Ascorbic acid addition, appearance

Additional papers on the oxidation of L-ascorbic acid have appeared as follows with the peroxodisulphate ion (SoOp )... 

Many reactions catalyzed by the addition of simple metal ions involve chelation of the metal. The familiar autocatalysis of the oxidation of oxalate by permanganate results from the chelation of the oxalate and Mn (III) from the permanganate. Oxidation of ascorbic acid [50-81-7] C HgO, is catalyzed by copper (12). The stabilization of preparations containing ascorbic acid by the addition of a chelant appears to be negative catalysis of the oxidation but results from the sequestration of the copper. Many such inhibitions are the result of sequestration. Catalysis by chelation of metal ions with a reactant is usually accomphshed by polarization of the molecule, faciUtation of electron transfer by the metal, or orientation of reactants. 

Recently, the decomposition of N-sulfonyloxy-AAF under aqueous conditions has been further examined and appears to be consistent with this overall mechanism (50). That is, the major products appear to be 1- and 3-sulfonyloxy-AAF with small amounts of AAF, 4-hydroxy-AAF, and a dimer formed by addition of the electrophile onto the aromatic ring of another AAF molecule (51). Furthermore, the relative yields of AAF could be increased by addition of the reducing agent, ascorbic acid (52). 

Antioxidants should be labelled on the retail package with the specific chemical name or with the EC number. The legislation of member states of the EU is influenced by the decision taken within the EC. Some food standards are fully based on EC Directives and some are still based on national considerations. There may be differences between European states, for instance, the utilisation of ascorbic acid as antioxidant for egg products is permitted in France but prohibited in Germany. These differences concern usually the utilisation of antioxidants in various food commodities. The specification of antioxidants mentioned in EC Directives are respected by all member states. But it is still generally required that individual countries of the European Union as well as the central organisation should be approached. The requirements appearing in the EC Directives on additives must be applied by the member states. This means in the first place that for those categories of additives for which a Community positive list exists, member states may not authorise any additives which do not appear on the positive list. 

The same authors (G8, G7) also found very substantial decreases in riboflavin (approx. 80%), and niacin (P9) fared little better. When mixtures were irradiated unusual events occurred. Riboflavin and ascorbic acid were each protected by niacin. Addition of cystine or cysteine apparently sensitized the niacin (P10). Since initial rates were not given, and the doses were considerably above the oxygen breakpoint (Sec. IIIA2), no mechanistic interpretation is possible. There also appears to be some doubt about the reliability of the colormetric assay used by these workers. 

It has been suggested that there may be some benefit of using tryptophan in selected patients, particularly those with psychomotor retardation (3). Unfortunately, most of these reports have appeared as letters to the editors of journals (4-6) or as preliminary communications (7). In addition to the possible absence of any consistent effect, there are many plausible reasons to explain the variability in response. Tryptophan has been given in both the racemic and monomeric (levorotatory) forms, both alone and together with a number of substances intended to increase the synthesis or availability of serotonin, including monoamine oxidase (MAO) inhibitors (8), potassium or carbohydrate supplements (9), and co-enzymes such as pyridoxine or ascorbic acid (10). It has also been... 

Within experimental limits, leaves labeled with l-[5- C]- or l-[6- C]ascorbic acid gave comparable results (Table III). Additively, the C in CO2, sugars, and malic acid accounted to 62-63% of that present in the leaves. Another 7% appeared in the residue as glycans. The total amount of C found in hexose or products of hexose metabolism of l-[5- C]- or L-[6- C]ascorbic acid labeled leaves was similar to that found in tartrate (and CO2) after labeling with l-[1- C]- or l-[4- C]-ascorbic acid. Cleavage of the carbon chain of ascorbic acid at the C4-C5 bond accounts for these observations. 

In a study with experimental animals (62), both ascorbic acid (2.5 mM/kg dose) and zinc as zinc sulfate (1.4 mM/kg dose) increased ethanol clearance from the blood of intoxicated, 250-g rats when sterile solutions of the respective compounds were injected intraperitoneally. The effects appeared to be independent, because neither additive nor synergistic effects on clearance were noted when the two agents were injected simultaneously. 

On the other hand, Figure 11 indicates that the dispersion state of W/O/W emulsions becomes to be unstable in the presence of electrolytes in the aqueous phase. External appearance of the W/O/W emulsions also indicates that the various organic acids such as acetic acid, citric acid, ascorbic acid, etc. are the efficient ingradients to rupture the oil layer, but that the addition of salts promotes the aggregation formation among the dispersed globules more than the rupture of the oil layer. 

Reviewing the studies in which nonheme iron absorption has been assessed at various levels of ascorbic acid in test meals composed of either single food items or food mixtures it appears that, within any individual study, additional increments of ascorbic acid consistently increased absorption of nonheme iron (Table 1). Considering the wide differences in experimental conditions, the various studies incorporating 12,5 to 1000 mg ascorbic acid indicate clearly the enhancing effect that ascorbic acid has on nonheme iron absorption. 

Metabolic Roles. Ascorbic acid is an electron donor required for a variety of oxidative processes. It is readily regenerated by glutathione, NAD, and NADP and thus has a long biological half-life. Currently, there are eight known human enzymes that require ascorbic acid, and they are listed in Table 8.5. The precise metabolic roles have not been completely elucidated, but it appears that in the met-alloenzymes, ascorbate reduces the active metal site. In addition to these specific enzymes, ascorbic acid seems to function as a free-radical scavenger in the aqueous phase of plasma and cells. 

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