Vitamin C stability

Table 9-15 Vitamin C Stability in Fortified Foods and Beverages after Storage at 23°C for 12 Months, Except as Noted...

Use Antioxidant for fats and oils, source of vitamin C, stabilizer, emulsifier. 

Physical Properties. Table 3 contains a summary of the physical properties of L-ascorbic acid. Properties relating to the stmcture of vitamin C have been reviewed and summarized (32). Stabilization of the molecule is a consequence of delocalization of the TT-electrons over the conjugated enediol system. The highly acidic nature of the H-atom on C-3 has been confirmed by neutron diffraction studies (23). 

HALLIWELL B (2001) Vitamin C and genomic stability . Mutation Research, 475, 29-35. 

Choy et al. [193] reported that vitamin A (retinoic acid), vitamin C (ascorbic acid) and vitamin E (tocopherol) could be intercalated into Zn/Al LDHs by the coprecipitation method. In solutions, these vitamins are normally all sensitive to light, heat and oxygen, and it was proposed that incorporating the molecules into a layered inorganic lattice may lead to their stabilization, resulting in a wider range of potential apphcations. 

Vitamin C (ascorbic acid) is also a well-known antioxidant. It can readily lose a hydrogen atom from one of its enolic hydroxyls, leading to a resonance-stabilized radical. Vitamin C is acidic (hence ascorbic acid) because loss of a proton from the same hydroxyl leads to a resonance-stabilized anion (see Box 12.8). However, it appears that vitamin C does not act as an antioxidant in quite the same way as the other compounds mentioned above. 

Vitamin C, also known as L-ascorbic acid, clearly appears to be of carbohydrate nature. Its most obvious functional group is the lactone ring system, and, although termed ascorbic acid, it is certainly not a carboxylic acid. Nevertheless, it shows acidic properties, since it is an enol, in fact an enediol. It is easy to predict which enol hydroxyl group is going to ionize more readily. It must be the one P to the carbonyl, ionization of which produces a conjugate base that is nicely resonance stabilized (see Section 4.3.5). Indeed, note that these resonance forms correspond to those of an enolate anion derived from a 1,3-dicarbonyl compound (see Section 10.1). Ionization of the a-hydroxyl provides less favourable resonance, and the remaining hydroxyls are typical non-acidic alcohols (see Section 4.3.3). Thus, the of vitamin C is 4.0, and is comparable to that of a carboxylic acid. 

Peroxide formation has also been observed in multivitamin solutions for parenteral nutrition. Lavoie and co-workers [30] have studied the action of light, air, and composition on the stability of multivitamin formulations, and also total parenteral nutrition (TPN) admixtures containing and not containing vitamins and fatty acids. They analyzed the generation of peroxide in multivitamin solutions and in TPN for adults and neonates. The analysis of multivitamin solutions for enteral use revealed the presence of peroxides at the initial opening of the bottle. The levels were higher in Poly-Vi-Sol (vitamin A, Vitamin D, and vitamin C, vitamin Bb riboflavin, and... 

The annealing temperature of 400 °C might indicate the stability of Vitamin C and so be used as baking additive.lt has an optical absorption at UVB region and may be used as non-toxic UV-absorber.115... 

Substances that guarantee the chemical and mechanical stability of the cornea are mostly collagen type I and X that are mainly made of proline and hydroxy-proline. Other substances that are present in a considerable amount are proteins (pK between 5.3 and 9), vitamin C (pK = 4.2), bicarbonate, glutathione, and lactate. (For more details about pK refer to Chap. 3, Sect. 3.2.4.1)... 

Vitamin B Complex + Vitamin C Instant Granules (2 RDA of Vitamins) 5. Chemical stability of the granules (20-25 °C)... 

A number of reference materials for vitamins in foods are under development. Extensive analysis and stability testing have been conducted to assess the potential of vitamin-enriched milk powder, wholemeal flour, and margarine as well as lyophilized brussels sprouts, mixed vegetables, and pork liver for use as reference materials (193-196). The certification study for vitamin C in the brussels sprouts reference material has been completed. However, methodology problems continue to have a significant negative effect on the development of reference materials. 

Ascorbic acid, known more familiarly as vitamin C, is used not only as on acidulant but also as a stabiliser within the soft drinks system, and its antioxidant properties serve to improve the shelf-fife stability of flavour components. Many of the ingredients used in flavourings are susceptible to oxidation, particularly aldehydes, ketones and keto-esters. Ascorbic acid shields these from attack by being preferentially oxidised and lost, leaving the flavour component unaffected. 

The only vitamins likely to be found in unfortified soft drinks are vitamin C (either added as an antioxidant or deriving from fruit materials) and vitamin A precursor (beta-carotene, added as a colour). However, soft drinks provide a good medium for vitamin fortification, the limitations being solubility (for fat-soluble vitamins), flavour impairment (for example the meaty notes of thiamine) and stability. 

The well-known susceptibility of vitamin C to thermal and oxidative degradation has focused interest in derivatives of increased stability. In general, partial modification of the enediol system leads to two isomers, both of which have markedly lower reducing power and are therefore stabilized against oxidation. However, vitamin C activities tend to decrease in these substituted derivatives. 

To improve the long-term stability of the common nickel oxide anodes, surfactants, such as substituted polyglycol ethers, are added to the electrolyte 291). Merck has proposed a combined process (in which about 80 % of the diacetonesorbose are oxidized electrochemically, and the remainder conventionally 292)) and a special procedure for the work-up procedure by electrodialysis (removal of the unconverted diacetonesorbose 293)). It is said that Merck is using the electrosynthesis of diacetoneketogulonic acid for the industrial production of vitamin C. 

One of the main problems of topical application of vitamin C is that it is extremly unstable, so hydrophilic derivatives like sodium ascorbyl phosphate and lipophilic esters with fatty acids were synthesized to improve stability.43,44 However, an efficient increase in vitamin C levels after topical application of different ascorbic acid derivatives including magnesium ascorbyl phosphate, ascorbyl-6-palmitate, and dehydroascorbic acid to porcine skin could not be shown.42... 

Austria, R., Semenzato, A., and Bettero, A., Stability of vitamin C derivatives in solution and topical formulations, J. Pharm. Biomed. Anal., 15, 795, 1997. 

---