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Vitamin C content of fruit juices

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Title : The vitamin C content of fruit juice Objective : To investigate and compare the vitamin C content in various fruit juice Introduction: Vitamins are a group of complex organic compounds which play an essential role in animal metabolic processes but which the animal cannot synthesise. Vitamins do not provide energy however, in their absence, the animal develops certain deficiency diseases or other abnormal conditions. Vitamins together with proteins, carbohydrates, fats and mineral salts are essential constituents of the food of animals. Certain animals can synthesise certain vitamins. All animals which require vitamin D can synthesise it from ergosterol1 in the presence of U.V light. With the exception of vitamin D, the human body cannot make its own vitamins, and some cannot be stored. Therefore, one must obtain vitamins from a food on a daily basis. A person's diet must provide all the necessary vitamins. Vitamin C or Ascorbic acid is a water-soluble vitamin. Vitamin C cannot be stored by the body as it is not a fat-soluble vitamin. Excess vitamin C leaves the body through the urine. Thus, we need a constant supply of vitamin C in our diet. The chemical compound of vitamin C is C6H8O6 while its IUPAC name is 2-oxo-L-threo-hexono-1,4-lactone-2,3-enediol. Image 1: 3D structure of vitamin C 2 Image 2: 2D structure of vitamin C 3 Vitamin C is essential for the growth and repair of tissues. ...read more.


10. The volume of 0.125g/100ml vitamin C solution required to decolourise the DCPIP solution is observed and recorded in a table (Table 1). 11. Steps 7 to 10 are repeated two times for each concentration of vitamin C solution and the average of the result is obtained. 12. Steps 7 to 11 are repeated by using vitamin C solution of concentration 0.250g/100ml, 0.500g/100ml, 0.750g/100ml and 1.000g/100ml. 13. The results are tabulated and a graph of vitamin C required to decolourise DCPIP solution against concentration of vitamin C solution is plotted (Graph 1). B) DETERMINATION OF VITAMIN C CONTENT OF FRUIT JUICE 1. Fresh orange is squeezed to prepare fresh orange juice. 2. This procedure is repeated with the fresh lime and fresh star fruit to prepare fresh lime and fresh star fruit juice. 3. 0.5ml of 1% DCPIP is measured by using a 3ml syringe and placed in a test tube. 4. 3ml of the prepared fresh orange juice is measured using a clean 3ml syringe. 5. The fresh orange juice is added drop by drop into the test tube containing the DCPIP solution until the DCPIP solution has been decolourised. 6. The volume of fresh orange juice required to decolourise the DCPIP solution is observed and recorded in a table. ( Table 2) 7. Steps 3 to 6 are repeated two times for each type of fruit juice and the average of the result is obtained. ...read more.


Each experiment carried out is also repeated twice or thrice to ensure the reliability of the result. The average value for each type of fruit juice is determined by dividing the sum of all the reading for that particular fruit juice by the number of readings taken. By repeating the same procedure, random errors such as parallax error can be minimized. The content of vitamin C of each type of fruit juice can be determined more accurately and may be closer to the theoretical value. A syringe with a needle or a smaller scale such as a 1ml syringe may also be used to improve the accuracy of the volume of vitamin C solution or fruit juice used. This is because an instrument with a smaller scale is more precise than an instrument with a bigger scale. Safety Precautions: The experiment must be carried out in a careful manner. A lab coat should be worn to prevent clothes from being stained dark blue by the DCPIP solution. Closed shoes should be worn in the lab to provide adequate protection in case of any mishaps. When cutting the tablet into smaller parts, the knife should be handled with care. Conclusion: The lower the volume fruit juice used to decolourise the DCPIP solution, the higher the concentration of vitamin C in the fruit juices. Orange juice contains the highest amount of vitamin C when compared with lime juice and star fruit juice. The hypothesis is accepted. ...read more.

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The writer has produced a clear and well-written account of an investigation into relative vitamin C concentrations in fresh and commercial fruit juices. While much of the report reflects good scientific practice, there were, however, a number of shortcomings that need to be addressed before this can be considered A-grade standard work. [1] The choice of juices to be tested needed to be justified. Furthermore, data from manufacturers together with researched values for vit. C concentrations in these juices should have been discussed prior to testing. [2] The hypothesis was not fully supported by research. [3] Controlled variables were not fully identified and dealt with. [4] The method used to construct a standard curve was very inaccurate - although this was commented on in the evaluation. [5] Anomalies were not identified. [6] The discussion of results was rather brief and did not really address the difficulties of comparing fresh and commercial juice. These are common weaknesses in investigation reports and students aiming for the higher grades need to address all these issues in their work. In this particular case, it would take a relatively small effort on the writer's part to rectify the shortcomings and turn this into a high quality piece of A'Level work.

Marked by teacher Ross Robertson 10/04/2013

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