1. Procedure for Testing the pH of Various Foods Hands-on module Food Safety Scientist Curriculum © 2014 Board of Regents, South Dakota State University iGrow.org This project was supported by the USDA NIFA grant number 2011-38411-30625

2. iGrow.org Purpose of the Lab What is pH? The acidity of food is measured on a scale of 0-14. The lower the pH the higher the acidity Why is pH important in food? pH is a factor in food that contributes to the growth of microorganisms – yeast, mold, fungi and bacteria. Foods with a higher pH are more susceptible to microbial growth as opposed to highly acidic foods. © 2014 Board of Regents, South Dakota State University iGrow.org

3. iGrow.org Materials pH paper Sample Cups pH meter (optional) Buffers (for calibration) Constituents with different pH levels © 2014 Board of Regents, South Dakota State University iGrow.org

4. iGrow.org Constituents with Different pH Levels pH can be tested with household items. If using pH test strips, consider examples that produce a noticeable color change. © 2014 Board of Regents, South Dakota State University iGrow.org ConstituentpHConstituentpH Liquid Drain Cleaner14Canola Oil6 Bleach13Mouth Wash5 Soapy Water12Hand Soap5 Window Cleaner11Hand Sanitizing Gel4 Ammonia Cleaner10Spaghetti Sauce3 Baking Soda + Water8Apple Cider3 Club Soda7Lemon Juice2 Raw Egg7 Water7 Milk6

5. iGrow.org Procedure 1. Pour different constituents into sample cups 2. Cut 8 cm strips of the pH paper 3. Dip the each strip into a sample 4. The strip will immediately change color in accordance to the pH 5. Compare the pH strip with the color guide to determine the pH © 2014 Board of Regents, South Dakota State University iGrow.org

6. iGrow.org Procedure If supplies are available, use a calibrated pH meter to test the constituents. Compare the pH strips with the pH meter reading. Which method is more accurate? Why? Which method is more likely used in a food safety laboratory? Why? © 2014 Board of Regents, South Dakota State University iGrow.org

7. iGrow.org Recording Data © 2014 Board of Regents, South Dakota State University iGrow.org Constituent Hypothesized pH Color of pH Strip pH Reading

8. iGrow.org Discussion 1. Were any of the results surprising? Which ones and why? 2. What else are pH strips used for? 3. What other than food has a pH? 4. What other factors control the growth of microorganisms other than pH? 5. How can pH be changed? © 2014 Board of Regents, South Dakota State University iGrow.org