L. delbureckii subsp. lactis(leichmannii), L. rhamnosus and L. plantarum were used as assay organisms for the determination of vitamin B12, folic acid, and biotin, respectively.
The optimized bacteria were suspended NaCl solution, and the transmittance of the bacteria suspensions were maintained to 60–80% before usage. One drop of the inoculum was added in each assay tube.
After sterilization of the sample plus medium for 5 min, the tubes were incubated at 37 C for 19–20 h. At last, the turbidity was measured with a spectrometer reader at 550 nm.