Hypothesis
Using the common background knowledge I have read or seen in various diet-related TV programs as well as my biological knowledge, my hypothesis is following: The meal-plan for a day that we have made does contain all the nutrients that could have been tested for, therefore it is possible to say that the meal-plan was pretty successful; however due to the limitation of testing methods, some of the nutrients that are needed for proper body functioning such as vitamins, minerals, fatty acids could not be determined to be present.
Variables
- Independent: food products with different nutrients
- Dependent: color of the substance after the reaction indicating the presence of a certain nutrient
- Control:
- Amount of solution added for the test should be approximately the same
- During the pretest, the amount of solutions tested should have similar amounts (25ml)
- The food products are better to be ground into smaller particles
- During the Benedict test and HCl/Benedict test, the test-tubes have to be in a boiling water bath for certain amount of time (3min and 2min respectively)
- The color observed and recorded should be the one after the reaction is done
- Distilled water has to be added to the food products before they are tested in order to make the contact better
Apparatus
- Boiling water bath
- Test-tubes (for each pure substances as well as the food products)
- Test-tube rack
- Test-tube holder
- pH paper
- Glass rod
- Waste beaker
- Cleaning beaker
- Pipettes
- Stopwatch
- Grinder
- Marker to label
- Potassium iodide (solution in alcohol)
- Benedict reagent
- Hydrochloric acid (HCl 1.0M)
-
Sodium hydrogen carbonate solution (NaHCO3 0.1M)
-
Copper sulphate solution (Biuret: 1% CuSO4)
- Sodium hydroxide (NaOH 10%)
- Protein
- Starch
- Glucose
- Milk
- Cereal
- Bread
- Juice
- Cheese
- Apple
- Pasta
- Lattice
- Meat
- Tomato
- Yogurt
- Red wine
- Onion
Data Collection/ Data Process
As it was briefly explained in the introduction, the pretest took place before the actual experiments were performed. The substances used are distilled water (as control), protein, starch and glucose. Unfortunately, we did not have sucrose and lipid which meant we could not use the HCl/Benedict test.
Results for the each test are represented in the following table, Table 1:
§ Table 1 – Pretesting results
N/A – not applicable
From the table above, the color change of different substances as the chemicals for the specific test were added. N/A stands for ‘not applicable’ and it means either that there was no material to be tested on (sucrose; lipid) or the test could not be repeated.
For the Iodine test, the control (distilled water) shows yellow color and no change as well as for the glucose and protein. This is due to the fact that Iodine itself has yellowish color. However, starch shows significant change in its color; it turned black. The data says black even in capital letters emphasizing that it was completely black color. According to the research, the color is supposed to turn blue black therefore the test can be assumed to have been successful.
Biuret test is known to determine the presence of protein by showing the purple color. The table shows that the test showed clear purple color of protein substance whereas other ones have a blueish color which is a control color.
There's one especially different color in the Benedict's test as well; it is orange. The substances tested except for glucose show blue/green color. This proves that the Benedict's test indicates presence of glucose by changing the color into orange.
The last test which was HCl/Benedict test could not really be used since we did not have any simple reducing sugars that could easily be broken down into non-reducing ones by HCl (such as sucrose).
The actual tests were done on small amounts of every food product in the diet plan, and the results were recorded and analyzed.
As a reminder, in Iodine test the indicating color is blue black and it determines presence of starch. The table below shows the color changes that different food products had after adding the Iodine droplets.
§ Table 2 – Iodine test results
The bold letters are the ones have significant color change for the Iodine test. The products are: cereal, bread and pasta. Three of the products are assumed to have starch as their components. The diet plan seems to have succeeded to have at least one of the essential nutrients.
There are two products that have dark yellow color: yogurt and apple, which might cause confusion. However, based on what I know and I’ve learned, starch is energy stored in plants, therefore it will not make sense if there is starch present in yogurt which is a dairy product, produced by animals. Also, since the part of an apple we tested was a body of it but not a seed, apple is not supposed to contain starch. The conclusion, therefore, is that the slight difference in colors can be ignored. The reason why they show a little darker yellow color than others might be because of the initial color of the food product or, in case of yogurt, the thickness of the solution (when the substance is thick, the color appears to be matte, darker.). Another confusion that we had in this set of data is Red Wine; it shows purple color. However, since wine is not made of grape seeds but the flesh of grape, it is assumed that there is no starch present. So the purple color is just from the initial color of the wine, dark red.
Biuret test determines the presence of protein by showing the color purple. The results were following:
§ Table 3 – Biuret test result
The result was actually very surprising. We could not see any purple color in the test tube filled with milk! Though, other products that we assumed as protein-containing products had positive result. Dairy products are normally, commonly known to contain a lot of protein. One of the big reasons why many people tend to drink it is, actually, protein! So it was very shocking that it did not show any positive reaction of presence of protein. This test could not be repeated due to the time limitation, therefore it is not possible to evaluate if it was a random error, but just depending on the data collected, it can be concluded that milk does not have enough protein (or not at all) to show the purple color by Biuret solution.
The products that showed positive results are: yogurt, meat (chicken) and cheese. The yogurt especially reacted very fast and very clearly. Since it had a white color initially, it was very easy to see the color. It is very hard (almost impossible) to determine the amount of protein with the simple test as Biuret test, however, I would still suppose yogurt has the most amount of protein than meat or cheese due to the fact that it had darker and clearer purple.
In this test, again, Red Wine is causing the confusion with its initial color. Even though it is showing the dark blue-black color, it can be ignored.
All the other products did not seem to have any kind of color change, however, there were three products that contain protein, therefore it is concluded that the diet plan has achieved to have another essential nutrient.
Benedict test generally shows orange color, indicating the presence of non-reducing sugar (monosaccharide, some disaccharides). Depending on the amount of non-reducing sugar, it can also show more yellow, green (smaller amount) or red and brown (bigger amount). This was proven in the pretest by adding the solution into glucose. The data collected is shown in Table 4.
§ Table 4 – Benedict test result
For this test, there were very many products that showed positive outcome. All the products except for bread, cheese and meat appeared to react to the Benedict solution and turn into one of the indicating colors.
Fruits such as apple and tomato as well as fruit juice seem to have shown clear strong orange color. It is very assumable that they contain simple sugars because we all know that they normally have at least a little bit of a sweet taste. Onion and lettuce, the vegetables had relatively weak color, close to yellow, showing that it contains less amount of glucose than fruits.
Pasta, bread and cereal also showed positive reaction of presence of glucose. For bread, though, the color was positive only one time out of two. This might have occurred because of not evenly mixed dough during the production of the bread e.g. when the sugar was added.
The dairy products also appeared to contain glucose in them. Milk contained relatively larger amount of it than yogurt, since it showed orange color whereas yogurt had a light yellow color.
Wine was again a confusing product to analyze; it didn’t have any change in the first trial, but it did have an orange precipitate on the next trial. So it is assumed that it does contain glucose based on the fact that it is made of grapes that have glucose in them, however it isn’t shown clear and it is hard to evaluate what caused the error.
Other products, cheese and meat did not show the orange color for this Benedict test so it is concluded they do not have glucose in them.
Glucose is made up of carbohydrates in a rather simple structure, and carbohydrates are known to play an important role in producing energy; therefore, it is very important that we have a lot of products that contain glucose. However, too much of it will have overload of the nutrients which will make a person become fatter. Since the lab is not designed to find out the proper balance of the diet plan, it is not that relevant to talk about amount of glucose, however I’d like to stress that the plan should not contain too many products that contain specifically a lot of one nutrient.
The last test was HCl/Benedict test and it was performed however the results are not relevant since we could not determine the nutrient for the test during the pretest due to the fact that we were missing sucrose which would have given a positive result for us.
Conclusion
The conclusion that can be drawn from the data analysis of the experiment is that, the plan for daily diet did have all the essential nutrients that we could test for (proteins, and starch, glucose which are carbohydrates). It contained starch for every single meal (cereal, bread and pasta), proteins by cheese, yogurt and meat, but not milk (very surprisingly) and also glucose by every products except for 2~3.
Evaluation
There are a lot of different things to be evaluated on for this experiment.
First of all, the designed experiment was not good enough to achieve the purpose of the lab which was <Deciding whether the diet plan includes the products that contain all six essential nutrients>. It did, however, answer the designed research question, but if the experiment had more extended methods, it could have clarified the conclusion for the diet plan. In order to improve this, more tests should be performed so that the presence of other essential nutrients such as fatty acids and vitamins can be tested. Therefore, more tests and methods should be researched and learned.
Secondly, the fact that we missed some materials to run the test on was very shame. Even though we performed the HCl/Benedict test, we could neither analyze the data nor draw the conclusion out of it, since we did not have sucrose to pretest. Also we did not have lipids; it wasn’t a big problem in this lab since we didn’t have any test for lipids (fatty acids); however it is possible that we could have seen any kind of interesting result. I hope for the next time, or for the others who will perform this experiment will certainly have these materials.
The tests were done by different groups due to the time limitation. Therefore it is very hard for me to evaluate for the random errors that might have occurred during the tests. I am not aware of any details or mistakes my other classmates might have missed of made since I was not present next to them. That also makes it hard for me to analyze the data collected. For the improvement, we should all make sure that we try to write every single detail and small mistakes to be put into consideration and share them with one another, and of course this has to be done with clear academic honesty.
One of the tests, Biuret test did not have any data for repeated experiment. When there is no repeat, the data is less reliable since the errors can’t be determined and evaluated. This was due to the time limitation, but more because of the efficiency of working method. As it is clearly seen, all the other tests were repeated. Looking at the fact that the method of Biuret test is even easier than Benedict test (since the test tubes need to be put into a waterbath), it can be decided that the performance needs to be done more efficiently. The simplest solution can be testing the products twice at the same time, therefore have two test tubes for each product tested at the same time. In this way, the experiment can be repeated and also we get to compare the two test tubes to analyze the result better.
Another problem that has to be evaluated is the food products. There were some products that caused confusion of determining the indicating color because of their initial color. For instance, wine had a dark purple/red color which was hard to see the colors for every test because either it had a similar color with the indicating color (black, purple), or it was too dark/strong to see the indicating color (orange). For the next time it would be handy if we try to avoid the products with initial colors that are too strong/dark or similar to the indicating color.
Characteristics of different food products were also very hard to overcome. For example, yogurt was too thick to be put into a test tube which made it impossible to put similar amount for the repeat. We tried with the pipette as well as the spoon but it did not work out well. Next time, the method of the experiment should be considered while we choose the products to be tested on. Some products that had a large size had to be ground or cut or broken, and this was also hard to do so since some or them were simply too difficult to cut or break. Chicken meat for example was so hard to cut that we gave up cutting it too small in the end. This might have affected our result because when the particle is too big, due to the surface and volume ratio, it has much less contact with the solution to react. There should be some better materials to improve this (e.g. sharper knife) or some better methods such as using a blender to make the products into smaller particles.
The hypothesis was proven to be true through the result of this experiment and even though it was a lab with many lacks and inconveniences, it was very interesting and enjoyable to observe and analyze the reactions.
[1] Essential Nutrients – AB workouts - - 21/10/10
[2] Benedict's Test for Reducing Sugars – Biological Sciences at Ohio University -
- 21/10/10
[3] Simple Biochemical Tests on Carbohydrates - - 21/10/10
[4] Biuret Test For Proteins – SCUM Doctor.com - - 21/10/10
[5] ‘Iodine Test’ by - 7/23/2010 – Buzzle.com Intelligent Life on the Web - - 21/10/10
[6] Starch – Virtual Chembook - - 21/10/10
by
aminearrifi (student)
