Scope: The following method is applicable to grain, flour, cereal products and starch products. For samples with a very low nicotinic acid content (e.g., unenriched flours, starch products) or for those giving highly pigmented extracts (e.g., baked products) the microbiological method is more suitable than the chemical method.
Principle: The method is based upon the reaction of nicotinic acid with cyanogen bromide to give a pyridinium compound. The latter undergoes rearrangement yielding derivatives that couple with aromatic amines to produce colured compounds. Under the correct conditions, the optical density of the colour produced is proportional to the nicotinic acid present, and may be measured with a photoelectric colorimeter or a spectrophotometer.
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