FoodMASTER Middle: Milk
Students will understand the nutritional components of milk (carbohydrates) as they test three types of milk for the sugar glucose before and after adding the digestive enzyme lactase to determine which milk(s) contain the sugar lactose. They will also explore the nutritional composition and health benefits of consuming milk, research food sources of calcium, vitamin D, and phosphorus and devise ways to add bone-strengthening food to their diet. Grades 6-8
Student Lab Materials, per group of 4-5 students:
- 3 test tubes (any size) with stoppers containing 20 mL of unknowns A (rice), B (cow), and C (soy) milk
- 1 test tube rack or beaker
- 1 1/2 crushed lactase enzyme pills
- 12 glucose strips
- 2-3 paper napkins or paper towels
- 1 Glucose Reference Color Chart (or use the chart on your glucose strip bottle)
- 1 kitchen timer or stopwatch
- safety goggles
- aprons (optional)
- Optional: Cups and various milks (aside from lab milk) to allow students to sample)
Investigating Your Health Activity:
- Magnificent Milk student handout, 1 per student
calcium: an abundant chemical element that makes up the body’s bones, and is essential to most physiological processes in the body
carbohydrate: an organic compound that is the main source of energy for the body; composed of carbon, oxygen, and hydrogen atoms
digestion: the process of breaking down food by mechanical and enzymatic action into substances that can be used by the body
disaccharide: a sugar made of two molecules (e.g., sucrose, maltose)
lactase: an enzyme produced by the large intestine which breaks down lactose
lactose: a disaccharide sugar present in milk which contains glucose and galactose units
monosaccharide: a simple sugar molecule that cannot be broken down further into smaller molecules
osteoporosis: a medical condition that affects older women and is characterized by decreases in bone mass with decreased density and enlargement of bone spaces producing porosity and fragility
phosphorus: a chemical element that is found in bone and teeth and is also important to chemical body processes
vitamin D: a family of compounds derived from cholesterol; essential for normal bone, tooth, and blood health, and is found especially in fish-liver oil, egg yolk, and milk
Did You Know?
- To consume an equivalent amount of calcium found in an 8-ounce glass of milk, you'd have to consume 1/4 cup of broccoli, 7 oranges or 6 slices of wheat bread.1
- Farmers measure milk in pounds, not gallons.1
- The average cow produces 6-8 gallons of milk per day.1
Background Agricultural Connections
FoodMASTER (Food, Math and Science Teaching Enhancement Resource) is a compilation of programs aimed at using food as a tool to teach mathematics and science. For more information see the Background & Introduction to FoodMASTER. This lesson is one in a series of lessons designed for middle school.
Milk, cheese, yogurt, and ice cream are all part of the dairy group. Drinking milk helps build strong bones. Unfortunately, most Americans do not drink or eat enough foods from the dairy group every day. For this reason, it is important to learn about the science and nutrition of dairy foods. In this lesson, students will explore milk by learning about the importance of the digestive enzyme lactase and the many health benefits associated with consuming dairy products.
Different types of milk vary in nutritional composition (i.e. protein, lipid, carbohydrate). Milk from mammals (e.g. cows, goats) contains the carbohydrate lactose (milk sugar). Milk from plants contains other dietary sugars, for example, soy milk contains sucrose and rice milk contains glucose. Almonds and coconuts are also sources of milk. Almond and coconut milk contain no cholesterol or lactose, coconut milk, however, is very high in saturated fat and consumption should be moderated. Both lactose and sucrose are disaccharides. A sugar composed of two simple sugars is a disaccharide. A molecule of lactose is made up of the two monosaccharides, glucose and galactose. One simple sugar unit is a monosaccharide. A molecule of sucrose is made up of the monosaccharides glucose and fructose. The human digestive system uses specific enzymes to breakdown the disaccharide molecules into their component monosaccharides, which are then absorbed and utilized by the body. Enzymes are protein molecules that change the rate of a reaction without being depleted in the process. Lactase is the enzyme that acts on lactose, and sucrase acts on sucrose. Digestion of this nature occurs primarily in the small intestine. People who are lactose intolerant lack a sufficient amount of lactase to breakdown the lactose sugar.
The following factors influence the curdling properties of milk:
- Bacteria: Bacteria can be added when making cheese or yogurt, but can also develop as milk begins to sour.
- Acids: Acids can be found in juices or vegetables. The addition of an acid will result in the precipitation of casein, the most abundant milk protein. Acid produces a soft and spongy texture due to the decreased pH.
- Tannins: Tannins can be found in coffee or tea. They will curdle milk in the presence of acid and heat. For example, if you add slightly old milk to coffee, you may see curdles form.
Dipping a glucose strip in rice milk should automatically allow for the identification of rice milk. Since the glucose in soy milk (glucose + fructose = sucrose) and cow’s milk (glucose + galactose = lactose) is bound, rice milk is the only milk type with free or unbound glucose. Bacteria will convert lactose to lactic acid causing milk to curdle. This process can take from 4 to 16 hours to complete. Milk curdled by bacteria has similar characteristics as milk curdled with acid. Additional information regarding the role of bacteria in yogurt production is included in the Magnificent Microbes lab found in
Students may wonder if the enzyme drops or solutions have glucose in them. Allow students to test the drops with the glucose strips to test concentration. Students will find that the drops are negative for glucose.
The lactase enzyme works best at room temperature. This enzyme will break down the carbohydrate in milk, lactose. Our bodies need lactase to digest lactose. Without this enzyme, our bodies cannot break down this disaccharide into two monosaccharides, glucose and galactose. Simple sugars that cannot be broken down are called monosaccharides.
- Introduce the lesson by reading the clues below and ask the students to make a guess for which food item you have described.
- This food should be consumed after you exercise because it has protein for your muscles, carbohydrates to give you energy, and electrolytes to keep you hydrated.
- This food is produced by all mammals, but cattle provide most of it for our food supply.
- This food is the most abundant source of the nutrients necessary for strong and healthy bones.
- This food starts on a farm called a "dairy."
- This food can be processed into other healthy foods such as cheese and yogurt.
- What food is it? Milk!
- Ask students how the words lactose, lactase, and digestion relate to milk. If needed allow students to quickly research the words or discuss with a neighbor. Conclude with students that lactose is a carbohydrate in milk. It breaks down in the digestive system from a disaccharide to a monosacharride with the help of the enzyme lactase.
- Ask students to list the types of milk they have seen at the grocery store. (Answers could include soy, almond, rice, coconut, cow, and goat's milk.) Ask students, "Do all types of milk have lactose?" Inform students that today's lab is going to answer this question.
Explore and Explain
Lab 1: Explicit Enzymes
- Review information found in the Background Agricultural Connections section of the lesson, lesson Procedures, and the attached Essential Files.
- Prepare materials for each group. It is recommended that you plan approximately one-week ahead to allow time to gather needed materials. Note the following:
- For this investigation, be sure to use fresh milk (milk that has not been previously used/opened) and the same amount of milk in each tube. Cow and soy milk can be found in the refrigerated section of the grocery store. Eggs are often stored nearby. Rice milk will be found in a non-refrigerated section, such as the baking or juice isle; however, location can vary.
- When purchasing glucose strips make sure the chart provided on the bottle matches the chart provided in the curriculum. If you are unable to match strips, students will need to use the chart provided on the glucose strip bottle (vs. the one provided) for the investigation.
- Prepare milk type samples (1 sample per type per group). Fill each test tube with 20 mL of milk. Disguise each milk type’s identity by labeling the prepared samples: A = Rice Milk, B = Cow’s Milk, C = Soy Milk. Plug each test tube.
- To ensure the glucose test strips work properly, test them prior to teaching the lesson with positive and negative controls. Follow the directions on your brand of strip. Dip a strip into a) glucose solution (positive control), and b) water (negative control). Wait for the length of time specified by strip directions. Compare color changes to the key on the bottle to determine glucose concentrations. If the strips indicate no glucose (or less than 2%) is present in the glucose solution, discard or return the strips, they are defective. New strips must be obtained to proceed with the investigation. The results obtained from these control tests can be explained to the class and recorded on the board for reference. If time allows, you may consider having students participate in this step.
- Distribute lab materials. It is recommended that materials are organized into stations for easier distribution. Students should be arranged in small groups of 4-5. Each group should receive the lab supplies outlined in the Materials section as well as 1 copy of the Transformation Station handout and the Explicit Enzymes lab sheet.
- Ask students to begin by reading Transformation Station and completing the "Think About It" questions for this lab investigation.
- Before beginning the lab investigation require students to wash their hands.
- Optional: Allow students to taste each milk type prior to beginning or after investigation procedures. This process is important for increasing student exposure to healthy foods and decreasing the likelihood that students will be tempted to taste foods included as investigation materials. Emphasize the importance of practicing good food safety behaviors by not consuming substances used as part of the lab investigation.
- Launch lab by asking students to make a prediction about which milk type will react with the lactase drops. Students should also predict what will happen to the glucose concentrations of each milk type. Encourage students to refer to the table in the reading when making predictions.
- Show students the provided video lab demonstration, Lab I: Explicit Enzymes. The video will help students understand how to read a negative and positive test for glucose. As students proceed through the lab, they should get the following results:
- Rice Milk (Unknown A): Before adding lactase, rice milk should be positive for glucose. After adding lactase, rice milk will still be positive for glucose. Rice milk is made from rice and is composed of primarily glucose. Glucose is a monosaccharide and cannot be broken down further.
- Cow’s Milk (Unknown B): Before adding lactase, cow’s milk should be negative for glucose. After adding lactase, cow’s milk should be positive for glucose. Cow’s milk contains the disaccharide lactose. The enzyme lactase breaks down lactose (disaccharide) into its component monosaccharides (glucose + galactose). This breakdown results in the release of glucose, which is why a positive test results after adding the enzyme. Similar reactions occur in the body (digestion) after consuming dairy products. When individuals lack the lactase enzyme they may have difficulty digesting dairy foods, particularly milk.
- Soy Milk (Unknown C): Before adding lactase, soy milk should be negative for glucose. After adding lactase enzyme, soy milk will still be negative for glucose. Soy milk is made from soybeans and is primarily composed of sucrose. Lactase cannot break down sucrose. Instead, the enzyme sucrase would be needed to break down the disaccharide further.
- Allow students to work in small groups on the Explicit Enzymes lab sheet to further explore the topic and respond to lab questions. Encourage students to refer to the table in the reading to help support their conclusions.
- (Optional) Launch the lab extension by allowing students to share their data to complete a class comparison of their results.
- Follow-up with a class discussion about enzymes and their role in digestion.
Investigating Your Health: Magnificent Milk
- Instruct students to research the role calcium, vitamin D, and phosphorus play in bone formation prior to beginning the investigation. Students should seek to identify specific dairy food sources of calcium, vitamin D, and phosphorus and the health benefits of consuming low-fat dairy products.
- Using the information found in the Background Agricultural Connections section or information learned from researching dairy, students should examine the food labels of milk with varying fat content (i.e. whole, reduced fat, low-fat, and skim).
- Students can find food labels in the grocery store, they can access the USDA’s FoodData Central, or use the table provided below.
- Give each student one copy of the Magnificent Milk student handout. This assignment is designed to be completed either as homework or in class. If completed in-class, allow students to work in small groups on the worksheet to further explore the topic and respond to questions.
- Follow-up with a class discussion about student findings related to the health benefits of dairy foods and student generated ideas for increasing consumption of “bone-strengthening” foods in their diet.
Enzymes are sensitive to pH changes. To further explore enzymes, investigate with varying temperatures and pH levels. After manipulating temperature or pH of cow’s milk, repeat the investigation by adding lactase and measuring glucose concentrations.
Enzymes are sensitive to temperature changes. At cold temperatures the test strips will detect glucose but to a lesser extent. Very hot temperatures will deactivate the enzyme and it will not work at all. The test strip will not detect glucose at high temperatures.
After conducting these activities, review and summarize the following key concepts:
- Milk, provided most commonly by cattle in the United States, provides many key nutrients to a balanced diet.
- The primary carbohydrate found in cow's milk is the disaccharide, lactose.
- During digestion, the enzyme lactase breaks down lactose.
This lesson was partnered with East Carolina University. The FoodMASTER program was supported by the Science Education Partnership Award (SEPA) which is funded from the National Center for Research Resources, a component of the National Institutes of Health.
- Primary Authors:
- Virginia Stage, PhD, RDN, LDN
- Mary White
- Ashley Roseno, MAEd, MS, RDN, LDN
- Melani W. Duffrin, PhD, RDN, LDN
- Graphic Design: Cara Cairns Design, LLC