Used in microbiological assays to determine the concentration of folic acid in pharmaceuticals and biological samples. Supports the growth of microorganisms like *Lactobacillus casei*, which require folic acid for growth—the greater the folic acid content in the sample, the more microbial growth occurs, measured via turbidity. This method is widely applied in quality control of vitamins, fortified foods, and dietary supplements to ensure accurate labeling and potency. Also used in research settings to assess folic acid metabolism and bioavailability.