FOOD CHEMISTRY EXPERIMENT BOOK

Unit 1. CARBOHYDRATES

Teacher Activity Guide

Student Activity Guide

Figure 1

Activity/Experiment

Cryptic Carbohydrates

Cool Carbs

Unit 1. CARBOHYDRATES

Teacher Activity Guide

Expected Outcome

Activity Objective

Activity Length

Scientific Principles

Vocabulary

Amylase is an enzyme that hydrolyzes starch polymers to yield glucose and maltose.Salivary amylase begins the chemical breakdown of large starch molecules into smaller sugar molecules.

Carbohydrate is a compound of carbon and water with the basic formula CnH2On-. [Note:condensation products, such as sucrose, have one less H2O and a formula CnH2O(n-1)].Carbohydrates are the most abundant of all carbon-containing compounds, composingnearly three-fourths of the dry mass of all plant life on earth. Examples of carbohydrates include glucose, sucrose (table sugar), starch, and cellulose.

Cellulose is a polymer of glucose, linked by beta-1,4-glycosidic bonds. It is a complexcarbohydrate similar in structure to starch. Examples are cotton, wood, and paper. As part of the human diet, cellulose helps prevent constipation and fights colon cancer.Fructose is a sugar occurring naturally in a large number of fruits and honey. It is thesweetest of all common sugars. It is a simple carbohydrate with the formula C6H12O6.

Galactose is a simple sugar having the same chemical formula (C6H12O6) as glucose andfructose, but a different arrangement of its atoms. It is an isomer of glucose with ahydroxyl group on carbon 4 reversed in position. Galactose is often found incarbohydrates used in cellular recognition, such as blood types and neural receptors.

Glucose is a simple sugar (C6H12O6) and the primary source of energy for all mammalsand many plants. It is also known as dextrose, grape sugar, and corn sugar. It is about half as sweet as table sugar.

Hydrolysis is a chemical process whereby a compound is cleaved into two or moresimpler compounds with the uptake of the H and OH parts of a water molecule on eitherside of the chemical bond that is cleaved. During digestion, the intestinal enzyme sucrasehydrolyzes (adds water to) sucrose (C12H22O11) to produce glucose (C6H12O6) + fructose(C6H12O6) in the intestinal tract.

Hemiacetal is a product of the addition of an alcohol to an aldehyde. An aldehyde is acompound containing the radical CH=O, reducible to an alcohol (CH2OH) and oxidizableto a carboxylic acid (COOH).

Isomers are two or more molecules with the same number and kind of atoms, butdifferent arrangements of those atoms.

Lactase is an enzyme that hydrolyzes lactose into glucose and galactose, which can beabsorbed into the bloodstream.

Lactose is a disaccharide composed of galactose and glucose linked by a beta-1,4-glycosidic bond. Lactose is found in cow’s milk and other dairy products.

Maltose is a disaccharide composed of two molecules of glucose linked by an alpha-1,4-glycosidic bond. It is obtained from the hydrolysis of starch, and is used to flavor somecandy. Maltose must be hydrolyzed to glucose before it can be absorbed and taken intothe bloodstream.

Polymers contain two or more monomers. Starch is a polymer of the monomer glucose.Protein is a polymer of amino acids.

Starch is a polymer of glucose, linked by alpha-1,4-glycosidic bonds. Starch is acomplex carbohydrate found in green plants, and an important source of energy foranimals and humans. During the day, green plants store energy by converting glucose tostarch. At night, plants convert starch back to glucose for growth.

Stereochemistry is the branch of chemistry concerned with the spatial three-dimensionalrelations of atoms in molecules. For example, stereochemistry refers to the relativepositions of atoms or groups of atoms in the molecule or compound and the effect of these positions on its properties.

Sucrose (C12H22O11) is a disaccharide made up of glucose and fructose. Sucrose isobtained from cane sugar, sorghum, and sugar beets. Sucrose is the name for commontable sugar, which can’t be used by the body unless it is broken down by the enzymesucrase into monosaccharides by the process of digestion. Absorption of glucose andfructose occurs in the small intestine.

Materials Required

• Sure-Jell ®
• Heatproof gloves
• Concentrated fruit juice (apple, grape), thawed, if frozen
• Balance or scale
• Granulated sugar
• Graduated cylinder
• Water Heatproof pad
• 600-milliliter beakers
• Stirring rod/spoon/wooden Popsicle
• Bunsen burner w/ stands or hot plate stick

Instructional Strategies and Procedures

Teaching Tips

• The foods produced in these experiments are not to be consumed.
• Purchase the regular Sure-Jell. It contains pectin, acid and dextrose (glucose).
• You can use either frozen juice concentrate or the nonrefrigerated, aseptically processed juice concentrates found in the fruit juice section of the supermarket.
• Caution the students against overheating the jelly. Once the jelly starts to boil, it will bubble up and over the top of the beaker.

SAMPLE DATA TABLE - JELLY CONSISTENCY

*Jelly results based on the use of Mott’s ® In-A-Minute Unfrozen Grape Concentrate.

Key Questions and Answers

1. How did the consistency of the jelly change when you changed the ratio of sugar to pectin?

   When you used half the normal amount of sugar, the jelly was runny; when you used twice the sugar, the jelly was soft and did not hold its shape.

2. Why did the consistency change when you changed the ratio of sugar to pectin?

   There is an optimum ratio for jelly formation. The addition of sugar increases the firmness of the gel by aiding in the formation of polymer junctions. The addition of too much sugar, however, interferes with the gelling process. Although the mechanism for this reaction is not known, it is thought that very high concentrations of sugar dehydrate the pectin molecules to such an extent that some of the entrapped water is pulled out of the gel and back into solution. The result would be a softer gel that would not hold its shape.

Web sites for more information on carbohydrates

http://maize.agron.iastate.edu/ - Iowa State University. Contains general, technical, and production information on corn.

http://205.156.215.10/ - A. E. Staley Manufacturing Company. Information on food and industrial starches, sweeteners, and corn wet milling processing.

http://osu.orst.edu/instruct/nfm236/starch/index.htm - Oregon State University. Information on starch, its uses and composition.

Student Activity Guide

CARBOHYDRATES

Carbohydrates are the primary products of plant photosynthesis. The simplifiedlight-driven reaction of photosynthesis results in the formation of a carbohydrate: nH2O+ nCO2 -(CH2O)n- + nO2. This type of carbohydrate is found in the structures of plants and is used in the reverse reaction of photosynthesis (respiration) or is consumed as fuel by plants and animals.

Carbohydrates are widely available and inexpensive, and are used as an energysource for our bodies and for cell structures. Food carbohydrates include the simplecarbohydrates (sugars) and complex carbohydrates (starches and fiber). Before a bigrace, distance runners and cyclists eat foods containing complex carbohydrates (pasta,pizza, rice and bread) to give them sustained energy.

Carbohydrates are divided into monosaccharides, disaccharides, and polysaccharides. As shown in the following molecular model structures, carbohydratesmay be found as hexagon (6-sided, see Figure 1A) and pentagon (5-sided, see Figure 1B) shaped rings.

Monosaccharides

Monosaccharides are single-molecule sugars (the prefix “mono” means one) thatform the basic units of carbohydrates. They usually consist of three to seven carbonatoms with attached hydroxyl (OH) groups in specific stereochemical configurations. Thecarbons of carbohydrates are traditionally numbered starting with the carbon of thecarbonyl end of the chain (the carbonyl group is the carbon double-bonded to oxygen).The number of carbons in the molecule generally categorizes monosaccharides. Forexample, three-carbon carbohydrate molecules are called trioses, five-carbon moleculesare called pentoses, and six-carbon molecules are called hexoses.

Ribose and 2-deoxyribose are pentoses, and both have a crucial role inreproduction as polymers known as ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). One of the most important monosaccharides is glucose (dextrose). This molecule is the primary source of chemical energy for living systems. Plants and animals alike use this molecule for energy to carry out cellular processes. Mammals producepeptide hormones (insulin and glucagon) that regulate blood glucose levels, and a disease of high blood glucose is called diabetes. Other hexoses include fructose (found in fruit juices) and galactose.

Different structures are possible for the same monosaccharide. Although glucose and fructose are identical in chemical composition (C6H12O6), they are very different instructure (see molecular models). Such materials are called isomers. Isomers in generalhave very different physical properties based on their structure.

Figure 1

Disaccharides

Disaccharides are classified as oligosaccharides (the prefix “oligo” means few or little). This group includes carbohydrates with 2 to 20 saccharide units joined together.Carbohydrates containing more than 20 units are classified as polysaccharides.

Polysaccharides

Starch is the predominant storage molecule in plants and provides the majority ofthe food calories consumed by people worldwide. Most starch granules are composed of a mixture of two polymers: a linear polysaccharide called amylose and a branched-chain polysaccharide called amylopectin. Amylopectin chains branch approximately every 20-25 saccharide units. Amylopectin is the more common form of starch found in plants.Animals store energy in the muscles and liver as glycogen. This molecule is more highly branched than amylopectin. For longer-term storage, animals convert the food calories from carbohydrates to fat. In the human and animals, fats are stored in specific parts of the body called adipose tissue.

Cellulose is the main structural component of plant cell walls and is the most abundant carbohydrate on earth. Cellulose serves as a source of dietary fiber since, as explained below, humans do not have the intestinal enzymes necessary to digest it.

Starch and cellulose are both homopolymers (“homo” means same) of glucose.The glucose molecules in the polymer are linked through glycosidic covalent bonds.There are two different stereochemical configurations of glycosidic bonds—an alphalinkage and a beta linkage. The only difference between the alpha and beta linkages isthe orientation of the linked carbon atoms. Therefore, glucose polymers can exist in two different structures, with either alpha or beta linkages between the glucose residues. Starch contains alpha linkages (see Figure 1D) and cellulose contains beta linkages. Because of this difference, cornstarch has very different physical properties compared to those for cotton and wood. Salivary amylase only recognizes and catalyzes the breakdown of alpha glycosidic bonds and not beta bonds. This is why most mammalscan digest starch but not cellulose (grasses, plant stems, and leaves).

Food Uses of Carbohydrates

Carbohydrates are widely used in the food industry because of their physical and chemical properties. The sweet taste of sucrose, glucose, and fructose is used to improve the palatability of many foods. Lactose is used in the manufacture of cheese food, is a milk solids replacer in the manufacture of frozen desserts, and is used as a binder in themaking of pills/tablets.

Another useful aspect of some carbohydrates is their chemical reducing capability. Sugars with a free hemiacetal group can readily donate an electron to another molecule. Glucose, fructose, maltose, and lactose are all reducing sugars. Sucrose ortable sugar is not a reducing sugar because its component monosaccharides are bonded toeach other through their hemiacetal group. Reducing sugars react with the amino acidlysine (see Unit 3, Proteins, Figure 1A) in a reaction called the Maillard reaction. This common browning reaction produced by heating the food (baking, roasting, or frying) is necessary for the production of the aromas, colors, and flavors in caramels, chocolate, coffee, and tea. This non-enzymatic browning reaction differs from the enzymatic browning that occurs with fresh-cut fruit and vegetables, such as apples and potatoes. Carbohydrates can protect frozen foods from undesirable textural and structuralchanges by retarding ice crystal formation. Polysaccharides can bind water and are used to thicken liquids and to form gels in sauces, gravies, soups, gelatin desserts (Jell-O ® ),and candies like jelly beans and orange slices. They are also used to stabilize dispersions,suspensions, and emulsions in foods like ice cream, infant formulas, dairy desserts,creamy salad dressings, jellies and jams, and candy. Starches are used as binders, adhesives, moisture retainers, texturizers, and thickeners in foods.