Chemistry Reference
In-Depth Information
The formation of FMN and FAD is ATP-dependent and takes place
mainly in the liver, kidney and heart. All enzymatic steps are under the
control of thyroid hormones:
Flavokinase: Riboflavin + ATP
!
flavin mononucleotide + ADP
FAD pyrophosphorylase: FMN + ATP
!
flavin adenine dinucleotide
+PP
FAD + apoenzyme/protein
!
covalently bound flavins
13.3.2.
Sources of Riboflavin
Tables 13.5 and 13.6 summarize dietary sources of riboflavin and its
concentration, especially in the milk of various species and dairy products.
Heat treatment has only negligible effects on riboflavin concentrations,
whereas exposure of milk to sunlight results in a loss of 20-80% of riboflavin.
Thus, storage in dark bottles, light-tight wax cartons or special polyethylene
terephthalate (PET) bottles is recommended (Mestdagh et al., 2005).
The photodegradation of riboflavin catalyses photochemical oxidation
and a loss of ascorbic acid. Gamma radiation of 10 Gy destroys about 75% of
riboflavin in liquid milk; while milk powder shows no losses even at higher
doses.
Storage influences riboflavin concentrations as follows: condensed milk
looses 28 or 33% of its initial riboflavin content when stored at 8-128C for
2 years or 10-158C for 4 years, respectively; ice-cream looses 5% when stored
at -238C for 7 months. No losses were found in fresh milk stored at 4-88C for
24 h or in dried milk powder stored for 16 months.
In cheese, most of the losses (66-88%) of the original riboflavin of the
milk appear to occur during whey drainage, while ripening has almost no
effects. However, in some cheese varieties, the concentration is higher in the
outer layers due to microbial synthesis. High-pressure tests for thermal
sterilization processes led to different results for the decay of the vitamin
dependent on the matrix of the respective food tested.
13.3.3.
Riboflavin Deficiency
Riboflavin is essential for humans, animals and some microorganisms.
Among humans, seniors and adolescents seem to be at particular risk of
deficiency (Powers, 2003); the recommended uptake is given in Table 13.2.
In some cases, recommended uptake is related to energy intake and 0.6 mg
riboflavin per 1000 kcal is considered adequate. Milk and milk products
(excluding butter) can contribute about 30% of total riboflavin supply
(Scholz-Arens, 2004).
