The soluble substrates (AZO-polysaccharides) are used for the quantitative analysis of enzyme activity performed in the test tubes. They can also be used in gel / agar plate activity screenings.They are added to the media mixture at a concentration of 0.05-0.2%, then the mixture is incubated in the boiling water batch until the substrate had dissolved. When the substrate is fully dissolved the agar is added and the media autoclaved. If the activity you are screening for is produced by the organism you will see a clearing zone. See pictures below:

Product Page (Soluble Chromogenic Substrates)