Ascorbic acid nitrosamine inhibitor

Evidence exists that the relative solubility of amines and inhibitors in heterogeneous oil-water systems could be decisive in formation of nitrosamines and blocking these reactions, Nitrosopyrrolidine formation in bacon predominates in the adipose tissue despite the fact that its precursor, proline, predominates in the lean tissue (5,6,7). Mottram and Patterson (8) partly attribute this phenomenon to the fact that the adipose tissue furnishes a medium in which nitrosation is favored, Massey, et al, (9) found that the presence of decane in a model heterogeneous system caused a 20-fold increase in rate of nitrosamine formation from lipophilic dihexylamine, but had no effect on nitrosation of hydrophilic pyrrolidine. Ascorbic acid in the presence of decane enhanced the synthesis of nitrosamines from lipophilic amines, but had no effect on nitrosation of pyrrolidine. The oil-soluble inhibitor ascorbyl palmitate had little influence on the formation of nitrosamines in the presence or absence of decane. 

N-Nitrosamine inhibitors Ascorbic acid and its derivatives, andDC-tocopherol have been widely studied as inhibitors of the N-nitrosation reactions in bacon (33,48-51). The effect of sodium ascorbate on NPYR formation is variable, complete inhibition is not achieved, and although results indicate lower levels of NPYR in ascorbate-containing bacon, there are examples of increases (52). Recently, it has been concluded (29) that the essential but probably not the only requirement for a potential anti-N-nitrosamine agent in bacon are its (a) ability to trap NO radicals, (b) lipophilicity, (c) non-steam volatility and (d) heat stability up to 174 C (maximum frying temperature). These appear important requirements since the precursors of NPYR have been associated with bacon adipose tissue (15). Consequently, ascorbyl paImitate has been found to be more effective than sodium ascorbate in reducing N-nitrosamine formation (33), while long chain acetals of ascorbic acid, when used at the 500 and lOOO mg/kg levels have been reported to be capable of reducing the formation of N-nitrosamines in the cooked-out fat by 92 and 97%, respectively (49). 

Ascorbic acid has been found to be the most effective and useful inhibitor of amine nitrosation [23]. Ascorbic acid inhibits the formation of DMN from oxytetracycline and nitrite, and also from aminophenazone (aminopyrine) and nitrite. Tannins are present in a variety of foods, competing with secondary amines for nitrite and thus leading to a reduction in the amount of nitrosamine formed [24]. 

Inhibitors of nitrosation generally function by competing with the amine for the nitrosating agent. An inhibitor would thus react with nitrite at a faster rate than with amines. The inhibition reaction has recently been reviewed ( 35). The ability of ascorbate to act as a potent inhibitor of nitrosamine formation has resulted in the use of the vitamin in nitrite-preserved foods and pharmaceuticals. Furthermore, the effectiveness of ascorbate in inhibiting nitrosamine formation is dependent on (1) the concentration of ascorbate (an excess is required) (2) pH (ascorbate is nitrosated 240 times more rapidly than ascorbic acid) (3) the reactivity of the amine toward nitrosation and (4) the extent of oxygenation of the system. 

Cousins et al. (38) have reported the formation of ascorbic acid 6-0-sulfate, 27, from the esterification of ascorbic acid with sulfur trioxide in sulfuric acid. The 6-sulfate derivatives have been proposed for use as anti-cholesteremics and as inhibitors of nitrosamine formation. 

Several ascorbic acid derivatives were examined by Pensabene et al. (570) for their ability to inhibit nitrosation of pyrrolidine in a model system developed to simulate the lipid-aqueous-protein composition of bacon. While sodium ascorbate was quite effective in the aqueous phase, a combination of an ascorbyl ester with sodium ascorbate gave a better effect in the lipid phase (Table XX). The use of ascorbates and tocopherol as inhibitors of nitrosamine formation and oxidation in foods of the aqueous and lipid type has been reviewed by Newmark and Mergens (326). These compounds in combination could be markedly useful in preventing food contamination with nitrosamines and/or nitros-amides in cured meats such as bacon. 

In anaerobic systems, ascorbic acid/ascorbate reacts with all of the nitrosating agents shown in Scheme 1. These reactions are generally faster than the reactions between amines or amides and the respective nitrosating agents, and ascorbic acid has been shown to be an effective in vitro inhibitor of amine nitrosation via competition for these agents (17,24). These results have been extended to more practical areas such as the prevention of nitrosamine formation in foods and in vivo (20, 21,22). 

The direct extraction using different solvents is a more rapid alternative than the distillation for determination of A-nitrosamines in soils. The soil, altogether with suitable nitrosation inhibitors such as ascorbic acid and tocopherol, is homogenized with a suitable extraction solvent. The solvent is then filtered and purified prior to the analysis. You et al. extracted 100 g of soil with a 50 ml portion of DCM during 20 min. The samples were then filtered to remove insoluble particulates. Afterwards, the filtrate was treated with anhydrous sodium sulfate and concentrated under a stream of dry nitrogen at 30°C. The nitrosamines were analyzed by HPLC with a precolumn... 

The most highly developed and validated method for sampling volatile A-nitrosamines from tobacco smoke employs an aqueous buffered solution (pH 4.5 citrate-phosphate) with 2.10 M ascorbic acid contained in several impingers connected in series. Ascorbic acid is added to the solution as a nitrosating inhibitor to prevent the formation of artifact A-nitrosamines from the... 

The possibility of the formation of nitrosamines and their concentrations in foods depend on many factors, such as the presence and quantity of amines and their precursors, type and quantity of nitrosation agents, pH, temperature, reaction time, composition of food (such as fat content), method of heat treatment, presence of substances that catalyse nitrosation reaction (e.g. rhodanides and to a lesser extent chlorides), and the presence of inhibitors (e.g. ascorbic acid, its esters and salts, sulfur dioxide, phenolic antioxidants, such as gallates and melanoidins). 

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