Niacin concentrations

Niacin determinations have similarly been performed by Lieck (1954) on samples of liver tissue, heart, and skclct il muscle obtained from calves and from adult cattle the analyses showed essentially ctiual niacin concentrations for the immature and the mature animals. In contrast to this, analyses made by Denton et al. (1947) on liver and muscular tissue specimens from chickens between 6 and 18 weeks of age revealed a definite decrease in the niacin levels of these tissues with age. 

Niacin. The average niacin content of milk is only 0.08 mg per 100 g so, two glasses of milk make little contribution (2 to 3%) to the 15 mg niacin RDA for adults. Nevertheless, milk and milk products are among the most effective pellagra-preventive foods because of (a) the complete availability of niacin in milk and (b) the presence of the amino acid tryptophan (about 46 mg tryptophan per 1 00 g milk) in milk protein, which can be used for the synthesis of niacin in the body. (A dietary intake of 60 mg tryptophan is equivalent to 1 mg niacin.) Thus, the niacin value of milk is considerably greater than is reflected by its niacin concentration. Also, it is noteworthy that pasteurization does not destroy the niacin content of milk. 

Most foods of animal origin contain nicotinamide in the coenzyme form (high bioavialability). Liver and meat are particularly rich in highly bioavailable niacin. Most of the niacin in plants, however, occurs as nicotinic acid in overall lower concentrations and with a lower bioavailability. The major portion of niacin in cereals is found in the outer layer and its bioavailability is as low as 30% because it is bound to protein (niacytin). If the diet contains a surplus of L-tryptophan (Ttp), e.g., more than is necessary for protein synthesis, the liver can synthesize NAD from Trp. Niacin requirements are therefore declared as niacin equivalents (1 NE = 1 mg niacin = 60 mg Trp). 

The infrared technique has been described in numerous publications and recent reviews were published by Davies and Giangiacomo (2000), Ismail et al. (1997) and Wetzel (1998). Very few applications have been described for analysis of additives in food products. One interesting application is for controlling vitamin concentrations in vitamin premixes used for fortification of food products by attenuated total reflectance (ATR) accessory with Fourier transform infrared (FTIR) (Wojciechowski et al., 1998). Four vitamins were analysed - Bi (thiamin), B2 (riboflavin), B6 (vitamin B6 compounds) and Niacin (nicotinic acid) - in about 10 minutes. The partial least squares technique was used for calibration of the equipment. The precision of measurements was in the range 4-8%, similar to those obtained for the four vitamins by the reference HPLC method. 

Many common foods (such as citrus fruits), pharmaceuticals (such as AspirinT ), and some vitamins (such as niacin, vitamin B3) are weak acids. When a weak acid dissolves in water, it does not completely dissociate. The concentration of the hydronium ions, and the concentration of the conjugate base of the acid that is formed in solution, depend on the initial concentration of the acid and the amount of acid that dissociates. 

Pharmacokinetics Niacin is rapidly absorbed from the Gl tract peak serum concentrations usually occur within 45 minutes. The plasma elimination half-life is approximately 45 minutes. Approximately one third of an oral dose is excreted unchanged in the urine. 

Niacin is present in foods mainly as coenzyme NAD and NADP, which are hydrolyzed in the intestine, and it is adsorbed as nicotinamide or nicotinic acid. The free forms, nicotinamide and nicotinic acid, only allowed to be added in fortified foods [403], occur naturally in limited amounts. Instead, niacin occurs as nicotynil ester bonded to polysaccharides, peptides, and glycopeptides. In general, niacin is widespread in foodstuffs (cereals, seeds, meat, and fish). High concentrations are present in roasted coffee beans as a primarily product of the roasting process [417]. 

Milk contains about 0.1 mg niacin per 100 g and thus is not a rich source of the preformed vitamin. Tryptophan contributes roughly 0.7 mg NE per 100 g milk. In milk, niacin exists primarily as nicotinamide and its concentration does not appear to be affected greatly by breed of cow, feed, season or stage of lactation. Pasteurized goats (0.3 mg niacin and 0.7 mg NE from tryptophan per 100 g) and raw sheep s (0.4 mg niacin and 1.3 mg NE from tryptophan per 100 g) milk are somewhat richer than cows milk. Niacin levels in human milk are 0.2 mg niacin and 0.5 mg NE from tryptophan per 100 g. The concentration of niacin in most dairy products is low (Appendix 6A) but is compensated somewhat by tryptophan released on hydrolysis of the proteins. 

Vitamins are required for satisfactory development or function of most yeasts. Wickerham (177) devised a complete yeast medium which included eight vitamins biotin, pantothenic acid, inositol, niacin, p-aminobenzoic acid, pyridoxine, thiamine, and riboflavin. The concentrations of these growth factors varied widely with inositol in the greatest concentration and biotin in trace amounts. Many of these vitamins are considered major growth factors for yeast multiplication and development, as noted in several studies and reviews (178, 179, 180, 181, 182). Generally, the benefit of adding vitamins to musts and wines has not been established as a normal winery practice. This lack of response is because vitamins occur naturally in sufficient quantities in grapes and are produced by yeasts themselves (3). 

Ascorbic acid, thiamine, riboflavin, and vitamin B12 requirements increase in hyperthyroidism (issue concentrations reduced Vitamin A massive doses of vitamin A inhibit secretion of TSH thyroid hormones required for carotene and retimene conversions Vitamins A, D, E. and K requirements increased in hyperthyroidism tissue concentrations reduced in Vitamin B, . niacin conversion to phosphorylated reactive forms impaired in hyperthyroidism... 

CM Ward, VC Trenerry, I Pant. The application of capillary electrophoresis to the determination of total niacin in concentrated yeast spreads. Food Chem 58 185-192, 1997. 

The desugaring of cane juice concentrates the heat- and alkali-stable vitamins in the final molasses. Even after this accumulation, only myo-inositol may have reached the level of minimum dietary requirements.109 Niacin, pantothenic acid and riboflavin are also present in significant quantities109 the thiamine, pyridoxin, pantothenic acid, biotin and folic acid contents of molasses have been estimated by bioassay.110 111 The biotin content of Hawaiian and Cuban molasses was 2.1 and 1.7 gammas per gram, respectively.119 The antistiffness factor (closely related to stigmasterol) has been found in cane molasses.88 89 The distillery slop from the yeast fermentation of molasses is marketed as a vitamin concentrate this product also contains vitamins originating in the yeast. 

Either niacin or niacinamide can be selectively isolated from the hydrolysis by varying the hydrolysis time and nitrile concentration. A higher hydrolysis temperature favors production of niacin. 

Resolution Solution Prepare a solution containing equal volumes of the Standard Preparation and of a niacin solution similarly prepared and having the same concentration. 

In the liver, there is litde utilization of preformed niacin for nucleotide synthesis. Although isolated hepatocytes will take up both vitamers from the incubation medium, they seem not to be used for NAD synthesis and cannot prevent the fall in intracellular NAD(P), which occurs during incubation. The enzymes for nicotinic acid and nicotinamide utilization are more or less saturated with their substrates at normal concentrations in the liver, and hence are unlikely to be able to use additional niacin for nucleotide synthesis. By contrast, incubation of isolated hepatocytes with tryptophan results in a considerable increase in the rate of synthesis of NAD(P) and accumulation of nicotinamide and nicotinic acid in the incubation medium. Similarly, feeding experimental animals on diets providing high intakes of nicotinic acid or nicotinamide has relatively little effect on the concentration of NAD (P) in the liver, whereas high intakes of tryptophan lead to a considerable increase. It thus seems likely that the major role of the liver is to synthesize NAD(P) from tryptophan, followed by hydrolysis to release niacin for use by extrahepatic tissues (Bender et al., 1982 McCreanor and Bender, 1986 Bender and Olufunwa, 1988). 

The result of this is that at low rates of flux through the kynurenine pathway, which result in concentrations of aminocarhoxymuconic semialdehyde below that at which picolinate carboxylase is saturated, most of the flux will be byway of the enzyme-catalyzed pathway, leading to oxidation. There will be Utde accumulation of aminocarhoxymuconic semialdehyde to undergo nonenzymic cyclization. As the rate of formation of aminocarhoxymuconic semialdehyde increases, and picolinate carboxylase nears saturation, there will be an increasing amount available to undergo the nonenzymic reaction and onward metabolism to NAD. Thus, there is not a simple stoichiometric relationship between tryptophan and niacin, and the equivalence of the two coenzyme precursors will vary as the amount of tryptophan to be metabolized and the rate of metabolism vary. 

Despite our understanding of the biochemistry of niacin, we still cannot account for the characteristic photosensitive dermatitis in terms of the known metabolic lesions. There is no apparent relationship between reduced availability of tryptophan and niacin, and sensitivity of the skin to ultraviolet (UV) light. The only biochemical abnormalities that have been reported in the skin of pellagrins involve increased catabolism of the amino acid histidine leading to a reduction in the concentration of urocanic acid, a histidine metabolite that is the major UV-absorbing compound in normal dermis (see Figure 10.6). 

Measurement of liver and other tissue concentrations of NAD(P) gives a precise estimate of niacin nutritional status and seems to be the most sensitive indicator in experimental animals. Measurement of the whole blood concentration of NAD (P) may serve the same purpose there is a good correlation between blood and liver concentrations of nicotinamide nucleotides in experimental animals. The sensitivity of the method is such that reproducible determinations can be carried out on finger-prick samples of 200 /xL of blood (Bender etal., 1982). 

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