Lab Report

Discussion

From our experiment, we used an average of 5.60 ml of standard ascorbic acid solution for fully titration of 2.00 ml dye solution. While for 0.50 ml of dye, average volume of ascorbic acid used was 1.40 ml. We stop the titration when the dye solution has turned from dark blue to red and in the end to colourless.  

For titration of 2.00 ml dye solution with 50.00 ml citrus fruit juice, we used an average of 10.20 ml of citrus fruit juice for fully titration. From this result, we further calculate and found out that ascorbic acid present in citrus fruit juice is 54.90mg/100g. The vitamin C found in the citrus fruit juice is lower when compared to the vitamin C found in standards. Usually there is only 40-45 mg of ascorbic acid present in 100ml of citrus juice (Fennema, 1996). Many factors will contribute to different amount of ascorbic acid present in food sample, and source of the food will be one. Besides, processing process may either increase or decrease the amount too. Extremely high temperature and oxidation will decrease ascorbic acid content in food by destroying its structure (Fennema, 1996).

For the sample of raw cabbage, we used an average of 32.00 ml of raw blended cabbage juice for fully titrate 2.00 ml dye solution. By calculation with the result obtained, the ascorbic acid present in raw cabbage is 17.50 mg of vitamin C per 100g sample. The cabbage had been peel and blend into mashed form before we started our experiment. This preliminary treatment could cause loss of vitamins such as ascorbic acid, folate and thiamin.

        For titration of 0.50 ml dye solution with 25 ml of boiled cabbage sample juice, we only used 0.14 ml of boiled cabbage juice to complete the titration. In further calculation, there was 3.28 mg of vitamin C per 100 g of sample. In order to certify there was an aqueous extraction occurred during blanching of cabbage, we ran the titration for the blanching water used as well. From the result determined, we used 0.14 ml of blanching water to completely titrate 0.5 ml of dye solution. The amount of vitamin C found in the blanching water for cabbage after calculating was 4.07 mg per 100g sample. This amount indicated that the amount of vitamin C lost from the cabbage during blanching. The high amount of losses might due to the overheating and destroyed of cabbage cell tissues during sample preparation. Besides, the vitamin C or ascorbic acid has high solubility with water or able to dissolve in water. Thus, when we cooked the cabbage, the ascorbic acid (vitamin C) will diffuse out to the boiling water and automatically dissolved in it.