Beyond twenty four hours of fermentation, the test tubes could change color altering the results of the experiment. The reading could possibly show a negative response when it was truly positive to begin with. Phenyl red is added to the test tube and functions as a pH indicator. It will turn a pink or fuchsia color if an alkaline setting is present and yellow in an acidic environment. The addition of this chemical is also used as a medium to determine gram negative enteric bacteria. If the pH of a solution is 6.8or below, the phenol red will turn the solution yellow. If the pH of the solution is 7.4 or higher, it will turn a pink/fuchsia color.
If the solution turns yellow, that states an acid end product formed which indicates the bacterium utilized the carbohydrate. If the carbohydrate was not used the end product will be ammonia which means the solution has turned yellow. Bacteria contain DNA which are coded for certain enzymes in which the organism contains. Numerous carbohydrates can be fermented, but not all bacteria can ferment every single one. In order for a particular type of organism to ferment a specific carbohydrate, it needs the accurate enzyme built inside in order to convert a specific carbohydrate.
Hands-on-Labs. (2012). A Laboratory Manual of Small-Scale Experiments for the Independent Study of Microbiology. Englewood, CO. Available from www.labpaq.com
Read more: Aldehydes and Ketones Lab Report Conclusion