Abstract
Lactobacillus delbrueckii subsp. lactis ATCC 7830 is used as an official indicator for the vitamin B_<12> (B_<12>) bioassay based on the calibration curve method. The strain is, however, unstable in the sensitivity to B_<12> frequently and it is difficult to generate reproducible calibration curves on the basis of the growth of the strain. We found L. delbrueckii strains derived from a fermented vegetable, sunki, tend to require B_<12> for growth strictly. Additionally, the growth of such strains showed a high correlation with B_<12> (cyanocobalamin) concentration in media. In this study, L. delbrueckii strains were evaluated based on the correlation stability for screening of superior B_<12> bioassay indicators and finally the strain NRIC 0700 was proposed. Moreover, the improvement of sample treatment conditions and of regression models for calibration curves contributed to the development of accuracy of the bioassay.
