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Untitled Prezi

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Leeza Kerr

on 22 April 2015

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Introduction to the Iodine test for Starch

The indicator used is called potassium iodide. The starch coil molecule inside of the sample combines, with the potassium iodide forming a complex causing the color change viewed. Potassium iodide changes from amber colored to blue-black in the presence of starch. Glycogen could also be tested for using the starch test, but it's positive test varies.
Hypothesis
Results for all Samples
Vegetable juice
: + starch - protein
Sucrose
: - starch - protein
Glucose
: - starch - protein
Water
: - starch - protein
Carrot juice
: + starch - protein
Apple juice
: + starch - protein
Egg albumin
: - starch + protein
Honey
: + starch - protein
Amino Acid Lysine
: - starch + protein
Bovine serum albumin (BSA)
: - starch + protein
Salad dressing
: + starch + protein
*Protein supplemental drink mix
: - starch + protein
*Granola bar
: + starch + protein
*Protein enriched cookie
: + starch + protein

*
samples were chosen by participating group members.

Materials
Introduction to the
Biuret Test for Protein

The indicator used is copper sulfate. Copper sulfate complexes with peptide bonds in proteins. A sample containing protein changes a purple color in the presence of this indicator.
4 controls, 2 unknowns, 11 provided samples, 3 chosen samples.
38 test tubes: one for starch test and one for biuret test, besides for the control samples
test tube rack
disposable pipettes for indicator solutions
50% ethanol 50% water for dissolving food samples
mortar and pestle for breaking up food
potassium iodide/ starch indicator
copper sulfate/protein indicator
vortex mixer
Experimental Method
All test tubes were labeled with the sample names and put into the test tube rack
~ 1 mL of each sample was added to the specified test tube taking care not to contaminate with used pipettes
Label any pipettes to not cross contaminate samples
Any hard solid samples such as carrots or granola bars were mashed using a mortar and pestle and mixed with ethanol to form a liquid
~ 1 mL of this liquid was also transferred to its specified test tube
To the specified test tube 5 drops of starch or protein indicator was added
color changes could either be written down or recorded by taking a photo
Control tests:
Results for Starch & Protein
Positive tests for starch and protein
at high and low concentrations. Higher concentrations
had a more vivid
color in each sample
For this experiment the hypothesis consisted of the predictions of whether or not a sample would react positively or negatively to the iodine and biuret tests.
The controls containing protein or starch were obviously predicted to be positive. The unknown sample did not have predictions. The following are the rest of the predictions of the samples.



Qualitative Assays:
The Iodine and Biuret Test

Rachel Johnson
Leeza Kerr
David Crawford
Ignacio Fernandez

Results
Sucrose & Glucose
The results of the tests on sucrose and glucose were predicted. Both the iodine and biuret test came out negative. this holds true because glucose and sucrose are sugars.
Distilled Water
Carrot Juice
The carrot juice sample tested positive for starch as seen by the dark purple-blue colored sample. The sample tested negative for protein. This agreed with our prediction for the sample.
Apple Juice
The apple juice sample tested negative for the iodine and biuret tests. based on the tests the apple juice doesn't contain starch or protein.We had predicted the apple juice to contain starch.
Vegetable Juice
For the iodine and biuret tests vegetable juice came out negative. The vegetable juice had neither starch or protein, which was unexpected. We had predicted it to be positive for starch.
Results
Protein Supplement Drink Mix
The protein drink mix tested positive for the biuret and iodine test. It was hard to tell but both samples got darker in color when the indicator was added. The protein drink sample contained both starch and protein. It was predicted that the sample would contain protein and not starch.
Protein Enriched Cookie
The protein cookie tested positive for the biuret test and negative for the starch test. The cookie sample contained protein and no starch. It was predicted that the sample would contain starch and protein.
Chocolate chip
Granola Bar
The granola bar tested negative for the biuret test and positive for the iodine test. The granola bar sample contained starch and no protein. It was predicted that the sample would contain starch and protein.
Discussion
Most of the results of the iodine and biuret tests were as predicted. The result of the tests on vegetable juice were not predicted. Vegetables contain starch yet the test for starch proved to be negative. This result could have been due to the amount of processing the vegetables in the juice went through and what vegetables were used to make it. There could have been very little starch present leading to a very minimal color change that was not detected by our group. The same could have led to the results obtained from the tests on the apple juice sample. The apple juice was predicted to have starch content because apples are known to be rich in starches yet the iodine test proved negative. The fact that the juice was made from apple juice concentrate may have led to the results.
Water is a negative control for this experiment. It did not test positive for starch or protein. The indicators kept their original color as seen in the photo. The iodine test sample stayed amber and the biuret test sample stayed a dilute blue color.
Discussion Continued...
The unknowns were identified as chicken and beef stock due to their smells colors and iodine and biuret test results.
In order to reduce ambiguity in the iodine and biuret tests the samples should be re-tested multiple times. The error that could have possibly occured in the experiment was cross contamination of food items. This contamination could have occured with preparation such as when mincing and grinding with the mortar and pestle. The samples brought by group members were pre-packaged lowering the possibility of contamination. It is possible that predicting the test result could have influenced how the color of the test was perceived. In the case of the biuret test of the amino acid lysine. The resulting color wasn't completely purple it was mainly the color of the indicator. The biuret test would not have a positive result for this sample because there are no peptide bonds just free amino acids. The observations that the biuret test result was positive is invalid due to pre conceived misconceptions about the sample.
Results
Unknown A & B
Unknown sample "A" tested negative for the biuret test and positive for the iodine test. This sample contained starch and no protein. Unknown sample "B" tested negative for the biuret test and slightly positive for the iodine test. This sample contained possibly glycogen and no protein.
Amino Acid Lysine
Lysine tested negative for the iodine test and positive for the biuret test. These results were predicted. The lysine sample contained protein and no starch.
Salad Dressing
The salad dressing sample was negative for both the iodine and biuret tests. It was predicted that both tests would be positive. The salad dressing sample did not contain starch or protein.
BSA & Egg Albumin
The bovine serum albumin (BSA) and egg albumin both tested positive for the biuret test. The egg albumin tested negative for starch, but the BSA had a slight positive for starch. Both samples were predicted to contain protein and not starch. The slight color change in the iodine test on the BSA sample could be due to glycogen present.
The honey sample tested negative for both the iodine and biuret tests. The sample was predicted to be positive for starch and negative for protein. The tests proved honey does not contain starch or protein.
Honey
Discussion: Iodine test results
It was observed that not all of the iodine test resulting colors were the same. For example the BSA sample compared to the negative control; distilled water sample. The color of the positive iodine test results varied . Not every sample containing starch turned dark black-blue like the control, but rather had a slight brown color not consistent with the amber color of the indicator. As said in the introduction this could have been due to the presence of glycogen, but it could also have something to do with the type of starch in the sample. In the journal article
A New Method for Quantifying Iodine in a Starch-Iodine Matrix
it is explained that different starch chains have different complexes with iodine. Color and wavelengths of absorption of the iodine starch complex depend on the length of the polymer. From this experiment it would be near impossible to use our qualitative results to come to conclusions about the different starches in the sample.
Predicted Results
The controls were all assumed to be positive for their respecting tests. The unknowns were not counted in the predictions.
Vegetable Juice
: + starch, - protein
Sucrose
: - starch, - protein
Glucose
: - starch, - protein
Water
: - starch, - protein
Carrot Juice
: + starch, - protein
Apple Juice
: + starch, - protein
Egg Albumin
: - starch, + protein
Honey
: + starch, - protein
Lysine
: - starch, + protein
BSA
: - starch, + protein
Salad Dressing
: + starch, + protein
Granola Bar
: - starch, + protein
Protein Cookie
: + starch, + protein
Protein supplement
: - starch, + protein

References
Seidman, L.A., Mary Ellen Kraus, Diana L. Brandner, Jeanette Mowery. 2011.
Laboratory Manual for Biotechnology and Laboratory Science the basics
. Pearson Education. San Fransisco, California. Pages 205-208.

Manion, B..A., B.E. Holbein, M.F. Marcone, K. Seetharaman. 2010.
A New Method for Quantifying Iodine in a Starch-Iodine Matrix
. Carbohydrate Research. 345: 2698-2704.

#33 Food Test 4 - Biuret Test for Proteins. Digital image. Http://igbiologyy.blogspot.com/2012/12/33-biuret-test-for-proteins.html. 23 Dec. 2012. Web.

Charles, Ophardt. Starch and Iodine. Digital image. Http://chemwiki.ucdavis.edu/Biological_Chemistry/Carbohydrates/Case_Studies/Starch_and_Iodine. 1 Jan. 2003. Web.
Color change is dependent on the number of peptide bonds present in the sample.

The more intense the color change, the higher the concentration of protein.
Starch molecules contain amylose and amylopectin.
Natural starches are a mixture of approximately 20% amylose and 80% amylopectin.
Amylose in starch is responsible for the deep blue color observed in the presence of iodine.
Protein cookie and protein drink mix contained 10 grams of grass fed whey protein concentrate (rBST/rBGH-free)

rBST - recombinant Bovine Somatotropine
rBGH-recomninant Bovine Growth Hormone
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