3.9 References 245by HPLC and thin layer chromatography.
Thin layers made of MgO or ZnCO 3 are suit-
able. These adsorbent layers permit separation
of carotenoids into classes according to the
number, position and configuration of double
bonds.
Identification of carotenoids is based on chro-
matographic data and on electron excitation spec-
tra (cf. 3.8.4.2), supplemented when necessary
with tests specific to each group. For example,
a hypsochromic effect after addition of NaBH 4
suggests the presence of oxo or aldehyde groups,
whereas the same effect after addition of HC1
suggests the presence of a 5,6-epoxy group. The
latter “blue hue shift” is based on a rearrangement
reaction:
(3.144)Such rearrangements can also occur during chro-
matographic separations of carotenoids on silicic
acid. Hence, this adsorbent is a potential source
of artifacts.
Epoxy group rearrangement in the carotenoid
molecule can also occur during storage of food
with a low pH, such as orange juice.
Elucidation of the structure of carotenoids re-
quires, in addition to VIS/UV spectrophotometry,
supplemental data from mass spectrometry and
IR spectroscopy. Carotenoids are determined
photometrically with high sensitivity based on
their high molar absorbancy coefficients. This is
often used for simultaneous qualitative and quan-
titative analysis. New separation methods based
on high performance liquid chromatography have
also proved advantageous for the qualitative and
quantitative analysis of carotenoids present as
a highly complex mixture in food.
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