Stability niacin

Niacin is one of the more stable water-soluble vitamins. Both nicotinic acid and nicotinamide are stable in air at ambient temperature (93,96). Aqueous solutions of nicotinic acid or nicotinamide can be autoclaved for short periods, e.g., 10 minutes at 120°C, without degradation. Nicotinic acid s stability in solution is independent of pH, but nicotinamide is stable only at neutral pH. Heating nicotinamide in 1 N acid or alkali at 100°C will induce its conversion to nicotinic acid. 

The niacin coenzymes are water soluble, but their stability is pH dependent (96). The reduced forms, NADH and NADPH, are stable in alkali but are rapidly decomposed in weak mineral acid solutions. In contrast, the oxidized forms, NAD and NADP, are unstable under alkaline conditions but are stable in acid. 

Due to the relative stability of the niacin vitamers, either acid or alkaline hydrolysis can be used to convert nicotinamide to nicotinic acid for quantitation of both vitamers as nicotinic acid (9,44). Acid hydrolysis is used to quantitate biologically available niacin. Alkaline hydrolysis releases both the biologically available and the unavailable vitamers and provides an estimate of the total niacin content. Because alkaline hydrolysis is much faster than acid hydrolysis, the latter is usually supplemented with enzymatic hydrolysis. The most common enzymes are takadiastase, papain, and clarase. On occasion, organic solvents such as methanol have been used to extract free nicotinic acid. 

Hageman GJ and Stierum RH (2001) Niacin, poly(ADP-ribose) polymerase-1 and genomic stability. Mutation Research 475,45-56. 

Additionally, sodium bicarbonate is used in solutions as a buffering agent for erythromycin, lidocaine, local anesthetic solutions, and total parenteral nutrition (TPN) solutions. In some parenteral formulations, e.g., niacin, sodium bicarbonate is used to produce a sodium salt of the active ingredient that has enhanced solubility. Sodium bicarbonate has also been used as a freeze-drying stabilizer and in toothpastes. 

Many vitamins are quite stable under normal processing conditions and present little or no stability problems in finished pharmaceutical products. These include biotin, niacin, niacinamide, pyridoxine, riboflavin, and a-tocopheryl acetate. Others that can present problems are ascorbic acid, calciferol, calcium pantothenate, cyanocobalamin, fola-cin, and retinyl esters. Overages above label claim are customarily added to vitamin formulations as a means of maintaining the claimed level of each vitamin for the expected shelf life of the products. The percent overage for a particular vitamin such as L-ascorbic acid will vary... 

Hudson CJ, Lin A, Cogan S, Cashman F, Warsh JJ. The niacin challenge test Chnical manifestation of altered transmembrane signal transduction in schizophrenia Biol Psychiatry 1997 41 507-513. Ikonomov OC, Manji HK. Molecular mechanisms underlying mood stabilization in manic-depressive ill-... 

Thiamine is particularly sensitive to thermal processing the published retention values range from 0 to 95% (Killeit, 1994). Wheat flour extruded with no added water suffered large thiamine losses, and increased barrel temperature decreased the vitamin only at the slowest feed rate used (250 g/min versus 500 and 750 g/min) (Andersson and Hedlund, 1990). In the same study, extrusion conditions did not affect the content of riboflavin (B2) or niacin ascorbic acid (C) decreased with higher temperatures at 10% moisture. Since enriched wheat flour is an important source of B vitamins in the United States, care must be taken to protect these vitamins. Relatively little is known about the stability of synthetic vitamins compared with natural sources, or the effects of added vitamins as opposed to endogenous nutrients. 

Accurate IDMS measurements ultimately depend upon a standard of accurately known concentration. It is important, then, to use as a standard a material of known purity and of good stability. Niacin is not a primary... 

Several vitamins have some desirable additional effects. Ascorbic acid is a dough improver, but can play a role similar to tocopherol as an antioxidant. Carotenoids and riboflavin are used as coloring pigments, while niacin improves the color stability of fresh and cured and pickled meat. 

Like choline, which is part of the compounds which are commonly called lecithins, inositol is an important component of phospholipids which help to stabilize blood cholesterol and prevent its deposition on the walls of arteries. Sometimes, the administration of inositol has helped to reduce accumulations of fatty substances (lipids) in the blood and the liver. Hence, it is designated as an agent which aids in the utilization of lipids (a lipotropic factor). However, it appears that the actions of inositol are closely tied to those of such other nutrients as choline, essential fatty acids, phospholipids, niacin, and vitamin B-6 (pyri-doxine). Finally, it is noteworthy that the heart muscle contains high levels of inositol, which suggests that it has an important cardiac function. 

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