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

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.

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 has 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 (from 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 used in this lesson 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 to increase food safety without changes to the foods’ structures. 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.

Science and our Food Supply Modules

This lesson was developed as a portion of an entire unit of lessons focusing on food safety from farm to table. Use the following links to see the remaining lessons:

Module 1: Bacteria

• Understanding Bacteria
• The 12 Most Unwanted Bacteria

Module 2: Farm

• Chain of Food

Module 3: Processing and Transportation

• Blue's the Clue: Souring Milk for Science
• Mystery Juice
• Ultra High Pressure Treatment

Module 4: Retail and Home

• Supermarket Smarts
• Cooking Right: The Science of Cooking a Hamburger
• A Chilling Investigation
• Crossed Up!
• Hands Off, Bacteria!

Module 5: Outbreak and Future Technology

• Outbreak Alert - Shigella
• Beef Blasters

Evaluation

• Lose a Million Bacteria (The Game)