Carbohydrates: Structure and Properties | CH 106, Lab Reports of Chemistry

Download Carbohydrates: Structure and Properties | CH 106 and more Lab Reports Chemistry in PDF only on Docsity! CH106 Lab 22: Carbohydrates 293 LAB 22: CARBOHYDRATES: STRUCTURE AND PROPERTIES PURPOSE: To use physical and chemical tests to distinguish between simple and complex carbohydrates. To apply the chemistry of carbohydrates to cooking. SAFETY CONCERNS: • Always wear safety goggles. • Concentrated Sulfuric Acid is dangerous to skin, eyes, and clothes. Wash with soap and copious amounts of water if contacted. CARBOHYDRATES: Carbohydrates are the major components of plants, comprising 60 to 90% of their dry weight. They are produced by the process of photosynthesis in green leaves. SIMPLE CARBOHYDRATES: The common small, or simple carbohydrates, are made of one (mono) or two (di) units. Glucose, galactose, and fructose are simple monosaccharides that combine to form disaccharides such as maltose, lactose, and sucrose. Examples of Monosaccharides: Formula Structure Common Source Fructose C6H12O6 C C C C C O HO OH OH H H H OH H H C HH OH HO H OH H OH O HO OH H In honey Glucose C6H12O6 H OH OH H H OHH OH H O OH C O H C C C C OH HO OH OH H H H H CH H OH In fruits, vegetables, corn syrup CH106 Lab 22: Carbohydrates 294 Examples of Disaccharides: Formula Structure Common Source Sucrose C12H22O11 H OH H OHH OH H O OH HO OH H O HO OH H H O H In sugar cane and sugar beets Lactose C12H22O11 H OH H H OHH OH H O OH OH H H OHH OH H O OH O H In Milk COMPLEX CARBOHYDRATES: The complex carbohydrates amylose, and cellulose are long chain polymers of the simple carbohydrate glucose. Examples of Complex Carbohydrates: (Polysaccharides) Common Source Amylose: Polymer of α-D-glucose H OHH OH H O OH O H H H OHH OH H O OH O H OHH OH H O OH O H O H H H n Starches: Rice, wheat, potatoes, beans Cellulose: Polymer of β-D-glucose n H H OHH OH H O OH O H H H OHH OH H O OH H H OHH OH H O OH O O O H H Plant Fibers: Cotton, wood, stems, leaves Amylose, and its branched relative, amylopectin, are major components of starches, the energy storage carbohydrates found in tubers and edible roots. Amylose and amylopectin are polymers of D-glucose in which the anomeric carbon of each glucose unit is in the alpha (α) form. CH106 Lab 22: Carbohydrates 297 Tests for reducing sugars are commonly performed in medicine to identify the simple sugars present in blood or urine that may be indicators of metabolic problems or disease. Ketoses also act as reducing sugars because the ketone group on carbon 2 isomerizes in the presence of the base present in the Benedict’s reagent (NaOH) to give an aldehyde group on carbon 1 than can then be oxidized. C C C C C O HO OH OH H H H OH H H C HH OH HO H OH H OH O HO OH H C O H C C C C OH HO OH OH H H H H CH H OH NaOH C C C C C OH HO OH OH H H H OH H C HH OH Fructose Isomerized to an aldehyde Sucrose is not a reducing sugar because it has no hemiacetal groups. Under the conditions of the Benedict’s reagent, the acetal groups of the 1,2-glycosidic bond of sucrose cannot convert to open-chain aldehydes that would oxidize. Iodine Test for Polysaccharides: Amylose, the unbranched chain polymer of α-D-glucose in starch, coils into tight spirals. Elemental iodine, I2, which is normally yellow-brown in color, will fit inside the amylose coil and complex with the OH’s inside the spiral. The resulting amylose-iodine complex is a deep blue-black color. I2 (yellow/brown) Amylose Helix I2 I2 I2 I2 I2 Amylose/I2 Complex (blue/black) Iodine, I2, is commonly used as a test for the presence of amylose starch. Legal U.S. dollar bills made from a linen fabric will not react with iodine; however, the mark of the iodine pen on bills made from starched paper will show the characteristic dark blue sign of a counterfeit. CH106 Lab 22: Carbohydrates 298 Hydrolysis of Disaccharides & Polysaccharides: Each bond connecting monosaccharide units (the glycoside bond) can be broken by hydrolysis; the reaction with water in the presence of a catalyst. Disaccharides can thus be hydrolyzed into two monosaccharides. Long chain polysaccharides can be hydrolyzed into shorter chains or further into simple sugars. In the laboratory we can catalyze sugar hydrolysis reactions with acid, or we can use catalytic enzymes that are specific for each carbohydrate. Sucrose is hydrolyzed into glucose and fructose by catalysis with the enzyme, sucrase. Maltose hydrolyses into glucose with maltase. Lactose hydrolyses into galactose and glucose with lactase. H+, H2O or Sucrase H OH H OHH OH H O OH HO OH H O HO OH H H O H HO H OH H OH O HO OH H H OH OH H H OHH OH H O OH Sucrose Glucose Fructose + Amylose and amylopectin are easily hydrolyzed into shorter chains of glucose called dextrins which are then further hydrolyzed into the disaccharide maltose and then to glucose (blood sugar) itself. In our bodies the hydrolysis of starches in digestion is catalyzed by the enzymes amylase and maltase. People vary in the amount of amylase in their saliva or urine. Starch (Amylose, Amylopectin) H+, H2O or Amylase Dextrins Maltoses D-Glucoses H+, H2O or Amylase H+, H2O or Maltase The hydrolysis of cellulose can be catalyzed in the laboratory with acid or by the enzyme cellulase found in certain bacteria. The human body does not contain the enzyme cellulase and so cannot convert cellulose into glucose for use as an energy source. Therefore, the long chain of cellulose stays intact for use as fiber. Digestion & Absorption: Before the cells of your body can utilize the energy stored in carbohydrates present in your diet, the carbohydrates must be digested and absorbed. Digestion is the process by which complex molecules are broken down (hydrolyzed) into simple molecules. These simple molecules pass through the intestinal wall into the bloodstream during absorption. The digestion of carbohydrates begins in the mouth as teeth tear food into tiny pieces; smaller pieces have a greater surface area and will be digested faster. Saliva contains the enzyme, amylase, that begins the hydrolysis of starch to dextrins and then to maltose. After swallowing, the food enters the stomach where protein and fat digestion begin but carbohydrate digestion temporarily ceases; the low pH of the stomach’s gastric juice inactivates the salivary enzymes. As food passes into the small intestine it is neutralized by alkaline pancreatic and intestinal juices. Those juices also contain an enzyme that renews the hydrolysis of complex carbohydrates. Eventually all polysaccharides and disaccharides are broken CH106 Lab 22: Carbohydrates 299 down to glucose, fructose, and galactose. These monosaccharides are small enough in size to pass through the intestinal wall and are absorbed into the blood. After circulating in the blood, fructose, and galactose are converted into glucose by the liver. The glucose in the blood may be immediately used to provide energy for cellular activities or it may be stored as glycogen in the liver and the muscles. Absorption is a form of dialysis; the movement of small molecules through a membrane. In Part II of this experiment a solution of starch and glucose will be placed inside a cellophane dialysis bag. After the dialysis bag has been immersed in water for a length of time, the water will be tested for the presence of starch and glucose. Dehydration; Caramelization: When carbohydrates are either heated or reacted with acid, H’s and OH’s combine and leave as water, HOH. As water molecules begin to escape the carbohydrate begins to turn yellow, then brown, and then eventually black. If all of the OH’s on a carbohydrate are removed as water then all that remains of the compound is black carbon charcoal. This phenomenon is observed when food or wood is burned to blackness. C O H C C C C OH HO OH OH H H H H CH H OH H+1 or Heat C O H C C C C HO OH OH H H H CH H OH C O H C C C C HO OH H H CH H OH C O H C C C C H C H OH C complexes (black) Possible Dehydration Intermediates (yellow to brown) + H2O's As paper (a cellulose product processed with acid) ages it slowly dehydrates and turns yellow. Scrap-bookers prefer “acid-free” paper that will stay white longer. Caramel candy is sugar that has been heated so as to partially dehydrate. Loss of some of the OH’s from sugars results in a caramel brown color and also gives the characteristic taste of browned carbohydrates. A common method for making sauces and gravies uses the formation of a “roux”. Flour or starch is heated in oil until it browns. Water or milk is then added and the mixture heated to a thick sauce. The word “roux” is French for “red” and at some point in history came to mean flour that had been cooked long enough to change color. The fat and flour undergo browning reactions when cooked giving flavorful dehydrated molecules in much the same way as the caramelization process. The more the flour is browned the less power it has to thicken since some of the starch molecules shorten as well as dehydrate in the heating process. Therefore, more of a dark brown roux is needed to thicken a given amount of liquid than if using a pale roux. CH106 Lab 22: Carbohydrates 302 6. Report any discrepancies in your results. Did each sample give you the results expected? Explain any anomalies. 7. Dispose of the Benedict solutions in a designated waste container. VI. Hydrolysis of Starch: 1. Collect about 5 ml (one teaspoon) of saliva by spitting into a tube or beaker. 2. Break off a piece of saltine cracker13 approximately the size of a small pea. Crush the cracker into a fine powder with a mortar and pestle. 14 3. Place equal sized sprinklings of crushed cracker bit into separate test tubes labeled tube #1 and tube #2. 4. To tube #1 add 5 mLs of water. To tube #2 add 5 mLs of saliva. Mix each tube thoroughly, and allow them to sit at room temperature for at least 5 minutes. 5. Test each sample with the iodine test for the presence of starch as in Part IV by adding one drop of iodine solution (I2-KI) to each tube. Mix. Record your observations. 15 6. Test each sample for the presence of reducing sugars (glucose) with the Benedict’s test as in Part VII by adding 3 mLs of Benedict’s reagent to each tube and heat in a boiling water bath for 5 minutes or until a color change occurs. Record your observations. VII. Dehydration: A. Dehydration with Heat; Caramelization: 1. Obtain two 250 mL beakers. Into one pour about 10 mLs solid sucrose and into the other pour about 10 mLs solid starch or flour. 2. Observe the color, odor, chemical changes, etc. as you heat each sample over a hot plate or laboratory burner while stirring constantly.16 Stop heating when the samples starts to turn caramel brown. Record all observations on your report sheet. 17 3. Return the beaker of caramelled sugar to the hot plate to continue the dehydration just until you have observed that the sugar is turning black. Remove from heat. 4. Clean the beaker by boiling hot tap water in it until the burnt sugar is dissolved enough to be washed out. 13This experiment could be done with starch in any form. Cornstarch or bread crumbs also work. 14In the absence of a mortar & pestle place the cracker in a square of waxed paper. Fold the waxed paper over the cracker and crush. 15Not all people have the same amount of amylase in their saliva. Check the results of other class members to see how their amylase reacted. 16Stirring constantly keeps the sugar from burning. 17Notice any steam, water vapor, which may come from the reaction. The high heat forces the O’s and H’s to leave the carbohydrate as water. Once the O’s and H’s have left as water it is just the C’s, charcoal, which are left behind. CH106 Lab 22: Carbohydrates 303 B. Dehydration with Acid: 1. Fill a 50 mL beaker about ½ full with solid sucrose. 2. Move the beaker of sucrose to the fume hood. Pour 10 mLs concentrated Sulfuric Acid18 onto the sucrose and observe the color, odor, and chemical changes. Record all observations. 3. Place a drop19 of concentrated Sulfuric Acid on a piece of paper towel. Record your observations. VIII.PRACTICAL APPLICATIONS IN COOKING: (Instructor’s Choice) A. Gak 1. Mix completely 2 level Tablespoons of cornstarch20 with 1.5 teaspoons (7.5 mLs) of water in a small beaker. Pour this mixture into your hands and play with the results of this Gak and describe its texture on the report sheet. 21 B. Preparation of Gravy: Cornstarch method 2. In a separate beaker, heat ½ cup (120 mLs) of water22 (or broth). 3. With constant stirring, pour the corn starch gak23 made in Part XA into the hot water and bring to a boil for 1 minute or until smooth and bubbly. 24 Describe your results on the report sheet. C. Preparation of a Cheese Sauce: Roux method 1. Melt 2 level Tablespoons of triglycerides (fat)25 in a beaker over low heat stirring constantly. 2. Blend in 2 level Tablespoons of mixed Amylose & Amylopectic (cornstarch or flour)20 (and seasonings like salt, pepper, or dry mustard if making a real cheese sauce) Cook over low heat, stirring until mixture is smooth and bubbly. The mixture will brown as the amylose dehydrates. 3. Remove from heat. Stir in ½ cup (120 mLs) water (milk for a real cheese sauce) then stirring constantly, bring to a boil for 1 minute or until smooth and bubbly. (If really making a cheese sauce; blend in ½ cup cheese, cut up or grated. Stir until cheese is melted.) 4. Describe your results on the report sheet. Compare a sauce made with flour to that made with cornstarch. D. Preparation of Caramel Candy: 26 18Concentrated Sulfuric Acid is dangerous to your skin, eyes, and clothes. Do not breathe the vapors. Wash with copious amounts of water if contacted. 19Wiping the con H2SO4 from a dripping container would get the drop of acid you need on the paper towel. 20Various starches can be used as thickeners. Cornstarch gives a more transparent sauce. Flour gives a cloudy sauce because it contains insoluble suspended proteins. 21More water or starch may be added to reach the desired consistency. The gak should be cutable like a solid yet pourable like a liquid. If you pour the gak into your hand and squeeze it should crumble. 22The liquid could be broth that would become gravy. Adding gak to a pot of boiled vegetables and meat will create a thick soup or stew. 23If you add dry flour or starch to hot water H- bonding will occur on the surface of the starch granules and your gravy will be lumpy. 24You can vary the proportion of starch to liquid to make your gravy thinner or thicker. 25Any fat can be used. Gravies can be made by adding flour to melted shortening, margarine, or butter or the fat left behind from cooked meats like hamburger, bacon, or sausage. 26Find a recipe or make up one of your own. Be sure your method uses actual dehydration of sugar rather than some other more instant method. CH106 Lab 22: Carbohydrates 304 CH106 Lab 22: Carbohydrates 307 LAB 22: CARBOHYDRATES: NAME___________________ REPORT: PARTNER_________DATE___ I. Sweetness: Fructose Glucose Sucrose Aspartame Splenda Saccharin Order of Sweetness (Your Taste) Order of Sweetness (From Text) Compare your taste w/ text: II. Absorption: Solution inside tubing Solution outside tubing Iodine Test (for starch) Observations: Starch is Present or Not Present (circle one) Observations: Starch is Present or Not Present (circle one) Benedict’s Test (for glucose) Observations: Glucose is Present or Not Present (circle one) Observations: Glucose is Present or Not Present (circle one) Error Analysis: Are these results expected? Explain ___1. The dialysis tubing used to test absorption in Part II represents what part of the body? A. the stomach B. the lungs C. the intestines D. the throat 2. Why is it necessary that you digest (hydrolyze) starch food? III. Solubility: 1. Glucose 2. Sucrose 3. Starch Solubility (cold) Solubility (hot) 3. On the given structure of glucose, show how water molecules hydrogen bond to all possible locations: H O O H H OH O H O O H H H H H CH106 Lab 22: Carbohydrates 308 CHEMICAL REACTIVITY: IV. Iodine Test, I2: 1. Glucose 2. Sucrose 3. Starch Observation (color) Conclusion (Is Amylose present? Yes or No) Explanation (Why did this result occur?) ___4. Why does the blue color of Iodine disappear when amylose reacts with saliva? A. Saliva causes the amylose chain to uncoil so Iodine is no longer trapped. B. Saliva reacts with iodine causing it to be unable to complex with the amylose coil. C. Saliva causes the amylose chain to break into short chains and then into glucose which does not coil and so does not trap iodine. D. Amylase in saliva will replace the I2 in the amylose coil and so remove the color. V. Benedict’s Test: 1. Control 2. Fructose 3. Glucose 4. Sucrose 5. Lactose 6. Starch Color after Heating w/ Benedict’s Ion produced (circle one) Cu2+ or Cu1+ Cu2+ or Cu1+ Cu2+ or Cu1+ Cu2+ or Cu1+ Cu2+ or Cu1+ Cu2+ or Cu1+ Sugar Type (circle one) Reducing or nonreducing Reducing or nonreducing Reducing or nonreducing Reducing or nonreducing Reducing or nonreducing Reducing or nonreducing Error Analysis Is this result reasonable. Why or why not? 1. Show the equation for the reaction between lactose and Benedict’s reagent. ___2. Sucrose is a nonreducing sugar because A. it makes a person gain weight B. it does not contain a hemiacetal group C. it is a monosaccharide D. it is a disaccharide CH106 Lab 22: Carbohydrates 309 VI. Hydrolysis: Crushed Cracker in Water Crushed Cracker in Saliva Iodine Test (for starch) Observations: Starch is Present or Not Present (circle one) Observations: Starch is Present or Not Present (circle one) Benedict’s Test (for glucose) Observations: Glucose is Present or Not Present (circle one) Observations: Glucose is Present or Not Present (circle one) Explanation: How do the results indicate if hydrolysis has occurred? Error Analysis: Are these results expected? Explain ___1. Why do crackers and toast have the potential to taste sweet after chewing in your mouth? A. Amylose is naturally sweet tasting. B. Amylose reacts with amylase in saliva and produces glucose which tastes sweet. C. Amylose reacts with sucrase and produces sweet tasting sucrose. ___2. Why do infant formulas often contain mixes of dextrins and maltose rather than starch? VII. Dehydration with Heat and Acid: Observations for Each Explanation Heat on Sucrose Heat on Starch (What is the heat doing and why?) Acid on Sucrose Acid on Cellulose (What is the acid doing and why?) Show the reaction of partial caramelization of sucrose: (Show any potential product). H OH H OHH OH H O OH HO OH H O HO OH H H O H heat or H+