Carbohydrates [PDF]

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.

Background Information: 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. 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: Monosaccharides Fructose

H

C6H12O6

C

O

C

H

H

C

OH

H

C

OH

H

C

In fruits, vegetables, corn syrup

C12H22O11

H OH

OH

H

O OH

C O

H OH

OH

H H

OH H

OH

H

H

C

OH

HO

C

H

H

C

OH

H

C

OH

H

C

H

In sugar cane and sugar beets

HO H

O

H

HO

H

H

OH

O

H OH

Glucose

C6H12O6

Sucrose HO OH

HO

In honey

Disaccharides: OH C H

H OH

H

H

OH

H O H

HO

O

OH OH

Lactose

OH

H OH

C12H22O11

OH

O

H O

OH

In Milk

H

H

OH

OH

O

H OH

H

H H

H

OH

H OH

H

OH

Complex Carbohydrates (Polysaccharides): The complex carbohydrates amylose, and cellulose are long chain polymers of the simple carbohydrate glucose.

Examples: Amylose: Polymer of alpha-D-glucose In Starches: i.e. Rice, wheat, potatoes, beans

O

H

OH

OH

OH

H

H

OH

O

H

H

H OH

H OH

H

H

OH

H OH

H

H

O

O

O

O

H

H

O H

OH

n

Cellulose: Polymer of beta-D-glucose

OH OH OH

In Plant Fibers: i.e. Cotton, wood, stems, leaves

H OH

O

H

H

H

OH

O

H

CH243 Lab 22: Carbohydrates(S15)

H

H

OH

H

H H

H

O

H OH O

O

H OH

O

H O

H

OH

n

1

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 () form.

Cellulose is plant structure material like that of wood, stems, and leaves. The major function of cellulose for us is not as a source of glucose for energy, but rather as fiber to keep our digestive tract clean. Cellulose is a polymer of D-glucose in which the anomeric carbon of each glucose unit is in the beta () form.

Sweetness: Simple carbohydrates are called saccharides from the Latin term saccharum (sweet) because of their sweet taste. Many of the small carbohydrates, mono and disaccharides, are used as sweeteners. They fit into the taste receptor sites on our tongues and send the signal to our brains that we call sweet. Artificial sweeteners are not usually carbohydrates and are not metabolized in the same way as natural sugars. Artificial sweeteners mimic the shape of simple sugars and will fit into the same taste receptor sites that natural sugars do and so send to our brains a similar “sweet” signal.

Examples of Artificial Sweeteners: OH Sucralose Cl O

Cl H OH

“Splenda”

C12H19O11Cl3

Saccharin

H

O H

H

N

HO

H

O

H OH H

O

C7H5NSO3

H

H

“Sweet’N Low”

Cl

OH

S O

O

Aspartame O

C14H18O5N2

C

NutraSweet® “Equal”

OH

CH2 O H2N

CH

C

CH2 O NH

CH

C

O

CH3

Using sucrose (common table sugar) as a standard (given a “sweetness value” of 1.00) the following list shows the relative sweetness of common natural and artificial sweeteners.

Relative Sweetness Lactose Galactose Maltose Sorbitol

0.16 0.30 0.33 0.36

Glucose Honey Sucrose Invert Sugar Fructose

0.75 0.97 1.00 1.25 1.75

Sodium Cyclamate Aspartame Saccharin Sucralose

30 180 450 600

Solubility: Mono and Disaccharides are soluble in water since they have many exposed OH’s along their surfaces which can easily hydrogen bond with water. Larger carbohydrates can still be soluble depending on the positioning of their OH’s. If the OH’s are abundant on the exterior of a carbohydrate (even a large one) then hydrogen bonding with water can occur and the carbohydrate can be made to dissolve in water. If, however, there is internal hydrogen bonding within a carbohydrate, or coiling that may prevent water from hydrogen bonding to the OH’s, then the carbohydrate will not dissolve in water. Starch granules, tightly coiled strands of amylose and amylopectin, are not soluble in water at ordinary temperatures and so are convenient forms in which to store the plant’s excess energy supplies. Roots and seeds are the organs in which starch is usually concentrated. Forms of amylose starch can be made to be soluble by heating in water so as to disrupt the solid packing of the strands. The coils unravel into long strands of amylose which have OH’s more exposed to hydrogen bond with water. Not only are the uncoiled strands more water soluble but they can also tangle with each other to form gels. We often use these “unraveled” starch strands as thickeners in cooking or for stiffening fabrics. Although there are some forms of soluble fiber (like in oatmeal), most plant cellulose is not water soluble even with heating. Cellulose strands have a lot of internal hydrogen bonding with themselves and each other. They form tight, twisted cables that make very strong structure material that does not unravel even in hot water.

2

CH243 Lab 22: Carbohydrates(S15)

CHEMICAL REACTIONS OF CARBOHYDRATES: Seliwanoff’s Test for Ketoses vs Aldoses:

When monosaccharides are mixed with hot hydrochloric acid and resorcinol (Seliwanoff’s reagent) ketohexoses will quickly produce a red color but aldohexoses will react slower and produce a light orange-pink color. This test is most sensitive for fructose, which is a ketose. Any polysaccharides or disaccharides tested will hydrolysis to monosaccharides in the aqueous hydrochloric acid of the reagent. OH Monosaccharides

HCl, H2O heat

+

Ketoses = Red Aldoses = Pink

OH Resorcinol

Benedict’s Test for Reducing Sugars: All of the monosaccharides and most of the disaccharides can be oxidized. When their cyclic (furanose or pyranose) hemiacetal structures open an aldehyde group formed, HC=O, is available for oxidation to a carboxylic acid. Benedict’s reagent, a basic solution of Copper (II) Sulfate, (CuSO4 in NaOH) is commonly used for this purpose. The oxidizing agent, CuSO4, is blue in color which is characteristic of many Cu2+ compounds. When the blue Cu2+ of CuSO4(aq) causes the sugar aldehyde to oxidize it becomes reduced itself to Cu1+ in the form of Copper I oxide, Cu2O(s) which is a brick red precipitate. A sugar that reduces blue Cu2+ to brick-red Cu1+ is called a reducing sugar. The color of the precipitate varies from green to gold to red depending on the concentration of the reducing sugar. O OH O

H H OH

OH

H H

OH H

OH

O

C

H

H

C

OH

HO

C

H

H

C

H H

C

OH

H

C

OH

HO

C

H

OH

H

C

OH

C

OH

H

C

OH

C

H

H

C

Cu+2 (blue)

OH

Cu1+ + (brick red)

H OH

Glucose

Gluconic Acid

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

OH H

C

O

HO

C

H

H

C

H

C

H

C

H

HO OH O H

HO

H OH

H

OH

C

C

H

H

C

OH

HO

C

H

OH

H

C

OH

OH

H

C

OH

H

C

C

OH

HO

C

H

OH

H

C

OH

H

C

H

C

H OH

O

OH H

NaOH

H OH

Fructose

H OH

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.

Tollen’s Test:

Aldehydes react with silver ions (from AgNO3) to form carboxylic acids and silver metal. The silver metal coats the inside of the test tube to form a silver mirror. CH243 Lab 22: Carbohydrates(S15)

3

Colorization of Iodine: Test for Polysaccharides: Amylose, the unbranched chain polymer of -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 I2

I2 (yellow/brown)

I2 I2 I2

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.

Amylose/I2 Complex (blue/black)

Amylose Helix

Hydrolysis:

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. 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 a 50:50 mixture of glucose and fructose by catalysis with the enzyme, sucrase. Maltose hydrolyses into glucose with maltase. Lactose hydrolyses into galactose and glucose with lactase. OH

OH O

H H OH

HO H

H O H

H

HO

O

OH OH H

OH

H

H+, H2O or Sucrase

O

H

HO OH

H

OH H

H

+ H

OH OH

Glucose

Sucrose

OH O

H OH

HO

H OH

H

OH

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

H+, H2O or Amylase

Maltoses

H+, H2O or Maltase

D-Glucoses

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 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.

4

CH243 Lab 22: Carbohydrates(S15)

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. O

O

C

H

H

C

OH

HO

C

H

H

C

OH

H

C

OH

H

C

H OH

C H+1 or Heat

O

O H

H

C

HO

C

H

C

OH

H

C

OH

H

C

H OH

C

C

H H

C

HO

C

C

H

C

C

H

H

C

H

C

OH

C

C

H

C

OH

C + H2O's complexes (black) H OH

Possible Dehydration Intermediates (yellow to brown)

As paper (a cellulose product processed with acid) ages it slowly dehydrates and turns yellow. Acid acts as a catalyst to make the dehydration faster. Scrap-bookers prefer “acid-free” paper that will stay white longer.

Caramelization occurs when carbohydrates (small or large) partially dehydrate and decompose with heat or acid to give flavorful molecules.

Loss of some of the OH’s from sucrose, glucose, and fructose results in a caramel brown color and also gives the characteristic taste of browned caramel candy. Loss of some of the OH’s from amylose in starch also results in browning. 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. Flour undergoes browning reactions when cooked giving flavorful dehydrated molecules in much the same way as the caramelization process. A common method for making sauces and gravies uses the formation of a “roux”. Flour or starch (complex carbohydrate; amylose and amylopectin) is heated in oil until it browns. Water or milk is then added and the mixture heated to a thick sauce. 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. 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.

Gluten: Gluten is a protein complex formed from the proteins glutenin and gliadin found in wheat and related grains such as barley and rye. It gives elasticity to dough, helping it rise, keep its shape, and creates a chewy texture. Without it, there would be nothing to hold the gas that makes bread rise. You might think of gluten as the rubber of a balloon: The stronger it is, the more gas it can hold. High-protein flour will make a dough with strong gluten, good for hearty yeast breads. However, for many baked goods, like pastries and pie crusts, pastry chefs want to avoid gluten development so prefer lowprotein flours that yield delicate, tender doughs. In baking, gluten is mainly used for the light texture and distinct taste it gives bread. But as a protein it is also nutritious. When flavored it becomes a vegan “meat” (called seitan) and it is a common chewy protein addition to vegetarian or vegan stir-fries and stews. CH243 Lab 22: Carbohydrates(S15)

5

NOTES:

PROCEDURES:

1

There will be a variety of results here as personal tastes vary.

ACTIONS:

PHYSICAL PROPERTIES: I. Sweetness: 1. Taste a small sample of each sugar or sweetener available and rank them in order of sweetness.1 (#1 being the sweetest.)

2

Do your tastes match the predicted order or are there discrepancies?

2. On the report sheet, record the predicted order of sweetness from your textbook. Compare your taste results with the predicted order and report your observations.2

II. Absorption:

3

1. Obtain 5 inches (about 13 cm) of dialysis tubing. Open the tubing under a stream of tap water and then tightly tie one end of it closed with heavy thread.

Dialysis Bag Set Up:

2. Into the open end of the tubing pour 5 mLs of a 1% starch solution. 3. To the tubing of starch now add 5 mLs of 20% glucose solution and then tie the open end of the tubing tightly closed with heavy thread. 4. Under a gentle stream of tap water gently and quickly rinse off the outside of the filled tubing to remove any solutions that may have leaked or spilled during filling. 5. Tie both ends of the filled dialysis tubing to a stirring rod and suspend the bag in a 150 mL beaker of deionized water as shown. 3 6. Note the start time and allow the bag to remain in the water while you continue with the rest of the laboratory procedures (at least an hour if not more). 7. After at least 1 hour, remove the dialysis tubing, cut the string at one end, and pour the contents into a clean beaker. This is the “inside” sample. The water remaining in the 150 mL beaker will be the “outside” sample. 4

8. Obtain 4 test tubes. Into 2 tubes put 1 mL of the “inside” sample (label “In”) and into the other 2 tubes put 1 mL of the “outside” sample (label “Out”) to test.4 9. Test one “inside” sample and one “outside” sample for the presence of starch by adding 1 drop of I2/KI to each tube as in the iodine test for starch Part IV. 10. Test the other “inside” sample and “outside” sample for the presence of glucose with the Benedict’s test for reducing sugars in Part VI.

6

CH243 Lab 22: Carbohydrates(S15)

You are testing to see if any starch or glucose passed through the dialysis tube into the beaker water.

III. Solubility:

Notes:

1. Obtain 3 stoppered test tubes.

Into tube #1 put a corn kernel sized scoop2 of glucose (a monosaccharide). Into tube #2 put a corn kernel sized scoop of sucrose (a disaccharide). Into tube #3 put a corn kernel scoop of corn starch (a polysaccharide).

2. To each tube add 5 mLs water.3 Stopper and shake each tube to mix. Record the solubility of each (S = soluble, I = insoluble, and PS = only partially soluble) on the report sheet. 3. If any of the samples are not completely soluble in cold water, warm their test tubes by letting them stand in hot water or carefully4 warm them over the flame of a laboratory burner. Record the solubility of each. Make note of any thickening properties of starch. 5 4. Save these samples to use in the next section (Part III).

IV. Hydrolysis: Reaction of Amylase with Starch 1. Take the 3 samples you used to test for solubility and number them (#1 glucose, #2 sucrose, & #3 starch6) 2. Into another tube numbered #0 put about 5 mLs water. Put it first in your line up of sugar samples to use as the control.7 3. Obtain 2 more clean test tubes.  Label one tube #4. Pour ½ of the contents of starch tube #3, into tube #4. This will give 2 starch samples to compare.  Into the other tube spit enough saliva to measure about 1 inch. 4. Pour the saliva into starch tube #4. 5. Set tubes (#0 through #4) aside for about 20 minutes.

Colorization of Iodine, I2: Test for Amylose:

6. After about 20 minutes: a. Into sample tubes #0-4 add 1-2 drop of Iodine, Potassium Iodide (I2, KI) solution.8 Stopper and shake each to mix. b. Observe and record the color of all samples and note the presence of amylose. 9

CH243 Lab 22: Carbohydrates(S15)

2Use

the same size sample for each item so you can compare solubilities. 3This

measurement does not need to be exact. Make the first measurement with a graduated cylinder and then estimate the others by comparing the levels with that of the 1st tube. 4If

heating with a flame, hold the tube with a wire test tube holder high in the flame just enough to warm it. Point the tube away from people. Avoid loss of water from heating. If water is lost add more to maintain 5 mLs of solution. 5To

further explore the thickening properties of cornstarch you can make Gak:  Mix completely 2 level Tablespoons cornstarch15 with 1.5 teaspoons (7.5 mLs) of water in a small beaker. More 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. Adding gak to a pot of broth or boiled vegetables and meat will create a gravy or thick soup or stew. You can vary the proportion of starch to liquid to make your gravy or stew thinner or thicker. 6This

experiment could be done with starch in any form even crushed crackers or bread crumbs. 7A

control sample should show no reaction. We use it as a reference to which we can compare the others to tell if a reaction has taken place. 8Iodine,

I2, turns dark blue if it complexes with the spiral form of amylose in starch. 9Not

all people have the same amount of amylase in their saliva. Check the samples of other class members to see how their amylase reacted.

7

14

V. Seliwanoff’s Test for Ketoses: 1. To each sample tube in set “C” add about 1 mL6 of Seliwanoff’s14 reagent and then place them in the boiling water bath for about 8 minutes. Continue with the rest of the lab while waiting.

Seliwanoff’s reagent is a solution of hydrochloric acid and resorcinol. 15

2. Remove the test tubes and observe the colors produced.

15

VI. Benedict’s Test for Reducing Sugars:

Ketohexoses will produce a red color; aldohexoses will turn light orange.

1. Set up a boiling water bath by filling your largest beaker 1/4th full of water and heating on a hot plate.

18

2. Obtain 6 clean test tubes and label them 1-6. Place 1 mL (or 20 drops)6 of the following samples into each of the tubes:  Into tube #1 put 1 mL of deionized water as control samples. 10  Into tube #2 put 1 mL of 1% fructose.  Into tube #3 put 1 mL of 1% glucose.  Into tubes #4 put 1 mL of 1% sucrose.  Into tubes #5 put 1 mL of 1% lactose.  Into tubes #6 put 1 mL of 1% starch.

19

3. From Part II, the absorption test, you saved samples to test. Place the Inside (“In”) sample tube and the outside (“out”) sample tube saved from Part II in your line up of samples to test.

21

Benedict’s reagent is a solution of copper (II) sulfate in sodium hydroxide. Benedict’s reagent will react with any carbohydrate that can form a free aldehyde group in solution. These “reducing” sugars will reduce the blue Cu2+ ions in the solution to produce red Cu1+ ions instead. 20

Dispose of the Benedict solutions in a designated waste container. Tollen’s Reagent (to be made within

one hour of use):



4. To each sample tube add 3 mL of Benedict’s reagent.18 Stopper and shake each to mix. 5. Place all 8 tubes into the boiling water bath at the same time with the stoppers on very loosely so they do not pop off during heating. Remove the tubes after about 5 minutes and record any color changes. 6. On the report sheet circle the ion responsible for the color of each solution after the reaction is complete. Label each sample as reducing or nonreducing. 19 7. Report your conclusions. waste.20

Explain any anomalies.

Dispose of

VII. Tollen’s Test 1. Put 20 drops of glucose solution into a small clean and dry test tube with stopper. 2. Add 20 drops of freshly prepared Tollen’s reagent.21 Stopper and shake until glass tube is coated with silver. 3. Discard waste into designated silver waste container.

8

CH243 Lab 22: Carbohydrates(S15)

   

Add concentrated ammonium hydroxide dropwise to 10 mL of 0.1M silver nitrate solution until the initial precipitate just dissolves. Mix with a glass stir rod. Add 5 mL of 0.8M KOH solution; a dark precipitate will form. Add more con ammonium hydroxide dropwise until the precipitate just redissolves. Dispense from a dropper bottle. To avoid the formation of explosive silver nitride, discard any remaining active solutions by washing down the drain with plenty of water.

VIII. Dehydration / Caramelization: A. Dehydration of Sucrose with acid

1. Into a 50 mL beaker pour solid sucrose up to about the 25 mL mark. 2. Move the beaker of sucrose to the fume hood. Pour 10 mLs concentrated Sulfuric Acid10 onto the sucrose and observe the color, odor, and chemical changes. Record all observations.

B. Dehydration of Cellulose with acid

3. Place a drop11 of concentrated Sulfuric Acid on a piece of paper towel. Record your observations.

C. Caramel12: Dehydration of Sucrose with heat 1. Prepare a beaker of ice water for use in step 4. 2. Into a 250 mL beaker put about 10 mLs of solid sucrose and 10 mL water. 3. Observe the color, odor, chemical changes, etc. as you heat the sucrose over a hot plate or laboratory burner while stirring constantly. 13 Observe the color changes as heating progresses. Stop heating when the sugar turns to a deep caramel brown liquid.14 Record all observations on your report sheet. 4. Drop some of your hot liquid caramel into ice water and record the results.

10Concentrated

Sulfuric Acid is dangerous to your skin, eyes, and clothes. Do not breathe the vapors. Wash with copious amounts of water if contacted. 11Wiping

the con H2SO4 from a dripping container would get the drop of acid you need on the paper towel. 12To

make a caramel syrup at home 1. Heat 1 c sugar and 1 cup water in a heavybottomed saucepan. Place over medium heat and cook, stirring occasionally, until the sugar dissolves and comes to a boil. Continue cooking, brushing down the sides of the pan with a wet pastry brush but without stirring, until mixture becomes golden amber in color. 2. Immediately remove from heat and add 1 cup water. Return to heat and continue stirring until mixture becomes liquid. Transfer to a heatproof container and let cool completely before using. 13Stirring

constantly keeps the sugar from

burning. 14Notice

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 all of the O’s and H’s have left as water it is just the C’s, charcoal, which would be left behind. 15Any

fat can be used. Gravies can be made by adding flour to the fat left behind from cooked meats like hamburger, bacon, or sausage. 16Use

equal amounts of oil and flour when making roux. 17Other

5. Clean the beaker by boiling hot tap water in it until the caramel is dissolved enough to be washed out.

D. Roux: Dehydration of Amylose and Amylopectin with heat

1. Melt 2 level Tablespoons of shortening or oil15 in a beaker over low heat stirring constantly. 2. Gradually blend in 2 level Tablespoons16 of flour17 and whisk to make smooth. 18 3. Cook over low heat, stirring constantly. The flour will turn darker shades of brown as the amylose dehydrates. 19 4. Remove from heat. Stir in ½ cup (120 mLs) water20 then stirring constantly; bring to a boil for 1 minute or until smooth and bubbly. Liquid amounts can be varied for a thinner or thicker sauce. 21

starches can be used as thickeners. Cornstarch gives a more transparent sauce. Flour gives a cloudy sauce because it contains insoluble suspended proteins. 18Seasonings

like salt, pepper, or dry mustard can be added also. 19The

color ranges from a peanut butter color to a dark brown (red brown or color of milk chocolate) and has a nutlike odor. It will be very thick and pasty. 20For

making cheese sauce use milk then once mixture is smooth and bubbly blend in ½ cup grated cheese and stir until melted. 21As

your roux gets darker, it gains flavor and color but loses some of its thickening power. Dehydration and decomposition result in shorter carbohydrate chains that taste great but do not tangle and thicken as well as longer chains. 22

An additional experiment could be done to compare a sauce made with flour to that made with cornstarch.

5. Describe your results on the report sheet. 22 CH243 Lab 22: Carbohydrates(S15)

9

IX. Gluten Content in Flour: 1.

Obtain ½ cup of all-purpose flour22 and place in a beaker or bowl.

2.

Slowly add about 60 mL (¼ cup) water to the flour and mix. Adjust with a little more flour or water a little at a time to create a dough that can be worked with your hands.

3. Knead23 the flour/water mixture until it forms a soft, rubbery ball of dough. Make note of the texture, flexibility, and elasticity. Let the dough ball sit for about 10 minutes if there is time. 4. Place the dough under a gentle flow of cold water at a sink faucet while holding23 and gently squeezing to allow the starches and other water soluble components to dissolve and wash away. 24 Be careful not to let the dough disintegrate. 5. Once no more starch appears to wash away25, press out any extra water and place your gluten ball on a baking sheet. Note the changes in size and texture.26 6. Bake the gluten balls in an oven for about 1520 minutes at 232oC (450oF). 27

22A

variety of wheat based flours may be used and the amount of gluten in them compared. Possible flours to use could be:  whole wheat flour  bread flour  all-purpose flour  pastry flour  gluten flour  instant flour  cake flour A qualitative comparison could be made just by comparing the sizes of the gluten balls produced. A quantitative comparison could be made by determining the percent gluten in each type of flour. To determine the percent gluten measure the mass of the flour used and the mass of gluten produced then calculate as follows: Mass gluten obtained x 100 = % gluten Mass Flour Used 23When

you knead dough, you help two proteins in wheat flour, gliadin and glutenin, form gluten. 23Try

cupping your hands around the ball and squeezing gently to remove the starch. With lowgluten cake or pastry flours, you may want to put the dough in cheesecloth in order to hold it together. 24You’ll

notice the water turning milky as it washes away the starch. 25You’ll

know the starch is gone when the wash water no longer becomes milky. 26Your

dough ball will become a gummy, slimy network of gluten protein strands. 27Flavor

the gluten before baking with soy sauce, ginger, garlic, and seaweed or other spices to make the vegan “meat” called seitan.

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CH243 Lab 22: Carbohydrates(S15)

LAB 22: CARBOHYDRATES: PRE LAB EXERCISES:

NAME_____________ DATE______________

More than one answer may be required. Give all correct answers. ___1.

Which of the following are not carbohydrates? A. fructose C. aspartame E. saccharin B. glucose D. cellulose F. sucrose

___2.

The major component of paper is _____ A. amylose B. cellulose C. glucose

D. cellulite

___3.

What is most important in making a carbohydrate water soluble? A. The ratio of O’s relative to C’s in the structure. B. The ratio of OH’s relative to C’s in the structure. C. The ratio of OH’s available to hydrogen bond with water relative to C’s in the structure. D. Monosaccharides are water soluble but the others are not.

___4.

Seliwanoff’s test is used to distinguish A. a ketose from an aldose. B. a monosaccharide from a disaccharide. C. a monosaccharide from a polysaccharide D. a reducing sugar from a nonreducing sugar.

___5.

Which of the following statements explains the basis for obtaining a positive Benedict’s test? A. A secondary alcohol is being oxidized to form a ketone. B. A primary alcohol is being oxidized to form an aldehyde. C. An aldehyde is being oxidized to form a carboxylic acid. D. A tertiary alcohol cannot be oxidized easily.

___6.

When a dilute iodine solution is placed on a slice of bread, the solution turns dark blue because bread contains A. glucose B. sucrose C. protein D. amylose

___7.

Amylose differs from amylopectin in that _____ A. Amylose is digestible by humans but amylopectin is not. B. Amylose is branched but amylopectin is a straight chain. C. Amylopectin is branched but amylose is a straight chain. D. Amylose is a polymer of -D-glucose but amylopectin is a polymer of -Dglucose.

___8.

Why does a solution made of starch get thick when heated in water? A. Granules of starch uncoil to give long strands that tangle into a gel. B. Starch granules stack in an organized pattern that makes the mixture solid. C. Starch is insoluble so just forms complexes of suspended solids which thicken the mixture. CH243 Lab 22: Carbohydrates(S15)

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12

CH243 Lab 22: Carbohydrates(S15)

LAB 22: CARBOHYDRATES:

NAME___________________ PARTNER_________DATE___

REPORT:

I. Sweetness: Rank in order of sweetness from 1-6 (#1 being the most sweet) 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 Iodine Test

Observations:

(for glucose)

Observations:

Present or Not Present

(for starch)

Benedict’s Test

Starch is

Solution outside tubing Starch is Present or Not Present

(circle one) Observations:

Glucose is

(circle one) Observations:

Glucose is

Present or Not Present

Present or Not Present

(circle one)

(circle one)

Conclusion/Explanation/Analysis: Why were the results this way? Explain any anomalies.

___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 starch food be hydrolyzed in digestion rather than left in polymeric form?

3. Why do infant formulas often contain mixes of dextrins and maltose rather than starch?

CH243 Lab 22: Carbohydrates(S15)

13

III. Solubility: 1. Glucose Solubility

cold

2. Sucrose

hot

cold

3. Starch

hot

cold

hot

Conclusion/Explanation/Analysis: Why were the results this way? Explain any anomalies.

1. On the given structure of glucose, show how water molecules hydrogen bond to all possible locations: O

H O

H H O

H

O

H

H H

O H H

O H

IV. Hydrolysis /Iodine Test, I2, for Starch 0. Control Observation

1. Glucose

2. Sucrose

Color

Color

Color

3. Starch Color

4. Starch + Saliva

(Amylose) Amylose?

(Amylose + Amylase) Color Amylose?

Yes or No

Yes or No

(circle one)

(circle one)

(> 20 min w/ I2)

Conclusion/Explanation/Analysis: Why did these results occur? Explain any Anomalies.

V. Seliwanoff’s Test: 1.Control

2.Fructose

3.Glucose

4.Sucrose

5.Lactose

6.Starch

Observation Conclusion Ketose (K) or Aldose (A) ?

Conclusion/Explanation/Analysis: Why did these results occur? Explain any Anomalies.

___4.

Why does sucrose turn red with Seliwanoff’s reagent? A. Sucrose is a ketose B. Sucrose is an aldose C. Sucrose hydrolyses in the acidic Seliwanoff reagent to produce a ketose which then reacts to turn red. D. Sucrose hydrolyses in the acidic Seliwanoff reagent to produce an aldose which then reacts to turn red.

___5.

What does sucrose become upon hydrolysis in acid? ____________________________________

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CH243 Lab 22: Carbohydrates(S15)

VI. Benedict’s Test: 1. Control Color after Heating w/ Benedict’s Ion produced (circle one)

2. Fructose

Cu2+

Cu2+ or

3. Glucose

Cu2+

4. Sucrose

Cu2+

5. Lactose

Cu2+

or

Cu2+

or or or Cu1+ Cu1+ Cu1+ Cu1+ Reducing Reducing Reducing Reducing Reducing Sugar Type or or or or or (circle one) nonreducing nonreducing nonreducing nonreducing nonreducing Conclusion/Explanation/Analysis: Why did these results occur as they did? Explain any Anomalies. Cu1+

1.

6. Starch

or Cu1+ Reducing or nonreducing

Show the equation for the reaction between lactose and Benedict’s reagent.

___2.

Sucrose is a nonreducing sugar because it A. makes a person gain weight

B. does not contain a hemiacetal

C. is a monosaccharide

D. is a disaccharide

VII. Tollen’s Test: Reaction: Draw the reaction of glucose with Tollen’s reagent.

Observations:

Conclusions/Explanation/Analysis: Why were the results as they were? Explain any anomalies

CH243 Lab 22: Carbohydrates(S15)

15

VIII. Dehydration with Heat and Acid: A-D. Dehydration with Heat and Acid: Observations Acid on Sucrose

Acid on Cellulose

Heat on Sucrose (Caramel)

Heat on Amylose (Roux)

Conclusion/Explanation/Analysis: Why did these results occur?

Give an explanation that covers all of these results.

Show the reaction of partial caramelization of sucrose: (Show any potential product). OH O

H H OH

H

H

OH

HO H

H H

HO

O

OH OH

___ 4. ___ 5. ___ 6.

16

heat or H+

O

H

OH

The gaseous substance that is driven off of sucrose when it is heated is __ A. CO2 B. SO3 C. CH4 D. H2O The gaseous substance that is driven off of sucrose when it is reacted with acid is __ A. CO2 B. SO3 C. CH4 D. H2O The black residue left over after complete dehydration of a carbohydrate is ___ A. C B. SO3 C. HSO2 D. H2O

CH243 Lab 22: Carbohydrates(S15)

IX. Gluten from Flour: Observations: Describe what you observed in the process of forming and isolating gluten.

Conclusion/Explanation/Analysis: What did you learn from isolation of gluten?

CARBOHYDRATES: RELATED EXERCISES:

NAME __________

___1.

Glucose (C6H12O6) is soluble in water but is not soluble in hexane (C 6H14) because __ A. compounds that have many OH’s have polarity that attracts polar water but repels nonpolar hexane. B. compounds that contain oxygen will repel compounds that don’t. C. hexane is an organic solvent and glucose is not an organic compound. D. glucose has fewer hydrogens than hexane.

___2.

Cellulose is essential in human nutrition because _____ A. it is undigestible so remains as long strands that act as fiber. B. it can be hydrolysed to form glucose which will be used as blood sugar. C. it is undigestible and so acts as filler in food products so we can avoid calories. D. it can be digested to form glucose which will be used as blood sugar.

___3.

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.

___4.

Why does the blue color of Iodine disappear when amylose reacts with saliva? A. Amylase in saliva causes the amylose chain to uncoil so Iodine is no longer trapped. B. Amylase in saliva reacts with iodine causing it to be unable to complex with the amylose coil. C. Amylase in 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.

___5.

Which carbohydrate(s) would you expect to produce both a reddish-orange solid with Benedict’s and a red color with Seliwanoff’s reagent? A. Fructose B. Glucose C. Sucrose D. Lactose E. Amylose

___6.

Which carbohydrate(s) would give both a color change with Benedict’s and a light pink-orange color with Seliwanoff’s reagent? A. Fructose B. Glucose C. Sucrose D. Lactose E. Amylose

___7.

Which carbohydrate(s) would not produce a color change with Benedict’s, would produce a light pinkorange color with Seliwanoff’s reagent, and would turn a blue-black color with iodine reagent? A. Fructose B. Glucose C. Sucrose D. Lactose E. Amylose

CH243 Lab 22: Carbohydrates(S15)

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