food chem final

8/7/2019 food chem final

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F.3.2 Discuss the Factors that Affect the Shelf Life and Quality ofFoodF.3.2 Discuss the Factors that Affect the Shelf Life and Quality ofFood

Water contentWater content-- loss of nutrients, browning and rancidity. Dryloss of nutrients, browning and rancidity. Dryfoods will spoil if they absorb water due to the microbacteriumfoods will spoil if they absorb water due to the microbacterium

Chemical change (change in pH)Chemical change (change in pH)-- off flavours, colour changes,off flavours, colour changes,

browning and loss of nutrientsbrowning and loss of nutrients LightLight-- rancidity, vitamin loss and fading of natural coloursrancidity, vitamin loss and fading of natural colours

TemperatureTemperature-- higher temperature increases the rate of otherhigher temperature increases the rate of otherforms of spoilageforms of spoilage

Exposure to airExposure to air-- increases the rate of oxidationincreases the rate of oxidation

Presence of bacteria, enzymes and chemical reactants in thePresence of bacteria, enzymes and chemical reactants in theproductproduct

Thats why we have refrigerators, store it in cupboards, use darkThats why we have refrigerators, store it in cupboards, use darkcanisters and have special inert gases injected into products thatcanisters and have special inert gases injected into products thatare crispyare crispy

Factors Affecting the Shelf Life

and Quality of Food


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Rancidity of FatsRancidity of Fats

Rancidity generally occurs in fats and isRancidity generally occurs in fats and isperceived by our senses as when they haveperceived by our senses as when they havegone offgone off-- disagreeable smell, taste, texture ordisagreeable smell, taste, texture orappearanceappearance

Can be caused by enzymes secreted by bacteriaCan be caused by enzymes secreted by bacteria

or through oxidationor through oxidation

F.3.3 Describe the Rancidity of Fats


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Hydrolytic RancidityHydrolytic Rancidity

Associated with the presence of water

Of the three major components of food (fats/lipids,

carbohydrates, and protein), lipids are most responsiblefor rancidity

Results in the formation of fatty acids

Conditions: when food is contaminated by bacteria and

heated


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Steps in Production of FoodSteps in Production of Food

Raw Materials

Processing

Packaging

Storage and Distribution

Consumption

Chemical reactions for

rancidity begin

Rancidity begins to appear


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Hydrolytic RancidityHydrolytic Rancidity

Water and fat can come together for months without reaction

Rate of reaction between the two are only significant when asuitable catalyst is present and temperature is raised

Typical catalyst include lipase enzymes and acidic enzymes


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Hydrolysis of Triglyceride byHydrolysis of Triglyceride by

WaterWater

Reactant: fat and water

catalyst: lipase which is a water-soluble enzyme thatcatalyzes the hydrolysis of ester chemical bonds

Product: glycerol and fatty acids- very volatile and have

unpleasant odors and flavors which causes rancidity


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Examples of Fatty Acids CausingExamples of Fatty Acids Causing

RancidityRancidityButanoic acid (in butter), hexanoic acid and octanoic acid

Plamitic acid, stearic acid and oleic acid gives chocolate an

oily or fatty flavour

Lauric acid gives palm and coconut oil in cocoa butter

substitutes a soapy flavour (their sodium salts are soaps)

Good fatty acids include Omega 3 found in foods such as fishoil (best source), flax seed oil, hemp oil, walnut, tofu, eggs

beans


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Omega 3Omega 3


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Butter and Butanoic AcidButter and Butanoic Acid


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Lauric Acid in Cocoa ButterLauric Acid in Cocoa Butter


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Flavour ThresholdFlavour Threshold

Fatty acids products of hydrolysis of chocolate are

palmitic, stearic and oleic acids

Flavour threshold of 50 mg/kg and are usually described

as fatty or oily

Hydrolysis of butter and milk produce short chain acids

such as butanoic, hexanoic etc. with flavour thresholds of

1-10 mg/kg

Thus hydrolytic rancidity is more important in animal fats

than for vegetable fats


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Oxidative RancidityOxidative Rancidity

Due to the oxidation of the carbon-carbon bonds in

unsaturated fatty acids

Via a free radical process, the double bonds undergo a

cleavage (breakdown), releasing volatile aldehydes and

ketones

Catalyzed by transition metal ions (copper and iron) and

accelerated by presence of light; metal ions are trace

contaminants of oils that have been processed or stored in

metal vessels

Metalloproteins such as hemoglobin and chlorophyll from

meat products and vegetables can be source of copper,

manganese, magnesium and iron


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Mechanism for OxidativeMechanism for Oxidative

RancidityRancidity


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Free Radical Chain ReactionFree Radical Chain Reaction

Initiation: RH R- + H-

Propagation: R- + O2 ROO-

Termination: ROO- + RH ROOH + R-

Light especially UV, accelerates the initiation stage of lipid

oxidation

Hydroperoxides are decomposed by radiation, thermal

energy, metal catalysis or enzyme activity to form

additional radicals; lead to further reaction to form hydroxy

acids, keto acids, aldehydes which cause the rancid odor


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Items that undergo OxidativeItems that undergo Oxidative

RancidityRancidity


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Oxidative Rancidity (cont.)Oxidative Rancidity (cont.)

Not all flavours from oxidation give off unpleasant smells/tastes

Aldehydes with unsaturation at the 2 position are sweet and

pungent at shorter chain length and sweet, fatty and green at longer

chain lengths

Aldehydes with conjugated saturation at the 2 and 4 positions are

noted for as sweet and oily

These 2-4 denials with chain length of 8 to 12 carbons make a

positive contribution to the flavour of chocolate


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F. 3.5 Describe ways toF. 3.5 Describe ways to

minimize the rate of rancidityminimize the rate of rancidityand prolong the shelf life ofand prolong the shelf life of

food.food.


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1. Processing1. Processing

Examples include:Examples include:

limiting lipase hydrolysis by storing dairy limiting lipase hydrolysis by storing dairy

products at low temperatures (refrigeration)products at low temperatures (refrigeration) reducing light levels during storage or reducing light levels during storage orstoring in coloured glassstoring in coloured glass

keeping moisture levels low during keeping moisture levels low duringprocessingprocessing

(adding salt or sugar, smoking).(adding salt or sugar, smoking).


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2. Packaging2. Packaging

using an inert gas, which minimizes contactusing an inert gas, which minimizes contactwith oxygen, by covering foodwith oxygen, by covering food

using low using low--gasgas--permeability packaging filmpermeability packaging filmoror

hermetic sealinghermetic sealing

minimizing the amount of air in the minimizing the amount of air in theheadspaceheadspace

above oil and canning.above oil and canning.


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3. Adding Additives3. Adding Additives

sodium sulfite, sodium hydrogensulfite and citric acid sodium sulfite, sodium hydrogensulfite and citric acidto delay the onset of nonto delay the onset of non--enzymic browningenzymic browning sodium and potassium nitrite and nitrate for curing sodium and potassium nitrite and nitrate for curingmeats, fixing colour and inhibiting microorganismsmeats, fixing colour and inhibiting microorganisms

sodium benzoate and benzoic acid as antimicrobial sodium benzoate and benzoic acid as antimicrobialagents in fruit juices, carbonatedagents in fruit juices, carbonatedbeverages, pickles and sorbic acid, propanoic acid,beverages, pickles and sorbic acid, propanoic acid,calcium propanoatecalcium propanoateand sodium propanoate for delaying mould and bacterialand sodium propanoate for delaying mould and bacterial

growth in breads and cheesesgrowth in breads and cheeses ethanoic acid and benzoic acid for delaying mould and ethanoic acid and benzoic acid for delaying mould andbacterial growth in pickled meats and fish products, andbacterial growth in pickled meats and fish products, andalso adding to flavour.also adding to flavour.


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F.3.6 Describe the traditionalF.3.6 Describe the traditionalmethodsmethods

used by different cultures to extendused by different cultures to extendthe shelf life of foods.the shelf life of foods.

Methods include fermentation,Methods include fermentation,preserving, pickling, salting, addingpreserving, pickling, salting, addingsugar, and smoking.sugar, and smoking.


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1. Fermentation1. Fermentation

Used to lower pH to a level which inhibitsUsed to lower pH to a level which inhibitsbacterial and enzymatic activitybacterial and enzymatic activity

Fermentation involves using goodFermentation involves using good

microorganisms to grow in foods.microorganisms to grow in foods. Involves adding a starter organism to theInvolves adding a starter organism to the

food, and allowing it to mature until the pH isfood, and allowing it to mature until the pH islow enough to prevent further deteriorationlow enough to prevent further deterioration

of the foodof the food Fermentation requires specific starting pHFermentation requires specific starting pH

and temperature conditionsand temperature conditions


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the good microorganisms often operatethe good microorganisms often operateby eating away at spoilageby eating away at spoilage--sensitive partssensitive partsof the food, and releasing chemical byof the food, and releasing chemical byproducts, thus often changing physicalproducts, thus often changing physicalproperties of the food including textureproperties of the food including textureand tasteand taste

Examples include cheese and wineExamples include cheese and winefermentationfermentation


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Cheese fermentation:Cheese fermentation:

LactobacilliLactobacilli is added tocheese as a starter,is added tocheese as a starter,and it digests milk lactose, and releases lacticand it digests milk lactose, and releases lacticacid.acid.

Lacticacid then reacts with an added enzymeLacticacid then reacts with an added enzymetocurdle the milk.tocurdle the milk.

The cheeseThe cheese--maker drains offthe whey andmaker drains offthe whey andcompacts the curds, and then variouscompacts the curds, and then variousmicrobes are further added to help ripen thismicrobes are further added to help ripen thisproductinto mature cheeseproductinto mature cheese


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Wine Fermentation:Wine Fermentation:

Yeasts are added to crushed grapesYeasts are added to crushed grapes

Yeasts then eat away at the grapesYeasts then eat away at the grapessugars, and release alcohol as thesugars, and release alcohol as thechemical bychemical by--product.product.


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2. Preserving2. Preserving

Includes canning, freezing, drying, andIncludes canning, freezing, drying, andvacuum sealing foods.vacuum sealing foods.

The canning process involves using heatThe canning process involves using heatto kill off microorganisms .to kill off microorganisms .

Freezing process involves freezing food soFreezing process involves freezing food sothat most chemical and biologicalthat most chemical and biologicalprocesses (including that of theprocesses (including that of thesurrounding microorganisms) are stopped.surrounding microorganisms) are stopped.


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2. Preserving2. Preserving

Drying process involves taking outDrying process involves taking outmoisture from the food, sincemoisture from the food, sincemicroorganisms all need moisture tomicroorganisms all need moisture tosurvive.survive.

Vacuum sealing process involves takingVacuum sealing process involves takingaway the oxygen that microorganismsaway the oxygen that microorganisms

need to survive.need to survive.


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3. Pickling3. Pickling

Can be done by preserving food byCan be done by preserving food byanaerobic fermentation in brine (solutionanaerobic fermentation in brine (solutionof salt in water) to produce lactic acidof salt in water) to produce lactic acid

Can be done by marinating and storing itCan be done by marinating and storing itin acidic solution, usually vinegar.in acidic solution, usually vinegar.

This is what gives pickles its sour taste!This is what gives pickles its sour taste!

In acidic foods such as pickles, the growthIn acidic foods such as pickles, the growthof bacteria and fungi is greatly slowed.of bacteria and fungi is greatly slowed.


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4. Smoking4. Smoking

Smoke is an antimicrobial and an antioxidantSmoke is an antimicrobial and an antioxidant

Smoking process involves passing smokeSmoking process involves passing smoke--filled air produced from a flame, usuallyfilled air produced from a flame, usually

burning on wood, over the food.burning on wood, over the food. Smoking process usually is not effective bySmoking process usually is not effective by

itself for preservation process, and needs toitself for preservation process, and needs tobe coupled with another preservation processbe coupled with another preservation process

(which would very often be drying)(which would very often be drying) This is because smoke only touches theThis is because smoke only touches the

surface of the foodsurface of the food


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4. Smoking4. Smoking Smoking is very often practiced for theSmoking is very often practiced for the

taste it producestaste it produces

Wood smoke produces over 400 chemicalWood smoke produces over 400 chemical

compounds, including methanal, which iscompounds, including methanal, which isa significant antimicrobiala significant antimicrobial

However, wood smoke also producesHowever, wood smoke also produces

carcinogens such as 3,4

benzpyrenecarcinogens such as 3,4

benzpyrene


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5. Salting5. Salting

Salting is used as a form of preservationSalting is used as a form of preservationbecause most bacteria, fungi or anybecause most bacteria, fungi or anypathogen cannot survive in highly saltypathogen cannot survive in highly salty

conditionsconditions This is because when bacteria is in contactThis is because when bacteria is in contact

with concentrated solution of salt, waterwith concentrated solution of salt, waterpasses through the cell membrane out ofpasses through the cell membrane out ofthe bacteria into the solution throughthe bacteria into the solution throughosmosis.osmosis.

Then, the bacteria cells becomeThen, the bacteria cells become

dehydrated, and are unable to undergodehydrated, and are unable to undergo


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6. Adding Sugar6. Adding Sugar

Foods such as jams and condensed milkFoods such as jams and condensed milkare protected from fungal moulds becauseare protected from fungal moulds becauseof their high concentration of sugar.of their high concentration of sugar.

If the surface of the jam is exposed andIf the surface of the jam is exposed andwater condenses there, the surfacewater condenses there, the surfaceconcentration of sugar can be reduced toconcentration of sugar can be reduced to

a level where fungal moulds can grow.a level where fungal moulds can grow.


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F.3.7 Define the termF.3.7 Define the term antioxidant.antioxidant.

Anti means against, oxidant refers toAnti means against, oxidant refers tothe chemical process ofoxidation.the chemical process ofoxidation.

Antioxidant therefore suggests goingAntioxidant therefore suggests goingagainst the process ofoxidationagainst the process ofoxidation

The term antioxidant can be defined asThe term antioxidant can be defined as aa

molecule or substance that delaysmolecule or substance that delaysthe onset or slows the rate ofthe onset or slows the rate ofoxidation, effectively extending theoxidation, effectively extending the

shelf life of foods.shelf life of foods.


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AntioxidantsAntioxidants

Antioxidants are found naturally andAntioxidants are found naturally andsyntheticallysynthetically

In natural conditions, animals and plantIn natural conditions, animals and planttissues can produce their owntissues can produce their ownantioxidants, but foods cannot, andantioxidants, but foods cannot, andoxidation is bound to follow from exposureoxidation is bound to follow from exposure

to both air and sunlightto both air and sunlight Oxidation of food causes nutrient loss, andOxidation of food causes nutrient loss, and

changes in chemical compositionchanges in chemical composition

Oxidation of fats and oils causes rancidityOxidation of fats and oils causes rancidity


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AntioxidantsAntioxidants

Oxidation of food can also lead to colourOxidation of food can also lead to colourchanges of the foodchanges of the food

For example, the flesh of an apple:For example, the flesh of an apple:


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Common Natural Antioxidants andCommon Natural Antioxidants and

Their SourcesTheir Sources Naturally occurring antioxidants include:Naturally occurring antioxidants include: vitamin C (ascorbic acid) in citrus fruits, green peppers,vitamin C (ascorbic acid) in citrus fruits, green peppers,

broccoli, green leafy vegetables, strawberries,broccoli, green leafy vegetables, strawberries,redcurrants and potatoesredcurrants and potatoes

Characterised by the cyclic or ring compound createdCharacterised by the cyclic or ring compound createdfrom the reaction betweenfrom the reaction between COOH andCOOH and OH groups in aOH groups in amolecule; molecule of water is eliminated in processmolecule; molecule of water is eliminated in process

F.3.8 List Examples of Common Naturally Occurring Antioxidants and Their Sources


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VITAMIN CVITAMIN C


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Vitamin EVitamin E

Vitamin E (tocopherols) found in wheatgerm, nuts, seeds, wholeVitamin E (tocopherols) found in wheatgerm, nuts, seeds, wholegrains, green leafy vegetables, vegetable oils (canola) and soyagrains, green leafy vegetables, vegetable oils (canola) and soyabeanbean

Tocopherols are antioxidants that demonstrate vitamin E activityTocopherols are antioxidants that demonstrate vitamin E activity

Characterized by chromanol ring with hydroxyl group that canCharacterized by chromanol ring with hydroxyl group that candonate hydrogen atom to reduce free radicalsdonate hydrogen atom to reduce free radicals 8 forms of Vitamin E (4 tocopherols and 4 tocotrienols) with8 forms of Vitamin E (4 tocopherols and 4 tocotrienols) with

(alpha)(alpha)--tocopherol most common and preferentially absorbed bytocopherol most common and preferentially absorbed byhumanshumans

-tocopherol


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VITAMIN EVITAMIN E


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--carotenecarotene

Found in carrots, squash, broccoli, sweetFound in carrots, squash, broccoli, sweetpotatoes, tomatoes, kale, cantaloupe, melon,potatoes, tomatoes, kale, cantaloupe, melon,

peaches and apricotspeaches and apricots


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SeleniumSelenium

Found in fish, shellfish, red meat, eggs, grains,Found in fish, shellfish, red meat, eggs, grains,chicken and garlicchicken and garlic

Present at active site where enzymes preventPresent at active site where enzymes preventlipids from autolipids from auto--oxidation in cell membranesoxidation in cell membranes Required in pancreas for digestion andRequired in pancreas for digestion and

absorption of lipids, including vitamin Eabsorption of lipids, including vitamin E


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Structural Features ofMajorStructural Features ofMajorSynthetic Antioxidants in FoodSynthetic Antioxidants in Food

1)1) Butylated Hydroxyanisole (BHA)Butylated Hydroxyanisole (BHA)-- composedcomposed

from 2from 2-- and 3and 3--terttert--butylbutyl--44--hydroxyanisolehydroxyanisole2)2) Butylated Hydroxytoluene (BHT)Butylated Hydroxytoluene (BHT)3)3) Propyl Gallate (PG) formed by esterification ofPropyl Gallate (PG) formed by esterification of

gallic acid and propanolgallic acid and propanol

4)4) Trihydroxybutyrophenone (THBP)Trihydroxybutyrophenone (THBP)5)5) TertTert--butylhydroquinone (TBHQ)butylhydroquinone (TBHQ)

F.3.9 Compare the Structural Features of the Major Synthetic Antioxidants in Food


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Synthetic AntioxidantsSynthetic Antioxidants


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They all contain a phenolic group andThey all contain a phenolic group andmost contain a carbon atom bondedmost contain a carbon atom bondeddirectly to three methyl groupsdirectly to three methyl groups

The phenolic and tertiary butyl group areThe phenolic and tertiary butyl group arefree radical scavengers that react with andfree radical scavengers that react with andremove the free radicals involved in theremove the free radicals involved in the

oxidation of the foodoxidation of the food

Therefore they help to prolong shelf lifeTherefore they help to prolong shelf life

Trihydroxybutyrophenone(THBP)


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Advantages of AntioxidantsAdvantages of Antioxidants

Vitamins CVitamins C-- reduce risk of cancer andreduce risk of cancer and

heart disease by inhibiting formation ofheart disease by inhibiting formation offree radicals, is vital for production offree radicals, is vital for production ofhormones and collagenhormones and collagen

Vitamin E and carotenoids also reduce riskVitamin E and carotenoids also reduce riskof cancer and heart diseaseof cancer and heart disease

carotene helps with vitamin A synthesiscarotene helps with vitamin A synthesis

F.3.10 Discuss the Advantages and Disadvantages Associated with Natural and Synthetic Antioxidants.


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Disadvantages of AntioxidantsDisadvantages of Antioxidants

People think that synthetic antioxidants are lessPeople think that synthetic antioxidants are lesssafe since they are artificialsafe since they are artificial

Natural antioxidants are more expensive andNatural antioxidants are more expensive andless effective and can add unwanted colour andless effective and can add unwanted colour andleave an aftertasteleave an aftertaste

Synthetic antioxidants are food additives, soSynthetic antioxidants are food additives, sothey must be regulated by policies andthey must be regulated by policies andlegislation to remain safelegislation to remain safe-- in developingin developingcountries, policies are less strictcountries, policies are less strict

Always too much of something is not good!Always too much of something is not good!


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Western Culture: Cranberries, Blueberries, Chocolate, Red

wine

When red wine is made, the skins and seeds fermenting in the

grape juice create high levels of resveratrol

Antioxidants in Traditional Foods

Phenols are radical scavengers that reduce the free radicals that

damage cells and also prevent fat from clogging arteries


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Through research dark chocolate has been found tocontain four times the amount of antioxidants than

tea

Theobromine


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Anthocyanins

Catechin

Berries Powerful Antioxidants


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Eastern Culture: Ginseng, Green Tea, Tumeric

Contain large quantities of polyphenolic substances; tea

leavesferment and undergo polymerization


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Foods of both cultures have high capabilities in modulating

human metabolism in a favourable manner for reducing the

likelihood of cancer

food chem final

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