Walsh 1 Zach Walsh Dr. Baker Cell Bio 214 Title: Concentration of Starch in Our Food Abstract: Experiments were done to better understand how to figure out how many carbohydrates, most specifically starch, starch, there were in food. Being able to see how many carbohydrates are in food is important for people who are on low-carb diets to lose weight or for health reasons. Starch is a storage molecule that comes in two forms: forms: amylose and amylopectin. The amount of starch can be figured out by a Lugol’s iodine test which tests to see how much amylose is in the solution or food. When it is added, it will change colors going from yellow to blue or dark blue depending on how much starch/amylose is present. Hypothesized that the Lugol’s iodine test would give an accurate amount of actual starch concentration in food. Two solutions were made of either cooked or uncooked starch and increasing amounts of concentration from each type were tested. Absorbency was measured by a spectrophotometer that looks at the coloring of the solution and for our results it looked at it at 620 nm. Standard curve graphs were made for both both cooked and uncooked data. The absorbency was measured against the concentration. The equation for the best-fit line was found for both graphs. Theoretical percent yield was calculated by using the foods nutrition label and then compared with the actual percent yield. Major differences were found between the two two yields. The hypothesis that the iodine test test was able to give an accurate amount of starch starch content in food was rejected. rejected. The iodine test
Walsh 2 only tested the solution for amylose starch, which is o nly about 20% of starch found in food. Introduction: Are you on a diet? Most diets these days eliminate or greatly reduce the amount of carbohydrates in a person’s meal. They reduce them because carbohydrates are polysaccharides that store energy, the most important one for us is starch. Starch is comprised of large units of glucose joined by glycosidic bonds. It is the most common carbohydrate found in our diets and is present in large amounts in common foods like potatoes, wheat and corn. It comes in two forms: amylose and amylopectin. Amylose is linear and forms a helix helix while amylopectin is branched. When too much starch is present, our bodies store it as fat and save it for later use. The build up of fat can cause health problems later on in in life. “Obesity creates wear on the joints, joints, leading to osteoarthritis. The accumulation of fat around the windpipe can interfere with breathing when muscles relax in sleep” sleep” (Underwood 2). By consuming less starch the the body begins to break down the starch that it has stored as fat to use as energy. To see how many carbohydrates are consumed in a particular food, look at the nutrition nutrition label. Knowing how much starch and other carbohydrates are in food allows for people to monitor their diet and help them stay healthy. We performed our experiments to determine how much starch is present in various foods that are consumed regularly. In our first experiment we took known cooked and uncooked starch concentrations in mg/ml and determined their absorbency by performing a Lugol’s iodine starch test. test. The iodine reagent was added to the solutions solutions and if “a blue black color results if starch is present. If starch amylose is not present, then the color will
Walsh 3 stay orange or yellow. Starch amylopectin does not give the color, nor does cellulose, nor do disaccharides such as sucrose in sugar” (Ophardt). The test determines if starch is present or not and if it is present the results can be used in a spectrophotometer to get its absorbency at 620 nm. Using the data that we got from our experiment we created created concentration curves for cooked and uncooked starch. The concentration of starch starch was the independent variable and absorbency was the dependent variable. We continued our experiment and figured out the absorbency of six foods that we then compared to the concentration curves to figure out their starch content. For our second experiment we used food that we brought in and made them into solutions. We basically performed the same steps as the ones from our first experiment. However, we tested each food three times for more accurate results. Using the results we calculated the actual concentration of starch and compared them to the theoretical concentrations that were taken from the nutrition labels. The purpose of performing experiment 1 was to “learn how to do an iodine starch test to determine starch content” (BG214 Lab Handout, 2012). Using the experience and knowledge that we gained from experiment 1 we created our own experiment to figure out the the starch content in foods that are consumed regularly. By comparing the theoretical and actual percent yield of starch concentrations we can determine how accurate the iodine test is. We hypothesized that Lugol’s iodine test is a good indicator for figuring out the actual percent yield concentrations and gave values close to the theoretical percent yield in food. Methods and Procedures: Uncooked Starch test: 8 test tubes were taken and labeled A-H and had a stock solution of starch [1 mg/ml] added to it mixed with distilled water so that the tubes concentrations
Walsh 4 (mg/ml) were Tubes H 0, G .1, F .2, E .3, D .4, C .5, B .6 and A .7 respectively. respectively. Each tube had a final volume of 20 ml. 1 ml of iodine solution solution was added to each tube and if the solution turned black then a + was recorded to indicate starch was wa s present and if it remained yellow a – was recorded recorded to indicate the absence of starch. The absorbency was then determined by using a spectrophotometer set at 620 nm. Set at 620 nm because that’s the frequency of blue light which is the color the solution turns if starch is present. Each tube was placed in the spectrophotometer after being wiped down with kim wipes to ensure that the tubes were clean. The tube whose starch concentration was 0 mg/ml, was used as the blank and used between each sample. sample. The absorbencies of the tubes were then recorded. Cooked Starch test: The same procedure and methods were used with the cooked experiment as in the uncooked experiment except for the final starch concentrations. The tubes final starch concentrations in mg/ml were: Tube A .35, B .30, C .25, D .20, E .15, F .10, G .05 and H 0 and they had a final volume of 20 ml. Quantitative Comparisons: 12 test tubes were taken, 6 of them were labeled #1-6 A and the rest were labeled #1-6 B. 20 ml of a different different solution, whose concentration was 1g/1L of water, was added to each tube. Tubes #1 received potato juice, #2 onion juice, #3 gravy, #4 milk, #5 Karo syrup syrup and #6 was unknown. 1 ml of iodine solution solution was then added to the tubes labeled A while tubes B were left alone so that they could function as blanks for their corresponding tubes. Absorbencies were taken using the spectrophotometer set at 620 nm. Composition of our Food: Foods that were tested were a bagel, sugar cookie, orange juice, dog food and apple jacks. The foods were crushed up using a mortal and pestal and
Walsh 5 1 gram of food was measured out using an electronic balance and then added to 1,000 ml of water and liquefied using a blender. 20 ml of each solution was then added to 2 test tubes either A or B, 10 test tubes total. 1 ml of Lugol’s iodine reagent was then added to the A tubes. B tubes left left alone, they functioned as Blanks. The tubes absorbencies were then taken at 620 nm and recorded. Process was repeated an additional 2 more times for accurate readings. The theoretical percent yield of starch starch content is calculated by: (Carbohydrates – (Dietary Fibers + Sugars) / Total mass of 1 serving size) x 100. Standard curve of uncooked starch: y = .482x Standard curve of cooked starch: y = 6.2071x The actual/tested value of starch content was given by substituting y with the absorbency value, then solve for x by dividing both sides by the rate of change. Then multiply what x equals by 100 to get the percent yield starch concentration for that food. Results: The concentration curves for cooked and uncooked have a positive linear trend so that as the concentrations increased, the absorbencies increased as well (Figure 1, 2). The line that best fit each data set is linear meaning that that it changes at a constant rate. rate. The standard curve keeps potential mistakes or inaccuracies in c heck as well as prevent overlapping ove rlapping standard error bars from affecting the significance of the data.
Walsh 6 Figure 1. Standard curve of uncooked starch
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Figure 1. Known starch concentration in the uncooked foods was represented by an absorbency value. R^2 shows how close of a fit the data is to the line, the closer to 1, the better fit. R^2 of .98 is high showing that the data is close.
Table 1. Uncooked starch concentrations and absorbency data for uncooked concentration curve. Tube Starch Concentration (mg/ml) Absorbency @ 620 nm Standard Error A .7 .354 .047 B .6 .263 .0204 C .5 .258 .0245 D .4 .186 .0163 E .3 .136 .0100 F .2 .1 .0100 G .1 .046 .0040 H 0 .002 .0020 Table 1.
Walsh 7
Figure 2. Standard curve of cooked starch
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Figure 2. Known starch concentration in cooked food was represented by an absorbency value. R^2 shows how close of a fit the data is to the line, the closer to 1, the better fit. R^2 of .99 is extremely high indicating how close a fit the data is. The standard error bars do not overlap meaning that all of the data points are statistically significant.
Table 2. Cooked starch concentration and absorbency data for cooked concentration curve. Tube Starch Concentration (mg/ml) Absorbency @ 620 nm Standard Error A .35 2.16 .117 B .30 1.84 .111 C .25 1.55 .105 D .20 1.26 .086 E .15 .97 .071 F .10 .64 .047 G .05 .31 .022 H 0 0 .001
Walsh 8 Table 3. Starch concentration test data of different foods. Average Actual % yield of Theoretical % yield Food +/- Test Absorbency @ 620 Starch of Starch nm Concentration Concentration Potato Juice ++ 2.473 39.84% 68.18% (cooked) Powdered Milk .069 14.32% 0.0% (uncooked) Onion Juice .043 8.92% 0.0% (uncooked) Karo Syrup .053 10.99% 26.67% (uncooked) Gravy + 1.08 17.40% 4% (cooked) Sugar Cookie + .2405 3.87% 26.67% (cooked0 Minute Maid Orange Juice .0605 12.55% 1.67% (uncooked) Bagel ++ .427 6.88% 35.63% (cooked) Apple Jacks +++ 1.1645 18.76% 34.72% (cooked) Dog Food + .2245 3.62% (cooked) Table 3. Actual % yield gives the percent of starch in our foods we found in our solution. Theoretical % yield gives the percent of starch that the nutrition labels give. Discussion: Our hypothesis was that the Lugol’s iodine test would be helpful in seeing if the theoretical percent yield of starch concentration would be close to or match the actual percent yield of starch concentration. There were large differences in our data that made it hard to compare them. Powdered milk for example, has a theoretical yield of 0% while while our actual yield was 14.32%. These differences could be the cause of several factors such as the fact that if the solution wasn’t stirred before it was measured than the solution could have had a lower concentration than the 1 mg/ml that was being tested for with the iodine, lowering its absorbency. Another factor that could have had an affect affect is that the
Walsh 9 Lugol’s iodine test only responds to amylose in the food and it won’t react to amylopectin starch, which is also present in food. “Starches are mixtures of amylose (1020%) and amylopectin (80-90%)” (Ophardt). Since amylopectin is more abundant than amylose, the nutrition label most likely did another test that included amylopectin in its starch content not just amylose like in our experiment. Another thing that would have given us different results is that there are so many different brands of food for one item and the food can be produced in different places where they slightly vary how the food is made causing a possible change in starch starch concentration. The nutrition label is made only for that brand and its universal for that specific specific food or juice. Human error is another reason why our data was off. off. When creating the solution not all of the solute could have been dissolved when we tested the absorbencies. Our data did not support our hypothesis because the iodine test wasn’t able to accurately determine the total starch content in food. It would be more effective for people to calculate the starch starch content from the foods nutrition label. References: BG214 Lab Handout. “Determining the Macromolecular Composition of Food.” Feb. 16, 2012. Wofford College, Spartanburg, SC. Ophardt, Charles E. Virtual ChemBook . Elmhurst: Elmhurst College, 2003. Electronic. Underwood, Anne and Jerry Adler. “What You Don’t Know About Fat.” Newsweek 2006: WK 3. Electronic.