I am working on anaerobic bacteria. And the media suggests using l-cysteine as a reducing agent to exclude oxygen from the media. It even recommends purging with nitrogen. When, I use the same composition along with agar to make semi-solid media it shows the color of Alamarblue turning colorless indicating oxygen being reduced. But same media composition in liquid culture (without agar media) does not show Alamarblue turning colorless. I would like to know, the reason for this phenomenon.