Beta-Carotene

Beta-carotene (b-carotene; BAY-tuh KARE-oh-teen) belongs to a family of organic compounds called the carotenoids. The carotenoids are all brightly pigmented (colored) compounds found in a number of plants, bacteria, algae, and fungi. Betacarotene is responsible for the yellowish to orange color of pumpkins, apricots, sweet potatoes, nectarines, and, most notably, carrots. The compound also occurs in spinach and broccoli, but in such small concentrations that the green chlorophyl presentmasks the orange color of beta-carotene. In its pure form, beta-carotene occurs as purple crystals shaped like thin leaflets.

In plants, algae, and photosynthetic bacteria, beta-carotene plays an important role in photosynthesis, the process by which plants convert water and carbon dioxide into carbohydrates and oxygen. In nonphotosynthetic bacteria and fungi, beta-carotene protects the organism against the harmful effects of light and oxygen.

Animals require beta-carotene for normal growth and development, but are unable to manufacture the compound themselves. As a result, they must ingest some beta-carotene from plant sources in order to stay healthy. The compound is a provitamin, a substance that is converted in the body to a vitamin. Beta-carotene is converted into vitamin A, whose role in the body is the maintenance of strong bones and teeth and healthy skin and hair. Beta-carotene also acts as an antioxidant, a substance that attacks free radicals in the body that may cause cancer. It may also protect against heart disease and strengthen the body’s immune system.

Beta-carotene was first isolated by the German chemist Heinrich Wilhelm Ferdinand Wackenroder (1789–1854), who extracted the compound from carrot roots in 1831. The compound was first synthesized in 1950 by the Swiss chemist Paul Karrer (1889–1971).

Beta-carotene can be obtained from natural sources by crushing or pulverizing the source (such as carrots) and adding a solvent that will dissolve the organic components of the plant. These components can then be separated from each other by chromatographic techniques. A major commercial source of beta-carotene obtained by this method is the algae Dunaliella salina, which grows in large salt lakes in Australia. The compound can also be prepared synthetically by one of two methods, the BASF and the Roche methods, both named after the pharmaceutical firms where they were developed. Both methods of preparation begin with long-chain hydrocarbons containing about twenty carbon atoms each. These hydrocarbons are then joined to each other to form the 40-carbon beta-carotene compound.

Beta-carotene has two uses: in vitamin supplements and as a food additive. Anyone who eats a healthy diet that includes foods rich in vitamin A, such as fish oil, liver, eggs, butter, and orange or yellow vegetables and fruits, will get adequate amounts of beta-carotene. However, many people take vitamin supplements to ensure that they have enough beta-carotene (as well as other vitamins) in their daily diet. Although some warnings have been issued about taking too much vitamin A, there is no clinical evidence that an overdose of the vitamin does any long-term harm to a person.

Beta-carotene is used as a food additive to increase the color intensity of a product. It is used primarily with yellow and orange foods, such as butter and margarine, although it is sometimes added to ice cream and fruit juices as well. Beta-carotene is used in only very small amounts as a food additive. In these amounts, it poses no health hazard to humans or other animals. The compound has also been used in experiments to test its effectiveness against certain diseases, such as lung cancer. In such cases, it has been found to be more harmful than beneficial, increasing the risk of cancer and death among people participating in the studies.

Chlorophyll : The Green

  Chlorophyll (KLOR-uh-fill) is the pigment that gives
plants, algae, and cyanobacteria their green color. The name
comes from a combination of two Greek words, chloros,
meaning ‘‘green’’ and phyllon, meaning ‘‘leaf.’’ Chlorophyll is
the substance that enables plants to create their own food
through photosynthesis.
At least five forms of chlorophyll exist. They are:
• chlorophyll a (also known as a-chlorophyll), with a formula
of C55H72O5N4Mg
• chlorophyll b (also known as b-chlorophyll), with a formula
of C55H70O6N4Mg
• Chlorophyll c1, with a formula of C35H30O5N4Mg
• Chlorophyll c2, with a formula of C35H28O5N4Mg
• Chlorophyll d, with a formula of C54H70O6N4Mg
Chlorophyll a occurs in all types of plants and in algae.
Chlorophyll b is found primarily in land plants. Chlorophyll
c1 and chlorophyll c2 are present in various types of algae.
Chlorophyll d is found in red algae.

   All forms of chlorophyll have a similar chemical structure.
They have a complex system of rings made of carbon
and nitrogen known as a chlorin ring. The five forms of
chlorophyll differ in the chemical groups attached to the
chlorin ring. These differences result in slightly different
colors of the five chlorophylls.
   French chemists Pierre-Joseph Pelletier (1788–1842) and
Joseph-Bienaime´ Caventou (1795–1877) first isolated chlorophyll
in 1817. In 1865, German botanist Julius von Sachs
(1832–1897) demonstrated that chlorophyll is responsible
for photosynthetic reactions that take place within the cells
of leaves. In the early 1900s, Russian chemist Mikhail Tsvett
(1872–1920) developed a technique known as chromatography
to separate different forms of chlorophyll from each
other. In 1929, the German chemist Hans Fischer (1881–
1945) determined the complete molecular structure, making
possible the first synthesis of the molecule in 1960 by the
American chemist Robert Burns Woodward (1917–1979).

   Plants make chlorophyll in their leaves using materials
they have absorbed through their roots and leaves. The
synthesis of chlorophyll requires several steps involving
complex organic compounds. First, the plant converts a common
amino acid, glutamic acid (COOH(CH2)2CH(NH2)COOH)
into an alternative form known as 5-aminolevulinic acid
(ALA). Two molecules of ALA are then joined to form a ring
compound called porphobilinogen. Next, four molecules of
porphobilinogen are joined to form an even larger ring structure
with side chains. Oxidation of the larger ring structure
introduces double bonds in the molecule, giving it the ability
to absorb line energy. Finally, a magnesium atom is introduced
into the center of the ring and side chains are added to
the ring to give it its final chlorophyll configuration.
   Plants store chlorophyll in their chloroplasts, organelles
(small structures) that carry out the steps involved in photosynthesis.
Each chloroplast contains many clusters of several
hundred chlorophyll molecules called photosynthetic units.
When a photosynthetic unit absorbs light energy, chlorophyll
molecules move to a higher energy state, initiating
the process of photosynthesis. The overall equation for the
process of photosynthesis is 6CO2 + 6H2O ! C6H12O6 + 6O2.
That simple equation does not begin to suggest the complex
nature of what happens during photosynthesis. Botanists
divide that process into two major series of reactions: the light
reactions and the dark reactions. In the light reactions, plants
use the energy obtained from sunlight to make two compounds,
adenosine triphosphate (ATP) and nicotinamide adenine
dinucleotide phosphate (NADPH). ATP and NADPH are
not themselves components of carbohydrates, the final products
of photosynthesis. Instead, they store energy that is
used to make possible a series of thirteen different chemical
reactions that occur during the dark stage of photosynthesis
that result in the conversion of carbon dioxide and water
to the simple carbohydrate glucose (C6H12O6).

Riboflavin: The Vitamin B2

 

 

Riboflavin (REY-bo-FLAY-vin), commonly known as vitamin
B2, is an orange-yellow crystalline solvent with a bitter
taste. It is relatively stable when exposed to heat, but tends
to decompose in the presence of light for extended periods of
time. Riboflavin is used in the body for a variety of functions,
including the metabolism of carbohydrates for the
production of energy and the production of red blood cells.
Riboflavin was found in 1879 by Alexander Wynter Blyth (1844-1921) who noticed a compound in cow’s milk that glowed with a yellow fluorescence
when exposed to light. Blyth called the compound
lachtochrome (lachto- = ‘‘milk’’ and -chrome = color), but was
unable to determine its chemical composition or its chemical
properties. In fact, it was not until the 1930s that the
chemical nature of the compound was determined. The
Swiss chemist Paul Karrer (1889–1971) and the Austrian-
German chemist Richard Kuhn (1900–1967) independently
determined the chemical structure of riboflavin and first
synthesized the compound. The name riboflavin is derived
from the fact that the vitamin was first found in association
with the sugar ribose.

   Naturally, plants and microorganisms can synthesize riboflavin.
Some foods rich in riboflavin are brewer’s yeast, dark
green vegetables, mushrooms, legumes, nuts, milk and other
dairy products, sweet potatoes, and pumpkins. Bacteria that
live in the human digestive tract are also able to synthesize
some riboflavin, but not enough to meet the body’s requirement
for the vitamin.
   Riboflavin is produced synthetically using either the
genetically-modified bacterium Bacillus subtilis or a fungus
called Ashbya gossifyii. The bacteria or fungus are cultured
in a large vat that has been seeded with small amounts of
riboflavin. Over time, the organisms generate large quantities
of riboflavin until some desired amount of the compound
has been produced. The vat is then heated to a
temperature sufficient to kill the bacteria or fungi, leaving
crystalline riboflavin behind. The riboflavin is then separated
and purified.

   The human body needs riboflavin to use oxygen efficiently
in the metabolism of amino acids, fatty acids, and
carbohydrates. The vitamin is involved in the synthesis of
niacin (another B vitamin), it activates vitamin B6, and it
helps the adrenal gland to produce hormones. It helps the
body make antibodies to fight disease and infection, regulates
the thyroid gland, and is important in maintaining healthy
hair, nails, and skin. Riboflavin is especially important during
periods of rapid growth because it is involved in the formation
and growth of cells, especially red blood cells.
The human body needs riboflavin to use oxygen efficiently
in the metabolism of amino acids, fatty acids, and
carbohydrates. The vitamin is involved in the synthesis of
niacin (another B vitamin), it activates vitamin B6, and it
helps the adrenal gland to produce hormones. It helps the
body make antibodies to fight disease and infection, regulates
the thyroid gland, and is important in maintaining healthy
hair, nails, and skin. Riboflavin is especially important during
periods of rapid growth because it is involved in the formation
and growth of cells, especially red blood cells.
most likely to suffer from riboflavin deficiency problems are
those with anorexia (a condition in which people refuse to
eat adequate amounts of food), older people with poor diets,
alcoholics (because alcohol impairs a person’s ability to
absorb and use the vitamin), and newborn babies being treated
for jaundice by exposure to ultraviolet light (because
light destroys riboflavin).

Retinol: The Vitamin A

  Retinol (RET-uh-nol) is the scientific name for vitamin A,
a vitamin found only in animals. It occurs as a yellowish to
orange powder with a slight brownish cast and is a relatively
stable compound. Retinol is converted in the body from an
alcohol to the corresponding aldehyde, retinal (C20H28O), one
of the primary chemical compounds involved in the process
by which light is converted to nerve impulses in the retina of
the eye. Vitamin A is also required for a number of other
biochemical reactions in the body, including growth and
development of tissue and maintenance of the immune system

  Vitamin A is synthesized in animal bodies through a
variety of pathways. One important source of vitamin A is a
group of related compounds called the carotenes, substances
responsible for the yellowish or orangish appearance of
fruits and vegetables such as carrots, sweet potatoes, squash,
cantaloupe, apricots, pumpkin, and mangos. Some leafy
green vegetables, such as collard greens, spinach, and kale,
are also good sources of the carotenes. The most important of
the carotenes is b-carotene (beta-carotene), C40H56. The oxidation
of carotenes in animal bodies converts them to retinol.

  The chemical structure of retinol was determined in 1931
by Swiss chemist Paul Karrer (1889–1971), and the compound
was first prepared synthetically shortly thereafter by Austrian-
German chemist Richard Kuhn (1900–1967). The first
successful process for producing retinol commercially was
developed in the mid-1940s by German chemist Otto Isler
(1920–1992), then employed at the pharmaceutical company
Roche, located in Sissein, Germany. Isler’s process involved a
complex series of reactions that begins with the combination
of a fourteen carbon hydrocarbon and a six carbon hydrocarbon
to create the fundamental backbone from which the
retinol molecule is constructed. Regular production of vitamin
A began in 1948 with a projected output of 10 kilograms
per month, which before long was raised to 50 kilograms per
month. The Roche plant at Sissein continues to produce
retinol today.
  Vitamin A is probably best known for its role in maintaining
normal vision. Deficiencies of the compound are
likely to manifest themselves earliest in a variety of eye
problems, most commonly night blindness. Night blindness
is a condition in which one loses the ability to distinguish
objects in reduced light. If left untreated, vitamin A deficiencies
may lead to decreased ability to see in normal light and,
eventually, to complete blindness.
  But vitamin A has been shown to have a number of other
functions in the body. It is essential for the maintenance of
growth, bone formation, reproduction, proper immune system
function, and healing of wounds. A number of additional
claims have been made for the compound, although evidence
is not as strong as it is for the above functions. For example,
it may be effective in preventing or treating a variety of
conditions such as measles, intestinal parasites, osteoporosis,
inflammatory bowel disease, bone marrow disorders, certain
types of cancer, tuberculosis, peritonitis, osteoarthritis, food
poisoning, Alzheimer’s disease, miscarriage, and HIV/AIDS.
In each of these cases, evidence is not yet strong enough to
show a clear-cut connection between retinol and disease, but
research is being conducted to determine how strong the
association may be.
  Retinol is available commercially in a variety of formulations,
including tablets, capsules, and creams. Such products
usually contain a modified form of retinol that is more easily
absorbed by the body. For example, a product known as
tretinoin is a synthetic form of retinol known as all-trans
retinoic acid. The term all trans means that all of the double
bonds in retinoic acid are located on the same side of the
molecule. Products containing tretinoin are used to treat
acne, pimples, wrinkles, blackheads, freckles, sun-spots, and
even pre-cancerous lesions. They work by increasing the rate
with which the skin sheds old cells and replaces them with
new cells.
  Vitamin A supplements in pill or capsule form are available
in two formulations, those that contain retinol and
those that contain beta carotene. It is not possible to take
too much of the latter type of vitamin A. The body will not
convert excess amounts of carotene into retinol but will,
instead, excrete the excess in the urine or stool. An excess
of retinol-based vitamin A, by contrast, may result in certain
medical problems. Since the vitamin is fat soluble, in
may be stored in body fat and reach relatively high concentrations
if too much is ingested. An excess of retinol in the
body may be associated with liver damage, osteoporosis,
rash, fatigue, bone and joint pain, nausea, insomnia, and
personality changes.