Riboflavin light sensitivity

The SP procedure of water-soluble vitamins from multivitamin tablets is particularly challenging due to the diverse analytes of varied hydrophobicities and pfC. Water-soluble vitamins (WSVs) include ascorbic acid (vitamin C), niacin, niacinamide, pyridoxine (vitamin B ), thiamine (vitamin Bj), folic acid, riboflavin (vitamin B2) and others. While most WSVs are highly water soluble, riboflavin is quite hydrophobic and insoluble in water. Folic acid is acidic while pyridoxine and thiamine are basic. In addition, ascorbic acid is light sensitive and easily oxidized. The extraction strategy employed was a two-step approach using mixed solvents of different polarity and acidity as follows ... 

This action of catechic tannins is due to their high absorption capacity for ultraviolet light, especially that absorbed by riboflavin at 370 nm, which prevents it from reacting with methionine. This explains why red wines, with their high procyanidin content, are much less light-sensitive. Inhibition of the amino acid photolysis reaction may also be explained by the fact that phenols are scavengers of free radicals. 

Moran, J.K. Schwarz, K. Light sensitivity of riboflavin in amino acid diets. Fed. Proc.. 1978, 37, 671. 

Folic acid was purified in the middle of the twentieth century, and research on the chemical structure of this compound and on its synthesis have been continuously conducted [1,2]. The first total synthesis of riboflavin was achieved in 1935 [3,4]. Riboflavin is a yellow compound, and its solutions emit a yellow-green fluorescence. Riboflavin is sensitive to light, and it gave lumiflavin when exposed to a light under basic conditions. Under neutral conditions it gave lumichrome by releasing the D-ribose moiety. 

Riboflavin 7,8-dimethyl-10-(r-D-ribityl)isoalloxazine (RF), a yellow-green, light-sensitive compound, is widely distributed in animal and plant cells. In biological systems, the two coenzyme forms flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) are predominant (Fig. 1). These terms are formally incorrect, because FMN is no nucleotide and FAD is no dinucleotide. However, these names are still accepted. Some authors use also the name riboflavin to designate the coenzyme form of the vitamin and take vitamin B2 as a general term. Some basic physicochemical properties of these flavins are outlined... 

The presence of substantial amounts of flavins in retina has been known for some time. The detailed function of the light-sensitive flavins in the eye as well as pathophysiological consequences of riboflavin deficiency or overload conditions are not known to date. Batey and coworkers have analyzed the flavin content in retinal tissue from rats and rabbits in some detail (76-78). Retinas from two to three rats were isolated and homogenized. Flavins were extracted by a hot water treatment and analyzed by reversed-phase HPLC (Table 5). The... 

Photolytic. When propachlor in an aqueous ethanolic solution was irradiated with UV light (>, = 290 nm) for 5 h, 80% decomposed to the following cyclic photoproducts W-isopropyloxindole, W-isopropyl-3 hydroxyoxindole, and a spiro compound. Irradiation of propachlor in an aqueous solution containing riboflavin as a sensitizer resulted in completed degradation of the parent compound. 3-Hydroxypropachlor was the only compound identified in trace amounts which formed via ring hydroxylation (Rejtb et al, 1984). Hydrolyzes under alkaline conditions forming W-isopropylaniline (Sittig, 1985) which is also a product of microbial metabolism (Novick et al., 1986). 

Riboflavin is stable to heat but is extremely sensitive to light, a fact of some nutritional significance. Do not leave bottled milk in the sunshine (see Fig. 15-8) Many products of photolysis are formed (Fig. 3-5). Among them is lumichrome. 

One major reason for nutrient loss and off-flavor development today is due to extended exposure to fluorescent light in food retail display cases. Many foods and beverages are susceptible to light-induced reactions, especially those with photo-sensitizers. Natural pigments found in foods that commonly act as photochemical initiators are flavonoids, riboflavin (vitamin B2), chlorophyll, heme, and vitamin K. 

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