Abstract
Effect of bound niacin in cereals on microbioassay of niacin using Lactobacillus plantarum was investigated.
As it was established that nicotinic acid was not liberated from bound niacin in cereals by autoclaving for 30 min at 120°C with 0.1 N H2SO4, free niacin sample solution was prepared from cereals by this method.
Non-diffusible niacin was extracted from wheat bran by Mason method, then purified by ionexchange chromatography to prepare bound niacin.
Although 1/3 of bound niacin in the culture medium was incorporated into the bacterial cells, no appreciable amount of free niacin was determined in the cells under rapid microbioassay condition which was incubated for 3-4 hr. However, the bound niacin incorporated into the cells under the conventional microbioassay condition incubated for 21 hr was acid hydrolyzable.
As the bound niacin preparation had 25 % of activity of nicotinic acid for the rapid assay, it is possible that free and bound niacins in wheat product are determined by the rapid assays for sample solution extracted with 0.1 N H2SO4 and with 1 N NaOH.
