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Carbohydrates
- 1. Chem 31a- BIOCHEMLAB Name: Hazelyn M. Benabaye Date Performed: November 19, 24 Group No: 6 CARBOHYDRATES Experiment No. 3 Results and Discussion Table1. Structural formulas for carbohydrates MONOSA CCHARI DES STRUCTURES FISCHER HAWORTH CHAIR glucose
- 2. fructose Table1.1 Disaccharides (Haworthand Chair structures) Lactose Haworth Chair Maltose Haworth Chair Sucrose Haworth Chair
- 3.
- 4. Table1.2 Benedict’s testfor reducing sugars Compound Color Reducing Sugar (yes/no) water blue No glucose red-orange Yes fructose red-orange Yes sucrose blue-green No lactose red-orange Yes maltose reddish brown Yes starch blue No glycogen orange Yes Benedict’s test for reducing sugar is a test that determines the amount and presence of reducing sugar in a particular solution. Sugars are classified as either reducing or non-reducing sugar based on their ability to act as a reducing agent during Benedict’s test. The reagent in Benedict’s test for reducing sugar is the Benedict’s solution which contains copper (II), sodium carbonate, and sodium citrate. The copper solution gives a blue coloration. It reacts with the electrons from the ketone or aldehyde group of the free reactive carbonyl group on the carbohydrate to form cuprous oxide (a red- brown precipitate). This precipitate is formed due to the reduction of the Cu2+ ions to Cu+ ions, In the process, the carbohydrate is oxidized. The color of the precipitate is dependent on the volume of reducing sugar present. This means that the more free carbonyl groups present, the increase in the amount of precipitate formed. The reducing agent for reducing sugars is the aldehyde functional group (COOH), the formyl group. Reducing sugars have either an aldehyde functional group or a ketone group in an open chain form which is then converted into an aldehyde. Reducing sugars are simple sugars and they include all monosaccharides and most disaccharides. Examples of monosaccharides are glucose, fructose and galactose and examples
- 5. for reducing disaccharidesare the lactose and maltose. Disaccharides sucrose is not a reducing sugar. In fact, sucrose is the most common non-reducing sugar., Based on the Benedict’s test that was conducted, water and starch had no change in color. Therefore, water and starch have no non-reducing sugars present. Glucose and fructose had its change color of red-orange while the food sample which is the cake turned orange; this means that a moderate amount of reducing sugar is present on the said compounds. On the other hand, maltose had its color change of reddish brown; this means that a large amount of non-reducing sugar was present. We didn’t obtain the accurate result for lactose, but lactose is a reducing sugar. Table 2.3 Barfoed’s test for monosaccharides Compound Color Monosaccharides (yes/no) water blue No glucose light orange Yes fructose red orange Yes sucrose blue No lactose blue No maltose blue No starch blue No food sample (cake) blue No Barfoed’s test is used to distinguish monosaccharides from disaccharides. Monosaccharides are reducing sugars and they react faster with the reagent in order to form such color change. Whereas, reducing disaccharides reacts slower than monosaccharides. Based on the results that were obtain from the experiment, water, sucrose, lactose, maltose, starch, and the food sample had the same color of blue upon heating. Only glucose and fructose had a change in its color. Glucose turned into light orange while the fructose turned into red orange. This means that only glucose and fructose were monosaccharides. Barfoed’s test
- 6. used copper (II)ions in a slightly acidic medium, reducing monosaccharides were oxidized by the copper ion in solution in order to form carboxylic acid and an orange precipitate of copper (Ii) within five minutes. Reducing disaccharides goes the same reaction but do so at a slower rate. The non-reducing sugar gave a negative result. Barfoed’s reagent comprises of cupric and acetic acid in solution. Monosaccharides readily react with the reagent in order to cause a reduction in the 𝐶𝑢2+ ions to 𝐶𝑢+ ions forming𝐶𝑢2 𝑂. The reason behind this is that monosaccharides, they oxidized readily in weak acid solutions. Disaccharides can as well reduce the cupric ions; however, its reaction is much slower. Table2.4 Seliwanoff’s test for ketohexoses Compound Color Ketohexose/Aldohexose water light orange Aldohexose glucose light pink Aldohexose fructose red Ketohexose sucrose red Ketohexose lactose light pink Aldohexose maltose light pink Aldohexose starch light pink Aldohexose food product (cake) flesh colored Aldohexose Seliwanoff’s test is used to distinguish between aldohexose and ketohexose. Seliwanoff’s reagent consists of resorcinol crystals dissolved in equal amounts of water and hydrochloric acid. Upon heating the solutions, the formation of a red precipitate indicates a positive result. Based on the experiment, only fructose and sucrose had the positive result. They both formed a red precipitate which indicated that it is a ketohexose. Other compounds had light pink/light orange color; this indicates that they are aldohexose. The acid hydrolysis of polysaccharides and oligosaccharides yields simple sugars. The dehydrated ketose then reacts with the resorcinol in order to produce a red color. Aldose may
- 7. react slightly toproduce a light pink color. Fructose and sucrose are two common sugars that yield to a positive result. Sucrose is a disaccharide that consist fructose and glucose, that is why it had a positive result. The test reagent dehydrated ketohexose in order to form 5- hydroxymethylfurfural. Aldohexose reacts slowly much slower that ketohexose to give 5- hydroxymethylfurfural, that is why it had only a light red color. Once the 5- hydroxymethylfurfural was produced, it then reacts with resorcinol that gave a dark red condensation product. Sucrose hydrolyzes to give fructose, which eventually reacted, that is why it produced a dark red color. Table 2.5 Iodine test for polysaccharides Compound Color Polysaccharides (yes/no) water yellow No glucose light orange No fructose light orange No sucrose yellow No lactose red orange No maltose red orange No starch black Yes (amylase) food product (cake) black Yes (amylase) Iodine test is used for the detection of starch in the solution. The black color is due to the formation of starch-iodine complex. Starch contain polymer of α-amylose and amylopectin which forms a complex with iodine to give the black color. Based on the experiment, only the starch and the food product cake had the positive result. They both formed into a black precipitate. Therefore, both the food product and starch are polysaccharides. Other compounds had a negative result.
- 8. Starch is composedof a straight chain subunit know as the amylase. Amylose is responsible for the reaction with iodine. The amylase subunit of starch is made up of a straight chain of alpha-glucose monomers that are connected by alpha 1á4 glycosidic bonds. In solution, the amylase exists as a helically coiled structure. When the iodine was added, the molecules of iodine became trapped within the helical structure and formed a complex one. Iodine has usually a black color that causes the black coloration of starch which indicates that amylase is present. The same with the food product cake, cake also result to a black precipitate because cake has an ingredient of starch that had caused its black coloration. Table 2.6 Hydrolysis of di- and polysaccharides Compound Benedict’s Iodine Sucrose(hydrolyzed) Yellow orange light yellow Starch (hydrolyzed) blue black This test is performed in order to breakdown to the monomer monosaccharide units. The hydrolysis of the sucrose enabled the following results; in benedict’s test, the solution reduced the 𝐶𝑢2+ ions to 𝐶𝑢+ that resulted to the formation of the yellow orange precipitate. This means that there was the presence of a reducing sugar in the solution, and since sucrose is not a reducing sugar; the hydrolysis had created a monosaccharide that contains a free reactive carbonyl group. In the Iodine’s test, the presence of amylase facilitated the reaction with the reagent to form a black compound. HCl breakdown the 1á2 glycosidic bond that links the glucose and fructose monomer together to form sucrose. This break causes the release of two monosaccharides. Sodium hydroxide was then added in order to neutralize the pH of the solution since the presence of acid in the solution might disrupt the alkalinity of the benedict’s and iodine reagent that were added after. Once it were hydrolyzed, the two reducing sugar were formed. This means that when benedict’s test was performed, the solution was able to reduce the reagent and formed a yellow
- 9. orange precipitate. InIodine’s test, the presence of amylase gave a positive indication which means that it is a polysaccharide. On the case of starch, after adding a significant amount of hydrochloric acid to the starch solution and heating the test tubes for a while, the iodine proved that a starch is a polysaccharide and there is the presence of amylase because it formed into a black precipitate. Once enough sodium hydroxide was added to the starch solution, it became slightly basic. This experiment showed that starch can be rehydrated with HCl and heat. This breaks the molecules up into single glucose molecules again causing the positive result in iodine’s test. H= molecules break up the glucose molecules. However, because these have strong bonds, heat was performed in order to create movement and weaken the bonds. This same process can also be applied to sucrose in order to achieve a similar result, but this will happen much faster because there are just enough bonds in sucrose compared to starch. Compare the results of the Benedict’s test with sucrose before and after hydrolysis. Why are they different? Before hydrolysis, sucrose formed into a blue-green precipitate, whereas after hydrolysis it formed into a yellow precipitate. Sucrose is called a non-reducing sugar because it does not reduce copper sulphate, thus the Benedict’s solution cannot break down the bonds of sucrose like other sugars. If sucrose is hydrolyzed to its constituent monosaccharides (glucose and fructose), it will give a positive Benedict's test. So sucrose is the only sugar that will give a negative Benedict's test before hydrolysis and a positive test afterwards. Boiling the test solution with dilute hydrochloric acid for a few minutes will hydrolyze the glycosidic bond forming the two monosaccharides or (reducing sugars) that will now be capable of reacting with the Benedict's solution.
- 10. Compare the resultsof the Benedict’s test with starch before and after hydrolysis. Why are they different? Before hydrolysis, starch formed a blue precipitate, whereas after hydrolysis it had a different color. Benedict’s reagent reacts with reducing sugars in order to produce a precipitate. Since starch is not a reducing sugar, Benedict’s test had a negative result. However, the hydrolysis of starch produces glucose which will react to Benedict’s reagent. As a result, benedict’s test after hydrolysis had a positive result. Compare the results of the Iodine test with starch before and after hydrolysis. Why is there a difference? Before and after hydrolysis on iodine’s test, both starch turned into a black precipitate which indicates a positive result because of the presence of amylase. Table 2.7 Fermentation test Carbohydrates Height of the bubbles Fermented (yes/no) Glucose 3.3 cm Yes Fructose 2.1 cm Yes Sucrose 2.0 cm Yes Lactose 1.8 cm Yes Maltose 1.4 cm Yes Starch 6.5 cm Yes Fermentation test using yeast is used to determine which carbohydrates substrates positively influence yeast fermentation since yeast seems to have greater ability to utilize certain carbohydrates. Fermentation is a process that is important in anaerobic conditions when there is no oxidative phosphorylation to maintain the production of ATP (Adenosine triphosphate) by
- 11. glycolysis. During fermentationpyruvate is metabolised to various different compounds. Homolactic fermentation is the production of lactic acid from pyruvate; alcoholic fermentation is the conversion of pyruvate into ethanol and carbon dioxide; and heterolactic fermentation is the production of lactic acid as well as other acids and alcohols. Typical examples of fermentation products are ethanol, lactic acid, and hydrogen. However, more exotic compounds can be produced by fermentation, such as butyric acid and acetone. Although the final step of fermentation (conversion of pyruvate to fermentation end-products) does not produce energy, it is critical for an anaerobic cell since it regenerates nicotinamide adenine dinucleotide (NAD), which is required for glycolysis. This is important for normal cellular function, as glycolysis is the only source of ATP in anaerobic conditions. Based on the results that were obtained from the experiment, all compounds were fermented. On the height of bubbles of each of the compounds, glucose was 3.3 cm, fructose was 2.1 cm, sucrose was 2.0 cm, lactose was 1.8 cm, maltose was 1.4 cm and starch was 6.5 cm. Table 2.8 Analysis of food products Food sample Benedict’s Test Barfoed’s Test Seliwanoff’s Test Iodine Test biscuit + + - + bread + + - + rice + - - + junk food (piattos) + + - + pork chop - - - + cake + + - + For the food samples that were brought by each group, the results on each tests had a positive result and a negative result. The food samples biscuit, bread, and cake had a positive
- 12. result in Benedict’s,Barfoed’s, and Iodine test whereas on Seliwanoff’s test, it had a negative result. On the other hand, the food sample rice had a positive result on both the Benedict’s test and Iodine test but it had a negative result in both Barfoed’s and Seliwanoff’s test. The junk food (Piattos) had a positive result on the three tests; the Benedict’s, Barfoed’s, and Iodine test but had a negative result on Seliwanoff’s test. Pork chop had a negative effect in Barfoed’s, Benedict’s, and Seliwanoff’s test but had a positive result on Iodine test. Conclusion Carbohydrates are the most abundant class of bioorganic molecules on planet earth. Although their abundance in the human body is relatively low, carbohydrates constitute about 75% by mass of dry plant materials. Green (chlorophyll-containing) plants produce carbohydrates via photosynthesis. In this process, carbon dioxide from the air and water from the soil are the reactants, and sunlight absorbed by chlorophyll is the energy source. There are several tests to use in order to determine a sample whether it is a carbohydrate or not, if it is a monosaccharide or a disaccharide etc. Some of the several tests use in determining carbohydrates includes, Benedict’s test for reducing sugars, Barfoed’s test for monosaccharides, Seliwanoff’s test for ketohexose, Iodine test for polysaccharides and hydrolysis of di- and polysaccharides. Benedict’s test for reducing sugar is a test that determines the amount and presence of reducing sugar in a particular solution. Barfoed’s test is used to distinguish monosaccharides from disaccharides. Seliwanoff’s test is used to distinguish between aldohexose and ketohexose. Iodine test is used for the detection of starch in the solution. Lastly, the hydrolysis of di- and polysaccharides used to breakdown to the monomer monosaccharides. Fermentation is also a test that can be used in carbohydrates. Fermentation test using yeast is used to determine which carbohydrates substrates positively influence yeast fermentation. Those following test that were stated above can help you determine the most efficient methods for utilizing these test when dealing with carbohydrates.
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