Vitamin C (or ascorbic acid) is found in many fruits and
Vitamin C participates in reactions that are required
for the formation of the protein collagen.
When collagen is
produced a series of events occur inside and outside of the cell.
Vitamin C is an active inside of the cell and hydroxylates to the
amino acids proline and lysine.
These help form a precursor
molecule called procollagen that is later modified into collagen
outside of the cell.
Without vitamin C the formation of collagen
is disrupted, causing a wide variety of problems throughout the
Collagen is found wherever tissues require strengthening,
especially in those tissues with a protective, connective or
Collagen is critical to the maintenance of
bone and blood vessels and is essential for the healing of
Vitamin C aids red blood cell formation helping
preventing haemorrhaging and fighting bacterial infections.
Vitamin C can act as an antioxidant by donating electrons and
hydrogen ions and reacting with reactive oxygen species or free
Vitamin C is important for the absorption of iron and
reduces ferric iron to its ferrous form and is beneficial in the
treatment of those suffering from the iron deficiency anaemia.
Vitamin C is vital for the function of the immune system
especially for the function of lymphocytes.
Vitamin C can be
prepared by synthesis from glucose or extracted from plant
sources such as rose hips, blackcurrants or citrus fruits.
are among the few mammals that can not synthesise their own
vitamin C, and so must ingest it.
Many foods are known for their
ability to provide a source of vitamin C, but a number of factors
- such as processing method, storage conditions, and exposure to
light and heat - determine how much is actually present by the
time the product is consumed.
In addition to its nutritional
benefits, vitamin C is used as a photographic developing agent in
alkaline solutions and is used industrially as a reducing agent
The history of vitamin C.
Vitamin C was first
isolated in 1928 by the Hungarian biochemist Albert
In 1937, Szent-Gyorgyi received the Nobel Prize in
physiology and medical science for discoveries in the area of
biological combustion processes, particularly with regard to
vitamin C and fumaric acid catalysis.
Linus Pauling was the first
to realise the value of vitamin C towards the maintenance of a
healthy immune system and, in 1970, proposed that a regular
intake at far higher levels than the recommended daily allowance
(RDA) could help prevent and shorten the duration of the common
The medical community immediately voiced their strong
opposition to this theory, but many ordinary people followed the
advice of Pauling and noticed a great reduction in the frequency
and severity of their colds.
Certain recent medical advice does
seemingly confirm Pauling's original idea that vitamin C can
markedly reduce the severity of a cold and help prevent secondary
viral or bacterial complications.
Vitamin C intake.
Community RDA of vitamin C currently stands at 60 milligrams per
All of us require vitamin C, but some people need more than
others - such as those that have low nutrient diets, who are at
risk from vitamin C deficiency.
Many elderly men consume low
levels of fruits and vegetables and are also at risk.
conducted have shown that 20% of elderly men have low levels of
In addition, smokers and those individuals exposed to
cigarette smoke generally have lower levels of vitamin C, and may
need to consume roughly twice as much vitamin C as non-smokers.
Good sources of vitamin C include broccoli, brussel sprouts,
cauliflower, cabbage, green leafy vegetables, red peppers,
parsley, blackcurrants, strawberries, kiwi fruit, guavas and
The highest amounts of vitamin C are found in
citrus fruits and green vegetables bu,t because vitamin C is
quickly lost in cooking and processing, fresh fruits are often a
better source of nutrients.
In food, vitamin C can be partially
or completely destroyed by overcooking or long periods of
storage, as it is sensitive to heat, light and oxygen.
recommended a vitamin C intake of 1000 milligrams per day or more
as opposed to the current RDA.
One should realise that the RDA is
not based on what is required for optimum health, but is the
amount required to avoid the most obvious deficiency disease.
Many eminent medical and scientific experts are of the opinion
that the value is currently too low to provide optimum health and
protection against disease, especially as evidence continues to
emerge about the important health benefits at higher levels than
those once considered adequate to prevent scurvy.
Vitamin C has
been used as an alternative therapy for many years and numerous
doctors do not hesitate to recommend doses of 1-5 grams per day
for certain individuals.
A team of researchers at the National
Institute of Health in the United States recently completed a
study to determine the vitamin C requirement of healthy, young
It was found that a minimum intake of 1000 milligrams per
day was required to completely saturate the blood plasma with
The studies recommended that the vitamin C should be
taken in several doses throughout the day, as urinary excretion
increased rapidly for doses above 500 milligrams.
The benefits of
The Scottish physician James Lind first advocated the
use of fresh vegetables and ripe fruits back in 1753 to prevent
scurvy, with the British Navy adopting his advice some 40 years
The navy men were later nicknamed Limeys as they took lime
juice on long sea voyages to ward off scurvy.
A severe deficiency
of vitamin C can lead to the onset of scurvy, a disease that
causes swollen gums, loose teeth, a tendency of wounds to not
heal and excessive bleeding as well as bone malformations in
Fortunately, scurvy is rare nowadays in the UK due to
the wide availability of foods that are rich sources of vitamin
Research conducted by the National Institute on Ageing
reported that elderly people who took vitamin C and E supplements
had a 50% lower risk of dying prematurely from disease than those
individuals that did not use such supplements.
have shown that an adequate intake of vitamin C is effective in
lowering the risk of developing cancers of the breast, cervix,
colon, rectum, lung, mouth, prostate, and stomach.
his colleagues at the Vale of Leven Hospital in Scotland carried
out clinical studies on cancer patients subjecting them to large
daily doses of vitamin C in addition to their regular treatment.
They concluded that cancer patients who received doses of greater
than 10 grams per day lived longer, suffered less pain and had in
general, a better quality of life than similar patients who did
not receive the vitamin C.
Pauling believed that vitamin C
combats cancer by promoting collagen synthesis and thus
preventing growing tumours from invading adjacent tissue.
researchers now believe that vitamin C prevents cancer by
deactivating free radicals before they can damage DNA and
initiate tumour growth, while others think that vitamin C acts as
a pre-oxidant helping the bodies own free radical defence
mechanism destroy tumours in their early stages.
mechanism, it seems apparent that vitamin C may be effective in
preventing cancer, alleviating its symptoms and in certain cases
halting its progress for some individuals.
The work of Pauling
and his peers concerning the benefits of vitamin C has not been
without controversy, and for many years has divided medical
opinion and it is not unreasonable to suggest that the debate
will continue for many more years to come.
Research published in
the medical journal Lancet found that a 500 milligram daily
supplement of vitamin C could significantly reduce high blood
pressure in hypertensive patients.
High blood pressure is a
serious health problem in much of the world and a key risk factor
in heart disease and strokes.
The studies, performed by Boston
University School of Medicine and Linus Pauling Institute at
Oregon University, found that vitamin C supplements reduced blood
pressure without side effects, were inexpensive, and could yield
reductions comparable to certain prescription drugs used to treat
Patients were given 500 milligrams of vitamin C
daily and after a month the systolic, diastolic and mean blood
pressures had decreased by about 9%, enough to reduce a
moderately high blood pressure back to a normal level.
Voltammetry - a brief overview.
Jaroslav Heyrovsky first
introduced the concept of polarography circa 1922.
voltammetry is applied to designate the current-voltage
measurement obtained at a given electrode.
Polarography is a
special case of voltammetry referring to the current-voltage
measurement acquired using a dropping mercury electrode with a
constant flow of mercury drops.
With the Metrohm Multi Mode
Electrode (MME), the mercury is hermetically sealed in the
reservoir and suffices for around 200,000 drops - ensuring low
laboratory running costs.
The Dropping Mercury Electrode (DME) is
an electrode mode of the MME.
It is the classical mercury
electrode where the mercury flows freely from the glass capillary
until the mercury drop is knocked off by a tapping mechanism
after each voltage step time set in the measurement mode.
polarographic determination of vitamin C.
suitable not only for the quantitative determination of organic
substances but also for a large number of organic compounds.
determining factors as to whether organic substances can be
determined in an aqueous medium depend primarily on the
functional groups that characterise the redox properties.
ascertain whether a redox reaction is possible at a given
potential window of the mercury drop and whether the
determination is based on the reduction or oxidation of the
The determination is based on the oxidation of ascorbic
acid to dehydroascorbic acid:.
C6H8O6 - C6H6O6 + 2e- + 2H+.
redox potential depends on the pH and without adequate buffering
the pH at the electrode surface can be displaced by the oxidation
reaction of the ascorbic acid leading to peak broadening.
Degradation of vitamin C in orange juice.
A report conducted by
the Journal of the American Dietetic Association recommended that
orange juice should be consumed as soon as possible after
purchase or making a can from frozen concentrate, as the vitamin
C content decreases the closer one gets to the expiry date.
study was performed by Arizona State University on different
brands of orange juice in different types of containers: with
screw top caps, those which open and close like traditional milk
cartons, and the frozen kind that are reconstituted with water.
The analysis found that generally frozen reconstituted orange
juice contained more vitamin C than ready to drink type juice,
and screw top containers contained more vitamin C at opening than
that found in milk-like containers.
The level of nutrient from
frozen concentrate fell from 65 milligrams per serving to 45
milligrams two weeks later, and after four weeks to about 36
milligrams - a fraction of the figure stated on the label.
Fortunately orange juice has plenty of other nutrients that do
not degrade so quickly, including folic acid, potassium, vitamin
A, and trace minerals, so plenty of other nutritional value is
being added to the human diet as orange juice is consumed by a
large majority of the western world on a regular basis.
concluded that the vitamin C content of orange juice was variable
and dependant on the variety and maturity of the oranges, fresh
fruit handling, processing factors and packaging.
ready to serve orange juices were found to contain typically 25%
less vitamin C per serving than frozen concentrates, caused in
part by heat destroying the vitamin C.
It is a fact the majority
of food manufacturers add considerably more vitamin C than the
labelled value to compensate for the losses that occur due to
Method for analysis of vitamin C in orange juice.
10ml of deionised water, 1ml of acetate buffer (pH 4.64) and
0.5ml of orange juice sample were added to the reaction vessel in
the Metrohm 757 VA Computrace.
The role of the electrolyte and
additional solutions in voltammetry is crucial as many
determinations are pH dependent and the electrolyte can increase
the conductivity and selectivity of the solution.
was then degassed with nitrogen for a period of five minutes to
remove the electrochemically active oxygen, before the vitamin C
content was determined with two standard additions using the DME.
Automation with voltammetry.
For a large numbers of samples it is
possible to automate the process of voltammetry through the use
of an autosampler, pump units and liquid dosing units known as
The Metrohm 813 compact autosampler allows fully
automatic precise, reproducible analysis of multiple samples of a
similar nature and can accommodate a maximum of 18 samples that
are transferred using a peristaltic pump to the measuring vessel
of the Computrace.
The analyte concentration is determined by
means of automatic standard additions carried out by Metrohm 765
After each sample the measurement vessel is emptied and
rinsed by two Metrohm 772 pump units.
The sample data is entered
into a sample queue that is automatically processed by the 757
Conclusion of analysis of vitamin C in orange juice.
The determination of vitamin C in a variety of food related
matrices has been well documented for the likes of fruit juices,
fresh produce and canned products.
The polarographic method is
straightforward, requiring no sample extraction or handling
unless the sample is in a solid form, saving the user time as the
usual procedure is simply to dilute the sample and then run the
Often these types of food products will contain
coloured material or dyes that generally do not interfere with
Over recent years, voltammetry has
undergone a tremendous surge in popularity and today represents a
refined, clean simple technique that offers outstanding limits of
detection and is now the fastest growing analytical technique for
trace analysis and is eminently suited to the vitamin C analysis
of orange juice.
Voltammetry is an increasingly popular technique
that in many instances offers unrivalled detection limits even
when compared to vastly more expensive analytical techniques.
samples of orange juice, then, voltammetry often requires little
or no sample preparation and the result determined by standard
addition obtained in less than ten minutes.
The advantage of
using standard addition as a means of calibration and
quantification is that matrix effects present in the sample are
taken into account.
Voltammetry requires no specialist laboratory
infrastructure like expensive fume extraction; all that is
required is a sturdy bench top on which to mount the instrument
and a regulated flow of an inert gas.
The running and maintenance
costs of voltammetry are minimal, ensuring a cost effective
analytical solution to surpass the demands required by those
organisations interested in quantifying the levels of vitamin C
present in orange juice.