Title: The Vitamin C content of fruit juice Aim: To investigate the vitamin C content of fruit juice. Introduction: [2]Vitamin C, also known as the ascorbic acid or the L-ascorbate, is required for the growth and repair of tissues in all parts of our body. It is necessary to form collagen, an important protein used to make skin, scar tissue, tendons, ligaments, and blood vessels. Vitamin C is essential for the healing of wounds as well as for the repair and maintenance of cartilage, bones, and teeth.
Vitamin C is one of many antioxidants. It blocks some of the damages caused by free radicals, which are by-products that result when our bodies transform food into energy. It also helps reduce the damage to the body caused by toxic chemicals and pollutants such as cigarette smoke. The body does not manufacture vitamin C on its own, nor does it store it. It is therefore important to include plenty of vitamin C-containing foods in our daily diet. All fruits and vegetables contain some amount of vitamin C.
Foods that tend to be the highest sources of vitamin C include green peppers, citrus fruits and juices, strawberries, tomatoes, broccoli, turnip greens and other leafy greens, sweet and white potatoes, and cantaloupe. Other excellent sources include papaya, mango, watermelon, Brussels, sprouts, cauliflower, cabbage, winter squash, red peppers, raspberries, blueberries, cranberries, and pineapples. Vitamin C is sensitive to light, air, and heat, so we will get the most vitamin C if we eat fruits and vegetables raw or lightly cooked.
In this experiment, we will look into the difference in vitamin C content between fresh fruit juices and commercial fruit juices, where the manufacturers always claim that their juices restore the vitamin C contained in fresh fruits, thus the same amount of vitamin C is available in packaged fruit juices. We can purchase either natural or synthetic vitamin C, also called ascorbic acid, in the forms of tablets, capsules, chewable, powdered crystalline, effervescent, or liquids. Vitamin C can be purchased in dosages ranging from 25 – 1,000 mg. Buffered” vitamin C is also available if you find that regular ascorbic acid upsets your stomach. An esterified form of vitamin C is also available, which may be easier on the stomach for those who are prone to heartburn. As recommended, the best way to take vitamin C supplements is 2 – 3 times per day, with meals, depending on the dosage. Some studies suggest that adults should take 250 – 500 mg twice a day for any benefit. It is advisable to talk to our doctor before taking more than 1,000 mg of vitamin C on a daily basis and before giving vitamin C to a child.
Though vitamin C is water-soluble and we can get rid of it easily, we must however practice some precautions when taking vitamin C. Vitamin C supplements have a diuretic effect, so we should drink plenty of fluids when taking them. Most commercial vitamin C is made from corn. People sensitive to corn should look for alternative sources, such as sago palm. Vitamin C increases the amount of iron absorbed from foods. People with hemochromatosis (an inherited condition where too much iron builds up in the body) should not take vitamin C supplements.
While vitamin C is generally considered safe because our body gets rid of what it does not use, in high doses (more than 2,000 mg daily) it can cause diarrhea, gas, or stomach upset. If we experience these side effects, it is time to lower the doses. People with kidney problems should talk to their doctor before taking vitamin C. People who smoke or use nicotine patches may need more vitamin C because nicotine decreases the effectiveness of vitamin C in the body. Infants born to mothers taking 6,000 mg or more of vitamin C may develop rebound scurvy because their intake of vitamin C drops after birth.
Too little vitamin C can lead to signs and symptoms of deficiency, including: dry and split hair, gingivitis (inflammation of the gums), bleeding gums, rough, dry, scaly skin, decreased wound-healing rate, easy bruising, weakened tooth enamel, swollen and painful joints, Anemia, ability to fight infection, and possible weight gain because of slowed metabolism. A severe form of vitamin C deficiency is known as scurvy, which mainly affects older, malnourished adults. [3]In this experiment, we are going to find out which fruit juice provides the most amount of vitamin C.
We will use a blue substance called 2, 6-dichlorophenolindophenol (or DCPIP for short) as a reagent to test for vitamin C. It acts as an indicator where it changes from blue to pink with acids but loses its color in the presence of certain chemicals, one of which is ascorbic acid (vitamin C). DCPIP solution can be used to test for the presence of vitamin C in foods (but not for other vitamins which are entirely different kinds of chemical). It is an electron acceptor that is blue when oxidized and colorless when reduced. It is part of the Hill reagents family.
DCPIP is commonly used as a substitute for NADP+. The dye changes color when it is reduced, due to its chemical structure. The nitrogen atom in the center of the molecule is the atom that accepts electrons, and it changes the double N-C bond to a single bond, which forces bonds between carbons in the entire left ring to change. This microscopic shift in the DCPIP structure causes the macroscopic change in color, from dark blue to colorless. If vitamin C, which is a good reducing agent, is present, the blue dye, which turns pink in acid conditions, is reduced to a colorless compound by ascorbic acid.
Thus, DCPIP is a good indicator to test for the presence of vitamin C. It is important to take note that in a titration, when all the ascorbic acid in the solution has been used up, there will not be any electrons available to reduce the DCPIPH and the solution will remain pink due to the DCPIPH. The end point is a pink color that persists for 10 seconds or more. Here is the 2-D structure of DCPIP: The other name of DCPIP is 2,5-cyclohexadien-1-one; its molecular formula is C12H7NCl2O2 and its molar mass is 268. 1 g mol? 1 Y. Problem statement: Which type of fruit juice provides the most vitamin C?
Hypothesis: Lime juice provides the most vitamin C. Variables: Manipulated variable: The type of fruit juice used Responding variable: The volume needed to decolourise 0. 5ml of 1% DCPIP solution Fixed variable: The volume of 1% DCPIP solution (0. 5ml) Apparatus: syringes, test tubes, beakers, knife, white tile, test tube rack, glass rod Materials: fruit juice samples (artificial lime juice, orange juice, and star fruit juice), fresh fruits (orange, lime, and star fruit), vitamin C tablets (2000mg, 1500mg, 1000mg, 500mg, and 250mg), 1% DCPIP solution, distilled water, tissue paper.
Procedure: 1. 100ml of water is measured using a measuring cylinder and poured into a beaker. 2. Then, a 2500mg vitamin C tablet is put into the beaker and dissolved in the water using a glass rod to prepare the standard vitamin solution. 3. Steps 1 and 2 are repeated using 1000mg, 500mg, 250mg and 125mg vitamin C tablets respectively. Then, 20ml of each standard vitamin solution is measured out using a measuring cylinder and poured into a beaker. 4. 0. 5ml of 1% DCPIP solution is measured using a syringe into a test tube.
Then, slowly, each standard vitamin solution is added into the DCPIP solution, drop by drop, using another syringe, starting from the 2000mg standard vitamin solution and so on. A new syringe is used each time for each vitamin solution respectively. The volume of solution needed for the DCPIP solution to decolorize is observed and recorded. A table is tabulated. 5. Then, 0. 5 ml of 1% DCPIP solution is measured into a test tube using a syringe. Using another syringe, artificial star fruit juice is added into the DCPIP solution. Similarly, the volume of the fruit juice needed for the DCPIP solution to decolorize is observed and recorded. . Step 5 is repeated using artificial orange juice, artificial lime juice, fresh star fruit juice, fresh orange juice and fresh lime juice. The fresh juices are prepared in the beakers by squeezing the respective fruits, on the spot. Each time, a new syringe is used for a different fruit sample to avoid mixing. 7. All results are tabulated in a table. A graph of volume needed to decolourise 0. 5ml of 1% DCPIP solution against concentration of vitamin C is drawn. The vitamin C content of each fruit juice is determined using the formula as shown below:
Vitamin C content of fruit juice (%) = concentration of 1% standard vitamin C solution (%) x volume needed to decolourise 0. 5ml of 1% DCPIP solution (ml) volume of fruit juice used (ml) Result: 1. Table of standard vitamin C solution and volume needed to decolorize 0. 5ml of 1% DCPIP solution Standard vitamin C solution(%)
It acts as an indicator where it changes from blue to pink with acids but loses its color in the presence of certain chemicals, one of which is ascorbic acid (vitamin C). DCPIP solution can be used to test for the presence of vitamin C in foods (but not for other vitamins which are entirely different kinds of chemical). It is an electron acceptor that is blue when oxidized and colorless when reduced. In the action of DCPIP as an indicator for ascorbic acid, vitamin C is a good reducing agent. The blue dye, DCPIP which changes its color to pink when in acidic conditions, becomes colorless when it is reacted with ascorbic acid.
Hence, the solution does not turn colorless, but it remains pink due to the presence of DCPIPH. The pink color, or the end point, remains for about 10 seconds or more. The vitamin C 2-D structure The DCPIP 2-D structure As represented in the diagram below, nitrogen accepts electrons, changing the double N-C bond into a single bond, so forcing bonds in the left ring to change. This microscopic change in the structure of DCPIP brings about a macroscopic change in color – dark blue to colorless. A formula can be used to calculate the vitamin C content of the fruit juices.
Here is the formula: Vitamin C content of fruit juice= concentration of 1% standard vitamin C solution (%) x volume needed to decolourise 0. 5ml of 1% DCPIP solution (ml) volume of fruit juice used (ml) Based on the result, the volume needed to decolorize 0. 5ml of 1% DCPIP solution is the least for artificial orange juice. This means that it has a high level of ascorbic acid. Due to the high level of ascorbic acid which is a good reducing agent in orange juice, the volume needed to decolorize 0. 5ml of 1% DCPIP solution is the least, when compared to other fruit juices.
When compared to other juices, its vitamin C content is the highest. This proves why orange juice is much more sour in taste compared to other juices, due to the presence of hydrogen ions, representing the acidic properties of ascorbic acid. Artificial orange juice has a higher vitamin C content because its vitamin C content can be controlled by the manufacturer. The fresh fruit juices should have a higher content of vitamin C, logically, but due to some loss of vitamin C in the process of preparing the fruit juices, as a result, its vitamin C content decreases. Sources of error:
There may be parallax error which results in an inaccuracy of result. Besides, the end point of a titration for this reaction is difficult to ascertain due to the lack of complete decolourisation of the DCPIP. The brands of manufactured fruit juices used are different. This may result in a difference in the vitamin C content. The fruits are squeezed using bare hands. Vitamin C is prone to heat and oxidation. A lot of vitamin C might have been lost in the process. The star fruit used in the experiment is not ripe enough; this may affect the vitamin content in it and cause a difference in the result.
We can see from the result that it cannot decolorize the 0. 5ml of 1% DCPIP solution. Maybe this is the reason why. Safety precautions: A lab coat is to be worn at all times when conducting the experiment. The dark blue color of the DCPIP solution stains clothes. Lab coats should be taken off when leaving the laboratory to avoid the transfer of chemical substances outside the laboratory. Covered low-heeled shoes are also to be worn to protect our feet from any corrosive or toxic chemicals in the laboratory. Long hair must be tied up neatly.
Work table should be free of clutter to minimize the chances of spillage of chemicals and breakage of laboratory apparatus. Wash hands thoroughly after completing the experiment. Do not consume food used for the experiment or even our own food in the laboratory because it may be contaminated by chemical or toxic substances. Be careful when utilizing a knife to avoid injury. Limitations: There is a lack of fruits, therefore a lack of fruit juice samples. There should be a blending machine to squeeze the fruits instead of using bare hands to do so.
Using hands produces more heat and this may affect the vitamin C content in the juices. There is also a lack of time to carry out the whole experiment properly. Some of the steps are not done precisely. Modifications: [1]Since the end point of a titration for this reaction is difficult to ascertain due to the lack of complete decolourisation of the DCPIP, we may use starch-iodine in place of DCPIP solution. The ability of ascorbic acid to interfere with the starch-iodine reaction has been noted elsewhere. The materials needed and the respective steps are as follow: -Iodine 0. g dissolved in 100ml of 1% potassium iodide solution (approximately 0. 02 moles dm-3 Iodine in 0. 06 moles dm-3 KI) -0. 1% Starch solution 1. 1ml of starch is placed in a suitable receptacle and 1 drop of iodine solution added. 2. The ascorbic acid solution is then added drop wise until the blue-black color of the starch iodine complex disappears to leave a colorless solution. The above amounts were completely decolorized by 150? l of 0. 05% ascorbic acid and also by a few drops of fresh orange juice. The ascorbic acid reduces the iodine to iodide so it no longer forms the starch-iodine complex.
Reduction of iodine might also be the mechanism by which rinse aid inhibits the same reaction and thus be related to the findings of Hadi-Talab and Levinson (2000). This titration enables quantitative comparisons to be made. We should use the same brand of manufactured fruit juices. Use ripe fruits instead of unripe ones. Star fruit juice is difficult to be prepared due to the limitation of equipment, another type of fruit should be used instead. For example: watermelon. Conclusion: The vitamin C content of artificial orange juice is the highest among the other fruit juices used in the experiment. The hypothesis is rejected.
Reference:
- Hadi-Talab, R. and Levinson, R, (2000) Rinse-aid and the starch-iodine reaction SSR 81 99-101 Samotus, B. , Doerre, E. , Swiderski, A. , and Scigalski, A. , (1994)
- Photometric starch-iodine determination in plant materials as influenced by ascorbic acid – critical remarks. Acta Societatis Botanicorum Poloniae 63 49-52. Sharma, S. S. , Sharma, S. , and Rai, V. K. (1990)
- Interference of ascorbic acid with the starch-iodine reaction. Annals of Botany 65 281-283 Think Quest http://library. thinkquest. org/2690/exper/exp28. htm Safety
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