There are lots of proteins around the home that you can use use high protein media. Some of those used by professionals are meat, brain, egg, liver, gelatin, can add to TGY and other bases. Skim milk contains the disaccharide lactose and two protein complexes and is a useful medium covered on page b028 . Until I get this page completed, keep in mind you can use a meat grinder to grind any meat, soak the ground meat in water,and then boil it to produce and infusion broth as we did on page b022 to make Easy Broth. Above we learned some bacteria can deaminate one or more amino acids releasing ammonia.
Ammonia is basic and raises the pH of the medium.
You can detect this pH change by adding a suitable pH indicator. It is various shades of orange in between. Therefore, if you add phenol red to your meat or milk medium you will find some bacteria turn the medium red. Sometimes the medium is red at the top of the slant and yellow at the bottom. Three amino acids contain sulfur.