AsDiscussion:
In this experiment, ascorbic acid content of apple fruit juice in different conditions was determined by indophenol dye method. The reduced form of ascorbic acid (which is also known as Vitamin C) were determined by this procedure. This was because ascorbic acid is a strong reducing agent. Ascorbic acid was extracted and titration performed in presence of metaphosphoric acid-acetic solution. When titrated with fixed amount of 2, 6-dichlorophenolindophenol red indophenol dye, it was oxidized to dehydroascorbic acid (Kumar et al. 2013). At the end of titration, the dye was reduced to a colourless compound. Thus, the reaction with end point was determined easily by observing the colour change in order to allow the calculation of ascorbic acid concentration.
Based on the calculation of my group results, the molarity of standardeized 2, 6-dichlorophenolindophenol was 8.0425×10-4M, the molarity of fresh fruit juice was 4.4234×10-3M, the molarity of bubbling fruit juice was 4.1821×10-3M and the molarity of bubbling and copper sulphate (CuSO4) fruit juice was 1.8095×10-3M. From the sample results, the mean of the molarity of standardeized 2, 6-dichlorophenolindophenol was 7.9825×10-4M ± 5.6551×10-6M , the mean of the molarity of fresh fruit juice was 4.3426×10-3M ± 4.9089×10-9M, the molarity of bubbling fruit juice was 4.0663×10-3M ± 2.9212×10-8M and the molarity of bubbling and CuSO4 fruit juice was 1.8095×10-3M ± 4.2885×10-9M.
Fresh fruit had the highest concentration of ascorbic acid compare to bubbling, and CuSO4 and bubbling fruit juice. This was because ascorbic acid can be oxidized easily by bubbling air process. The more access the juice to bubbling air, the greater the degradation of ascorbic acid which caused it no longer effective. Bubbling and CuSO4 fruit juice had the lowest concentration of ascorbic acid because the bubbling air and CuSO4 promoted the oxidation reaction. The CuSO4 dissociated in the fruit juice to give Cu2+ which oxidized ascorbic acid to dehydroascorbic acid. Cu2+ acted as an oxidizing agent which accepted electron from ascorbic acid and, in the process, indophenol dye was reduced to colourless compound (Aurelia et al. 2010).
The ascorbic acid content of fresh fruit juice was 46.35mg/100g, the ascorbic acid content of bubbling fruit juice was 43.40mg/100g and the ascorbic acid content of bubbling and CuSO4 fruit juice was 19.31mg/100g. The ascorbic acid content on fruit juice product was 15mg/100g. Fruit juice product had the lower ascorbic acid content than fresh, bubbling and CuSO4 fruit juice because ascorbic acid might be oxidized during the manufacture process. Ascorbic acid in fruit juice can be oxidized easily when undergo heat processing or exposed to the air.
This experiment utilized the reductive property of ascorbic acid. Acetic acid was added in the procedure of the experiment acted as stabilizing acid to delay the oxidation of ascorbic acid at high pH by inactivating the catalytic effects of ascorbic acid oxidase, copper and iron. It also maintained proper acidity condition to perform titration.
The precaution of this experiment was carried out the procedure with minimum delay since ascorbic acid can be oxidized easily when exposed to air. During titration, the indophenol dye was titrated to the fruit juice drop by drop to avoid the excess unreacted dye appeared as rose pink in acid solution. The end point of the titration was defined as pale pink coluor that persisted at least 15 seconds of swirling. Disadvantages of indophenol method to determine ascorbic acid content were unable to determine ascorbic acid and dehydroascorbic acid directly (Sanusi et al. 2009). Other pigment of substances might easily influence in the observation of titration endpoint. However, indophenol method was still an effective and sensitive way to determine ascorbic acid content under development and proper techniques.
References:
1. Aurelia, P., Andrei, F. D., and Slawomir, K., 2010. Ascorbic Acid Determination in Commercial Fruit Juice Samples. Journal of Automated Methods and Management in Chemistry, 8, 145-148. 2. Kumar, G. V., Ajay, K. K., Raghu, G.R., and Manjappa, S., 2013. Determination of Vitamin C in Some Fruits and Vegetables. International Journal of Pharmacy and Life Sciences, 4, 2489-2491. 3. Sanusi, R. A , Ogunro, Y., and Nwozoh S., 2009. Effect of Storage Time on Ascorbic Acid Content of Some Selected“Made in Nigeria” Fruit Preserves. Pakistan Journal of Nutrition, 7, 730-732.