Vitamin E (Tocopherols)

 Vitamin E (Tocopherols)

(Antisterilitic factor)

Introduction

Since 1922 effects of vitamin E deficiency were studied in rats when Bishop and Evans announced the existence of a substance X, the absence of which in the diet, results failure in the reproductive capacity of rats: In 1936 Evans and Emerson isolated HC and synthesized vitamin E from the unsaponifiable fraction of wheat-germ oil

Chemistry

Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols.

There are commonly three varieties of tocopherols (Tokos=child-birth, Phero=to bear, suffix Ol signifies alcohol)-

·        α tocopherol

·        β tocopherol

·        γ tocopherol

They are unsaturated alcohols. The most active compound is β tocopherol contains one less methyl group.

The four tocotrienols (alpha, beta, gamma and delta) are similar in structure to the four tocopherols with some differences in structure.

Properties

·        soluble in fat and fat-solvents

·        heat-stable

·        exist naturally as yellow oil

·        can withstand cooking and stable in heat in the absence of oxygen

·        Withstand acids at elevated temperatures

·        The vitamin activity is destroyed by ultra-violet light as well as by oxidation

·        They are excellent anti oxidants. They prevent other vitamins present in food (e.g., vitamin A) from oxidative destruction.

Absorption

Free tocopherols and their esters are readily absorbed from the small intestine. Bile acids are necessary for absorption.

 

Distribution

Animal sources

·        Egg

·        milk

·        fish

·        muscles contain

Plant sources

·        vegetable seed oils

·        wheat

·        soybean

·        leafy vegetables

Functions

(1) Tocopherols are strong antioxidants and prevent unwanted oxidation in the body.

(2) Essential for normal function of muscle.

(3)Acts as a cofactor in the electron transfer system operating between cytochrome b and c thus it is important in energy metabolism.

Deficiency signs

In human no clear deficiency signs have been observed. However in some lipid metabolism disorders nerve problems have been observed.

 

Daily requirement

Average daily intake through normal diet is 15 to 20 mg, which seems sufficient.