Riboflavin photodegradation

On the other hand, riboflavin retention is affected by oxygen concentration, other components such as metal sulfates and amino acid chelates, water activity, and most of all, light exposure. Riboflavin photodegradation in liquid systems such as milk follows first order degradation mechanisms and is dependent on light intensity, exposure time and wavelength (Choe et al. 2005). 

Photolytic. When a dilute aqueous solution (1-10 mg/L) of bromacil was exposed to sunlight for 4 months, the TV-dealkylated photoproduct, 5-bromo-6-methyluracil, formed in small quantities. This compound is less stable than bromacil and upon further irradiation, the de-brominated product, 6-methyluracil was formed (Moilanen and Crosby, 1974). Acher and Dunkelblum (1979) studied the dye-sensitized photolysis of aerated aqueous solutions of bromacil using sunlight as the irradiation source. After 1 h, a mixture of diastereoisomers of 3-5ec-butyl-5-acetyl-5-hydroxyhydantoin formed in an 83% yield. In a subsequent study, another minor intermediate was identified as a 5,5 -photoproduct of 3-5ec-butyl-6-methyluracil. In this study, the rate of photooxidation increased with pH. The most effective sensitizers were riboflavin (10 ppm) and methylene blue (2-5 ppm) (Acher and Saltzman, 1980). Direct photodegradation of bromacil is not significant (Acher and Dunkelblum, 1979 Ishihara, 1963). 

The ionisation state of molecules in the solution state appears to be an important variable in photodegradation mechanisms. A recent pubhcation on riboflavin oral liquid preparations shows that the formulation is most photostable at pHs between 5 and 6, where the non-ionised form predominates [78]. The rate of photolysis increase 80-fold at pH 10.0, owing to increased redox potential. Conversely, at pH 3.0, the increased photolysis is associated with the excited singlet state, in addition to the triplet state. 

The stability of some vitamins is influenced by aw. In general, the stability of retinol (vitamin A), thiamin (vitamin Bj) and riboflavin (vitamin B2) decreases with increasing aw. At low av (below 0.40), metal ions do not have a catalytic effect on the destruction of ascorbic acid. The rate of loss of ascorbic acid increases exponentially as aw increases. The photodegradation of riboflavin (Chapter 6) is also accelerated by increasing aw. 

Massad, W., Criado, S., Bertolotti, S., Pajares, A., Gianotte, J., Escalada, J.P., Amat-Guerri, F., Carcia, N.A. (2004) Photodegradation of the herbicide norflurazon sensitised by riboflavin. A kinetic and mechanistic study. Chemosphere 57, 455—461. 

Photosensitization for the removal of certain pollutants in photolytic processes can contribute significantly to the degradation rate. Thus, Simmons and Zepp [88] observed increases of up to 26 times of the photodegradation rates of nitroaromatic compounds due to the action of natural or commercial humic substances with solar irradiation. In another work [89], the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) was irradiated in water with 300 nm light in the presence of different photosensitizers. This compound, which does not photolyze directly at this wavelength, could be degraded more than 95% in 5 hr when riboflavin was used as photosensitizer. 

Parks, O.W., Allen, C. 1977. Photodegradation of riboflavin to lumichrome in milk exposed to sunlight. J. Dairy Sci. 60, 1038-1041. 

Micellar catalysis of the photobleaching of riboflavin and riboflavin-5-phosphate was investigated in a recent e.s.r. study of the effects of polyoxyethylene(20) sorbitan monooleate and sodium dodecyl sulfate on the rate of formation and decay of an intermediate semiquinone radical (Kowarski, 1969). In the photodegradation of riboflavin-6-phosphate, both the rate of formation of the semiquinone radical and the rate constant for its decay were appreciably enhanced by the anionic and the non-ionic surfactant (Table 19). Similarly, the catalysis of the photobleaching of riboflavin by sodium dodecyl sulfate was found to be related to an increased rate of formation of the semiquinone radical. Hence, the micellar catalysis of the photodegradation of riboflavin and riboflavin-5-phosphate is the consequence of a combined effect of an increased rate of semiquinone radical formation and an accelerated rate of its decay (Kowarski, 1969). 

The photoprotective effect of the foil was demonstrated in studies using the highly photosenstive riboflavine solution. In spite of intense photo exposure, no photodegradation of the aluminum-wrapped riboflavine solution was detectable (35). 

The extent of photodegradation of riboflavin is not evident by either visual or spectrophotometric means (49). These results clearly demonstrate that these techniques, though rapid and easy to perform, are not appropriate in all circumstances and that good, validated, stability-indicating analytical techniques should be used to quantitatively determine the extent of photodecomposition. 

Trace metal impurities in buffer salts were found to enhance the oxidative degradation of prednisolone (78). Phenylephrine hydrochloride decomposes in the presence of heavy metal ions (79). The autooxidation of procaterol, a sympathomimetic amine, is enhanced in the presence of ferric ions (80). The photodegradation of riboflavin is enhanced by the presence of polysorbate 80 and sodium lauryl sulfate (81). 

Among the water-soluble vitamins subject to photodegradation during administration, thiamine, ascorbic acid, and riboflavine must be considered. A multivitamin product containing all of these vitamins was added to both 0.9% NaCl and 5% dextrose infusion solutions packaged in PVC and Clearflex containers. These admixtures were then exposed to photonic energy (2000 lux) for 24 hours and showed a rapid degradation of both riboflavine and ascorbic acid (95). 

Isoalloxazine-Containing Products from the Photodegradation of Riboflavin. Irradiation of riboflavin in deoxygenated aqueous... 

Figure 6. A. Pathways for photodegradation of riboflavin. B. Pathways for de-activatlon of flavins (FL) In aqueous solution Including reaction with quenchers (Q) and substrates (SH) and energy ( A ) losses through Internal conversion and emission steps.

MJ Akhtar, MA Khan, I Ahmad. High performance liquid chromatographic determination of folic acid and its photodegradation products in the presence of riboflavin. J Pharm Biomed Anal 16 95-99, 1997. 

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