Abstract
Additional studies were made on the microbiological assay for lipoic acid with Streptococcus faecalis 10C1. Turbidimetry was recognized as the preferable method for assay to acidtitration. It was also found that high-blank was occasionally referable to casamino acids added to the basal medium. Lipoic acid in a dilute solution during acid extraction at 120℃ for 1 hour was protected by the addition of a reducing agent such as cysteine under nitrogen atmosphere. Assay for lipoic acid in the extracts containing "Factor K" (an unidentified growth stimulating substance for lipoic acid requiring microorganisms discovered by one of the authors) was successfully carried out by eliminating the factor with cation exchange resin.
