Herbal Antioxidant 2010

8/8/2019 Herbal Antioxidant 2010

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Chemistry andChemistry and

Application ofApplication of

AntioxidantsAntioxidants

HandHand--OutOut Herbal ChemistryHerbal Chemistry--20102010

Antioxidants

R•, RO•, ROO•, O-2

1O2, -OH, H2O2,Cu, Fe

R•, RO•,ROO•,

1O2, O-2,

-OH, H2O2,

Cu, Fe

Prooxidant Jail

.

Function of Antioxidant on Lipid OxidationFunction of Antioxidant on Lipid Oxidation

• Inhibits or slows the formation of free alkyl

radicals in the initiation step• Interrupts the propagation of free radical chain

• Delays the start or slows the chemical reaction

rate of lipid oxidation.

Types of AntioxidantsTypes of Antioxidants

• Hydrogen donating compounds

• Singlet oxygen quenchers• Metal chelators

• Enzymes

• Oxygen scavengers and Reducing agents



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Characteristics of Hydrogen Donating AntioxidantCharacteristics of Hydrogen Donating Antioxidants

The major hydrogen donating antioxidants are

monohydroxy or polyhydroxy phenolic

compounds with various ring substitutions.

The antioxidant free radical does not initiateanother free radical due to the

stabilization of delocalization of radical.

Reaction of Antioxidants with RadicalsReaction of Antioxidants with Radicals

R + AH RH + A

RO + AH ROH + A

ROO + AH ROOH + A

• •

•

••

•

Reaction of Antioxidants with RadicalsReaction of Antioxidants with Radicals

R + A RARO + A ROA

ROO + A ROOA

•

• •

•

••

Effectiveness of AntioxidantsEffectiveness of Antioxidants

• The difference of one-electron reduction

potential

• The stability of antioxidant radicals• The resonance delocalization

• Further oxidation of antioxidant radicals



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Resonance of Antioxidant RadicalsResonance of Antioxidant RadicalsOH

C(CH3)3

OCH3

C(CH3)3

OCH3

O.

OCH3

C(CH3)3

O

.

C(CH3)3

OCH3

O

.

OCH3

C(CH3)3

O

.

R , RO , ROO RH , ROH , ROOH•• •

Stability of Antioxidant RadicalStability of Antioxidant Radical

O

C

CH3

CH3

CH3

OCH3

•

Targets of AntioxidantTargets of Antioxidant

• Antioxidants can react with peroxyl radicals

rather than alkoxyl radicals.

• The most prevalent radical is peroxyl (ROO·)

radical.

• Peroxyl radical has the lowest standard one

electron reduction potential among alkyl,

alkoxyl and peroxyl radicals

OH

C(CH3)3

OCH3

C(CH3)3(CH3)3C

CH3

OH

Synthetic AntioxidantsSynthetic Antioxidants

Butylatedhydroxyanisole(BHA) Butylatedhydroxytoluene (BHT)

O H

O HO H

C O O C3H

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Propyl gallate

O H

C ( C H3

)3

O H

Tertiary butylhydroquionone (TBHQ)



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Natural AntioxidantsNatural Antioxidants

Benefits

• Health implication

• Stability in food system

Limits

• Characteristic flavor

• Safety test required

TocotrienolsTocotrienols

O

HO

R1

R2

R3

CH3 CH3 CH3CH3

Trivial Name Chemical Name R1 R2 R3

α-Tocotrienol 5,7,8-Trimethyltocotrienol CH3 CH3 CH3

β-Tocotrienol 5,8-Dimethyltocotrienol CH3 H CH3

γ -Tocotrienol 7,8-Dimethyltocotrienol H CH3 CH3

σ-Tocotrienol 8-Methyltocotrienol H H CH3

Antioxidant Mechanism ofAntioxidant Mechanism of TocopherolTocopherol

• Transfer of phenolic hydrogen

• Scavenging of singlet oxygen

• Regeneration of tocopherol in the

presence of ascorbate

TocopherolTocopherol

A chain breaking antioxidant competes with

polyunsaturated lipid for the lipid peroxyl radicals.

α-Tocopherol α-Tocopheryl semiquinone •Lipid radicals

Lipid radicalsα-Tocopheryl quinone



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Ascorbic AcidAscorbic Acid

• Hydrogen donation to chain radicals

• Quenching of singlet oxygen

• Removal of molecular oxygen

• Regenerate tocopherol radicals

• Prooxidant Reduce ferric iron to more active

ferrous iron in the water phase

Ascorbic AcidAscorbic Acid

O

OH

O

HO

H

CH

CH2OH

OHO

O

O

HO

H

CH

CH2OH

OH

O

O

O

O

H

CH

CH2OH

OH

L-Ascorbic acid Dehydroascorbic acid

- H • - H •

•

Ascorbic Acid and Related CompoundsAscorbic Acid and Related Compounds

O

OH

O

HO

H

CH

CH2OC(CH2)14CH3

OH

O

O

OH

O

HO

H

CH

CH2OH

OH

L-Ascorbic Acid

O O

HO

H

CHO

CH2OH

H

OH

Erythorbic Acid Ascorbic Palmitate

Ascorbic acid can act as a prooxidant by

converting the reducing ferric to ferrous ion,which become more active catalysts of

oxidation in the aqueous system.



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Synergistic Effect of Tocopherol & Ascorbic AcidSynergistic Effect of Tocopherol & Ascorbic Acid

Ascorbic acid

α-Tocopherol

Dehydroascorbic acid

Lipid peroxyradical

α-Tocopheryl radical •

+ •H

- •H

>

<

Lipid hydroperoxide

ProoxidantProoxidant Mechanisms of MetalsMechanisms of Metals

Fe3+ + ROOH Fe2+ + ROO + H+

Fe2+ + ROOH Fe3+ + RO + OH-

Formations of alkyl free radical by direct reaction

Fe3+ + RH Fe2+ + R + H+

Activation of oxygen for singlet oxygen formation

Fe2+ + 3O2

Fe3+ + O-2

1O2

Formation of hydroxyl radical

Fe2+ + H2O2Fe3+ + OH- + OH

•

•

k 1

k 2

k 2 / k 1 = 105

•

•

MetalMetal ChelatorsChelators

Reaction between Metal andReaction between Metal and

HydroperoxideHydroperoxide• Rapid Exponential increase in oxidation during propagation step

β-Scission of alkoxyl radical to low molecular weight compounds

• Copper is 50 faster than ferrous ion in decomposing hydrogenperoxide

• Ferrous is 100 faster than ferric iron in decomposing hydrogenperoxide

• Ferrous is 1015 times more soluble than ferric iron

MetalMetal ChelatorsChelators

• Phosphoric acid

• Citric acid

• Ascorbic acid• Ethylene Diamine Tetra Acetate.(EDTA)

• Proteins such as Transferrin, Ovotransferrin

• Amino acids and Peptides



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Mechanism ofMechanism of MetalMetal ChelatorsChelators

Formation of complex ions or coordination

compounds with metals

• Prevention of metal redox cycling

• Occupation of all metal coordination sites

• Formation of insoluble metal complexes

• Steric hindrance of interactions between metals and

lipid intermediates

PhospholipidsPhospholipids

Phosphatidyl ethanolamine

CH2 O C

O

R1

CHOC

O

R2

CH2 O P

O

O

O CH2 CH2 NH2-

Phosphatic acid

-

CH2 O C

O

R1

CHOC

O

R2

CH2 O P

O

O

O-

M

OC

O

C H 2

OC

O

C H 2

N

C H 2

C H 2

O

O N

C

O

C H 2

C

O

C H2

Ethylene Diamine Tetra Acetate (EDTA)

Interaction ofInteraction of ChealatorChealator and Metaland Metal

2 Glucose + 2O2 + 2H2O 2 Gluconic acid + 2H2O2

GlucoseGlucose Oxidase/CatalaseOxidase/Catalase

2 Glucose + O2 2 Gluconic acid

2H2O2 2H2O + O2

Glucose Oxidase

Catalase

Catalase

Glucose Oxidase

Oxygen Scavenging

Enzymatic AntioxidantsEnzymatic Antioxidants



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SuperoxideSuperoxide DismutaseDismutase

2O2O2

- + 2H+ + H2O2

Superoxide anion participates in oxidative reactions

• Maintaining transition metals in their reduced, active state

• Promoting the release of metals bound to proteins

• Producing singlet oxygen

Superoxide Dismutase

+Catalase2H2O2 O 22H2O

3

GlutathioneGlutathione PeroxidasePeroxidase

H2O2 + 2GSH 2H2O + GSSG

LOOH + 2GSH LOH + H2O + GSSG

GSH: Reduced glutathione

GSSH: Oxidized glutathione

Oxygen Scavengers and Reducing AgentsOxygen Scavengers and Reducing Agents

• Ascorbic acid

• Ascorbic palmitate

• Erythorbic acid

• Sodium erythorbate

• Sulfites

Oxygen Scavenger MechanismsOxygen Scavenger Mechanisms

C H3 SH C H3 S S C H3½ O2+

O

OH

O

HO

H

CH

CH2OH

OH

O

O

O

O

H

CH

CH2OH

OH

H O2+

½ O2+ H O+

HO S OH

O

HO S OH

O

O

O

2

2



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SuperoxideSuperoxide DismutaseDismutase

2O2 O2- + 2H+ + H2O2SuperoxideDismutase

+Catalase O22H2O

3

2H2O2

• Producing triplet oxygen from superoxide anion

3

Multifunctional AntioxidantsMultifunctional Antioxidants

• Tocopherol

• Ascorbic acid

Antioxidant InteractionsAntioxidant Interactions

• Combination of metal chelator and free radical

scavenging antioxidants

• Combination of different antioxidants like

α- tocopherol and ascorbic acid

FlavonoidsFlavonoids

OH

OH

OHO

OOH

HO

Quercetin Flavonols

O

OH

O

OH

HO

Glucoside

OH

Cyanidin-3-glucoside Anthocyanins

Antioxidant SourcesAntioxidant Sources



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FlavonoidsFlavonoids

Secondary products of plant metabolism

• Metal chelating ability

• Superoxide anion scavengers

Anthocyanines, catechins, flavones, flavonols,

isoflavone, and proanthocyanidins

VegetablesVegetables

Cacao beans, Potato, Tomato, Spinach,

Legumes, Garlic, and Seaweed

Polyphenolic compounds

FruitsFruits

Wines: Anthocyanin

Polyphenolic compounds

TeaTea

HO

OH

O

OH

OH

OH

Epicatechin

HO

OH

O

OH

OH

OH

OH

Epigallocatechin



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Sesame SeedSesame Seed

Sesamol

O

O

OH

Sesamolinol

O

O

O

O O

OCH 3

OH

Herb and SpiceHerb and Spice

Sage, Ginger, Green pepper, Lavender and Rosemary

CH3

HO

OH CH3

CH3

H3C

HOOC

Carnosoic Acid

C

O

H3C CH3

HO

OH CH3

CH3

O

Carnosol

OH

OH

HO

OH

O

O

HOOC

Rosemarinic Acid

Reaction Rates ofReaction Rates of CarnosolCarnosol andand CarnosicCarnosic AcidAcid

OH

HO

H

HOOC

O

HO

H

HOOC

•

+ LOO• LOOH+

CarnosicCarnosic acidacid

33 ×× 101077 MM--11ss--11

OH

HO

C

H

O

O

O

HO

C

H

O

O

+

•

+

CarnosolCarnosol

22 ×× 101066 MM--11ss--11

LOO• LOOH

SoybeanSoybean

• Chlorogenic acid, caffeic acid, ferulic acid -

Metal chelation and singlet oxygen quenching

• Isoflavones - phytoestrogen effects -

Metal chelation and hydrogen donation



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O

O

OH

OH

COOH

OH

HO

HO

Chlorogenic acid

O

R OOH

Genistein OH OH

Daidzein H OH

Isoflavones R1 R2

1

2

Soybean

R

Ferulic acid Caffeic acid

Korean Red GinsengKorean Red Ginseng

HO

OCH3

COOH

Vanillic acid

OH

OOH

OH OOH

Kaempferol

HO

OCH3

CH CH COOH

HO

OH

CH CH COOH

Korean Red GinsengKorean Red Ginseng

Singlet oxygen quenchers: Caffeic acid> Kaempferol >

Vanillic acid > Salicylic acid > Ferulic acid

Linoleic acid in aqueous system under dark :

Kaempferol > Maltol > Vanillic acid > Saponin >

Salicylic acid > Ferulic acid

Metal chelation activity : Kaempferol > Maltol >

Vanillic acid > Ferulic acid > Caffeic acid

Herbal Antioxidant 2010

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