Sugars and foods
Students: Ana
Zubiarrain and
Maite Cortés
Experiment´s
date: 07/02/12
and 14/02/12
Teacher: Nuria Report´s date:
Aguado
From 21/02/12
to 23/02/12
Index
Introduction page ........................................................................ 3
Materials ......................................................................................... 5
Methods ........................................................................................... 6
Results............................................................................................. 7
Conclusion ...................................................................................... 7
Bibliography ................................................................................. 10
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Introduction page
In this experiment we have worked with sugars and food.
In one part of the experiment we have determined the presence of starch in
some foods. Starch is a carbohydrate which consists of a large number of glucose units
joined together by glycosidic bonds, which is called a polysaccharide. It is a white,
tasteless and odorless powder that is insoluble in cold water or alcohol. It is the most
common carbohydrate in the human diet. It is produced by all green plants as an
energy store and it is contained in large amounts in foods like potatoes, wheat, corn,
rice and cassava. Starch is processed to produce many of the sugars in processed
foods. Dissolving starch in warm water gives wheat-paste that can be used as a
thickening, stiffening or gluing agent (for example in papermaking, the largest nonfood application for starch). It consists of two types of molecules: the linear and the
helical amylose and the branched amylopectin. Depending on the plant, starch
generally contains 20 to 25% amylose and from 75 to 80% amylopectin.
To detect if some food contained starch, we used different methods and
solutions. One of the solutions was A&B Fehling, which we have already explained in
the previous lab report, and as we mentioned there, it only detects monosaccharides.
The other solution that we have used is Lugol's solution, which is a solution of
elemental iodine and potassium iodide in water. It is often used as an antiseptic and
disinfectant, and as a reagent for starch detection. These uses are possible since the
solution is a source of effectively free elemental iodine, which is readily generated
from the equilibration between elemental iodine molecules and triiodide ion in the
solution. This solution is available in different potencies of 1%, 2% or 5% iodine.
Anyway, Lugol's solution has more than one application:
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It is used as an indicator test for the presence of starches in organic
compounds, with which it reacts by turning dark-blue or black. Lugol will
stain starches due to iodine's interaction with the coil structure of the
polysaccharide. Lugol solution will not detect simple sugars such as
glucose or fructose.
It can be used as a cell stain, making the cell nuclei more visible and to
preserve phytoplankton samples.
Lugol's iodine is applied to the vagina and cervix during the colposcopy. By
the use of this, doctors can observe if the patient suffers from cancer,
because the tissue does not stain. This is called a Schiller's Test.
It is also used to visualize the mucogingival junction in the mouth. It is a
similar staining method to the one mentioned above.
Lugol's solution can also be used in various experiments to observe how a
cell membrane uses osmosis and diffusion.
It is also used as an oxidizing germicide; however, it is not very
recommendable because it may lead to scarring and discolours the skin
temporarily. To avoid this problem there is the possibility of using a
solution of 70% ethanol to wash off the iodine later.
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This solution is also used in marine aquariums. Lugol's solution provides a
strong source of free iodine and iodide to reef inhabitants and
macroalgae.
Lugol's solution decreases intraoperative blood loss during thyroidectomy
in patients with Grave's disease.
As it contains free iodine, Lugol's solution at 2% or 5% concentration without
dilution is irritating and destructive to mucosa, such as the lining of the esophagus and
stomach.
In this experiment we have also seen how the saliva amylase works. Saliva is a
watery substance produced in the mouths of humans and most animals, it is a
component of oral fluid. In mammals saliva is produced in and secreted from salivary
glands. Human saliva is composed of 98% water, while the other 2% consists of
electrolytes, mucus, glycoploteins, enzymes and antibacterial compounds. The
enzymes found in saliva are essential in beginning the process of digestion of dietary
starches and fats. These enzymes are also important while breaking down food
particles entrapped within dental crevices, protecting teeth from bacterial decay.
Saliva serves a lubricative function, wetting food and permitting the initiation of
swallowing, and protecting the mucosal surfaces of the oral cavity from desiccation.
This lubricative function of saliva helps to create a food bolus, and allows it to be
passed easily from the mouth into the oesophagus. Saliva also contains the amylase
enzyme, which is capable of breaking down starch into simpler sugars that can be later
absorbed or further broken down in the small intestine.
As we have said above, saliva contains enzymes. Enzymes are biological catalysts
or assistants. They consist of various types of proteins that work to drive the chemical
reaction required for a specific action or nutrient. Like all catalysts, enzymes work by
lowering the activation energy for a reaction, thus dramatically increasing the rate of
the reaction. As a result, products are formed faster and reactions reach their
equilibrium state more rapidly. Most enzyme reaction rates are millions of times faster
than those of un-catalyzed reactions. However, enzymes do differ from most other
catalysts in that they are highly specific for their substrates. Enzymes are known to
catalyze about 4000 biochemical reactions.
Enzyme activity can be affected by other molecules. Inhibitors are molecules that
decrease enzyme activity, on the other hand, activators are molecules that increase
the activity. Many drugs and poisons are enzyme inhibitors. Enzyme activities are also
affected by temperature, chemical environment and the concentration of substrate.
The enzyme that saliva contains is called amylase. Amylase catalyses the
breakdown of starch into sugars. It is present in human saliva, where it begins the
chemical process of digestion. Food that contains starch taste slightly sweet as they
are chewed because amylase turns some of their starch into sugars in the mouth. The
pancreas also makes amylase to hydrolyse dietary starch into disaccharides and
trisaccharides which are converted by other enzymes to glucose to supply the body
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with energy. Plants and some bacteria also produce amylase. There are three types of
amylase:
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Α-amylase: they are calcium metalloenzymes, completely unable to
function in the absence of calcium. By acting at random locations along
the starch chain, α amylase breaks down long-chain carbohydrates.
Because it can act anywhere on the substrate, α-amylase tends to be
faster-acting than β-amylase.
β amylase: It catalyzes the hydrolysis of the second α-1,4 glycosidic bond,
cleaving off two glucose units at a time. Β-amylase breaks starch into
maltose, resulting in the sweet flavor of ripe fruit. Both α amylase and β
amylase are present in seeds; β-amylase is present in an inactive form
prior to germination, whereas α amylase and proteases appear once
germination has begun.
γ amylase: It cleves α-(1-6) glycosidic linkages, as well as the last α-(1-4)
glycosidic linkages at the non-reducing end of amylose and amylopectin,
yielding glucose. Unlike the other forms of amylase, γ-amylase is most
efficient in acidic environments and has an optimum pH of 3.
Materials
Crucible x3
Pestle
Test tube x6
Pipette and bulb
Droplet
Ring clamp and stand
Utility clamp
Wire gauze
Bunsen burner
Beaker
Thermometer
Wooden tongs
Graduated cylinder
Glassware marker
Tap water
Lugol´s solution
A Fehling
B Fehling
Flour
Tangerine
Biscuits
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Starch dissolution (0.2% - 100mL)
Saliva
Methods
Part 1
In this experiment we analyzed the presence of starch in some food, in flour,
tangerine and biscuits to be more exact. First of all, we took 3 crucibles and cleaned
them, so that we could develop correctly our experiment without any pollution. Then,
we put some flour in one crucible, a segment of tangerine in another one and a piece
of biscuit in the third one. We smashed the tangerine and the biscuit with the pestle,
so that the solution that we were going to add could work correctly. When we had all
the food smashed in the crucible we took some drops of Lugol´s solution and poured
them in each crucible. We wrote down the results in our note book.
Part 2
In this part we analysed the presence of sugars in fruits. We used tangerine's
juice, which we obtained after smashing some segments of it. We divided the juice in
two different test tubes and added 5mL of water to each one. After having the juice
dissolved in water, we added 5mL of A Fehling to one test tube and 5mL of B Fehling to
the other test tube. We heated the test tubes in a water bath and annotated all the
results that we observed.
Part 3
In this last part of the experiment the objective was to see how our saliva works.
For this experiment we were going to need a %0.2 starch dissolution in 100mL and a
water bath, so we prepared them at the beginning in order to be able to develop the
experiment as fast as possible. Then, we took 4 test tubes and added 2mL of the starch
dissolution in each one. After adding that dissolution, we developed different
experiments in each test tube, so as to compare the results later.
In the first one we added some drops of Lugol solution and wrote down the results
that we could observe.
In the second test tube we added 1mL of A Fehling and another one of B Fehling.
We mixed the content of that last test tube and put it in the bath water that we had
already prepared. We heated it for some time, being careful not to exceed 100ºC.
In the third and the forth test tubes we poured our own saliva and heated them in the
water bath controlling the temperature, because it could not go over 40ºC since that is
the normal body temperature. After heating those test tubes we took the third one
and added some drops of Lugol´s solution, and annotated the results. In the forth test
tube we added 1mL of A Fehling and another one of B Fehling, and then heated it until
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we reached around 100ºC, like in the second test tube. We wrote down our
observations as well.
The only difference between the 1st and 2nd test tubes and the 3rd and 4th test
tubes was the presence of our saliva. The purpose of this was to compare the results in
order to draw our own conclusions of how the saliva works.
Results
Part 1
Flour + Lugol solution Dark dark blue, almost black. Positive
Tangerine +Lugol solution  Brown (same colour of Lugol). Negative
Biscuit + Lugol solution  Dark dark blue, almost black. Positive
Part 2
Tangerine juice + water + A Fehling  green + heat  turns blue.
Tangerine juice + water + B Fehling  Orange, it did not change the colour + heat  it
turns brownish. After some time, it becomes reddish.
Part 3
1st test tube  Starch dissolution + Lugol solution  Same colour as Lugol (brown).
After some time, dark precipitates. Positive
2nd test tube  Starch dissolution + A Fehling + B Fehling + heatBlue because of the
dissolution. After heating, it does not change. Negative
3rd test tube  Starch dissolution + saliva + heat + Lugol At the beginning nothing
happened. After some time, very few black precipitates appeared. Negative
4th test tube  Starch dissolution + heat + A Fehling + B Fehling + heat At first
transparent in the bottom, blue in the middle, and transparent in the top. After
heating, it started to turn green and after some time, a reddish layer appeared.
Positive
Conclusion
Part 1
In this part of the experiment the reagent was Lugol's solution and the analyte
starch. If there is starch, Lugol's solution turns dark-blue or black; if there is no starch,
the colour does not change. Flour and biscuits do have starch, while tangerine does
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not; that's why Lugol turned black with the flour and the biscuits and it did not change
with the tangerine.
Part 2
Tangerine contains large amounts of glucose, fructose and saccharose. The first
two are monosaccharides, while the third one is a dissacharide made of glucose and
fructose. The Fehling's solution is used to detect the presence of monosaccharides, so
the result should have been positive due to the presence of glucose and fructose. But
the right way to develop the test is by adding the same amount of Fehling's A and
Fehling's B, which provide copper (II) sulphate and oxygen respectively to form the
copper (I) oxide precipitates that indicate a positive result.
In this case, we did not add both solutions to the tangerine juice, we added
Fehling's A to one test tube and Fehling's B to another one instead, both of them
containing tangerine juice. Being the correct procedure the one explained at the
beginning, we do not understand why we followed the second one. We do not
understand the results either, even though we have searched in a large amount of
websites.
Part 3
In this part of the experiment we have seen how our saliva work.
In the first test tube we had starch and we added some drops of Lugol's solution; the
result was positive since Lugol reacts with starch as we have explained in the
introduction page. There was starch in the second test tube too, but instead of Lugol's
solution we added Fehling's solution. We heated the test tube and the result was
negative, no copper (I) oxide precipitates appeared. Thus, we can confirm that starch is
a polysaccharide, because Fehling's solution only has a positive result if the analyte is a
monosaccharide.
In the third and fourth test tubes, which already had starch, we added our saliva.
As it is explained in the introduction page, saliva amylases break strach's bonds and
turn it into monosaccharides. That's why in the third test tube (Lugol) we obtained a
negative result, because there were not polysaccharides anymore. Anyway, as we have
mentioned, a little bit of black precipitates appeared in the bottom, which mean a
positive result; we think that the amylases did not break all the starch's bonds, so
some polysaccharides remained producing a positive result. Finally, in the last test
tube, we added Fehling's solution and heated the mixture. As expected, the result was
positive, because as we have just said, starch was turned into monosaccharides which
are detected by this test.
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By developing this experiments, we have fully understood how saliva amylases
work, because the test that gave a positive result in the first part due to the presence
of polysaccharides gave a negative result in the second part, and the test for
monosaccharides that gave a negative result in the first part gave a positive result in
the second one. Everything happened due to the amylases that broke the starch's
bonds to turn it into simple sugars.
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Bibliography
 http://en.wikipedia.org/wiki/Lugol%27s_iodine
 http://en.wikipedia.org/wiki/Starch
 http://en.wikipedia.org/wiki/Saliva
 http://en.wikipedia.org/wiki/Enzyme
 http://en.wikipedia.org/wiki/Amylase
 http://www.wisegeek.com/what-are-enzymes.htm
 http://es.wikipedia.org/wiki/Glucosa
 http://es.wikipedia.org/wiki/Fructosa
 http://alimentos.org.es/carbohidratos-mandarina
 http://es.wikipedia.org/wiki/Fruta
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