Determination of water-soluble vitamins using a colorimetric microbial viability assay based on the reduction of water-soluble tetrazolium salts

► In a conventional method for the microbiological determination of water-soluble vitamins, the growth of the microorganism in relation to the vitamin is measured as turbidity. ► The WST-8 colorimetric method has been applied to the rapid proliferation assay of microorganisms. ► Compared with a conventional method, the application of WST-8 colorimetric method to a microbiological determination of water-soluble vitamins could lead to a decrease in incubation times and a good reproducibility in the assay. ► The WST-8 colorimetric assay is a useful method for the rapid and accurate determination of vitamin B6, biotin, folic acid, niacin, and pantothenic acid in a 96-well microtiter plate.