Biotin

The discovery and recognition of biotin as a member
of the water-soluble vitamin B complex resulted
from several independent lines of investigation. In
1933, Franklin E. Allison and his colleagues at the US
Department of Agriculture reported that the growth
and respiration of Rhizobium trifolii, a nitrogen-fi xing
bacterium found in the root nodules of legumes,
were stimulated by a factor, ‘coenzyme R’, extractable
from various organic sources. By the early 1920s, several investigators had isolated from various organic
sources crude fractions that contained a novel
growth factor for yeast. Eventually, in 1936, Fritz
Kögl and B. Tönnis, organic chemists at the University
of Utrecht in Germany, isolated from dried egg
yolk a crystalline substance that strongly stimulated
the growth of yeast. This growth factor, which Kögl
and Tönnis named ‘biotin’, was later shown to have
exactly the same stimulatory effect on Rhizobium as
coenzyme R. In this respect, at least, the two factors
were identical.

Further progress came from the fi eld of animal nutrition.
In 1927, Margaret A. Boas at the Lister Institute
of Preventive Medicine in London observed toxicity
in rats when raw egg white was used as a source of
protein in the animals’ diet. After a few weeks the rats
developed dermatitis and haemorrhages of the skin,
their hair fell out, their limbs became paralysed, they
lost considerable weight, and eventually they died.
Only raw or cold-dried egg white produced the toxicity;
cooking made the egg white harmless. This toxicity,
which Boas called egg white injury, was prevented
by a ‘protective factor X’ present in liver and other
sources. Paul György showed that biotin had the same
protective action against egg white injury as did protective
factor X, which he renamed ‘vitamin H’ (German
Haut, skin). György also showed that vitamin H
concentrates supported the growth of biotin-requiring
bacteria. In 1940 György and Vincent du Vigneaud
independently isolated crystalline vitamin H from
liver concentrates. It was soon proven that biotin and
vitamin H were one and the same compound.
The chemical structure of biotin was established by
du Vigneaud’s group in 1942 and in the following year
the vitamin was synthesized at the Merck Company,
USA.

Biotin is present in all natural foodstuffs, but the
content of even the richest sources is very low when
compared with the content of most other water-soluble
vitamins. Biotin is not commonly used in fortifi ed
foods, apart from infant formulas. Typical values of
some rich natural sources of biotin include ox liver
(33 μg per 100 g), whole eggs (20 μg per 100 g), dried
soya beans (65 μg per 100 g) and peanuts (72 μg per
100 g) (Holland et al., 1991). Other good sources include
yeast, wheat bran, oatmeal and some vegetables.
Muscle meats, fi sh, dairy products and cereals contain
smaller amounts, but are important contributors to
the dietary intake. Most of the biotin content of animal
products, nuts, cereals and yeast is in a protein-bound
form. A higher percentage of free, water-extractable
biotin occurs in vegetables, green plants, fruit, milk
and rice bran (Lampen et al., 1942).