Niacin Assay Medium, 500 g

Niacin Assay Medium is classified under the category of assay medium of vitamin assay medium. The other two categories of medium essential in vitamin assay are the inoculum media, used for preparation of inoculum to be used in the assay procedure, and maintenance media, used for maintenance of stock cultures used in assay procedures. Niacin Assay Medium is prepared according to the formula described by Snell and Wright (1) and modified by Krehl, Strong and Elvehjam (2) and Barton-Wright (3). This medium is recommended by AOAC (4) and USP (5). Niacin Assay Medium is used for the assay of Niacin (Nicotinamide) employing Lactobacillus plantarum ATCC 8014 as the test organism. Microbiological assay of Niacin is carried out by using L. plantarum ATCC 8014 as the test organism. Standard curve is obtained by using USP (5) Niacin reference standard with levels of 0.0, 0.025, 0.05, 0.075, 0.1, 0.125, 0.15, 0.2 and 0.25 mcg niacin per assay tube (10 ml). Niacin Assay Medium is used for both turbidimetric and acidimetric analysis. Turbidimetric determination is made after 16-18 hours incubation at 35-37°C. Acidimetric determinations are best made following 72 hours incubation at 35-37°C. Niacin Assay Medium is devoid of nicotinic acid but contains all other nutrients and vitamins essential for the cultivation of L. plantarum ATCC 8014. Addition of Niacin (Nicotinic acid) in specified increasing concentrations gives a corresponding growth response that can be measured turbidimetrically or titrimetrically. Stock cultures of L. plantarum ATCC 8014 are maintained on Lactobacilli Agar, AOAC (M366). Culture for assay is obtained by inoculating Lactobacilli Agar, AOAC (M366) and incubating at 35-37°C for 24-48 hours. These cultures are then inoculated into Lactobacilli Broth, AOAC (M367), to prepare the inoculum. Following an incubation at 35-37°C for 18-24 hours, the cells are centrifuged and washed thrice with 0.85% saline. The appropriate dilution of cells so obtained is used to inoculate tubes of Niacin Assay Medium (M040), containing increasing concentrations of Niacin. Using standard Niacin concentration, a standard curve is obtained. This standard is used to extrapolate the unknown niacin concentration. For detailed procedure, refer standard procedures (4, 5). Extreme care must be taken to avoid contamination of media or glassware used for microbiological assay procedures. Detergentfree clean glassware should be used. Even small amount of contamination by foreign material can lead to erroneous results. Storage and Shelf-life: Store below 8°C in a tightly closed container and use freshly prepared medium. Use before expiry date on the label. References: 1. Snell and Wright, 1941, J. Biol. Chem. 13:675. 2. Krehl, Strong and Elvehjem, 1943, Ind. & Eng. Chem., Ann. Ed. 15:471. 3. Barton-Wright, 1944, J. Biochem., 38:314. 4. Williams, (Ed.), 2005, Official Methods of Analysis of the Association of Official Analytical Chemists, 19th Ed., AOAC, Washington, D.C. 5. The United States Pharmacopoeia, 2006, USP29/NF24, The United States Pharmacopoeial Convention, Rockville, MD.