Determination of the age of Guava from the Oxalate Ion and Ascorbic Acid contents and the determination of the rate of change of Oxalate Ion and Ascorbic Acid contents with respect to the age of Guava

Dr. Dileesh S¹*, Alfiya Nasser A², Linju Baby², Tins George²

¹Assistant Professor, Department of Chemistry, St. Peter's College Kolenchery,

Ernakulam, Kerala, India-682311

²Department of Chemistry, St. Peter’s College, Kolenchery,

*Corresponding Author E-mail: sukumarandileesh@gmail.com, sdileesh@rediffmail.com

ABSTRACT:

The oxalate ion and ascorbic acid concentrations of the matured guava fruit at different stages of ripening were determined using reported procedures. The oxalate ion content was found to increase and the ascorbic acid content was found to decrease with the aging of the fruit. From the plot of oxalate ion concentrations and ascorbic acid concentrations against number days, the approximate age of the matured guava bought from market is determined by measuring their oxalate ion t and ascorbic acid contents. The age of the guava obtained by the oxalate and ascorbic acid methods were found to be almost the same making a chance of a linear relationship between the conversion of ascorbic acid to oxalate ion. This linearity is proved by plotting the concentration of ascorbic acid against the concentration of oxalate ion. An approximate study of rate of change of oxalate ion and the ascorbic acid contents were also determined from the standard plots of oxalate ion and ascorbic acid.

KEYWORDS: Guava, Rate, Kinetics, Ascorbic acid, Oxalate ion, Vitamin C.

INTRODUCTION:

Guava (Psidium guajava) is widely present in all most all parts of India. It is rich in ascorbic acid (Vitamin C), Vitamin B and other minerals and is considered as a healthy food. But being an oxalate rich fruit the over intake of it may cause the formation of Kidney stone in people. The potential antioxidant property of Guava is reported by L. Y. Yan et.al.¹ and J. Gull et. al.² It is already reported by several studies that the oxalate content in guava increases as it get ripens with a corresponding decrease in the ascorbic acid (Vitamin C) content^3,4,5 Various mechanisms are suggested for the increase of oxalate content in Guava.

Some of the various reasons are the chance of the incomplete oxidation of glucose to oxalate ion, or in the respiratory Krebs cycle the oxaloacetic acid formed may be converted to oxalate ion, or the ascorbic acid present in Guava is converted to oxalate ion^6,7

In this paper we have the oxalate ion concentration and ascorbic acid concentrations at various ripening stages of matured Gauva by reported procedures^8,9 We have observed that the oxalate ion content increases and ascorbic acid content decreases with ripening of guava. Using the standard plots of oxalate ion content and ascorbic acid contents against the age of the guava, the approximate age guava bought from the market is determined. It is also found that there is linear correlation between the decrease in the concentration of ascorbic acid and the increase in the concentration of the oxalate ion. From the concentrations oxalate ion and ascorbic acid against the age of the guava, approximate rates of variation of oxalate ion and ascorbic acid were also measured.

MATERIALS AND METHODS:

The matured guava for the standard study was collected from plant directly. The matured guavas under study were collected from the market. All chemicals were purchased from Merck and used after purification.

Estimation of oxalate ion and ascorbic acid:

The amount of oxalate ion was determined by titrating a 50 g of guava extract with standard potassium permanganate and that of ascorbic acid was determined by titrating against standard iodine solution by reported procedures.^8,9

RESULTS AND DISCUSSION:

The oxalate ion and ascorbic acid concentrations of the matured guava fruits at different stages are summarized in Table 1. Both oxalate ion content and ascorbic acid content were found to equal to the already reported values. The oxalate content increased from 5-9 g/litre(5-9g/50 g of Guava) and ascorbic acid concentration decreased from 71 to 36 mg/litre (71-35mg/50 g of Guava) as the guava gets ripened.

Table 1: The amount of oxalate ion and ascorbic acid concentrations of matured guava at different ripening stages. ascorbic acid

Guava	Oxalate ion (g/litre)	Ascorbic acid (mg/50 g)
2 days old	5.095	88
6 days old	6.345	71
10 days old	8.747	36

From the data it is seen that the oxalate ion concentration increases while the ascorbic acid concentration decreases as the fruit get ripens. Similarly we have determined the oxalate ion and ascorbic acid concentrations the three varieties of guavas (G1,G2,G3) purchased from the markets (Table 2). From these values the approximate age of the guavas were determined from the standard plots of oxalate ion concentration (Graph 1) and ascorbic acid concentration (Graph 2) against the age of the standard guava. Both of the plots obeyed linear fit.

Table 2: The amount of ascorbic acid and oxalate ion concentrations and the age of matured guava bought from the Market

Guava	Oxalate ion (g/litre)	Ascorbic acid (mg/50 g)	Age of matured guava by using xalate ion as standard	Age of matured guava by using ascorbic acid as standard
G1	7.035	57	7 days	8 days
G2	6.825	65	6 days	6 days
G3	7.733	58	8 days	7 days

The age of the matured Guava collected from the market varied from 6 to 8 days after plucking from the plant. The age obtained using oxalate ion plot and ascorbic acid plots were almost equal indicating that there is linear relation between the increase in the concentration of the oxalate ion and decrease in concentration of ascorbic acid. This linear relationship is proved by plotting ascorbic acid concentration against oxalate ion concentration as shown by graph 3.

Graph 3. The variation of ascorbic acid with that of oxalate ion

From the graph it is seen that ascorbic acid content decreases by 14 mg for every 1 g increase of oxalate ion.

A kinetic study of the rate of increase of oxalate ion and rate of decrease of ascorbic acid with respect to the age of the guava was also studied from graph 1 and graph 2.

Graph 1 is a straight line with equation y= 0.456 x + 3.99. The slope is positive, dy/dx = 0.456g/litre/ day indicating the oxalate ion concentration increases with time. i.e. the oxalate ion concentration increases by 0.456 g/litre/day. The intercept 3.99 g/lire gives an idea about the amount of oxalate ion when the matured guava plucked from the plant. Graph 2 is a straight line with equation y= -6.5 x + 0.104. So the slope is dy/dx = -6.5mg/day. i.e. the ascorbic acid concentration decreases by 6.5 mg/day. The intercept 104mg/50 g gives an idea about the amount of ascorbic acid present when the matured guava plucked from the plant.

CONCLUSIONS:

The oxalate concentration in the matured guava at different stages it’s ripening was determined by permanganometric titrations and the ascorbic acid concentration was determined by iodometric titration. The increase in the oxalate ion content and decrease in the ascorbic acid content followed a linear relationship. From the standard oxalate ion plot and ascorbic acid plot, the age of three varieties of guava purchased from the market was determined and it is found that the age of the three varieties were almost same. A kinetic study on the variation of oxalate ion and ascorbic acid ion concentration with respect to the age of the guava shows that and oxalate ion concentration increases with a rate 0.456g/litre/day and the ascorbic acid concentration decreases with a rate 6mg/50g/day.

ACKNOWLEDGEMENTS:

The author wishes to thank all the faculty members of Department of Chemistry, St. Peter's College Kolenchery for the constant support for doing this project.

REFERENCES:

1. Yan, L. Y; Teng, L. T. Jhi, T. J. Sunwaway Academic Journal, 3,2006,9-20.

2. Gull, J., Sultana B., Anwar F., Naseer, R., Ashraf, Ashrafuzzaman M. Molecules, 17,2012,3165-3180.

3. Muhammad I., Ibrahim, S. A., Kanoma A. I., Sani I., Garba S. International Journal of Agriculture, Forestry and Fisheries, 2(3), 2014, 60-65.

4. Navis, M. S., Subaila S., International Journal of Advanced Science and Research,2(1), Jan 2017,15-17.

5. Bashir H. A., Abu-Bakhr A., Abu-Goukh, Food Chemistry, 80,2003,557-563.

6. Prasad R., Shivay Y. S. Current Science,112(8),2017,Apr(25),165-67.

7. Curtin H,, Journal of Biological Chemistry,1955,539-48

8. www.titrations.info/iodometric-titration-Vitamin-C

9. 9.http://www.academia.edu/4089338/Experiment_report_file_of_amount_of_oxalate_ion_in_a_Guava

Received on 20.07.2017 Modified on 20.08.2017

Asian J. Research Chem. 2017; 10(5): 657-659.

DOI: 10.5958/0974-4150.2017.00111.0