FLUORESCENCE OF CUSTARD POWDER / RIBOFLAVIN
NEEDED

     -  Custard powder
     -  Water
     -  UV-light
     -  ( Sodium dithionite : Na2S2O4 )

PROCEDURE

         Mix custard powder in water, shake a bit and
     filter everything.
         The dissolved colorant Riboflavin (aka
     Vitamin B2 aka E101) in the yellow solution
     shows a strong yellow fluorescence under
     UV-light.

COMMENTS

         The experiment can be extended: If Na2S2O4
     (dangerous, prevent skin contact) is added:
     the fluorescence disappears, but re-appears
     under shaking. Reason for this is the
     reduction of Riboflavin by the dithionite to its
     non-fluorescent form, and its re-oxidation to its
     initial form by oxygen in the air.
         This cycle is a nice model cycle of the physio-
     logically very important FAD-FADH2 cycle  in all
     aerobic life (FAD = Flavin-adenin-dinucleotide,
     which is a derivative of Riboflavin).

Custard powder in water:
unfiltered and filtered.
Succinate
O2
Ubidihydrochinon
H2O2
Ubichinon
Fumarate
2 SO32-  +  4 H+  +  2 e-
non-fluorescent
Riboflavin-H2
fluorescent
Riboflavin
S2O42-  +  2 H2O
FAD
FADH2
Fluorescence of Riboflavin.