Degradation of ascorbic acid

It may be concluded that PEF, HHP, and IR are adequate techniques for the retention of bioactive compounds in fruit and vegetable products and may even enhance bioactivity of juices, purees, and fresh-cut produce. A greater degradation of ascorbic acid in comparison with phenolics and carotenoids is usually observed. 

As might have been expected, flavor deterioration followed the same pattern as did the degradation of ascorbic acid, i.e., the concentrates at 23.9°C deteriorated in flavor acceptability more rapidly than did those at 7.2°C those at 7.2°C deteriorated at a faster rate than did those stored frozen. The products stored at 23.9°C remained acceptable in flavor for about six months those at 7.2°C remained acceptable for eight to ten months. At -17.8°C, the products were still acceptable after a year of storage. 

Figure 17 Pseudo-first-order plot of thermal degradation of ascorbic acid (vitamin C) in a solid dosage form.

Another predominant furan, namely furfural, is described as sweet and bread-like caramellic. This furan can interact with hydrogen sulfide of juice to produce thiofurfural, a compound with a skunky odor (35). Furfural has an important role in the monitoring of citrus juice quality (36), and has an especially significant relationship to browning (34). The main source of furfural in aged citrus products is by oxidative degradation of ascorbic acid. Furans, such as deoxyfuroin, furoin and furil are probably formed by self-condensation of furfural (37). 

At pH 7.0 and 37 °C, the degradation of ascorbic acid continues further, the main products being threose, glyceraldehyde, xylosone, and 3-deoxyxylosone.551 Threose is more reactive compared with an aldopentose or an aldohexose. At pH 7.0 and 37 °C, it has a half-life of about 3.5 d. It seems probable that threose is a major factor in Maillard reactions involving ascorbic acid. 

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. 

Figure 29. Degradation of ascorbic acid in the presence of mannitol ([ascorbic acid] [mannitol] = 1 9) plotted according to the Weibull equation, (water content 2%). (Reproduced from Ref. 292 with permission.)...

Figure 101. Effect of silica gel and moisture content on the solid-state degradation of ascorbic acid during storage at 45°C for 3 weeks, o, 300 mg ascorbic acid , 300 mg ascorbic acid and 80 mg silica gel X, 300 mg ascorbic acid and 640 mg silica gel. (Reproduced from Ref. 451 with permission.)...

Figure 155. Linear relationship between heat flow and degradation of ascorbic acid in aqueous solution (pH 3.0-6.5,25°C). A, , Glass vials, ascorbic acid concentration 0.10% w/v A, glass vials, N2-purged , iglass vials, EDTA added O, stainless steel vessels X, stainless steel vessels, EDTA added +, glass vials, ascorbic acid concentration 0.01% w/v. (Reproduced from Ref. 628 with permission.)...

Choi et al. (2002) studied the retention of ascorbic acid with storage in blood oranges and observed a linear reduction in concentration with time. Fan et al. (2002) also observed a linear degradation of ascorbic acid in orange juice with time, whether irradiated or not. 

The Influence of Magnesium Trisilicate and Silicon Dioxide on the Thermal Degradation of Ascorbic Acid... 

The thermogravimetric data obtained for the thermal degradation of ascorbic acid samples are summarized in Tables 3.4 and 3.5. Based on these results, the heating rate of 10°C min was chosen for further analysis. The thermogravimetric data for thermal degradation of ascorbic acid samples at a heating rate of 10°C min in the three studied atmospheres are summarized in Table 3.2. The three thermogravimetric curves are shown in Fig. 3.14. 

Based on the TG and DSC experimental results it can be concluded that the excipients, that is, magnesium stearate, magnesium trisilicate, and Si02, have no substantial influences on the thermal stabihty of ascorbic acid. This result shows that the three compounds can be used (at least from a thermal point of view) as excipients, with no restrictions, for ascorbic acid tablet formulations, since they will not provoke or accelerate the thermal degradation of ascorbic acid. However, by comparison of Tables 3.5 and 3.7, it is evident that the temperature of the... 

Yuan, J.P. and Chen, F. Degradation of ascorbic acid in aqueous solution, J. Agric. Food Chem., 46, 5078, 1998. 

---