EXPERIMENT Food Safety Hands-On Labs, Inc. Version 42-0308 -00-01 Review the safety materials and wear goggles when working with chemicals. Read the entire exercise before you begin. Take time to organize the materials you will need and set aside a safe work space in which to complete the exercise. Experiment Summary: You will describe how microbes cause foodborne illness. You will discuss common methods used to maintain food safety. You will culture microbes collected from fresh foods to compare food handling techniques. You will relate experimental results to methods for improving food safety in your home. www.holscience.com 1 Hands-On Labs, Inc.
Objectives Upon completion of this laboratory, you will be able to: Describe the importance of food safety. Define foodborne illness. Explain how food becomes compromised by microbes. Discuss common methods used to preserve food safety. Culture microbes collected from fresh food sources. Relate experimental results to methods for improving food safety in your home. Time Allocation: 3 hours + 48 hours incubation (This experiment requires a 7-day-old sample of fresh milk. Plan your time accordingly.) www.holscience.com 2 Hands-On Labs, Inc.
Materials Student Supplied Materials Quantity Item Description 1 Bleach 1 Camera, digital or smartphone 1 Coffee mug 1 Distilled water 1 Hand soap 1 Isopropyl alcohol (rubbing) 1 Large cooking pot (at least 8 deep) 1 Leaf lettuce-fresh, unwashed 1 Oven mitt 1 Permanent marker 1 Roll of paper towels 2 Small containers of milk* 1 Source of tap water 1 Stove HOL Supplied Materials Quantity Item Description 1 Apron 1 Face mask with ear loops 1 Nutrient agar-18 ml tubes 2 Pairs of gloves 2 Petri dishes-60 mm 1 Safety goggles 2 Sterile swabs (2 per pack) 1 Test tube clamp 1 Test tube rack, 6 x 21 mm *Two containers of milk are needed. Open one container exactly 7 days prior to beginning the experiment and allow the second to remain closed until used in the procedures. Place both containers in a refrigerator when not in use. It is best if the two containers are purchased on the same date and have the same expiration date. Note: To fully and accurately complete all lab exercises, you will need access to: 1. A computer to upload digital camera images. 2. Basic photo editing software, such as Microsoft Word or PowerPoint, to add labels, leader lines, or text to digital photos. www.holscience.com 3 Hands-On Labs, Inc.
3. Subject-specific textbook or appropriate reference resources from lecture content or other suggested resources. Note: The packaging and/or materials in this LabPaq kit may differ slightly from that which is listed above. For an exact listing of materials, refer to the Contents List included in your LabPaq kit. www.holscience.com 4 Hands-On Labs, Inc.
Background The Importance of Food Safety The Centers for Disease Control and Prevention (CDC) estimates one in six Americans become ill from foodborne pathogens, 3000 of these individuals die from foodborne diseases each year. See Figure 1. Foodborne illnesses are obtained from consumption of food contaminated with microorganisms. Foodborne illnesses present a significant public health risk. Preventing the transmission of foodborne illness involves committed awareness on all levels of food processing and preparation, including those steps taken in individuals homes. Figure 1. Food Safety Progress Resort developed by the Centers for Disease Control and Prevention (CDC). Centers for Disease Control and Prevention Although this laboratory experiment focuses on microorganisms and food safety, it is important to remember that most microbes associated with food are not harmful to humans. In fact, many microbes play a beneficial role in relation to food by processes such as fermentation. How Food Becomes Compromised Prevention of foodborne illnesses is challenging because fresh foods are rarely grown in sterile conditions. Produce is exposed to microbes in the soil and from irrigation water. See Figure 2. When the exposed produce is not cleaned properly before consumption, foodborne illness in humans can occur. The butchering and processing of animal tissues may result in contamination with microbes that are found in the digestive system of the animal. Even though these microbes may not be harmful to the host animal, they may lead to foodborne illness in humans. www.holscience.com 5 Hands-On Labs, Inc.
Figure 2. Irrigation of spinach crop. Federico Rostagno Most steps involved in food handling can result in possible exposure to a foodborne illness. Clostridium botulinum is a soil-dwelling organism commonly associated with poor food handling and processing procedures. The spores of C. botulinum can infect individuals consuming home-canned root vegetables such as carrots and potatoes. Other examples of foodborne illness caused by microbes include: Escherichia coli and Listeria monocytogenes infections resulting from consuming raw vegetables irrigated with contaminated water. In addition, Salmonella infections may result from improper handling of raw poultry. According to the Food and Drug Administration, 48 million cases of foodborne illnesses occur annually in the United States. More than 200 known diseases are spread through contaminated foods. www.holscience.com 6 Hands-On Labs, Inc.
Food Safety in the Home Numerous precautions can be taken in one s home to reduce the incidence of foodborne illness. Proper hand washing before handling food is important, as is washing one s hands between handling different foods during preparation. To reduce the presence of microbes, fruits and vegetables should be washed with soap and water prior to being consumed raw. See Figure 3. Figure 3. Wash vegetables with soap and water to reduce microbe numbers. science photo Cross contamination, which is the transfer of bacteria from one food item to another, can be reduced by using different utensils and preparation surfaces for meats and produce. Finally, the proper usage of temperature, both hot and cold, can significantly reduce exposure to foodborne pathogens. Colder temperatures reduce the reproductive rate of most microbes. Cooking meat to an internal temperature of 160 F (71 C) kills most microorganisms. Discarding food that has been unrefrigerated for a prolonged period of time also reduces foodborne illnesses. www.holscience.com 7 Hands-On Labs, Inc.
Exercise 1: Food Safety Note: Two containers of milk are needed. Open one container exactly 7 days prior to beginning the experiment and allow the second to remain closed until used in the procedures. Place both containers in a refrigerator when not in use. It is best if the two containers are purchased on the same date and have the same expiration date. Part 1 of 2 In this laboratory, you will incubate microbes collected from unwashed and washed produce and from opened and unopened milk. After incubation, you will compare the number and types of microbes that develop from each food source and relate the results to practices for maintaining food safety in your home. 1. Approximately 1 hour before you begin this exercise, pour 2 agar plates. Refer to the appendix entitled Pouring Agar Plates for guidance with this procedure. Note: Plates may be poured in advance, stored in an airtight bag, and refrigerated for future use. 2. Clear a work area and gather all materials listed for this experiment. 3. Wash your hands thoroughly with soap and warm water. 4. Put on the safety gloves, face mask, apron, and goggles. 5. Disinfect the work surface by wiping it with a 10% bleach solution. 6. Using the permanent marker, divide the bottom of each agar plate into 2 sections. Label the sections of one plate Milk Fresh and Milk Opened. Label sections of the other plate Lettuce Washed and Lettuce Unwashed. See Figure 4. Figure 4. Labeled agar plate. 7. Remove a sterile swab from the packet and moisten with distilled water. 8. Rub the moistened swab on the surface of the unwashed lettuce. www.holscience.com 8 Hands-On Labs, Inc.
9. Transfer the sample to the Lettuce Unwashed section of the agar plate by rubbing the swab on the agar surface within the section until it is completely coated with inoculant. Note: Be careful to only inoculate the surface within the outlined section. 10. Place the used swab in a container of undiluted bleach. 11. Thoroughly wash the lettuce with soap and water. Pat it dry with paper towels. 12. Repeat steps 7-10 using the washed lettuce. 13. Remove a sterile swab from the packet and saturate with the milk that has been opened for 7 days. 14. Transfer the sample to the Milk Opened section of the agar plate by rubbing the swab on the agar surface within the section until it is completely coated with inoculant. 15. Place the used swab in container of undiluted bleach. 16. Open the fresh container of milk and repeat steps 13-15 for this sample. 17. Place the inoculated plates bottom-side up (inverted) in your incubation location for 48 hours. 18. Dispose of the used and bleached swabs in the garbage. 19. Wipe down your work area with a 10% bleach solution. 20. Wash and return items to your kit for future use. 21. Wash your hands thoroughly. Part 2 of 2 22. Observe the culture plates after 48 hours for microbial growth. If no colonies are observed, incubate for an additional 24 hours. Note: Do not remove the lids of the plates when observing. Unknown microbe cultures should always remain covered. 23. Wipe down your work area with a 10% bleach solution. 24. Wash your hands thoroughly with soap and warm water. 25. Put on your goggles, a new pair of gloves, face mask, and apron. 26. Gather the 2 incubated agar plates. 27. Observe each of the sections without removing the lid. Count the number of different colony types present in each section and record in Data Table 1 of your Laboratory Report Assistant. 28. Count the total number of colonies in each section and record in Data Table 1. www.holscience.com 9 Hands-On Labs, Inc.
29. Take a photograph of your developed plates. Resize and insert the image in to Data Table 2 of your Laboratory Report Assistant. Refer to the appendix entitled Resizing an Image for guidance with resizing an image. 30. Soak the incubated plates in undiluted bleach for 1 hour before disposal. 31. Wipe down your work area with a 10% bleach solution. 32. Wash your hands thoroughly with soap and warm water. Questions A. Why is food safety important? B. How does food become compromised by microbes? C. How can food safety be improved in the home environment? D. Based on the results recorded in Data Table 1, which foods contained the highest number and diversity of microbes? E. How will the results of this experiment impact your food safety practices at home? www.holscience.com 10 Hands-On Labs, Inc.