MATERIALS AND METHODS

SUMMARY: A modified basal medium was employed for the assay of nicotinic acid contained in various biological materials. Of the various possible comparisons of test material with standard nicotinic acid in the assay, the ‘internal standard’ method is preferable; by assaying the standard nicotinic acid in the presence of the test material, any discrepancies due to substances stimulating or inhibiting the nicotinic acid effect are minimized. Of the different extraction procedures tested, treatmen! of samples with N-NaOH and N-H,SO, gave the most satisfactory results; both N-NaOH and N-H,SO, appeared to convert a ‘precursor ’ in potato and bran, into nicotinic acid. 2 N-HCl extracts yielded lower values, but the conversion of the precursor was less effective with potato than with bran, suggesting different precursors in the two vegetable substances. The results of microbiological and chemical assay were in good agreement. The coefficient of variation of the microbiological results was of the order of 9 yo. In a previous paper (Kodicek & Pepper, 1948) we examined various factors which may influence the microbiological assay of nicotinic acid, and described a medium allowing a slightly higher acid production than with formerly described media. Within one experiment the agreement between tubes was close with a satisfactorily low standard deviation. Between different experi-ments, however, the variation for the respective levels was high. This paper deals with the application of the method to extracts of natural foodstuffs, including methods of extraction and the computation of results