COMPARATIVE STUDY OF VITAMIN C CONTENT IN SOME
FRUITS
Abstract: The project work deals with the
comparative study of Vitamin C (Ascorbic acid) content in some fruits. 5 species of commonly used citrus fruits such
as Orange, Grape fruit Lemon, Tomato and Pineapple were collected at the
ripening stage from an experimental field. Vitamin C content in fresh juice was
determined by two steps oxidation-reduction titration. The highest amount of
Vitamin C found in which fresh fruit juice is determined. The highest percentage of ascorbic acid was shown by orange followed by
lemon, grape fruit pineapple, and tomato.
*Key Words:
Ascorbic acid
Introduction
Vitamin C
(Ascorbic acid) is water soluble monosaccharide like substance. It is an
antiscorbutic agent and very essential to animals and human beings. It is
involved in certain metabolic process in them. Vitamin C is important for bones
and connective tissues, muscles, and blood vessels. Vitamin C also helps the
body absorb iron, which is needed for red blood cell production. Ascorbic acid is used to treat and prevent
vitamin C deficiency.
The
new name, ascorbic acid, is derived from a- (meaning "no") and
scorbutus (scurvy), the disease caused by a deficiency of vitamin C. Because it
is derived from glucose, many animals are able to produce it, but humans
require it as part of their nutrition. Other vertebrates which lack the ability
to produce ascorbic acid include some primates, guinea pigs, teleost fishes,
bats, and some birds, all of which require it as a dietary micronutrient (that
is, in vitamin form).
Ascorbic acid is
a naturally occurring organic compound with antioxidant properties. It is a
white solid, but impure samples can appear yellowish. It dissolves in water to
give mildly acidic solutions. Ascorbic acid was originally called L-hexuronic
acid. Chemical formula is C6H8O6 and molar
mass is 172.12g.mol-1 and have melting point 192˚C. In ascorbic acid
there is a keto-enol system is present.
Ascorbic acid is
classed as a reductone and it is a reducing agent.
Biochemical
functions of Vitamin C include interconversion of ascorbic acid and hydroascorbic
acid, collagen formation, bone formation, Iron and hemoglobin metabolism etc. The
objectives of this work were to determine the amount of ascorbic acid in
different fruits. 5 species of commonly used citrus fruits were collected at
the ripening stage from an experimental fieldThe highest amount of Vitamin C
found in which fresh fruit juice is determined.
Experimental
1.
Materials
Potassium iodate,
Potassium iodide, Sodium thiosulphate, Orange, Grape fruit, Lemon, Tomato and Pineapple.
Erlenmeyer
flask and burette.
2.
Sample preparation and testing
10 g of fresh
fruit were cleaned, chopped, into small pieces and passed through a juice
extractor. The juice was filtered through a whatsman paper No.1.The filtrate is
made up to 100 ml. The following standard solutions were prepared.
1)0.001 mol/dm3
potassium iodates solution.
2)0.005 mol/dm3
potassium iodide solution.
3)0.010 mol/dm3
sodium thiosulphate solution.
The Vitamin C
content in fresh juice was determined by oxidation –reduction titration. 2 ml
of potassium iodate solution (0.001 mol/dm3), 3ml of potassium iodide solution
(0.005 mol/ dm3), three drops concentrated H2SO4, three drops of starch
solution (as indicator) in a small Erlenmeyer flask, 1ml of fresh juice from
the made up solutions was added to the mixture, then swirled gently and was
directly titrated with Sodium thiosulphate solution.(0.010 mol/dm3).The
disappearance of the deep blue-black color makes the end point. A blank
titration was performed prior titration of each sample. Vitamin C content was
calculated based on the volume of Sodium thiosulphate delivered during the
titration.
Calculations
Ascorbic acid
(corresponding fruit juice) × Sodium Thiosulphate (Starch)
|
Volume of fruit juice (ml)
|
Burette reading (ml)
|
Volume of Sodium Thiosulphate (ml)
|
|
|
Initial
|
Final
|
||
|
|
|
|
|
|
|
|
|
|
Volume of Sodium
Thiosulphate solution used for blank titration = 3.6 ml
Volume of
unreacted Sodium Thiosulphate solution = - ml
Volume of
reacted Sodium thiosulphate solution
= 3.6 – -= - ml
Normality of
Sodium Thiosulphate solution = - N
1ml of 1N Sodium
Thiosulphate solution = 1 ml of 1N ascorbic acid
Therefore,
weight of ascorbic acid in the whole of the given solution
= - × 100/ 1000=
- g
% of ascorbic
acid in lemon = - × 100/10 = -%
Results and
discussion
The method is
based on oxidation of ascorbic acid to dehydroascorbic acid by iodine was used
for determination of Vitamin C content in fresh juice. A known amount of iodine
is generated by the reaction between iodates, iodide and sulphuric acid.
IO3-
+ 5I- (aqu) + 6H+ → 3I2 (s) +
3H2O
A measured
amount of fruit juice is added. The ascorbic acid reacts quantitatively with
some of the iodine as the iodine in excess.
Ascorbic acid +
I2 (s) → Dehydroascorbic acid + 2I (aqua)
The excess
iodine is then titrated against standard Sodium thiosulphate solution.
I2 (aqu) +
2S2O32- (aqu) → S4O6
(aqu) + 2I (aqu)
The validated
method was employed for determinations of Vitamin content in 5 fresh fruit
juice. Fruits in this study contained varied amount of Vitamin C. The results
were shown in Table: 2
Percentage of
ascorbic acid in different Fruits
|
No
|
Samples
|
Titre value (ml)
|
Wt. of ascorbic acid (mg)
|
Weight of sample (g)
|
% of Ascorbic acid
|
|
1.
|
Orange
|
2.5
|
193.78
|
10
|
1.9378
|
|
2.
|
Lemon
|
2.9
|
123.29
|
10
|
1.2329
|
|
3.
|
Tomato
|
3.4
|
35.22
|
10
|
0.3522
|
|
4.
|
Grape fruit
|
3.1
|
88.07
|
10
|
0.8807
|
|
5.
|
Pineapple
|
3.3
|
52.42
|
10
|
0.5242
|
From the table: 2
we see that sample orange contain the highest % of ascorbic acid approximately
1.9378% i.e. it contain the highest vitamin C content, lemon contains 1.2329%,
grape fruit contain 0.8807%, pineapple contain 0.5242% and tomato contain
0.3522%. In order to higher intake of Vitamin C from daily diet, eating fruits
with higher amount of vitamin is recommended.
Conclusion
The entire work
deals with the comparative study of Vitamin C content in some fruits. The different
types of fruits used were Orange, Lemon, Tomato, Grape fruit and pineapple. The
vitamin C content was calculated based on the volume of sodium thiosulphate
delivered during the titration. The Vitamin C content in fresh juice was
determined by oxidation reduction titration.
The method based
on oxidation of ascorbic acid to dehydroascorbic acid by iodine was used for
determination of vitamin C content in fresh juices. A known amount of iodine is
generated by the reaction between iodates, iodide and sulphuric acid. The
excess iodine is then titrated against standard sodium thiosulphate solution.
The validated method was employed for determination of vitamin C content in
fresh fruit juices
The highest
percentage of ascorbic acid was shown by orange (1.9378%) followed by lemon
(1.2329%), grape fruit (0.8807%), pineapple (0.5242%) and tomato (0.3522%).
Reference
1.
Organic
chemistry: I.L Finar, Logmans Scientific and technical, London
2. Essential
of Biochemistry: U. Sathyanarayana, Arunbhasen Books and Allied (P) Ltd.
Kolkatha 700009
3.
Chemistry:
An Inidan Journal1 (9) 2004-650-652
