Table 5.
Mass of ascorbic acid in serving of sample orange juices and corresponding Daily % values
(Using class average data)
Table 6.
Mass of ascorbic acid in serving of sample orange juice &corresponding daily % values
(Using my data)
Table 7.
Cost per litre of sampled orange juices
Table 8.
Calories and sugar content of varies samples of orange juice
Based on lab data, cost per litre, and nutritional information Tropicana Pasteurized “100% pure squeezed Orange Juice” is the best choice. This is because based on the results found in Table 8 Tropicana contains the fewest calories and second lowest sugar content, therefore making it a healthier choice. Tropicana also is shown to have the second highest vitamin C content based on the lab results (see table 5). Tropicana is also reasonably priced at $2.79 per litre which allows you to consume four servings. The only other comparable juice when considering lab data and nutritional information is fresh squeezed orange juice, as it comes out to be better than Tropicana in those regards. Where Tropicana becomes the best choice is when comparing the prices $2.79 per litre compared to $6.66 per litre fresh squeezed. Also when considering the convenience of the store bought Tropicana verse the effort and time taken into juicing fresh oranges Tropicana clearly is the better choice.
Only pulp free orange juices were tested because, pulp itself contains ascorbic acid which would then alter the amount of vitamin c found in juice. Pulp is also a solid and would not be able to account for its volume in solution to correlate to the titrated volumes therefore the experiment would not be accurate.
Twenty-four juiced navel oranges would be needed to make one container of Tropicana orange juice. No this is not a reasonable amount of oranges, considering that if Tropicana actually used that many oranges in their product the vitamin C content would be much higher as we can see from the lab results in Table 4, fresh orange juice contains a significantly higher amount of ascorbic acid. Also the cost would be as high as $11.98 per carton to make. The retail value of one carton of Tropicana is $4.89 therefore it is impossible that Tropicana contain only freshly squeezed juice.
There are significant differences to store bought orange juice and freshly squeezed juice most if not all can be explained by how the juices are processed. Store bought orange juice is pasteurized, meaning it is heated to a certain temperature to kill off bacteria and then cooled back down. This process disrupts the biological molecules found in fresh orange juice i.e. denaturation. Store bought orange juice is also stored in large containers for long periods of time unless the juice is stored in a vacuum the juice is exposed to air and oxidation starts to occur, further degrading the vitamin and mineral contents of the juice. Some store bought orange juices are packages in clear plastic containers, this allows for exposer to light. Exposer to UV light especially damages the vitamin C contents of the juice. Fresh orange juice is squeezed and consumed within minutes, hours, or at most a day preserving the vitamin C content. This process is far less disruptive to the biological molecules found in the fresh juice, therefore it retains more of its nutritional content, then store bought juice.
Discussion
The purpose of the lab was to determine the vitamin C content in various samples of orange juice and compare the percent daily values listed in the nutritional facts label on the various juices to the values found through the experimental data. Using the data found in table 3 and 6 it was found that one serving of Tropicana contains 118.3% of the daily recommend value of vitamin C., on the nutritional label of Tropicana it lists 120% of the daily recommended value of vitamin C per one serving. That is a percent error of only 1.42% thus deeming the experiment a success. The missing 1.7% can be accounted for in sources of error. The standard deviation was found for each sample use using the class data (see table 4). The standard deviations for minute maid, Tropicana and fresh squeezed juice were all above 1, suggesting that the data found for those samples varied significantly in numerical values. It can be concluded that these results will not be as reliable and the results of the sample with a standard deviation of less than one.
The class results produced percent daily values that were more than the labels on the nutritional values of the sample orange juices (see table 5) suggesting an overestimate of mg of ascorbic acid present in experimental samples used. Percent error for class data Tropicana is 46.1%, Simple orange is 49.8%, President’s choice 100% orange juice is 55%, minute maid is 8% and president’s choice frozen concentrate is 61.7%. These percent errors are calculated based on the percent present in the sample vs. the percent given on the label of the product. If in fact these percent’s found through the class data were correct the company who produced the juice with the exception of minute maid would have them be equal, as the consumer perceives more vitamins as better quality juice. Minute maid results of 88.3 mg of ascorbic acid found in 250ml shows that the data for this sample might be accurate considering the label on the product lists 160% DV of vitamin C. This is possible because the results show that for the minute maid sample it contains 147.2% DV this is only a small difference compared with the other results therefore this set of data can be considered accurate as well. This over estimate of mg of ascorbic acid in sample can be explained easily by human error. The indicator used for the lab produced a very subtle change. This would easily allow for over titration to occur, thus inflating the number of moles of iodine used to titrate the sample and therefore increasing the number of mg of ascorbic acid found.
Sources of error
There are a few potential errors that may have occurred during the course of this experiment that would alter the results found.
A graduated cylinder is only accurate to +/- 5% and so the actual volume of sample will not be completely accurate. Using that volume of sample for the titration the volume of titrant used to bring the reaction to completion will be skewed. Therefore the amount of ascorbic acid found in each sample could vary up to +/- 5% causing the results to differ. To eliminate this error the experiment should use a pipette as they are a more accurate measuring tool and would greatly reduce the percent of error in this experiment.
The electronic scale used for the weighing out of 0.50 grams of oxalic acid was only accurate to two decimal places. A difference in mass of oxalic acid could change the amount of moles of titrant needed to complete the titration and therefore change the mg of ascorbic acid found in each sample. To improve upon this error the experiment should use the most accurate balance available to weigh the mass of oxalic acid used.
The samples of orange juice were left open and in beakers, or in open containers for an unknown length of time. During this time evaporation could have taken place. This evaporation would lower the water content of the solution and increase of concentration of ascorbic acid in the solution. This would alter the results of the lab. This error could be improved upon by keeping all juice in sealed containers while not in use, thus eliminating any evaporation that might occur in any length of time.
Conclusion
The objective of the experiment was to calculate the milligrams of ascorbic acid present in sample orange juices and compare with the numbers listed on the labels of said juices. In conclusion the experimental data found in table 3 shows that Tropicana contains 7.10 mg of ascorbic acid per 25ml, which works out to be 118.3% of daily values of vitamin C per serving. This result shows that Tropicana does in fact contain the amount of Ascorbic acid claimed on the label of the product as it claims to contain 120% daily value (see table 5).The class data with the exception of the data recorded for minute maid, was an inflated result causing the milligrams of ascorbic acid to be over calculated. Minute maid contains 87mg of ascorbic acid per serving which is a daily % value of 147.2%. This result could be considered accurate aswell.
References
“Wilfred Laurier university department. Fall 2012. Determination of Vitamin C in orange Juice. Pages 18-21 in chemistry 110 lab manual. Wilfred Laurier University, ON, Canada.”
“Wilfred Laurier university department. Fall 2012. Determination of Vitamin C in orange Juice. Page 22 in chemistry 110 lab manual. Wilfred Laurier University, ON, Canada.”
Determination of Vitamin C by Redox Titration with Iodine. (University of Canterbury Sciences Outreach) (Accessed 17 September 2012)
Tropicana Pure premium. (Accessed 16 September 2012)
Calories in Orange juice Simply orange 100% Pure Squeeze Pasteurized Orange juice Pulp free
(Accessed September 16, 2012)
PC 100% Florida Orange Juice. (Accessed 16 September 2012)
Calories in Minute Maid (Canada) 100% orange juices from concentrate. (Accessed 16 September 2012)
Calories in 100% Pure Frozen Concentrated Orange Juice Pulp Free. (Accessed Sept 16, 2012)
75ml Freshly Squeezed Orange Juice. (Accessed Sept 16, 2012)
Percent Error (Percent Deviation, Relative Error). (Accessed September 17, 2012)
Appendix
Class Results: Average Milligrams of Ascorbic acid found in Samples