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⁺ → 3I_{2 (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 + I_{2 (s)} → Dehydroascorbic acid + 2I _(aqua)

The excess iodine is then titrated against standard Sodium thiosulphate solution.

I_{2 (aqu)} + 2S₂O₃^2- _(aqu) → S₄O_{6 (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