Question

What at is being metabolized if you see an alkaline reversion in carbohydrate fermentation lab?

Answer 1

During carbohydrate fermentation test, phenol red is used as pH indicator. When carbohydrates like glucose and fructose are metabolised, they produce acids which contribute to lowering of pH resulting in yellow color appearance of phenol red.

Alkaline reversion is the phenomenon of increase in pH of medium when carbohydrates are exhausted, resulting in red color appearance of phenol red.

Amino acids are metabolized if we see an alkaline reversion. Amino acids metabolized by deamination reactions resulting in release of ammonia which increases the pH of the medium. Phenol red shows red color as indication of alkaline condition.