Nicotinic acid microbiological assay

As with many of the vitamins, biological assays have an important historical role and are widely used. For example, microbiological assays use l ctobacillusplantarum ATCC No. 8014 (57,59) or l ctobacillus arabinosus (60). These methods are appropriate for both nicotinamide and nicotinic acid. Selective detection of nictonic acid is possible if l euconostoc mesenteroides ATCC No. 9135 is used as the test organism (61). The use of microbiological assays have been reviewed (62). 

Vitamins may be assayed by means of microbial electrodes constructed from cells whose metabolic activity or growth is dependent on the vitamin assayed. Such microbial strains are well known from the commonly used microbiological assays. For instance, the assessment of thiamine was performed by means of yeast cells immobilized in a calcium al inatte membrane. The difference in oxygen consumption before and after incubation with thiamine in the sample is related to the thiamine content [269]. Similar biosensors have been worked out for nicotinic acid (with Lactobacillus arabinosa) [270], nicotine amide (with B. pumilus and E. coli) [271], and L-ascorbic acid (with Enterobacter agglomerans) [272]. 

Weigh 1 to 5 g of the sample, finely ground, transfer to a conical flask with 50 ml of N hydrochloric acid, cover the flask with a small beaker and autoclave at 121° (15 lb steam pressure) for fifteen minutes. Cool, add 2 ml of 2 5M sodium acetate solution and adjust to pH 4-5 using bromocresol green as external indicator. Dilute to 100 ml with water, filter and extract an aliquot with anaesthetic ether. Adjust to pH 6-8 using bromothymol blue as external indicator and dilute as required so that the final solution contains about 01 mg nicotinic acid per ml. Proceed with the assay as described in Appendix VII on Microbiological Assays (p. 813). 

Dried Yeast, B.P.C., and Tablets of Yeast, B.P.C, (containing 5 grains of dried yeast), are assayed for nicotinic acid by the microbiological method given above. 

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