic peroxide(ROOR^')

• Radical
• superoxide anion (O_2 ^·-)
• hydroxyl radical (^·OH)
• nitric oxide (NO)
• peroxyl radical (RO·)

• flavor chnages = desirable or undesirable
• color changes = desirable or undesirable
• nutrient loss
• formation of harmful components

• breakdown of fats into carbonyl components in cheeses
• may be desirable in some cheeses and undesirable in others

TMAO (Trimethylamine N-oxide)

TMAO → TMA + 1/2 O₂    (by enzymes TMAO reductase or TMAO oxidase)

TMA is the nitrogenous substance responsible for the fishy smell

TMA → DMA (dimethylamine) + FA (formaldehyde) (by the enzyme TMA demethylase)

• FA (formaldehyde) formed causes cromlinkages between fish protein molecules during storage and make fish texture tough

• undesirable color changes include → browning of fruits and vegetables or bruising
• also, loss of color in salmonides during frozen storage as a result of the action of lipoxygenase or carotenoids

• 1. oxidation of vitamin c to form deoxyascorbic acid 
• product formed as loss vitamin C activity versus the substrate

2. oxidation of omega 3 fatty acids to form various carbonyl compounds accompanied by loss of nutrient value

• Natural antioxidants
• vit. A, E, C
• polyphenolic compounds
• chlorophyll
• carotenoids (B-carotene, lycopene)
• gluthione
• melatonin
• selenium
• lipoic acid
• coenzyme Q
• antioxidant enzymes; SOD (superoxide dismutase); catalase; glutathione
• e.g. peroxidase, glutathione reductase

• Anthocyanin pigments
• ex. cyanidin, malvidin, delphinidin
• found in food stuffs such as grapes and cranberries

• Carotenoid pigments
• ex. B-carotene, lutein, lycopene and cryptoxanthin
• found in pumpkin, mangoes, carrots, peppers and green leafy vegetables like spinach

• Vitamin E
• found in vegetable oils, avocados, nuts, seeds and whole grains

• (Poly) phenolics ex. catechins, caffeic acid, vanillin acid
• found in food products such as red wine, tea, thyme oregano

• Flavanoids
• found in green tea, tea, citrus fruits, red wine, onion, apples, soybeans, tofu, lentils, peas and milk

• Selenium
• found in seafood, offal, lean meat and whole grains

• Vitamin C
• found in oranges, blackcurrants, kiwi fruit, mangoes, broccoli, spinach, peppers and strawberries

• Vitamin E
• tocopherols are relatively heat stable (used in food products like crackers, baked goods and fried goods)

• act by hydrogen/electron transfer processes
• via donation of unsaturated bonds

• special case for* melatonin
• 1. free radical scavenger
• 2. stimulation of antioxidant enzymes

• Glutathione
•                    2 Glu - Cys - Glycine     (reduced glutathione)
•                                 |
•                                SH
•                                 ↓
•                       Glu - Cys - Gly         (oxidised glutathione)

• Selenium
• component of selenoenzyme and         * protein that participate in radical scavenging

• Selenoenzymes
• glutathione peroxidase
• thionedoxin reductase

• 1. Catalase reaction
• 2H₂O₂ →2H₂O +O₂

• 2. SOD reaction
• superoxide dismutase (SOD) has various metal ion cofactors (e.g. Cu, Mn, Fe...)
• Cu^₂+⋅SOD + O₂^- → Cu⁺⋅SOD + O₂  
• Cu⁺⋅SOD + O₂^- +2H⁺ → Cu²⁺⋅SOD + H₂O₂
• there is formation of:
• H₂O₂ → H₂O +1/2O₂ (by the enzyme catalase)

• 3. Glutathione peroxidase reaction
• glutathione can also breakdown H₂O₂:
• 2GSH +2H₂O₂ → GS-SG + H₂O + 1/2O₂
• (reduced form)    (oxidized form)

• GSH = reduced monomeric glutathione
• GS-SG = glutathione disulphide

• glutathione reductase then reduced the oxidized glutathione to complete the cycle
• GS-SG + NADPH⋅H+ → 2GSH + NADP⁺ (by enzyme glutathione reductase)

• stabilized by resonance
• phenolic ring systems
• donates electrons from phenolic group
• lots of controversy: ex. in Europe = banned
• used heavily in Canada and US

• Examples:
• BHA
• BHT
• propyl gallate (PG)
• tertiary butyl hydroquinone (t-BHQ)

2. Enzyme antioxidants + non enzyme antioxidants

• 3. based on molecule size, antioxidants may also be classified as:
• small molecule antioxidants
• large molecule weight antioxidants (the enzyme antioxidants)

• plants sources
• animals sources
• microbial sources

• carotenoids (fruits/veggies)
• chlorophyll (green leafy veggies)
• vegetable oils (vit. A/vit.E)
• nuts (vit.A/vit E)
• cereals (vit A/vit E)
• teas (polyphenolics)
• spices (polyphenolics)

• antioxidant enzymes
• carotenoids (crustaceans and salmonides)
• proteins/peptides/amino acids
• e.g. peptides from milk proteins, egg proteins, fish proteins (bioactive peptide) that have antioxidant capacity

***** (ADD stuff)****

• polyphenolic compounds
• carotenoids (eg. the yeast Phaffia rhodozyma is very ↑ in carotenoids pigments)

• Some food uses
• synthetics
• cookies and crackers 
• veggie oils/fats
• potato chips
• dry crackers and cereals
• margarine

• natural 
• fruit juices
• veggies oils
• breads

• Synthetic
• inexpensive
• much broader use
• medium to ↑ antioxidant activity
• use is very restricted by safety concerns
• interest in use is waning ↘ (declining)

• Natural
• expensive 
• less extensive use
• broader spectrum of activity
• safer
• interest in use is ↑

• 1. evaluation of antioxidant potency (TAC)
• total antioxidant capacity
• oxygen radical absorbance capacity (ORAC)
• total radical antioxidant potential (TRAP)

2. find the effect of deep fat frying on synthetic US** natural antioxidants

• antioxidants can inhibit microbial activity
• by destroying cell wall and exchange material
• can preserve food by preventative oxidation that flavor and also remove impact relative species that can damage* biomolecules and health
• some antioxidants also exert antimicrobial effects by interacting with bacterial cell walls and disrupting the cell walls to permit flow of material into and out of cells that can inactivate the cells
• isoflavones (a group of phenolics commonly found in plants) have been shown to inhibit plant pathogens
• BHA (phenolic antioxidants) has been shown to inhibit a broad range of bacteria
• tannins (also polyphenolics) are known to inhibit bacteria such as vibrio, clostridia, shigella, staphylococcus etc..

↑ levels of certain antioxidants can be toxic

• ex. selelnium
• ↑ levels of selenium (Se) can interact with other medications such as : anticoagulants, sedative and enhance their activities
• ↑ levels of Se can impair the action of cholesterol lowering  drugs, niacin, immunosuppressants and oral contraceptives

• BHA has been shown to cause proliferation of cells in the liver + lungs
• can result in enlarged liver + lungs
• BHT has also been shown to cause general cell proliferation
• PG = ↑ levels can cause heart damage

• conjugated systems = stabilize antioxidant molecules
• resonance and aromaticity have important contributions to antioxidant stabilization capabilities

• need to discover more potent natural antioxidants to replace synthetic ones (natural vs synthetic)
• need to develop foods that are more resistant to lipid oxidation
• ex. incorporation of physiologically active molecules in functional foods to resist oxidation
• ex. bioactive peptides, polyphenolics, carotenoids
• addition of herbs and spices such as poly unsaturated oils (tea extracts, herbs like sage and rosemary)
• combined use of natural antioxidants for synergy
• GMO approches to produce molecules with broader spectrum of activity and stability
• GMO used to enhance the production of compounds with improved resistance to oxidation
• tissue culture methods to show that cells can produce antioxidants molecules rapidly and ↑ in quantities