Ascorbic acid, anaerobic degradation

Anaerobic degradation of ascorbic acid in grapefruit juice is a zero-order reaction (20), but degradation of fish is either first or zero order depending on the type of fish (21). Ascorbic acid degradation in peas is... 

The past year was marked by relatively little activity in this area, -Wadke and Guttman reported on the base induced degradation of 9-methylisoalloxazine under both aerobic and anaerobic conditions. The initial product formed appears to be a carbinol amine. Finholt et al have continued their investigation of anaerobic hydrolytic degradations of ascorbic acid with a study on the effect of metallic ions on the over-all rate. Although the reaction appears to be accelerated by doubly and triply charged species, the effect was surprisingly small. 

Sulfur dioxide reduces dehydroascorbic acid to ascorbic acid and is therefore frequently used in combination with ascorbic acid, particularly in fruits and vegetables. It has been suggested that under anaerobic conditions, sulfite ion may catalyse degradation of ascorbic acid and readily adds across the double bond of the 3,4-dideoxypentosulos-3-ene (Figure 5.30) that is formed to yield 3,4-dideoxy-4-sulfopentos-2-ulose (5-126). Under aerobic conditions. 

Liquid Dosage Forms. In dry form and at very low moisture content, L-ascorbic acid is very stable, but in solution exposed to air or oxygen it is subject to oxidation accelerated by dissolved trace minerals (copper and iron) and light exposure, l-Ascorbic acid is a reducing agent and is subject to oxidative decomposition in solution. This proceeds first to dehydroascorbic acid, which has full vitamin C activity, but continues to diketogulonic acid and various other breakdown products. The degradation reactions are complex and vary with aerobic or anaerobic... 

S. Kamiya (n-ascorhic acid degradation by bacteria. I-IV. J. Vitaminol. 6, 217-235, 240-245, 1960) studied the degradation of L-ascorbic acid by anaerobically adapted cells of a species of Micrococcus. After conversion to diketo-L-gulonic acid, pyruvic acid was formed. 

The rate of aerobic oxidation of ascorbic acid depends on the pH, exhibiting maxima at pH 5 and 11.5. However, the reaction is much more rapid and the degradation more extensive in alkali. Degradative oxidation also occurs, albeit slowly, under anaerobic conditions. 

Ascorbic add. The ascorbic acid loss during storage showed an initial period of rapid loss followed by a period of slow loss. This behaviour can be described by a two simultaneous first order kinetic model. This means that two simultaneous reactions with different rates are responsible for the ascorbic acid degradation. It has been referred in literature that ascorbic acid is degraded by two simultaneous reactions one aerobic and other one anaerobic. The aerobic reaction dominates first and it is fairly rapid, while the anaerobic reaction dominates later and it is quite slow (6,7). Equation (1) was used to fit the experimental data. 

C (ppm) and k (days ) represent, respectively, the hypothetical initial amount of ascorbic acid and the rate constant associated with the slow reaction - probably the anaerobic degradation. 

The rate of anaerobic vitamin C degradation, which is substantially lower than that of noncatalyzed oxidation, is maximal at pH 4 and minimal at pH 2. It probably proceeds through the ketoform of ascorbate, then via a ketoanion to diketogulonic acid ... 

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