Phytochemicals

John Parry, Ph.D.

Rm 229, M.T. Carter Bldg

Agricultural Research Station

Phone: (804) 524-5957

Email: jparry@vsu.edu

Tocopherols (Vitamin E)• Eight vitamers:• ( ) tocopherol• ( ) tocotrienol• Prevent peroxyl radical propagation in lipids• The most conserved is -tocopherol• Found mainly in oils (wheat germ, corn)

Carotenoids

• Include: -carotene

• They are not direct antioxidants– They quench the energy of singlet O2 which is more

reactive than triplet O2

• Some carotenoids can be converted to vit. A

• Orange colored foods– They were found to be very high in pumpkin seeds

in a previous study, carrots, and sweet potatoes.

Essential Fatty Acids

• Linoleic acid (18:2n6)

• Linolenic acid (18:3n3)

• DHA (22:6n3)

• EPA (20:5n3)

• Some of these can be found in plant foods such as flax seed oil, basil seed oil, cold water fish

• Other sources:

Phytosterols

-sitosterol, -7 avenosterol, stigmasterol, etc.

• These molecules resemble cholesterol and have been shown to decrease cholesterol levels

Phenolic Antioxidants

• Phenolic compounds have been shown to have antioxidant properties in vitro when compared vitamin E and C

• The French Paradox– Initially the bioflavonoid content was the reason

• Recently resveratrol has been suggested as the reason for the paradox

Phenolic Antioxidants

• Are gradually losing popularity among scientist in the field while still publically demanded

• Jeff Moore

Free Radicals

• Biologically relevant free radicals:– Superoxide anion – O2

_

– Hydroxyl – OH (very reactive)

– H2O2 – not a free radical but very reactive

– Peroxyl – ROO

Enzymatic Antioxidants• Superoxide dismutase – 2O2

_ O2 + H2O2

Group of isozymes Kcat (turnover rate) 1 x 107 per second

• Catalase – H2O2 2 H2O + O2

• Kcat 1 x 106 per second

• Glutathione peroxidase – LOO LOH Group of isozymes

Free Radicals• Other biologically relevant damaging

molecules related to free radicals:

–Hydrogen peroxide – H2O2

– Fenton reaction• Fe (II) + H2O2 Fe (III) + OH_+ OH

– Peroxynitrite – ONOO _

• Formed by the reaction of nitrite and O2 _

• Reacts with CO2 forming a CO3 , and NO2

– Peroxynitrous acid – ONOOH (pKa ~ 6.8)• Forms OH and NO2

Antioxidants: Synthesized1. BHA – Butylated hydroxy anisole2. BHT – Butylated hydroxy toluene3. TBHQ – tert-Butylhydroxyquinone• All 3 of these are lipophilic (fat soluble)• These are added to foods to protect susceptible

fatty acids and fat soluble vitamins

Health concerns regarding synthesized antioxidants:• cause cancer in animal studies• damage DNA

Enzymatic Antioxidants• Superoxide dismutase – 2O2

_ O2 + H2O2

• Catalase – H2O2 2 H2O + O2 (Kcat 1 x 107)

• Glutathione peroxidase – LOO LOH

• These enzymes and enzyme systems are continually operating but genetic expression is upregulated during oxidative stress

Antioxidants: Non-Enzymatic

• Ascorbic Acid• Tocopherols (8 isoforms)• Carotenoids• Phenols and Polyphenols (found in plants)• Glutathione• Lipoic acid (a fatty acid with disulfide antioxidant)• Coenzyme Q (involved in electron transport chain)• Melatonin (• Bilirubin (a breakdown product of red blood cells)• Uric acid

Antioxidants: Non-Enzymatic

• Tocopherols (8 isoforms) -, -, -, -Tocopherol -, -, -, - Tocotrienol

-Tocopherol

-Tocotrienol

Antioxidants: Non-Enzymatic

• Vitamin E (-Tocopherol) is the most effective antioxidant of the 8 isoforms– Vitamin E protects lipid membranes from

oxidation of unsaturated fatty acids• Most susceptible tissues:

– It is stored in lipid membranes, adipose tissue liver, heart, muscle, and adrenal glands

– It is thought to be regenerated by vitamin C

Antioxidants: Non-Enzymatic• Vitamin A and Carotenoids

• Beta carotene has 2 beta ionone ring making it capable of forming 2 vitamin A molecules

Antioxidants: Non-Enzymatic• Over 700 carotenoids have been identified

comprised of 2 structural groups1. Some hydrocarbon carotenes

-carotene -carotene (1 vitamin A; has one ionone ring)– Lycopene

2. Some oxygenated xanthophylls -cryptoxanthin– Lutein– Zeaxanthin (corn)

The mechanism of antioxidant protection from the carotenoids is not from free radical scavenging but from the quenching of singlet oxygen (1O2)

Antioxidants: Non-Enzymatic

• Glutathione

– (GSH) – reduced form (90%)– (GSSG) – oxidized form (10%)– Consists of gly, cys, and glu– Thiol group is active– Used by glutathione peroxidase to reduce

peroxides

Antioxidants: Non-Enzymatic

• Glutathione– Can reduce the oxidized form of vitamin E– Is made in every cell of the body but primarily

the liver– Glutathione reductase is continually active and

is inducible when subjected to oxidative stress– NADPH can reduce GSSG to GSH

Antioxidants: Non-Enzymatic

• Phenolic compounds– Exist in virtually all plant foods– Very highly concentrated in spices

• Phenolic acids• Gallic acid, syringic acid, p-OH benzoic acid, vanillic

acid

• Hydroxycinnamic acids• Ferulic acid, p-coumaric acid, caffeic acid

• Polyphenolic acids• Anthocyanins, proanthocyanins

Antioxidant

Basic Phenol Radical Resonance for Stability

OH O O O O O

-H

+H

Phenolic Antioxidants

O

CH3

HO

O

OH

ferulic acid

OH

OH

HO O

OH

catechin

Fe++HO