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Science and Our Food Supply - Middle School Guide: Module 3 - Processing and Transportation

Science and Our Food SupplyTeacher's Guide for
Middle Level Science Classrooms

2007 Edition

Return to Table of Contents

MODULE 3 - PROCESSING AND TRANSPORTATION

ABOUT THE MODULE

Did you know that there are many ways to control bacteria during processing and transportation? This module focuses on several methods scientists use to keep our food safe.

Empty flask and half-filled test tube in a green circle as background Blue's the Clue - introduces pasteurization and the effect temperature has on reducing and controlling the growth of bacteria.

Empty flask and half-filled test tube in a green circle as background Mystery Juice - uses investigation to demonstrate how pasteurization reduces the number of microorganisms in juice.

Hand holding a pencil in a green circle background Ultra High Pressure Treatment - shows how foods are kept safe through processing, including the newest food preservation technology.

 

SCIENCE CONTENT

Video tape in a green circle background This section explains the specific science concepts presented in Module 3 of the video/DVD, including fascinating facts relative to the module. Read this section before watching the video module or conducting the activities and experiments.

PROCESSING

 

Food safety plays a major role throughout food processing.

Pasteurization

Dr. Charles Sizer in a lab coat displaying an egg in his hand
Dr. Charles Sizer discusses
pasteurization

 

Pasteurization is the process of using heat or irradiation to destroy microorganisms that could cause disease.
Modern dairy farms today may have up to 5,000 cows. All the milk is pooled, so if one cow is sick, there is a possibility to contaminate all the milk. That's why milk is pasteurized.

Milk was one of the first products to be pasteurized on a broad scale. In addition to dairy products, other pasteurized foods include fruit juices, chicken, beef, and spices.

One challenge scientists had was trying to figure out how to pasteurize an egg without cooking it. The solution was to heat the eggs up slowly to 57° C and maintain that temperature for 1 hour and 15 minutes. This time/temperature relationship inactivates the bacteria while keeping the eggs fluid.

Louis Pasteur (1822-1895), a chemist, was actually trying to prevent spoilage in wine and beer when he discovered pasteurization. Pasteurization was applied first in wine preservation. When milk producers adopted the process, it substantially reduced foodborne illness. You never know where science will lead you!

Time/Temperature Relationship

 

Traditional pasteurization is achieved by exposing foods to heat for a certain length of time. Bacteria are very heat-sensitive, and the higher the temperature, the quicker they can be inactivated. Using higher heat takes less time to kill pathogenic bacteria, whereas using lower heat takes more time.

FASCINATING FACTS

More than 1,000 different types of food are pasteurized.

 

Irradiation

 

broken double helix, being bombarded with electromagnetic radiation
Using gamma rays to
destroy bacteria

Irradiation is the process in which ionizing energy is used to kill foodborne pathogens. During irradiation, an intense pulse of energy is emitted, either from a gamma radiation source like Cobalt 60 or from an electrical source like an electron beam accelerator. The energy penetrates the food and destroys any bacteria.

Irradiation damages the microbe's DNA. Unless it can repair the damage, the microbe will die when it grows and tries to duplicate itself.

Ultra High Pressure (UHP) Treatment

 

Today, some food producers are beginning to use a new method for killing harmful bacteria in foods that contain water. It's called ultra high pressure (UHP) treatment.

Dr. Sizer demonstrates ultra high pressure treatment behind a protective shield using a glove box
Dr. Sizer demonstrates
ultra high pressure
treatment

This process destroys bacteria without the use of high temperatures or chemical additives. Thus, foods such as juices, salsas, cold-cuts, and other moist foods, are made safer while the vitamins, flavor, and freshness of the foods are maintained.

Using specially designed equipment, the food is subjected to 50,000 to 100,000 pounds of pressure per square inch. This ultra high pressure is maintained from 30 seconds to a few minutes depending on the food. The ultra high pressure interferes with the metabolism and structure of bacteria and destroys these living cells without altering the basic composition of the food.

Important Note: Despite pasteurization, irradiation, and ultra high pressure (UHP) treatment, food can still become contaminated if the basic rules of food safety are not followed all along the Farm-to-Table Continuum. It's important to always follow the 4 Cs of Food Safety: Clean, Cook, Chill, and Combat Cross-Contamination.

TRANSPORTATION

 

A man packing apples in a box coming off the belt
Proper packing is selected
for the product

The 4 Cs of Food Safety play a very prominent role in transportation. Keeping food safe and in good condition as it's shipped across the country or around the world is critical. There are many steps to shipping food safely and there's science behind each step.

The cold chain has to be maintained throughout the loading process, in transit, and during receiving.

The food is cleaned and precooled as it comes from the field or plant. The cooling extends product life by reducing field heat, rate of ripening, loss of moisture, rate of respiration, and the spread of decay.

Proper packaging is selected for the product. The shipping container is cleaned and properly loaded, making sure that the boxes are stacked tightly to lock in the cold during transit.

Proper temperature control can be tracked by satellites. Refrigerated containers usually have equipment that automatically records refrigeration system functions and the air temperature inside the container. This information provides a detailed record of refrigeration system performance during the trip.

Food is properly stored and cooled at the warehouse.

FASCINATING FACTS

Two elephants balancing on a thin dime is equivalent to 60,000 psi.

 

Flask and Test Tube Icon - large

BLUE'S THE CLUE

Time: One 45-minute class period, plus observation time over the next 2 to 3 days

LAB AT A GLANCE

This experiment introduces students to the effect of temperature on reducing and controlling the growth of and transportation. Students will use pasteurized and ultra high temperature (UHT) milk, and observe how different temperatures (heat, room temperature, chilling, and freezing) affect the growth of spoilage bacteria. They will also learn about the importance of pasteurization in keeping food safe.

FOOD SAFETY Plate, Knife and Fork CONNECTION

By learning about the effect of temperature on bacterial growth, students will be able to relate these findings to how they prepare and store food at home to help reduce bacterial growth.

 

GETTING STARTED

ABOUT UHT AND PASTEURIZED MILK

UHT milk is heated to at least 280° F (138° C) for 1 or 2 seconds, then packaged in sterile, airtight containers. Because of the high heat and special packaging, UHT milk contains fewer bacteria than conventionally pasteurized milk, and can be stored without refrigeration for up to 90 days. After opening, spoilage time for UHT milk is similar to that of conventionally pasteurized milk. Therefore, after opening, it should be refrigerated just like pasteurized milk.

Pasteurized milk is heated to at least 161° F (72° C) for 15 seconds. This process kills the pathogenic bacteria found in milk; however, it may not kill all the spoilage bacteria.

ADVANCE PREPARATION

  • Order methylene blue.
    Note: This experiment was designed using methylene blue chloride 1% (Educational Reagent Aqueous Solution from Fisher Scientific - catalog #S71326).
  • Mix 1 ml of methylene blue 1% solution in 25 ml of water.
  • Sterilize the test tubes, test-tube caps, pipettes, and pipette bulbs. (See Laboratory Procedures.)
  • Purchase pasteurized whole milk and ultra high temperature (shelf stable) whole milk. (Shelf stable milk can usually be found in the juice aisle. Ask your store manager to order it if it isn't available in your supermarket.)
  • Place all the equipment on a lab table.
  • Photocopy (Pasteurization), (Shelf Stable), and (Ultra High Pressure Treatment) of the Food Safety A to Z Reference Guide.
  • Photocopy the Blue's the Clue Data Table for each team.

 

MATERIALS

For the class

  • 3 to 6 test-tube racks, depending on the number of teams. Teams can share testtube racks.
  • Refrigerator with freezer compartment, if possible
  • Food Safety A to Z Reference Guide (See the pages above.)
  • Dr. X and the Quest for Food Safety video/DVD, Module 3 - Processing and Transportation

For Each Team of 3 to 4 Students

  • 60 ml of pasteurized, whole milk (10 ml/test tube)
  • 60 ml of ultra high temperature (shelf stable) whole milk (10 ml/test tube)
  • Methylene blue dilute solution (1 drop per test tube)
  • 6 sterile test tubes
  • 6 sterile test-tube caps or aluminum foil to cover the test tubes
  • Two sterile 10 ml pipettes
  • One or two sterile 5 ml pipettes or eye droppers
  • Sterile pipette bulbs or pipette aids
  • Permanent marker to label test tubes
  • Blue's the Clue Data Table

 

INTRODUCTION

SAFETYFIRST

 

  • DO NOT DRINK THE MILK USED IN THE LAB.
  • Never pipette by mouth. Always use a pipette bulb or aid.
  • Wash test tubes and other materials in hot, soapy water after the lab.
  • Before leaving the lab, wash your hands with hot, soapy water.
    Caution: Be careful not to spill methylene blue on the countertops or clothes; it may stain.

Explain to students that later in Module 3, they'll learn more about ultra high pressure treatment, but in this activity, they'll focus on pasteurization.
Now ask students:

  • Have you ever wondered why your parents are always asking you to put the milk back in the refrigerator? What might happen to that milk if it's left out at room temperature overnight?
  • In the video Module 1 - Understanding Bacteria, Dr. X talked about the Danger Zone. What precautions did he give about the "Zone"? What might be present in milk that has been left in the Danger Zone for more than 2 hours?

 

Video tape in a green circle background TIME TO TUNE IN  . . . Module 3 - Processing and Transportation

Introduce the video by explaining that on our next stop along the Farm-to-Table-Continuum, students are going to learn about Processing. Dr. X will beam them into the research lab of one of his scientist friends who looks at new ways to reduce the bacteria in our food through processing. Here are some things to think about while they watch the video/DVD:

  • What do cows, astronauts, and elephants have to do with food safety and food processing?
  • What is pasteurization?
  • How can an egg be pasteurized in the shell without cooking it?
  • How can some types of milk stay safe without being refrigerated?
  • What process keeps food safe in outer space?

Show video/DVD Module 3 - Processing and Transportation (Time: 7 minutes).

Video tape in a green circle background INSTANT REPLAY  Time to review and summarize.

  1. What's the relevance of cows, astronauts, and elephants to food safety and food processing? (Cows refer to pasteurization, astronauts refer to irradiation, and elephants refer to ultra high pressure treatment.)
  2. What is pasteurization? (Pasteurization uses heat to kill harmful bacteria in foods.)
  3. What is the time/temperature relationship? (Pasteurized milk is heated for a longer time at a lower temperature, and UHT milk is heated for less time at a higher temperature.)
  4. How can an egg be pasteurized in the shell without cooking the egg or breaking the shell? (Manufacturers use a time/temperature relationship to pasteurize eggs in the shell without cooking them. Heating eggs above 140° F [60° C] will cook them. Thus, using a lower temperature of 130° F [54° C] for a long time, 45 minutes, kills bacteria without cooking.)
  5. How can some types of milk stay fresh and safe without being refrigerated? (UHT milk contains fewer bacteria than conventionally pasteurized milk because it's heated to a higher temperature. It's also packaged in sterile, airtight containers. Therefore, UHT milk can be stored without refrigeration for up to 90 days.)
  6. So . . . what prevents astronauts from getting foodborne illness in outer space? (Irradiation of their food)

PROCEDURE

LAB 1Design and Conduct Experiment

 

  1. Ask students to form teams of 3 or 4 and encourage each team to develop a hypothesis on how temperature affects bacterial growth. Then ask them to design an experiment to test their hypothesis.
  2. Introduce the three materials teams must use for their experiment: regular pasteurized milk, ultra high temperature (shelf stable) milk, and methylene blue.
  3. Ask: How might you use methylene blue to help with your experiment? Students can research methylene blue and discover that it's an indicator dye used to determine the presence of bacteria in milk. Tell them they can use any of the other materials on the lab table. Also, there's a refrigerator and freezer they can use.
  4. Let teams discuss their hypotheses and experimental designs for 10 to 15 minutes. Then, begin posing the following questions to help students design well-thought-out experiments:
    • What are some ways you could test the effect of temperature on bacteria? What did you learn about the effect of temperature on bacteria in Module 1
      - Understanding Bacteria of the video/ DVD?
      (Heating is a way to kill bacteria, whereas chilling and freezing are ways to retard the growth of bacteria.)
    • Explain that one container of milk came from the refrigerated dairy case of the supermarket and the other from an unrefrigerated shelf. Let students examine each container.
    • What's an important difference between the two milk products? Is there any information on the labels that relates to our question about the effect of temperature on bacterial growth?
      (Students should discover that one is pasteurized and the other is treated using ultra high temperature.)
    • What are the similarities and differences between pasteurized and ultra high temperature treatments? (Both pasteurization and ultra high temperature use heat to kill bacteria. Ultra high temperature methods use higher temperatures than regular pasteurization. Also, products treated at ultra high temperatures are packaged in special airtight containers to prevent bacteria from getting into the product.)
    • Could there be differences in the growth of bacteria between the two milks? What do you think the differences might be?
      (The regular pasteurized milk should show bacterial growth sooner than the UHT milk because the pasteurized milk has more bacteria in it.)
    • Should you consider these differences when you design your experiments? Why? (Yes, both milks should be tested in all conditions.)
    •  How can you tell if bacteria are growing in the test samples? (Add methylene blue to each sample. If bacteria are growing, the methylene blue will become colorless and the milk will change from blue to white. This is not immediate, but happens over time.)
  5. Have each group present their hypothesis and experimental design to the class. Encourage students to discuss the merits of each suggested test. (One effective experimental design is to test pasteurized milk and UHT milk at three temperatures - room temperature, chilled, and frozen.)
  6. After the group discussions, give the teams time to revise their hypotheses and experimental designs.
  7. Let teams conduct experiments according to their designs. Note: The test tubes must be checked each day after the experiment is conducted. Since the color change happens over time, you could miss important findings if you don't check every day.

About Methylene Blue

Methylene blue is an indicator dye that, in anaerobic conditions, becomes colorless and is reduced to leucomethylene. Methylene blue loses its color in the absence of oxygen because bacteria use up the oxygen present in the milk. The rate at which it loses its color is a relative measure of bacteria present in milk.

T I P S

  • Carefully label all test tubes and test-tube racks.
  • The methylene blue will mix better if the milk is added to the test tubes before the methylene blue. Mix thoroughly by lightly tapping the test tubes with your fingers.
  • Gas will be produced, so don't close the test-tube caps tightly.

 

LAB 2Observe and Record

 

Option: Students can use the Blue's the Clue Data Table to record their results.

  1. Students should observe and record the time and any visual changes on day two of this lab activity. Ask: How did the data support or reject your hypothesis? What might happen if the chilled and frozen samples were left out at room temperature for several hours or overnight? Should we test them to find out? (Yes, let the chilled and frozen samples stand at room temperature until the following day. As they reach room temperature and remain in the Danger Zone for several hours, the bacteria will begin to grow. As this happens, the methylene blue will become colorless and the milk will change from blue to white. Observe and record the results.)
  2. What might happen if the UHT samples were left out at room temperature for another day? (If you let the UHT samples sit out at room temperature for another day or more, the color will change to white. Observe and record the results.)

LAB 3Observe, Record, and Report

 

FAQ

If bacteria in UHT milk don't grow rapidly, why do I have to keep the milk refrigerated after I open it?

Because there are fewer bacteria in UHT milk than in regular pasteurized milk, the spoilage bacteria in UHT milk take longer to grow. However, they will eventually multiply. You should always practice the safest precautions. Therefore, refrigerate the milk as soon as it is opened.

  1. Observe and record findings on the third day. Ask students: What happened to the frozen and chilled samples? What happened to the UHT samples?
  2. Give students 5 to 10 minutes to complete their Data Table.
  3. Have teams present their findings to the class. They should report both positive and negative results and discuss ways they would improve their experimental design.
  4. Remind students to include the relationship of their findings to food safety.

T I P

To find the results you can expect from this experiment,
see below.

 

 

Empty flask and half-filled test tube in a green circle as background INSTANT REPLAY Time to review and summarize.

  1. Were bacteria killed at the different temperatures? Why or why not? you tell?
    (No. Only heat kills bacteria. Room temperature isn't high enough to kill bacteria, and chilling and freezing do not kill bacteria, they just slow their growth. When the chilled and frozen milk reached room temperature, bacteria began to grow again.)
  2. What's a basic difference between conventionally pasteurized and UHT milk?
    (UHT milk can be stored on a shelf without refrigeration for up to 90 days.)
  3. Explain the importance of knowing about the Danger Zone in food safety.
    (Awareness of the Danger Zone helps people understand the importance of heating and chilling food, thus decreasing the amount of foodborne illness.)
  4. What do chilling, freezing, and heating do to bacteria?
    (Chilling and freezing slow down the growth, but heating kills the bacteria.)

Here are the results you can expect from this experiment:

Room temperature samples

  • The pasteurized milk will turn white by Lab 2 (day 2), indicating that there are some spoilage bacteria in the milk. At a temperature conducive to bacterial growth, they will multiply.
  • The UHT milk will still be blue by Lab 2 (day 2). This is because the UHT milk has fewer spoilage bacteria than regular pasteurized milk. Thus, it takes longer to see any bacterial growth. Bacteria do not quickly multiply in the UHT milk.
  • After leaving the UHT milk at room temperature for another day or two, the color will turn white, indicating that spoilage bacteria will ultimately grow in the UHT milk.

Chilled and frozen samples

  • Both the pasteurized and UHT chilled and frozen milk samples will still be blue by Lab 2 (day 2), indicating that cold temperatures retard bacterial growth.
  • After leaving the chilled and frozen samples at room temperature for another day or two, the color will change to white. This indicates that when the temperature rises into the Danger Zone (room temperature), bacteria can grow. It may take longer for the UHT milk to change to white because there are fewer spoilage bacteria in UHT milk than in regular pasteurized milk.

RESOURCES

SciLinks Logo

Keyword: Pasteurization
Go to: www.scilinks.org disclaimer icon
Code: FS302

SUMMARY

Temperature affects the growth of bacteria. Heating kills bacteria and chilling or freezing retards the growth of bacteria. Pasteurization is the process of destroying harmful bacteria that could cause disease by applying heat to a food; however, some spoilage bacteria may still be present. Bacteria grow more quickly in regular pasteurized milk than in UHT milk because the latter uses higher temperatures, thus killing more bacteria. Also, UHT milk is sealed in sterile, airtight containers.

EXTENSIONS

  • Test UHT milk that has an expiration date that has passed and UHT milk that has an expiration date in the future. See if the "expired" milk changes more quickly than the fresher milk.
  • Try this experiment using a variety of milk forms: powdered, skim, 1%, 2%, etc.
  • Relate your pathogen to this experiment and record the information in your food safety portfolio.
Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide

 

UP NEXT . . .
It's time for you to solve a mystery! In the next activity, we'll work in the lab to uncover all the juicy details.

BLUE'S THE CLUE DATA TABLE

Name ___________________________________________________ Date _______________ Class/Hour ___________

Day 1
Original Sample
Day 2
Describe Visual Changes
Day 3
Describe Visual Changes
Day 4
Describe Visual Changes

Room
Temperature

2 test tubes withsolutions labeled pasteurized milk and UHT milk

Pasteurized:

UHT:

Pasteurized:

UHT:

Pasteurized:

UHT:

Pasteurized:

UHT:

Refrigerated

2 test tubes withsolutions labeled pasteurized milk and UHT milk

Pasteurized:

UHT:

Pasteurized:

UHT:

Pasteurized:

UHT:

Pasteurized:

UHT:

Frozen

2 test tubes withsolutions labeled pasteurized milk and UHT milk

Pasteurized:

UHT:

Pasteurized:

UHT:

Pasteurized:

UHT:

Pasteurized:

UHT:

  1. How did the data support or reject your hypothesis?
  2. What do you predict will happen if the chilled and frozen samples are left out at room temperature for another day?
  3. What do you predict will happen if the UHT samples are left at room temperature for another day?
  4. Explain the relationship of your findings to food safety.

 

Flask and Test Tube Icon - large

MYSTERY JUICE

Time: Three 45-minute class periods

LAB AT A GLANCE

Using an inquiry approach, students will develop an investigation to determine the difference between two juices. Food safety will be discussed in relation to the results of the investigations. Students will have the opportunity to discover how pasteurization reduces the number of microorganisms in a food such as juice.

FOOD SAFETY Plate, Knife and Fork CONNECTION

Students will discover the importance of pasteurization to food safety. They will understand the importance of reading product labels that indicate whether or not a food has been pasteurized.


GETTING STARTED

ADVANCE PREPARATION

  • Do some juice "scouting" and find pasteurized and unpasteurized juice made from the same type of fruit. (If available, unpasteurized apple cider and pasteurized apple juice work well.)
  • If unpasteurized juice is not available, you can prepare your own (see below).
  • Use 2 pint jars or other clear containers that have lids. Wash and sterilize the jars and lids (see Laboratory Procedures).
  • Mark one container "A", and pour in 1 to 2 cups of the unpasteurized juice. Close the lid.
  • Mark the other container "B", and pour in 1 to 2 cups of the pasteurized juice. Close the lid.
  • Keep the containers closed and refrigerated until class time.

MATERIALS

For the class

  • Pasteurized and unpasteurized juice (1 to 2 cups of each) in clear containers
  • Place the equipment that students might use on a lab table.

For Each Team of 3 to 4 Students

  • 2 to 4 sterile Petri dishes with nutrient agar and covers
  • Sterile swabs
  • Parafilm or masking tape to seal dishes
  • Safety gloves

WHERE TO FIND UNPASTEURIZED JUICE

Unpasteurized juice may be found in the refrigerated sections of grocery or health food stores, cider mills, or farm markets. Unpasteurized juice must have this warning on the label:

WARNING: This product has not been pasteurized and therefore, may contain harmful bacteria that can cause serious illness in children, the elderly, and persons with weakened immune systems.

IF UNPASTEURIZED JUICE IS NOT AVAILABLE, PREPARE YOUR OWN

  • Use an unwashed fruit with soft skin that doesn't have to be peeled, such as grapes or peaches. Squeezed orange juice may not work well for this experiment because the low pH of the orange juice inhibits bacterial growth.
  • Do not peel the fruit, but remove any seeds or pits. Put the fruit in a blender and blend until you get enough juice to use with the class - about 1 to 2 cups. Strain the juice through cheesecloth to remove any flesh.
    Note: Purchase the same type of fruit juice that has been pasteurized. It's more intriguing for the students if the two juices look identical, or at least similar.

INTRODUCTION

Set the stage for the activity by saying to the class: I have a mystery for you to solve. Together, we're going to do some sleuthing! Here are two containers of juice.

  • Do you see any differences between them? Remember, all science begins with awareness. What's one way we become aware? (By making observations)

How do we make observations? (Through the use of our senses. Mostly, we use sight. But sound, taste [although not in this case], and touch are also ways to make observations.)

Can you determine which juice is safe to drink just by looking? Today, we're going to do some detective work, and plan and carry out an investigation. Then you'll report your findings to the class. It will be challenging! Let's get started . . .

SAFETYFIRST

 

  • NEVER DRINK ANY JUICE USED IN THE LAB.
  • Wash hands thoroughly before and after the lab.
  • Disinfect all lab surfaces before and after working in the lab (see Laboratory Procedures).
  • Wear safety gloves.
  • Seal inoculated Petri dishes using Parafilm or masking tape (see Laboratory Procedures).
  • Remind students never to open a dish with organisms growing in it. Some organisms could be dangerous pathogens. • After the experiment is completed, discard all disposable dishes using safe techniques (see Safety First in the Laboratory).

PROCEDURE

LAB 1Design the Experiment

 

Observe

  1. Assign students to work in teams of 3 or 4.
  2. Ask each team to record at least 5 observations about the juice. You may wish to help them understand the difference between observation and inference before they start. (Students may notice color and clarity differences. One juice may have some solids in it, etc.)
  3. Ask each team to share their best observations with the class. List them on the board.
  4. Ask the students what the different observations may mean.

Develop a Hypothesis

  1. Based on the class observations, challenge each team to come up with a hypothesis of which juice is pasteurized and which one is unpasteurized and have them explain why.

Solve The Mystery

  1. Now ask the students to solve the second part of the mystery by asking: Which juice is safe to drink and why?
  2. Ask each team to design an experiment to provide evidence for which juice is safe to drink. You may want to review pasteurization with the students. Students can use materials and equipment on the lab table.
  3. Challenge students to develop their experimental designs complete with a control (in this case, a standard of comparison).
  4. If your students come up with a variety of ways to determine which juice is safer to drink (pasteurized), that's great. Go for it!

LAB 2Conduct the Experiment

 

  1. Ask the students to review their experimental designs.
  2. Have teams carry out their experiments.
    Note: You may need to show the students how to dip the sterile cotton swab into the juice and then inoculate the dishes (see Laboratory Procedures).

LAB 3Collect, Organize, and Report Results

 

  1. Have teams observe the results of their experiment and report their results to the class.
    Note: The unpasteurized juice should have a greater number of organisms when samples of both juices are plated on agar plates.
  2. Together with the students, analyze the adequacy of the experimental designs. Ask students what they would do to improve their experiments.
  3. Ask the students to relate their findings to food safety.
  4. Review how the students used the various equipment, and how they designed their experiments, complete with controls.

MYSTERY JUICE

Empty flask and half-filled test tube in a green circle as background INSTANT REPLAY  Time to review and summarize

  1. Which juice would you prefer to drink, pasteurized or unpasteurized? Why?
  2. What effect would freezing have on microorganisms in unpasteurized juice?
    (Freezing does not kill bacteria. It only slows their growth.)
  3. How does pasteurization relate to your everyday life?
    (It keeps our food safe.)
  4. Can you tell if a food is pasteurized by looking at it?
    (No - you should read the product labels.)

SUMMARY

Pasteurization is the process of destroying microorganisms that can cause disease. This is usually done by applying heat to a food. In order to determine which mystery juice is pasteurized, both must be plated on agar plates and observed. The unpasteurized juice should have a greater number of organisms because it was freshly squeezed and may be contaminated from handling, etc. It hasn't been heated to destroy bacteria.

EXTENSIONS

  • Answer the question raised in the video by Dr. Sizer, "How can you pasteurize an egg in the shell without cooking it?"
  • Research why some milk can be stored on the shelf and some milk must be refrigerated.
  • Write a letter to Louis Pasteur to thank him for developing the process of pasteurization, and tell him how important this process is in lowering the incidence of foodborne illness. Also, explain how it makes foods more convenient for us today.
  • Research how people safely stored food prior to pasteurization, and choose which method you think was best - give reasons, specific details, anecdotes, and examples.
  • Research the history of pasteurization.
  • Relate your pathogen to this experiment and record the information in your food safety portfolio.

RESOURCES

SciLinks Logo
Keyword: Food Safety
Go to: http://www.scilinks.org/ disclaimer icon
Code: FS300

 

Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide

 

UP NEXT . . .
Besides pasteurization, what other process destroys harmful bacteria in foods? (Clue: It has to do with the pressure created by 2, 5-ton elephants balanced on a dime.) You'll discover and explore this process in the next activity.

 

Hand holding a pencil in a green circle background

ULTRA HIGH PRESSURE TREATMENT

Time: One 45-minute class  period

ACTIVITY AT A GLANCE

Students will explore various ways that have been used to preserve food over the ages. They will also learn about techniques used to process food today and hypothesize about other methods scientists might use to safely process food in the future. Finally, students will conduct a simulation of high pressure treatment and discover how it destroys bacteria without crushing the food.

FOOD SAFETY Plate, Knife and Fork> CONNECTION

Students will discover the relationship between the 4 Cs of Food Safety and food preservation methods. This finding will reinforce their understanding of why the 4 Cs are important in keeping food safe.

 

GETTING STARTED

MATERIALS

  • 2 empty plastic soda bottles (not rigid bottles)
  • 2 grapes
  • A variety of foods preserved in different ways, for example:
    - Tomatoes: fresh, sun-dried, canned
    - Fish: salted, fresh, canned
    - Fruit: fresh, dried, canned
    - Herbs: fresh, dried
  • Dr. X and the Quest for Food Safety video/DVD, Module 3 - Processing and Transportation

ADVANCED PREPARATION

  • Review the Background information.

 

INTRODUCTION

Start a discussion by asking: How do you suppose your great, great, great grandparents kept their food safe without refrigerators, sophisticated manufacturing processes, or without even having electricity? (Students may suggest salting, drying, canning, chilling, or freezing, etc. Ice houses kept foods chilled year round, and foods could freeze outside during the winter. List students' responses.)

  • What do all these methods have in common? (They either kill bacteria or slow down their growth. Plus, they all change the taste or texture of the food.)
  • In addition to destroying bacteria, what are some other issues scientists have to think about when they're developing methods to preserve food? (Scientists are continually searching for new methods to kill harmful bacteria in food without damaging the look, taste, texture, or nutritional value of food.)
  • Show a variety of foods preserved in different ways and discuss how each method may affect the texture, taste, nutritional value, color, etc. of the food. What are the positive and negative aspects of each method?

Video tape in a green circle background TIME TO TUNE IN  . . . Module 3 - Processing and Transportation

Here are some questions to think about while you are watching the video:

  • What new ways of processing foods did Dr. Sizer talk about in the video? (The discussion should lead to pasteurization, irradiation, and ultra high pressure treatment.)
  • What are the benefits of ultra high pressure treatment over other forms of pasteurization? (High pressure can kill bacteria without affecting the nutrition, color, or texture of food.)
  • Why can you use ultra high pressure treatment with orange juice and not a marshmallow? (Orange juice contains water that protects it from being crushed by the ultra high pressure. A marshmallow contains air and would be compressed to the size of a BB.)

Show video/DVD Module 3 - Processing and Transportation (Time: 7 minutes).

Video tape in a green circle background INSTANT REPLAY  Time to review and summarize.

  1. What new ways of processing foods did Dr. Sizer talk about in the video? (The discussion should lead to pasteurization, irradiation, and ultra high pressure treatment.)
  2. What are the benefits of ultra high pressure treatment over other forms of pasteurization? (High pressure can kill bacteria without affecting the nutrition, color, or texture of food.)
  3. Why can you use ultra high pressure treatment with orange juice and not a marshmallow? (Orange juice contains water that protects it from being crushed by the ultra high pressure. A marshmallow contains air and would be compressed to the size of a BB.)

PROCEDURE

Let's see how ultra high pressure treatment works:

  1. Ask two students to fill the 2 plastic bottles completely to the top with water, put a grape in each bottle, and tightly close the caps. The water bottle represents the ultra high pressure equipment and the grape is the food being pressurized.
  2. Ask: Who thinks they can crush the grape by squeezing the bottle? Have students try to crush the grape. Why can't you crush the grape? (Water in foods protects the food structure from physical damage during compression. As long as the food is mostly air-free and contains water, pressure doesn't "crush" the food.)
  3. Why is pressure being applied to the food? (Pressure is applied to kill the bacteria.)
  4. How are bacteria killed by the high pressure? (Bacteria are living organisms and the pressure affects their cellular functions. When high pressure is applied to all sides, the enzymes are inactivated.)

RESOURCES

  •  Food Safety A to Z Reference Guide (See the following terms - Bacteria, Canning, Freezing, Irradiation, Pasteurization, Pathogen, Preservation, Ultra High Pressure Treatment.) Also see the 4 Cs section.
  • Dr. X and the Quest for Food Safety video/DVD Module 3 - Processing and Transportation

SUMMARY

Throughout the ages, people have found ways to preserve food. Scientists are continually developing new, improved methods of preserving foods. In addition to pasteurization and irradiation, bacteria are now also killed by a new process called ultra high pressure treatment.

EXTENSIONS

  • Research and write about food preservation methods in different periods of time.
  • Hypothesize about other ways you can think of that science might help us preserve foods in the future. How would you design an experiment to test your hypothesis? Indicate which foods you'd use your "process" for.
  • Relate your pathogen to this experiment and record the information in your food safety portfolio.

 

Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide

 

UP NEXT . . .
You think this activity had pressure? Well, wait until you learn what it takes to manage a supermarket!

BACKGROUND

Use this information to help guide students through this activity and to help them understand the new technology of ultra high pressure treatment.

Preservation Methods

  • Preservation methods, such as salting, smoking, drying, canning, and freezing, have been used over the years to preserve food. As our scientific knowledge and engineering skills have advanced, so have food-preservation methods. All the early methods preserve food by affecting one or more of the variables needed for bacterial growth, such as temperature, moisture, pH, and nutrients. Many of the preservation methods have a relationship to the 4 Cs of Food Safety.
  • In order for preservation methods to be accepted, foods need to look and taste good. Scientists need to consider the taste, texture, and nutritional value of the food after it's been processed.

Ultra High Pressure Treatment (UHP)

  • The benefits of using pressure in the production of foods have been known for over 100 years. However, scientists and engineers have only recently developed the equipment necessary to efficiently and reliably generate the high pressure required to kill bacteria. The most recent use of ultra high pressure treatment is to kill both spoilage microorganisms and harmful pathogens, such as E. coli O157:H7 and Listeria monocytogenes, in foods.
  • Ultra high pressure treatment (UHP) works by exposing foods to pressure from 50,000 pounds per square inch (psi) to 100,000 psi for a short time (30 seconds to slightly more than 2 minutes).
  • High pressure can impact the life processes (protein function, enzyme action, and cellular membrane function) of living bacterial cells, thus causing the bacteria to die.
    - You could compare this to a fish accustomed to living in shallow waters suddenly being transported 7 miles down into the ocean, where the water pressure is about 18,000 psi. The fish could not withstand the pressure and would die.
  • Small macromolecules that are responsible for flavor and nutrition in food are typically not changed by pressure. Thus, high pressure can kill bacteria without affecting the nutrition, color, or texture of food.
  • The example of the grape in the water bottle (see procedure) illustrates that water in foods protects the food structure from physical damage during compression. As long as the food is mostly air-free and contains water, ultra high pressure processing does not "crush" the food. Foods such as deli meats, potato salad, salsa, and fruit pieces, can be exposed to high pressure to reduce spoilage and increase food safety without change to their structure. However, living bacteria can be destroyed by the effects of high pressure on their cellular functions.
  • UHP is particularly useful for foods that might be damaged or affected by heat. It's currently being used to preserve juices, salad dressings, fruit jams, salsas, soups, oysters, guacamole, and yogurt. Its application for other foods is currently being researched.

The pressure created by 2, 5-ton elephants balanced on a dime is roughly equal to 60,000 psi (pounds per square inch).