Today the glucose fermentation broth had Durham tubes to det

Today, the glucose fermentation broth had Durham tubes to detect gas production, but there were no Durham tubes in the lactose or sucrose media. Even without the Durham tubes, though, we can still figure out if gas was produced in the lactose or sucrose broth. Explain how. (your answer must be 60 words or fewer)

Solution

If lactose or sucrose is fermented the products formed are acidic, the pH of the medium will drop. A pH indicator such as phenol red used in the broth changes color from red to yellow, indicating a pH change to acidic. This confirms fermentation reaction.