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

A method for the determination of water-soluble vitamins using a colorimetric microbial viability assay based on the reduction of the tetrazolium salt {2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt (WST-8)} via 2-methyl-1,4-napthoquinone (NQ) was developed. Measurement conditions were optimized for the microbiological determination of water-soluble vitamins, such as vitamin B6, biotin, folic acid, niacin, and pantothenic acid, using microorganisms that have a water-soluble vitamin requirement. A linear relationship between absorbance and water-soluble vitamin concentration was obtained. The proposed method was applied to determine the concentration of vitamin B6 in various foodstuffs. There was good agreement between vitamin B6 concentrations determined after 24 h using the WST-8 colorimetric method and those obtained after 48 h using a conventional method. The results suggest that the WST-8 colorimetric assay is a useful method for the rapid determination of water-soluble vitamins in a 96-well microtiter plate.